How to connect a variable resistor to adjust the sound. Volume controls in tube amplifiers. How the regulator works

PERMANENT RESISTORS

First of all, a small reminder of the resistor designations:

Like any other element, resistors have such a parameter as their own noise, which is the sum of thermal and current noise.
Current noise is due to the discrete structure of the resistive element. When current flows, local overheating occurs, as a result of which the contacts between individual particles of the conductive layer change and, therefore, the resistance value fluctuates (changes), which leads to the appearance of current noise between the terminals of the EMF resistor. Current noise, like thermal noise, has a continuous spectrum, but its intensity increases in the region low frequencies, and the magnitude significantly exceeds the magnitude of the thermal noise.
All these effects depend on the current density. The larger it is, the greater the manifestation of these troubles. Therefore, by connecting 2 resistors in parallel (increasing the cross-sectional area and decreasing the current density), all these effects are reduced. The same can be done by taking a resistor with a larger overall power. It has a larger cross-section of the conducting layer and the current density in it will be less. By connecting 2 resistors in series, the noise is summed up, therefore it is highly undesirable to use a series connection of resistors in stages with a large amplification box. The total resistance of two resistors connected in parallel is calculated by the formula:

This noise depends on many factors, including the design of the particular resistor, including the resistive material and especially the end connections. Here are the typical values for excess noise. different types resistors, expressed in microvolts per volt applied to the resistor voltage (the rms value is given, measured over one decade of frequency):

Carbon Composite 0.10 μV to 3.0 μV

Carbon film 0.05 μV to 0.3 μV

Metal film From 0.02 μV to 0.2 μV

Wirewound From 0.01 μV to 0.2 μV

However, it is not entirely clear on what basis the conclusions were drawn that C5-5 or C5-16 do not contain inductance and the most striking example is mechanical opening:

The most acceptable option is considered to be the use of MLT-2 resistors for these purposes, however, the chances of getting rid of the inductance are not one hundred percent - a spiral from the resistive layer is clearly visible on the upper resistor:

Therefore, when buying MLT-2, you should pay attention to their appearance, and if it turns out that the resistive layer in the form of a spiral is not at all a reason to panic - yes, there will be inductance, but its value is too small - the inductance of the 100 Ohm resistor shown in the photo was 70 μH, and for resistors with a resistance of 1 , 0.68, 0.47, 0.33 and 0.22 Ohm, it will be ten times less.

RESISTORS VARIABLES

In addition to constant resistors in amplifiers, variables are used - to adjust the volume, balance, and, if necessary, tone. The quality of these resistors mainly depends on additional noise introduced by changing contact resistance between the resistive layer and the engine.

In addition to other parameters, variable resistors have one more - a group. This parameter shows by what law the resistance on the slider of the resistor changes depending on its position, for example, for rotary resistors, this will be the angle of rotation. Domestic resistors have 3 main and two auxiliary groups:

Group A- linear dependence of the change in resistance on the position of the engine, group B- logarithmic dependence, V- reverse logarithmic. The most popular are "A" and "B". "A" is used for linear adjustments, eg thermostats, engine speed controllers. "B" is the best option for adjusting the volume, since the human ear perceives an increase in volume according to the logarithmic law. Supporting groups AND and E usually used in pairs on double resistors - one "I" resistor, the other "E", which makes such a resistor ideal for adjusting the balance in stereo amplifiers.
Imported variable resistors have 4 groups:

Here you should immediately pay attention to the fact that the import group A has an inverse logarithmic dependence, i.e. to adjust the volume, just the resistors of the "A" group are required, and the group B has a linear relationship. Group W used to adjust the balance - usually the resistor slider is connected to the common wire, and the resistive layer acts as an attenuator, together with constant current-limiting resistors.
On some subspecies of variable resistors intended for volume control, taps are made from the middle of the resistive layer, much less often taps are made with a ratio of 1 / and 2/3. These resistors are convenient for implementing loudness-compensated volume controls. Loudness compensation allows you to equalize the illusion of a change in the frequency response of the path at low and high volumes - at low loudness it seems that the low and high frequency components of the signal decrease, therefore, the LF and HF boost is introduced in the regulator itself. One of the variants of the scheme of the loudness-compensated volume control and changes in its frequency response are given below:

There are two main types of variable resistors - rotary and slide ones. Both those and others have many subspecies in their composition, therefore, for brevity, only the popular ones are shown in the table:

	R12 series variable resistor The closest constructive neighbor is made on a textolite basis. They are widely used in portable audio equipment. They are available for vertical and horizontal mounting. The reliability is poor.

	The R12XX series - by design, consists of a getinax "horseshoe" with a carbon resistive layer applied. For more understanding, you should decipher the designation: R - ROTOR, i.e. rotary, the next two numbers indicate the diameter, but further on according to the specification. There are single and double. They are widely used in portable audio equipment and low-price automobiles. They are available for vertical and horizontal mounting.

	The RK11XX series, the same constructive RK14XX series, are available for vertical and horizontal mounting, the first numbers after the letters indicate the size:, there are double and single, they are not very popular in portable audio equipment, but they come across.

	RK12XX are popular in stationary mid-price category and high-end portable equipment, often flashed in car radios. There are single, double, quadruple. The size of a horseshoe with a resistive layer can reach 24 mm, of course in the name the first numbers will be 24. They can be with a switch, some models of this type have a tap from the middle. To increase reliability and reduce resistance between the contact of the engine and the resistive layer, it is better to use resistors of a larger diameter, if there are no restrictions on dimensions.

	Slide type variable resistors contain either the first or the second letter S - SLIDE in their abbreviation. They are single, double, with and without a branch from the middle. The first two digits after the letters indicate the stroke length of the engine, for example, for the upper SL101, the engine moves by 10 mm, and for the lower SL20V1 - 20 mm. Usually, in the middle position, the resistor slider is slightly fixed.

