for an amplifier (DACT potentiometer) practically does not change frequency response when adjusting the volume, which has a positive effect on the linearity of the entire amplification path at all volume levels.
The mechanical design of the DACT volume control has fine adjustment of the pressure of the motherboards, on which precision, thick-film, packageless chip resistors are located. This design solution makes it possible to adjust the gap and clamping force mechanical parts, in which natural mechanical fatigue of contact groups accumulates. Therefore, the life of the volume control (failure) depends only on the efficiency of the user.
Note that over many years of experimental work it was not necessary to further adjust the DACT potentiometer. However, in newer DACT volume controls, the contact plates (sometimes) do not have tight mechanical contact and the audio signal may not pass through.
It was experimentally found that the sound qualities and reliability of discrete miracle resistors DACT are at a high level, and in terms of sound quality they are comparable to the best examples of metal film resistors such as: VISHAY, HOLCO.
The high cost of the DACT potentiometer is compensated high quality sound reproduction, which is why this volume control is used only in exclusive High End Audio amplifiers. Price from $200.
The sound quality of Alps volume controls (of different types) corresponds to their price. Price 10 - 25$. Both Alps potentiometers reproduce sound approximately the same and (in our opinion) are not at all suitable for use in high-quality High End Audio amplifiers.
After the discrete DACT volume control, I don’t want to turn on the Alps potentiometer and listen to it - the sound is very muddy and dull. All conclusions that the difference in sound quality between different volume controls is not fundamental are based on a “false theory”. “Fake theory” - suggests the author who did not have the opportunity to experiment with audio components of this class, or does not have a decent amplifying sound path.
One of the important parameters of volume controls is the mismatch of the right and left channel sections, since this phenomenon determines the spatial characteristics of the entire amplifier.
- Section mismatch: "DACT" +/- 0.05dB.
- Section mismatch: "Alps" +/- 1.5 dB.
When submitting DC voltage(24v) to the Alps volume control, it begins to crackle (when rotated) and after three turns burns out irreversibly, this is due to the small passing current of the sliding contacts and their negative resistance. The DACT volume control easily and for a long time keeps a constant 60V (we did not check above), so there are no complaints about the general design of the DACT potentiometer.
This experiment was carried out solely to test the reliability of the regulators.
Sometimes low-reliability pass-through capacitors are installed in tube stages (in some CD players), and there is a real situation of breakdown of the dielectric of such a capacitor, which will cause a negative DC voltage to enter the amplifier input. Therefore, the overall survivability of the amplifier also depends on the reliability of the potentiometer.
I was about to make a step volume control on a permalloy trance for my preamplifier and plunged into the search for a suitable biscuit. Imported ones, like Shallco, are cool, and their price is higher than eggs - tens and hundreds of euros. I began to monitor the professional suitability of our domestic ones, and settled on PGK-11P2N.
An old proven example of the Soviet radio industry - ceramic biscuits, a simple axis rotation mechanism, silver blade contacts.
But for use as a volume control there is a significant disadvantage - switching with a break before make.
First, I disassembled the bib itself, then, using a 3mm diameter drill, I manually drilled out three rivets and got three parts - a getinaks washer, a ceramic bushing and a slider.
For the new slider I used (as well as for the AC terminals) the linings of the air HF conductor - silver copper.
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I would like to draw particular attention to the fact that the screw heads should not cling to the central current collector when the axis rotates. When assembling, remember to correctly orient the slider and ceramic sleeve on both biscuits.
The second inconvenience is the rather rigid movement of the axle. The steel ball is pressed against the axle disk by two powerful spring plates.
It was possible to soften the stroke by fully unbending the outer (most rigid) spring and easing the pressure of the inner one. To make the ride smoother, I updated the lubricant on the ball and disk of the axle.
At the end of the assembly, making sure that nothing interfered with the free movement of the slider, I applied conductive grease HCG (High-Conductive Grease) to its surface; it is used in repairing printers; you can also take our native Tsiatim-221 (I once used it lubricated contact groups current collectors of coils of circuits of 5 kW transmitters).
And in conclusion, I am once again convinced that there are quite worthy of attention things that are practically the same in quality, but very much better in price! You just need to lean over them and take a closer look.
Traditionally, a variable resistor is used to adjust the sound level - potentiometer, where the change in resistance is realized using an electrical contact that slides along the resistive layer. An example of well-known audio-grade regulators are Japanese ALPS. However, few people know that they also produce discrete step regulators, which are also installed in high-end equipment. This device consists of a series of fixed resistors that are switched in turn.
Despite the more complex device and design, they have certain advantages over a smoothly rotating potentiometer; this is an improvement in the quality of electrical contact compared to a slider. There is improved consistency between individual audio channels and they are less susceptible to dust and abrasions. In such a RG, crackling and rustling are practically eliminated. The discrete sound level control practically does not change the frequency response when adjusting the volume, which has a positive effect on the linearity of the entire amplification path at all volume levels. The price for them, naturally, is much higher than for ordinary ones, but we are not going to buy them, but will try to make them ourselves.