	Potentiometers DACT and ALPS are by design a multi-position rotary switch with installed SMD resistors. The resistor ratings provide an inverse-logarithmic dependence of the change in resistance when the potentiometer axis is turned. The contacts of the engine and "horseshoe" are made of materials with increased wear resistance and provide best contact for a VERY long time. Of course, the cost of such potentiometers is quite high.

	There is another group of potentiometers that can be called "successful", and in the literal sense of the word - these are potentiometers taken from old power amplifiers of the zero complexity group. Literally two months ago, such a potentiometer was purchased SUCCESSFULLY from a junk dealer for only 50 rubles. Oily, dusty, but the contacts are in VERY good condition.

The most popular resistors are discussed here.

WIRES AND CONNECTORS

After all the boards are ready, checked and washed, they must be installed in the case and connected to each other, and this requires wires and "connectors".
The best connection is soldering, but this is far from always convenient, and soldering can be different.
If a solder joint is used, solder is required for soldering. In radio-electronic equipment (REA), lead-tin solders of three main brands are used:
POS-40 - contains 40% tin and 60% lead, it is used ... Yes, it would be better not to be used ...
POS-60 - the most popular solder used for mounting electronic components, contains 60% tin and 40% lead. It has good spreadability, being in a liquid state, over time it can acquire an oxide film and become dull;
POS-90 is a solder consisting of 90% tin and almost 10% lead (the rest is for technological impurities). Quite often called food grade, since the lead content is minimal and can be used for soldering household items in contact with food. The soldering quality is quite high, but a slightly higher soldering iron temperature is required. The copper tip of the soldering iron burns out much faster than when using the POS-60. The surface of POS-90 practically does not oxidize from moisture.
There is another type of solder called lead-free or environmentally friendly. I didn't even want to look for the chemical composition - most electronic devices of a low price category are sealed with this light gray substance, it has a higher melting point compared to POS, being in a liquid state has low wettability, which makes it difficult to service the leads of electronic components and reduces the quality of soldering. Mechanical properties at the level of POS-40.
When brazing, fluxes are almost always used - substances that create a thin film on the surface of the parts to be brazed, which protects against oxidation, which occurs much faster at high temperatures. There are quite a lot of chemical compositions of fluxes, most are based on ordinary pine rosin, which can be used for soldering and by itself.
To improve the quality of soldering, it is recommended to twist the stripped cores of stranded wires as tightly as possible to each other - this creates the maximum possible number of points of contact that significantly reduce the resistance of the contacts.
It is highly undesirable to use connectors in the power section of the amplifier, even if they are self-clamping or screwed. Such a connection automatically doubles the number of connections:
1. The connector is soldered to the board;
2. The wire is screwed to the connector
If connectors with "dad-mom" are used, then the number of connections triples:
1. The male connector is soldered to the board;
2. The point of contact of the mating parts "dad-mom";
3. The female connector is soldered to the wires
Of course, the connectors greatly simplify access to the device modules, but they also reduce the reliability, so it is better to use connectors only on low-current circuits and reduce their number to the minimum possible.
Of course, one can argue that a lot of devices are assembled on connectors and nothing terrible happens.
Well, first you need to realize that when assembling in the factory, manufacturability is far from the last place - ease of assembly to increase the number of products, and only then the reliability of the connectors used is considered.
On the other hand, "nothing terrible" happens:

WIRES

In amplifiers, wires can be divided into two main groups - signal and power, and for power, you can also determine the wires through which control is performed, for example, the input selector relay. Signal wires are wires along which they actually pass sound signal from entrance to exit.
In the low-voltage signal part of the amplifier, it is better to use shielded wires, and it is better in isolation, since a shielded wire without insulation can come into contact with the case, a firebox, etc. points and making it possible to form a loop antenna that collects many pickups and impulse noise.
However, shielded wires are also different and the most affordable is the so-called "low-frequency wire for video", sold either double or quadruple.

Before buying, it is better to make a small anatomical dissection and make sure that the wire is a wire, and not a pathetic parody of it, and even made of some kind of steel alloy, which is VERY hard to solder:

The wire must have uniform insulation of the central core and a fairly dense, elastic and non-crumbling braid:

Moreover, the denser the braid, the better; ideally, the braid cores should be braided into a mesh tube, but recently such a wire comes across quite rarely:

Well, the "microphone" wire is quite good, it strongly resembles a coaxial cable, with a uniform, rather thick insulation of the central core, which significantly reduces the capacity of the cable and a dense braid. Quite often you come across economy-class "microphone" wires, in which a liquid braid, but the screening is preserved due to the use of foil.

It is better to use copper stranded wire as power and control wires at the rate of 4-5 A per mm2. Theoretically, you can use a large voltage - the wire will have time to cool down, but only a greatly reduced cross-section will contribute to a large voltage drop, therefore the supply voltage will strongly depend on the flowing current.
For preliminary stages, theoretically, this is not so critical - they do not consume large currents and the drop can be compensated for by increasing the capacitance of the power filter capacitors installed directly on the module board. However, does it make sense to deal with the problem if there is an opportunity to work around it?
For power cascades, power dips are more painful - not only does the peak of the music signal discharge the power filter capacitors, which are usually of minimal sufficiency, but also thin wires create an additional voltage dip. Hence, an earlier clipping occurs, which will already be heard.
In addition to the power supply, the power wires can be attributed to the wires leaving directly from the output of the power amplifier, going to the connection terminals, and then directly to the speaker.
Here a point of disputes and misunderstandings already arises, since almost everyone recommends using an acoustic wire (oxygen-free copper) for these purposes, but the reasons are sometimes called the most abstract.
Here you should dwell in more detail on the most popular:

Less active resistance

Copper wire is manufactured in the following grades:

In theory, everything seems to be correct, but ...
,
where R is the resistance of the conductive material (ohm)
l - wire length in meters
p- electrical resistivity of the material
A - cross-sectional area
PI - mathematical number
d - nominal wire diameter in millimeters
We take 10 meters with a cross-section of 1.5 mm square, we get a resistance for oxygen-free copper of 0.1147 Ohm, for the usual 0.12 Ohm. Even with a load of 2 Ohms, the resistance ratio is more than 16, however, no normal person for a two-ohm speaker will use a cross section of 1.5 mm sq - at least 2.5 mm sq.

Reduced SKIN EFFECT

Of course, at high frequencies, electrons are pushed out to the surface of the conductor and the skin layer thickness for a frequency of 100 kHz is 0.2 mm. However, the presence of many non-insulated cores in the wire makes it ONE conductor, the diameter of which is proportional to the total cross-section, and not to the cross-section of each core. An acoustic cable that really compensates for the SKIN EFFECT looks a little different than it is used to present in peripheral audio stores:

The cost of this cable will not be small at all. However, about the cost - there is still a dependence on where to buy this cable. For example, two prices for the same cable:

In an audio store, the cost of a wire is 96 rubles per meter, and in stores that deal with warm floors and lay an acoustic cable under the floors in the form of an additional service, it does not exceed 20 rubles per meter.
You can get out of the slouching if you really really want to get a cable without a SKIN EFFECT - make it yourself from a copper winding wire PEV-1 (PEV-2 is also suitable if it costs the same). The wire is measured with the required length and added to the required number of cores at the rate of 30 watts of amplifier output power per 1 mm square of wire cross-section. Then the tourniquet is twisted, but not tightly and wrapped along the entire length with keeper tape:

After that, both cores going to the speaker are wrapped with electrical tape, you can separately, you can just two. Such careful insulation is necessary to reduce the capacitance between the wires and improve the mechanical properties of the insulation - the varnish on the wire is not very strong.

From personal impressions:
Compared to a conventional speaker cable, a homemade one wins in the HF region and this is most pronounced at powers above 100 watts.
However, the sound is much more pleasant when using a full-range dynamic head and amplifier in the "Voltage Controlled Current Source" (ITUN) mode. Using additional block, called "Wire Length Compensator" (KDP), the sound also differed for the better.

Moreover, amplifiers with ITUN and KDP were connected with a PVA 2x2.5 wire, and a typical amplifier was acoustically produced by a store and homemade:

AND WHAT NOW ?!

To begin with, think about it, because oxygen-free copper has one rather serious plus - it does not oxidize as intensely as PVA, therefore it can be used where there is high humidity. The thickness and strength of the insulation is much higher than that of PVA, therefore, it can be handled not so carefully, and in the event of a puncture, the insulation tends to "tighten". The acoustic wire is much softer than PVA, therefore it can be used where the flexibility of the wire is important due to the inaccessibility of the places of laying.
The conclusion suggests itself - the speaker wire is ideal for use in car audio and on tour. In household complexes, PVA can also be dispensed with, and even an increase in the section will give some savings in comparison with an acoustic one of a smaller section.
In defense of PVA, we can also say that different manufacturers use veins of different diameters for the production of wires - the main thing for them is to maintain the cross-sectional area. Therefore, looking at the wire in several competing stores you can choose a wire with thinner veins, therefore softer.

And of course, see what exactly you are going to buy, so that there is no misunderstanding, the proposed one - in the photo one thing, but they sell something completely different, if you are inspired that the wire is free from the skin effect, then remember that such a cable looks a little different:

Literature:
http://www.electroclub.info
http://dart.ru
http://www.magictubes.ru
http://easyradio.ru
http://people.overclockers.ru
http://tech.juaneda.com
http://rexmill.ucoz.ru
http://ivatv.narod.ru/
http://irbislab.ru
http://www.audio-hi-fi.ru
http://diyfactory.ru
http://www.diyaudio.ru
http://www.bluesmobil.com
http://rezistori.narod.ru
http://sgalikhin.narod.ru

On a TDA1552 chip for sound control? A common double resistor. And if we have a quad connection for 4 channels? Someone suggests - a quadruple regulator :) And if we assembled a home theater for 6 channels? Here complex and expensive electronic volume controls on specialized microcircuits come into battle. And such a unit in complexity and price can surpass the amplifier itself. Nevertheless, there is a simple way out, how to implement the volume control function on just one transistor. The circuit proposed below from the radio amateur magazine allows one variable resistor to control the volume of several channels at once.

One diagram shows one channel of the volume control, and the other shows 4 channels at once. Naturally, there can be 5 and 10. The essence of the method is that by applying a positive potential to the base of the transistor through a resistor, the transistor opens and shunts the ULF input - the volume decreases.

A number of experiments have been carried out with this scheme. It turned out that the power supply of the base can be taken from 1.5V. The maximum voltage limit is determined by a 1k ohm limiting resistor. If we found 12V in the allowable, then the resistor must also be increased to 30 kOhm, safe for the base current. The current consumption of the base circuit in the open state is several milliamperes. In general, you will pick it up.

In the open state of the transistor, a very quiet sound due to the voltage drop across the silicon crystal. For the silence to be complete - you need to use a germanium transistor of the type MP36 - MP38.

The capacitors at the input and output of the electronic volume control are non-polar. We put any transistor low-power N-P-N, type KT315, KT3102, S9014, etc. Variable resistor for an electronic regulator for resistance in the range of 10-100 kOhm. Preferably with a linear characteristic.

When the engine is shorted to ground, all transistors will close and the volume will become maximum. By moving the engine to the power plus, we open the transistors a little and the sound will fade away. With a resistor that is connected to the plus of the power supply, we set the smoothness of the volume change along the entire turn of the resistor. So that it was not so, when after half of the turn the volume disappeared and we continue to turn it in vain. The use of this electronic volume control on the one hand will slightly increase the noise level, but on the other hand, it will reduce crosstalk on the wires, since now there is no need to pull twice the shielded wire from the output of the pre-amplifier to the input of the power amplifier.