Discrete volume control circuit
Three variants of DRG schemes
Shown above are three practical schemes such a regulator that you can assemble yourself. How many switching stages to choose - decide for yourself. In practice, 5-10 is enough. It is advisable to take high-quality resistors, with a power of 0.125-0.25 watts.
Naturally, you need a double switch to simultaneously adjust the volume on both channels of the stereo amplifier. It is recommended to shield the discrete switch itself in order to reduce the level of electromagnetic interference to zero. If you took a switch with too tight a move (which many Soviet ones do), disassemble it and loosen the spring. At the same time, clean the contacts with a soft student eraser.
On a TDA1552 chip for sound control? Regular double resistor. What if we have quad switching for 4 channels? Someone suggests - a quad controller :) What if we assembled a home theater with 6 channels? This is where complex and expensive electronic volume controls on specialized chips come into play. And such a unit can exceed the amplifier itself in complexity and price. However, there is a simple way out, how to implement the volume control function with just one transistor. The circuit proposed below from a 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 or 10 of them. 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 bypasses the ULF input - the volume decreases.
A number of experiments were carried out with this scheme. It turned out that the base power can be taken starting from 1.5V. The maximum voltage limit is determined by a 1 kOhm limiting resistor. If we found, say, 12V, then the resistor must be increased to 30 kOhm, which is safe for the base current. The current consumption of the base circuit in the open state is several milliamps. In general, you will choose.
When the transistor is open, a very quiet sound may be heard due to the voltage drop across the silicon crystal. For complete silence, you need to use a germanium transistor of the MP36 - MP38 type.
The capacitors at the input and output of the electronic volume control are non-polar. We install any transistor low-power N-P-N, type KT315, KT3102, S9014, etc. Variable resistor for an electronic regulator with a 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 slider to the power positive, we gradually open the transistors and the sound will begin to subside. Using the resistor that is connected to the power positive, we set the smoothness of the volume change throughout the entire rotation of the resistor. So that it doesn’t happen when after half a turn the volume disappears and we continue turning in vain. Using this electronic volume control, on the one hand, will slightly increase the noise level, but on the other hand, it will reduce interference on the wires, since now there is no need to pull a twice-screened wire from the preamplifier output to the power amplifier input.
There are special controls to change the sound settings. Based on their frequency, they are divided into active and passive. Additionally, the division is carried out according to the type of setting. The most common are considered to be digital regulators. They are created under different types amplifiers and have their own channel. To understand the operating principle of these devices, you should understand their design in detail.
How does the regulator work?
Microcircuits are considered to be an important element of the regulator. In terms of their parameters, they can differ quite a lot. If we consider professional models, then there are up to 100 different contacts. Additionally, the regulator contains a controller that is responsible for changing the limiting frequency of the device. Capacitors cope with interference in the device. In a simple model there are up to four of them. Usually found in the regulator. Their frequency is usually indicated in the labeling.
In professional models, electrolytic capacitors are installed. Their conductivity is much better, but they are expensive. Resistors in a standard circuit can be found up to ten units. They differ from each other in terms of ultimate resistance. The simplest models can boast a parameter of 2 Ohms. Resistors with such indicators are found quite often. Finally, the last element of the regulator should be called the closing mechanism. Most often it is presented in the form of a button, but there are models with a complex display system.
Application of electronic model
Electronic volume control is installed on almost all audio devices. You can change the oscillations different ways. Most often you can find smooth controllers, which allow you to very subtly infuse the sound, but there are also jump systems. In this case, the parameters are changed step by step and abruptly. Recording studios have multi-channel mixers. They allow you to adjust many effects. If we consider a combined electronic volume control, then much in this case depends on the speaker system.
Self-assembly of the regulator
In order to assemble a volume control with your own hands for a medium-power amplifier, you will need a microcircuit with at least 8 bits. It is best to use bipolar transistors for this. Usually they are presented in the store with the marking "2НН". Their average resistance fluctuates around 3 ohms. Controllers are mainly linear. They allow you to change the limiting frequency quite smoothly. In this case, the amplitude of the interference will depend solely on the capacitors.
For a regular regulator, it will be enough to install three of them. LEDs can only be used in conjunction with rectifiers. In some cases, in order to make a volume control with your own hands, it is also recommended to use a zener diode at the beginning of the circuit. This element significantly increases the performance of resistors and the regulator as a whole.
How are the headphone controls arranged?
The headphone volume control only has two capacitors. Distinctive feature Such devices can be called weak bandwidth. The signal in many models takes a long time. This is due to the fact that transistors are not designed for high power. Some models of regulators have resonators installed. They exist in different types and have their own parameters. Most often you can find their resistance parameter reaches 4 ohms. In turn, ferrite analogues can only withstand 2 ohms. The volume control for the headphones is connected to the speaker using a throttle.
Tone control circuit
The tone and volume controls are operational. It is suitable for amplifiers of different powers. Diodes in this case are installed quite rarely. Rectifiers are only available in models with less than three transistors. Resistors in devices are switched on with the marking “BC”. They have a pretty good one, but they are sensitive to high temperatures. The capacitors in many models are bipolar. The maximum resistance of the tone and volume controls can withstand 3 ohms. The standard model has a "PPA" socket for a regular ring. The inductor and resistor are connected only through a converter.