The volume control is a device that allows you to change the amount of electrical voltage at the output when you act on the controls, or when a control signal is received. It is used both as part of electronic equipment and as a separate product.

The volume control can be both a voltage regulator and a current regulator, because its task is to regulate the output power of the amplifier at some kind of load, that is, if the regulator is a variable resistor at the amplifier input, then it regulates the voltage that goes to the differential stage amplifier, thereby reducing or limiting the input level to the maximum. If the output power is adjusted at the amplifier output, for example, an additional resistance connected in series with the load, then this will already be a current regulator, since without load, the voltage at the amplifier output will be unchanged. It can also be called a current regulator - a resistor in the circuit feedback, which is implemented using a current sensor - a resistor, in series with the load of which, a signal is removed and fed to the inverting input of the amplifier.

Thus, it turns out that the variable resistor can act as both a current regulator and a voltage regulator, depending on where it is turned on.

You can also call the current regulator and the volume control in the ITUN amplifier, which stands at the input of the circuit. It regulates the input voltage, but thanks to the current feedback (the voltage is removed from the current sensor - an additional resistor when the current passes, the higher the current that passes through it, the greater the voltage drop across this resistor) the volume control itself does not regulate the current in the load, but further, according to the scheme, the current connection is carried out, for example, if this resistor is thrown out of the ITUN, then the connection will be only by voltage and the volume control will be a voltage regulator * in its purest form *. It's like a toggle switch and an electromagnetic relay, the toggle switch itself cannot pass large currents, and it gives a signal to a relay with powerful contact groups, and are there additional resistors in series with these contact groups - to the toggle switch * deeply and from a great height *.

The volume control is a variable resistor; in stereo amplifiers, it is a double variable resistor. The first two figures show the appearance of a dual variable resistor. The resistance of the variable resistor can be in the range from 20 to 100 kOhm, it depends on the design of the amplifier. The third and fourth figures show the circuit for switching on the regulator (one channel) and the correspondence of the conclusions to the circuit. The fifth figure shows how to properly solder the wires.

The current regulator can be a magnetic shunt in a transformer; this type of output power adjustment is used in welding machines for manual arc welding and, oddly enough, in rather expensive tube amplifiers.

A choke at the input with a variable inductance can also act as a volume control (the ferrite core moves along the thread in the form of a screw), as it was often arranged in old tube radios, and in fact there the sound never wheezed when the knob was turned, since there was no mechanical contact was, and therefore there was nothing to erase.

There were also volume controls, by means of magnetizing the voice coil in the speaker itself. It was very simple and effective, you can assemble such a volume control yourself, you just have to make your own magnetic system. The principle of operation is simple, instead of a permanent magnet, an electromagnet was used, and the voltage applied to its winding created the necessary current, which created a magnetic field, the greater this magnetic field was, the greater the sensitivity of the dynamic head, therefore, the lower the voltage was applied to the winding of the electromagnet, the more The speaker played quieter, and regardless of the power supplied to the voice coil. In the future, such a regulator was abandoned, and regulators began to be made on variable resistors at the input of the circuit, it is easier this way. But the speakers still remained such (without permanent magnets, with two coils), and they began to be connected to power transformers in series with the filaments of radio tubes, in this way (method) they killed two, if not three birds with one stone. First- getting rid of a bunch of old speakers, second- the quality of the power supply of the radio tubes improved and they served longer, since the coil in the dynamics acted as a choke for the filament and the current was more stable, which means that the work of the filament was more * smoother *, third- it was possible to get a much higher power of the dynamic head than when using an * expensive * (controversial statement) permanent magnet.

In this part of the article, we will talk about the aspects of matching Nikitin's volume control with an amplifier.
To obtain the declared parameters, reduce distortion and ensure smooth volume control, Nikitin's regulator must be matched to input impedance amplifier!

Let's consider in order:

General issues of regulator approval.
Coordination of the regulator with circuits on the op-amp and transistors.
Coordination of the regulator with tube stages.

1. General questions of approval.

To consider the general nuances of matching Nikitin's volume control with amplifiers, let us refer to the article " Distortions arising in the stages on the op-amp when regulating the signal level ", author V.A. Svintenok.

I will not cite it in its entirety (anyone interested will easily find it on the Internet). In it, the author, having conducted not entirely correct and incomplete experiments, confirmed the well-known fact that amplifiers in an inverting connection sound better and have less distortion than amplifiers in a non-inverting connection. This feature has long been noticed and tried to explain Douglas Selfie and Nikolay Sukhov(the author of the very "high fidelity amplifier"). The latter came to the conclusion that a similar effect is caused by the fact that in a non-inverting connection transition b-e the input transistor is outside the overall negative feedback circuit, which does not compensate for the Miller capacitance. Accordingly, for an amplifier with field-effect transistors at the input, this effect is either much weaker or not observed at all.

So, Nikitin's volume control also took part in the experiments described in the article. Sometimes, however, it is not entirely correct. It is not clear why it was necessary to take the characteristics of an unloaded regulator ??? I repeat once again that to ensure the declared parameters (adjustment step, adjustment uniformity, adjustment range, etc.), the regulator must be matched to the load!!!

Note: in this article, Nikitin's volume control is often referred to as "Ladder-type volume control".

So, the most interesting and useful conclusions from the article:

... As shown above, the non-inverting inclusion of an op-amp with resistors at the inputs does not allow the maximum potential of most microcircuits for nonlinear distortion to be realized. Inverting inclusion gives the series best characteristics: less nonlinear distortion, shorter and "softer" spectrum of distortion, no "threshold" (a sharp increase in the higher harmonics in the spectrum), the distortion and the spectrum are not influenced by the internal resistance of the signal source.

A standard construction of a level controller with a buffer follower in inverting connection is shown in Fig. 15. In practice, such a scheme is used quite rarely and this is due to the following. To keep the input impedance of the circuit at the same resistance valueRп and the law of change in resistance from the angle of rotation of the potentiometer knob is necessary for the resistors of the circuit to satisfy the conditionR>Rп (3 or more times). To get an acceptable input impedance of the circuit, you have to choose resistors high enough.R. This in turn leads to an increased noise level in the circuit.

However, consider this circuit as a starting point for this type of wiring.

For the circuit shown in Fig. 15, the maximum distortion will be in the upper position of the potentiometer sliderRп and correspond to the repeater in the inverting connection. Further, as the signal level at the output of the potentiometer decreases, the distortion at the output of the op-amp will proportionally begin to decrease. In this connection, it is enough to describe the behavior of the active element in the regulator by describing it at one point - at the point of observation of maximum distortions.

Table 10 shows the harmonic distortions for the input voltage of 2 and 4 volts for the inverter assembled according to the diagram in Fig. 15 with the nominal resistorsR = 5kOhm and with the controller transmission coefficient Kp = -1.

Table 10.

	Table 10 (1)
Ms type	OPA2134	AD8620	NE5532		OP275
Uin (in)
K g7% (5k)			0,000066	0,000035	0,000062

	Table 10 (2)
Ms type	LME49860	AD8066		AD826	JRC2114
Uin (in)
K g7% (5k)	0,000012	0,000032	0,000024		0,000092	0,000039

	Table 10 (3)
Ms type	THS4062	AD8599	LT1220	AD825
Uin (in)
K g7% (5k)

	Table 10 (4)
Ms type	LME49710		LM6171
Uin (in)
K g7% (5k)	0,000013	*5,210 -6**

Analyzing the data given in Table 10, one can notice that the choice of microcircuits for building signal level controllers with low distortion is much wider.

Best ICs in this inclusionLME49860, LME49710 andAD8066... In addition to excellent nonlinear distortion characteristics, they also have an excellent distortion spectrum: 2-3 harmonics at an input voltage of four volts.

Excellent characteristics andJRC2114, OP275 andNE5532... The spectra of the first two microcircuits contain 4 - 5 harmonics at an input voltage of 4 volts, butNE5532 is long, with a dip. It is best used when the input voltage is less than four volts.

Good spectra (four harmonics) at an input voltage of 4 volts and yAD826, THS4062, LT1220... MicrocircuitsOPA2134, AD5599 andAD8620 it is better to use at an input voltage of two or less volts. HaveLM6171 v inverting distortion is significantly higher, and the nature and behavior of the spectrum from the supply voltage is the same as in the non-inverting connection.

As mentioned above, in practice, it is problematic to realize the high distortion potential of this type of regulator due to the inherent disadvantages of this inclusion. So, to obtain an input resistance close to 10 kOhm, it is necessary to select rather high-resistance resistors (more than 30 kOhm) in the inverter circuit, which will lead to a significant increase in the noise of the regulator and reduce the number of microcircuits capable of working at a sufficiently high quality level in this connection. To a large extent, these problems can be solved if a ladder-type signal level control is used in this inclusion ...

… To do this it is necessary to disconnect the load resistor of the regulator from the common wire and connect it to the inverting input of the op-amp, as shown in Fig.16.

All the advantages of this regulator are preserved in this inclusion. With a controller gain of 0dB, the circuit is a unity gain inverter with an input impedance of 10kΩ. The maximum distortions of such a regulator correspond to the maximum signal at the input of the inverter and will correspond to the data values given in Table 10. At the input of the regulator, you can turn onRC circuit for limiting high frequencies without fear of increasing harmonic distortion. As the voltage decreases, distortion will also decrease, which is a normal and natural property of the regulator in this inclusion.

The maximum signal attenuation and frequency response are determined by the maximum attenuation of the regulator and its frequency response.

Running a little ahead, we can say that this is one of better solutions allowing to obtain the minimum achievable nonlinear distortion with a "soft" and short spectrum. In this inclusion, distortions are achievable that do not exceed the level of units of a hundred thousandths at 4 volts at the input with a monotonic decrease in distortion as the attenuation coefficient of the regulator increases.

The only “not strong” part of the regulator is noise. They will be determined by resistors (equivalent value no more than 6 kOhm) and the inverter noise transfer ratio (equal to two) ...

It should also be noted that in the course of experiments at non-inverting Turning on the amplifier, the author revealed an increase in distortion with an increase in the mounting capacity of the regulator. Therefore, when assembling the circuit in this version, special attention should be paid to the elements of the regulator, their location and installation method!

2. Coordination of Nikitin's volume control with circuits based on op-amp and transistors.

An example of matching Nikitin's volume control with non-inverting amplifier:

click-to-zoom

Here, the input impedance of the amplifier is determined by the value of the resistor R11. To match the volume control, its nominal value is 10 kOhm. If you need to get more gain from the op-amp, you can increase the value of the resistor R12.

Let me remind you that in this circuit the potential of the operational amplifier (in terms of parameters and sound quality) is not fully realized and the circuit is quite sensitive to the capacity (quality) of the installation. Therefore, it is recommended to use it only if absolutely necessary.

When using op-amp in inverting switching on the above disadvantages are eliminated:

click-to-zoom

Here, the input impedance of the amplifier is determined by the value of the resistor R11. For agreement with Nikitin's volume control, its value was chosen 10 kOhm.

Attention! In the above diagrams, the resistor values are indicated to match the Nikitin volume control with the load. 10kohm... If the regulator is designed for a different load (for example, using the table from) the values of the indicated resistors need to change on the appropriate.

An example of matching a regulator with a real amplifier:

the figure shows the input stage of the modernized power amplifier by V.Korol:

The cascade is made according to a push-pull scheme, and with identical parameters complementary transistors T1 and T2 due to mutual compensation of base currents, the input resistance of such a stage will be determined mainly by the value of the resistor R1.