How to configure the regulator in Windows?
Setting up the controller is quite simple. The icon for this item is located on the Start panel. By clicking on it once with the left key, you can change the limit frequency. In some cases, the user does not see the specified icon. This happens because the Windows volume control is not added to the notification area. It is usually transferred to automatic mode operating system. However, this action can also be performed manually through the control panel. The reason may also be the absence of the Sndvol.exe file. In this case, a copy of it must be saved on your computer.
Stereo control parameters
Their noise figure is around 70 dB. The nonlinear distortion parameter is usually 0.001%. The operating frequency range ranges from 0 to 10000 Hz. The input voltage of the device is 0.5 V. In many models, the controllers are installed reversible. The output voltage should be no more than 0.5 V. A stereo volume regulator usually has a pulse regulator. The device is powered through a unit with a voltage of up to 15 V.
Microphone models with controls
A microphone with a volume control is a common device today, and the microcircuit in it is usually of the MK22 series. The bandwidth of the models is quite high, the signal passes well. There are two diodes in a standard circuit. One of them is usually located near the locking mechanism. Capacitors are installed with various parameters. This is necessary in order to control frequencies of different magnitudes.
Their average resistance is up to 4 ohms. The capacitors in the regulator should only be electrolytic. In this case, this will give a large increase in the sensitivity of the device. There are up to eight resistors in a standard circuit. They maintain an average resistance of 3 ohms. The volume control directly locking mechanism is in the form of a controller.
Push-button controller circuit
The push-button volume control (diagram shown below) differs from other devices in that its diodes are arranged in pairs. As a result, the microcircuit transmits the signal to the resistor quite quickly. Many models do not have rectifiers, and this should be taken into account. There are up to three units of capacitors in the standard circuit. Their resistance is kept at a maximum of 2 ohms. The noise figure of such models fluctuates on average around 50 dB.
The nonlinear distortion indicator, in turn, is equal to 0.002%. Among the disadvantages, certain problems with unevenness should be noted. This is due to the small range of operating frequencies. In some cases, it makes sense to install an amplifier with a voltage of more than 15 V. In this case, the sound parameters will increase.
Passive regulators
The passive volume control differs from other devices in that it is multi-channel. Their average resistance is maintained at 3 ohms. Locking mechanisms are installed as standard. In turn, the controllers in them are exclusively digital. Thanks to this, it is possible to synchronize stereo sound in the device more accurately. Thus, the problem with unevenness disappears by itself.
Resistors in many models are of tuning type. A distinctive feature of professional models is the presence of a resonator. The output voltage of this element can reach up to 8 V. Most often, they are installed in regulators of the quartz type. There are two capacitors in the standard circuit. The chip in the system is designed for 8 bits.
Using Active Models
An active volume control is usually used for receivers whose power does not exceed 5 V. It contains resistors with a resistance of about 4 ohms. Quartz resonators are installed. A distinctive feature of these regulators can be called signal relays. Chokes, as a rule, are not used in devices. Amplifiers are specified only as operational type. In this regard, there is no need for rectifiers. You can find a wide variety of display systems in devices. For mobile devices This volume control is not suitable.
Combined regulator circuit
The combined volume control (diagram shown below) has no more than five capacitors. Transistors can only be used of the bipolar type. Their throughput is quite high. The average resistance is maintained at 3 ohms. Linear transistors are provided in the system. Stabilizers are specified only in professional models. Their maximum frequency does not exceed 4000 Hz.
How does a thin-compensated regulator work?
Regulators of this type Mainly used in radios. Their system is quite simple. The microcircuit in the device is installed in the "KR2" series. There is a controller directly linear type. Only one transistor is used. It is located next to the microcircuit.
There are only two capacitors. Most often you can find the electrolytic type. they can withstand 16 V. However, the output signal is perceived rather poorly by the device. There are no more than five resistors in the regulator. All of them are set with a maximum frequency of about 3000 Hz.
Professional models
Professional microcircuit regulators are multi-channel. Taking this into account, for normal operation they require it. It is usually located next to the capacitor. The system is designed for an 8-bit load. The closing mechanism in the device is installed as usual. The noise figure of the device reaches a maximum of 55 dB. The nonlinear distortion indicator in some cases can exceed 0.001%.
The operating frequency fluctuates on average around 2000 Hz. Such schemes rarely experience problems with uniformity. The output voltage of the device is 0.5 V. The resistor decoupling can withstand a maximum resistance of 3 ohms. Converters are provided in the system, and they are attached to the board only through a choke. There are about three capacitors in the standard model. They are quite enough to cope with various signals. It must be located near the device socket
Electronic tone controls
All electronic regulators are compact in size and can withstand high maximum voltage. In this case, they are not able to work without an amplifier. Stabilizers, as a rule, are used only linear ones. The diode circuits are located immediately behind the board.
Distortion by the device is suppressed by resistors. Stabilizers help the regulator cope with the maximum frequency. Rectifiers are installed extremely rarely. The energy consumption of such devices is high, and they do not require converters. You can see these devices on mixers quite often.