To match such an amplifier with Nikitin's volume control (by 10 kOhm), it is enough to install a 10 kOhm resistor R1:

click-to-zoom

3. Coordination of Nikitin's volume control with tube stages.

I suspect that some readers may find the regulator's input impedance (10kΩ) relatively low. Although in most modern devices ( sound cards, CD / DVD players) at the output there are buffers that allow you to connect a load of at least 2 kOhm, however ...

Suddenly someone wants to load tube stage to this regulator.

In this case, if there is no cathode follower at the output, to match the relatively low input resistance of the regulator with the high output impedance of the circuit (resistive tube stage or SRPP), you can use the buffer stage proposed by Zyzyuk (it must be turned on between the output of the tube stage and the volume control):

Setting up the circuit (performed with a short-circuited input - connect the free output C1 to the "common" wire of the circuit):

resistor R4 sets the quiescent current VT2 equal to 35mA.
resistor R1 is set to "0" constant voltage at the output of the circuit.

At the specified currents and voltages, no heat sinks are required for the transistors.

And even better would be to use "", picking up the input and output resistance.

Good luck with your creativity, high-quality sound and working schemes!

Somehow it so happened that with all the large number of reviews, I almost never wrote reviews of devices in one way or another related to audio equipment. Although, of course, I have an overview of the power supply for the power amplifier, but in my opinion this is quite an indirect relationship. And so I decided to pay attention to amplifiers, DACs and other audio devices and start with the volume control.
This volume control was chosen more for aesthetic reasons, since it is functionally very simple and therefore the review will not be very long today.

As you already understood from the preface, I will build some kind of amplifier, most likely with a DAC, but in this case it is not particularly important. I used to do a lot of this technique, but years passed and one was simply forgotten, a lot of new things appeared instead of the other, therefore I will partly remember, partly self-educate because mistakes and inaccuracies are possible, for which I will forgive in advance.

The topic of audio technology was indirectly touched on in, where I showed a power supply for a power amplifier. Most likely, this PSU will continue to take part, most likely as an experimental one to understand the difference between a switching and a conventional power supply, but this is a topic for future reviews, but for now I will move on to today's topic - the volume control.

It is clear that now the sound volume can be adjusted not only by interfering with the electrical path, but also programmatically directly from the source, but personally I do not really like this approach and I adhere to the "classic" solutions in the form of an analog volume control.

To begin with, it is worth saying that the volume controls are linear and logarithmic, as well as with loudness, I see no point in touching them, since this is more a matter of taste, but I will explain very briefly:

1. Linear or logarithmic.
Linear changes the division ratio in direct proportion to the angle of rotation of the regulator shaft.
The logarithmic (or, more correctly, the reverse logarithmic) is more suitable for human hearing, since at the very beginning the adjustment is very smooth, and towards the end it is more abrupt. The human ear is better at distinguishing the volume level weak sounds, therefore, at the very beginning, the adjustment is smooth. When the volume is high, the difference is less noticeable and there the adjustment can be coarse.

There are three main characteristics:
A (in the imported version B) - linear, the change in resistance linearly depends on the angle of rotation. Such resistors, for example, are conveniently used in power supply voltage control units.
B (in the imported version C) - logarithmic, the resistance at first changes sharply, and closer to the middle more smoothly.
B (in the imported version A) - inverse-logarithmic, the resistance at first changes smoothly, closer to the middle more abruptly. These resistors are commonly used in volume controls.
Additional type - W, produced only in imported version. S-shaped control characteristic, a hybrid of logarithmic and inverse-logarithmic. To be honest, I don't know where they are used.
Anyone interested can read in more detail.
By the way, I came across imported variable resistors in which the letter of the control characteristic coincided with ours. For example, a modern imported variable resistor having linear characteristic and the letter A in the designation.

2. Loudness.
At a low volume level, the human ear hears the MF range better, but worse than the LF and HF, therefore, forced frequency response correction is added to some regulators at the very beginning of the adjustment. Usually the loudness is switched off, since not everyone likes it and then there is an opportunity to have the original sound. The simplest loudness is a small capacitor between the input signal and the moving contact of the resistor. In the more "advanced" resistor has one or more taps, allowing you to adjust the correction more accurately.

For a better understanding, families of sensitivity curves of the human ear were built - averaged graphs of the dependence of this sensitivity for different frequencies of audible acoustic vibrations.

The figure below shows these graphs, called equal loudness curves, which have been adopted as an international standard.

Option to include a conventional variable resistor to obtain loudness compensation.

And the inclusion of a special resistor.

In my case, for the most part, you could just use a regular variable resistor. Below in the photo is an example of simple variable resistors, on the left it is more expensive, on the right it is simpler, but they have the same essence, a variable resistor. High-quality variable resistors are produced by Alps and they are very expensive.

But a much better option is a step regulator in the form of a set of switchable resistors. In fact, this is a multi-stage attenuator, the advantage of which is the setting of arbitrary control characteristics, but more importantly, a more accurate matching of the channel identity.
There are ordinary variable resistors with a ratchet, do not be confused, this is completely different, in fact there is just "emulation".

Step regulators are most often used in high-end equipment, for example, I first met it in the popular Odyssey 010 amplifier. By the way, if you wish and with some patience, you can make such a regulator yourself from a multi-position switch and selected resistors.

Or even so, essentially just a switch with a bunch of resistors.

If you replace the switch with a relay, you can make a more beautiful solution, which also has the ability to remotely control. For the sake of simplicity, the resistors are binary controlled in this case. By correcting the resistor values, you can also set the logarithmic characteristic.
By switching the division ratio using fixed resistors, you can get a relatively in a simple way large adjustment range, 1 relay - 2 levels, 2 relays - 4 levels, 3 relays - 8 levels.
The photo below shows a regulator with 256 adjustment steps. It is controlled by a special microcircuit - which converts analog signal from a variable resistor in binary code... In this case, the variable resistor simply changes the constant voltage and is not connected in any way in the signal circuit.
In this case, special relays must be used - signal, and not power, since at low voltages and currents, power relays cannot provide high-quality contact.
But besides, such a regulator has an advantage, it can be easily made multichannel by simply adding one more board with a relay in parallel.

On the bottom of the board, you can see a pair of resistors near each relay. In general, initially I had the idea to buy just such a regulator, but then I changed my mind and later I will explain why.

The well-known Nikitin regulator is assembled in approximately the same way, its advantage is that the input and output resistance is always constant, which has a better effect on the quality of work and less impact on the parameters of the rest of the circuit.

As it was written above, step regulators allow you to implement remote control, but if you wish, you can buy a regular regulator "with a motor" controlled by a special controller. In fact, it is, the shaft of the variable resistor can be rotated both manually and from the remote control, then a small motor with a gearbox will do it, while the adjustment knob will also rotate, and if you add some kind of position indication LED to it, it looks pretty spectacularly.

In general, I was thinking about which regulator to use and accidentally came across a very curious option that interested me more in the type of display, but more on that later.
The kit includes:
1. Regulator board
2. Control board with display
3. IR remote control
4. Light filter
5. Power supply and output wires
6. Flat cable for connecting boards, length 280mm
7. Knob of the regulator.

You can also buy separately
1. Power transformer 12 Volt 5 Watt - $ 2.22
2. Load control board - $ 3.7
3. Pay extra for gold-plated RCA connectors - $ 1.47

I bought in the "basic" configuration, since I have a transformer, you can make a relay board yourself, and I have little faith in the "gold-plated" connectors for one and a half bucks. I was worried so that the display would not be broken on the way, but nothing happened.

A set of all sorts of little things is nothing special, a blue filter, a cheap pen and a couple of wires.
For now, I will not remove the protective paper from the light filter, since I still put it in the case and would not want to scratch it.

The remote looks like some kind of AOC TV, moderately comfortable, but has a glossy body. It looks good, although there could be fewer buttons since most of them are unnecessary.
Inputs can be switched both with the Input 1-2-3-4 button, and with the Bright buttons in any direction.

The main board, on which the relay, the regulator and the power supply unit of the whole set are located.

I don’t know what was meant by "gold-plated" connectors, for which I had to pay extra separately, but I got them with such as in the photo. The board is able to switch signals from four sources, all inputs are assigned to one big block connectors.

Soldering in places on a C grade, although the overall workmanship was pleasant, neat, there are mounting holes, markings.

The board is powered by an alternating voltage of 12 Volts, although it worked for me without any problems even from 9. Some capacitors have Elna markings, although in my opinion in this case it does not matter, not to mention that the Chinese are still entertainers and believe such markings are not always possible.
Also, apparently there is a voltage multiplier on the board, since the display requires noticeably more than 12-15 volts. But there is nothing wrong with the multiplier, it would be worse if the developer supplied a pulse voltage converter.

Also, four voltage stabilizers are installed here, two (78L05 and 79L05) power the regulator, one 7805 powers the relay, the second is responsible for the control board.

And here is a regulator with a four-channel switch.

The signal level is controlled by a specialized chip manufactured by Cirrus logic. At the beginning of the review, the characteristics of the regulator were not indicated, but since they actually depend on the given chip, it would be more correct to bring them exactly in this form. Although correctness is a relative concept, since they refer to the original chip, and which one is here, I cannot say.

Above, I did not write in vain about step signal regulators. The fact is that this regulator is also stepwise. In the block diagram, the attenuator node is highlighted in red, i.e. divider, and green is an adjustable amplifier.
Unlike a conventional variable resistor, the regulator can work in two modes, attenuation (-95.5 dB - 0) and gain (0-31.5 dB), the attenuator is responsible for the attenuation, and the amplifier with a variable gain is responsible for the gain.

The circuit for switching on the regulator is extremely simple, therefore, the characteristics of the set are actually determined by the characteristics of the chip, although some parameters can, if desired, be spoiled by incorrect routing.
Initially, the regulator is two-channel, but judging by the datasheet, it allows cascading and can be used in multichannel systems, you just need one or more such chips.

The board contains a connector for connecting a control panel, as well as a chip unknown to me with an erased marking.

As mentioned above, the board can control the inclusion of an additional load. For this, there are relay connection contacts on the board. 5 Volts appear on these contacts when the regulator is turned on in operating mode, switching is negative.
This output can be used to control the supply of power to a power amplifier.

1. CS3310 regulator chip
2. Transistor assembly ULN2003 for relay control, it also controls an additional output.
3. Signal relays for a voltage of 5 volts. Somewhere at home there should be the same relays, only branded, I can compare later.
4. The chip unknown to me, why the marking was erased is a mystery.

The bottom of the board is empty, most of the polygons are used as a noise shield.

Since the regulator chip has digital control, the set includes a control and display board.

The control, respectively, can be both from the encoder and from the remote control, for this a photodetector is installed on the board, for obvious reasons the filter must also capture it.

And this is why I partially opted for this particular regulator model, VFD display, or according to our VLI (Vacuum Fluorescent Indicator).
Actually, because of this, this board can be called "warm and tube", since VLI is a real radio tube, though it has nothing to do with sound. The display is really the most common here, similar ones are used in calculators and similar devices where 9 characters are enough.

To be honest, I really like such things and I would not refuse such displays, but in the form of analogs to the usual 1602, 2004, etc., but they usually cost, they really look beautiful.

The control controller and other elements are placed on the reverse side of the board, and the board itself is made in the same design as the regulator board. However, there is a remark, the board is not entirely flat, it is slightly curved away from the front panel.

Regulator control controller and display driver.

The board has pins for connection external keyboard and space for jumpers.
1. Green - keyboard - mute, select input, adjust volume. Unlike the encoder, there is a mute function, but there is no off button.
2. Red - full operation mode (attenuator + amplifier) or only attenuator.
3. Yellow - disable the memory function of settings.

1. Microcontroller control - 12C5A60S2
2. Display Driver -
3. EEPROM, presumably for storing settings.
4. Soldering the photodetector. at first I decided that everything was bad, but later it turned out that such a view is only from the bottom, the soldering is excellent on top.

To check the regulator, I connected a 9 Volt power transformer, connected the boards with a loop and ... everything can be turned on.

With a flash, and without a light filter, trying to see anything on the display is unrealistic, although here I even corrected the image in Photoshop.

Without a flash or with some kind of light filter, everything is noticeably better, the indicator itself is very bright.

On the product page, there are examples of the use of this regulator, or rather, the design of the front panel with it, although in some variants a clearly different light filter is used, much longer.

For now, I have temporarily limited myself to a piece of green light filter, which I found at home and below I will tell you about the operating modes.
1. Disabled, only the point of the right digit is lit on the display.
2. After a short press on the encoder, the regulator switches to the main operating mode, while the display shows the inscription Hello, which then disappears. Above I wrote that the board has an output for turning on an additional load, power appears on it immediately after pressing the encoder. When power is applied to the board, it briefly clicks the relay; in standby mode, all relays are disabled. To put the board in standby mode, you need to keep the encoder pressed for about a couple of seconds.
3. The display shows the number of the switched on channel and the level of attenuation / amplification of the signal.
4. If you close the Mute contacts for a while, then dashes are displayed in the level field, re-closing the contacts again turns on the sound.
5, 6. Minimum can be -96 dB, maximum +31.5 dB. The datasheet indicated a range of -95.5 - +31.5 dB.

And in the last point shown, there is a small ambush, the full adjustment range is 256 levels, and since the encoder has 20 positions per revolution, to go from minimum to maximum, you need to make almost 13 full revolutions. Of course, I love smooth adjustment, but everything has its limits ... In my opinion, 30 steps of adjustment are enough, well, if you want smoothness, then 60-65, but 256 ...

Disabling the built-in amplifier allows the situation to be slightly improved, this gives two positive points:
1. The amplifier introduces less distortion in the signal (presumably)
2. Instead of 256 steps, there will be "only" 192 or 9.5 encoder revolutions.

You can further increase the convenience by replacing the encoder with a version with 24 positions, then there will be only 8 revolutions.

If you remove the P5 jumper, the built-in amplifier will turn off, and the maximum display will be 00.0, not 31.5. Also in the photo you can see different options for the included inputs, 1 and 4. The inputs will be switched by short pressing on the encoder.
There is a mode memory, but after the power is completely removed, the regulator will turn on to the mode that was before correct shutdown, there is no separate memory for each input, the volume level is one for all inputs. If the memory blocking jumper is soldered, then the first input and the signal level -46.0 dB will be activated each time it is turned on.

Due to the fact that the display is always on, the consumption from the operating mode remains almost unchanged, 187 mA in standby mode and 236 mA in operating mode. Consumption is indicated in AC, power is about 1.7 and 2.2 respectively.

Naturally, a small check was carried out, but for the most part I rather ran into the capabilities of my measuring instruments and, in particular, the oscilloscope. For a volume control, the key is usually the linearity of the adjustment, introduced distortion and channel separation, but somehow I don't even know how to check all this with one generator and a simple oscilloscope. With an input voltage of 2.65 Volts and a level of -70 dB, the voltmeter shows about 1 mV at the output.

For the test, a full analog generator 10 Hz - 100 kHz and a DS203 oscilloscope were used.
First, I checked how the picture looks at a frequency of 10 Hz.
1. Input signal

3. Output signal at the level of +8.5 dB
4. At +9.0 dB, clipping started, but it is determined by the input swing.
5. Level -45 dB
6. Level -30 dB

Frequency 20 kHz.
1. Input signal
2. The output signal is at the level of 0 dB.
3. Output signal at the level of +12 dB
4. Since the input signal swing is less here, the limitation began at +12.5 dB, with a further increase in the gain, the signal gradually turns into a rectangle.
5. Level -45 dB
6. Level -30 dB

The maximum that my generator can do is 100 kHz, at this frequency I also decided to check.
1. Input signal
2. The output signal is at the level of 0 dB.
3. Output signal at the level of +11.5 dB
4. The output signal is at 12.5 dB, at 12.0 dB the clipping was almost imperceptible so I chose 12.5 for clarity.

Since the power amplifiers are not yet ready, the DAC has not arrived at all, I tried a little with this amplifier, it works fine, according to at least the only serviceable channel :)
As a matter of fact, it is this amplifier that I will alter, I understand, clearly not Odysseus, but what we have. Although if we take into account that in fact only the body will remain from it, well, perhaps also a transformer and a radiator, I don’t think that this is important, although the same Odyssey has a much more solid appearance and design.

So far, I can briefly say that everything works, in this regard I have no complaints. The sound is regulated, the remote control works, the display shows all the necessary information, no sound distortions were noticed. I note the absence of pulse converters for powering the display, although the indication is still dynamic, but in this case it is a limitation of the display itself.
But there is also a drawback, the signal adjustment is too smooth, so I will most likely replace the encoder and turn off the built-in amplifier.
In addition, I would like to have a separate volume control for each input, but this is more like a "wishlist", because this is usually not used.

The overall workmanship is not bad, I don't see any frank jambs. Unfortunately, I can't check the originality of the regulator's chip.

This review was sponsored by an intermediary who took over the shipping costs.
The cost of the kit together with delivery to the reseller is $ 30.66, the cost of delivery from the reseller depends on various factors. The set weighs 364 grams, information from the order page from the reseller.

That's all for now, as usual I'm waiting for questions, tips, wishes and the like, I hope that the review was useful.

The product is provided for writing a review by the store. The review is published in accordance with clause 18 of the Site Rules.

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