Made a progressive volume control circuit

cruelfox

Made a progressive volume control circuit [Copy link]

 

The effect of installing it on my headphone amplifier: (The machine cannot be covered; the green PCB below is also an additional one, input switching circuit.) The board was made when the 5 yuan proofing started, but I just didn't start soldering. 5 double-pole double-throw relays can achieve 32-level volume control. The circuit principle and calculation can be referred to this webpage: (I won't post the URL to avoid post review) This is my first time using MELF resistors for production. I didn't expect that this small and round one is more difficult to solder than 0603 resistors - it is easy to run. I knocked a few of them away when I took them out of the material strip... It's hard to find them when they fell in the house. Although it's small, it's an order of magnitude more expensive than the direct-insert metal film resistor. It took me a lot longer than I expected to solder it (including resistor selection and matching), and this is without the control part. The MCU board will be made next weekend. Now I can control the volume by setting the relays one by one (finally my headphone amplifier without volume control is over, I can listen to it with different headphones), and the human brain will do the decoding

gmchen

Haha, using relay control will definitely minimize the noise! Are you planning to make automatic volume control next?

人去搂空

Thanks for sharing!

cruelfox

gmchen posted on 2019-6-3 06:59 Haha, with relay control, the noise is definitely the lowest! Are you going to make automatic volume control next?

Not automatic. The advantages of potentiometers are large adjustment range, simplicity, and left-right consistency. In fact, the ALPS 27 model I use is not a big problem. However, its attenuation characteristics and rotation angle ratio are not ideal. In actual use, it is basically only adjusted within a small angle range. The freedom of using resistors is greater, and each gear can be set by yourself. It can be done with a multi-band switch, but it is very expensive and can only make 24 gears at most. As a compromise, relays are used. The cascaded attenuation network can achieve accurate stepping of 2N gears according to dB. I did this with 5 relays, and the parts cost was comparable to an ALPS 27 potentiometer. As for the labor cost... DIY is pure hassle.

gmchen

cruelfox posted on 2019-6-3 13:38 I don't do automatic ones. The advantages of potentiometers are large adjustment range, simplicity, and left-right consistency. In fact, the ALPS 27 model I use has no big problems. But its attenuation...

Oh. The volume should be adjusted with an exponential potentiometer, and a linear potentiometer will definitely not work. But I don't know if this kind of potentiometer is still available. I haven't worked on audio circuits for many years, and I don't care about these things

gmchen

Also, can this circuit be realized using an R-2R network? I haven't thought about it carefully. If it can be realized, the types of resistors will be greatly reduced.

cruelfox

gmchen published on 2019-6-3 16:53 Oh. Exponential potentiometers should be used for volume adjustment, and linear potentiometers definitely won’t work. But I don’t know if this type of potentiometer is still available for sale now. It has not been available for many years...

There are many (type A) potentiometers dedicated to volume. This type will always exist because there is a demand. The problem is that it can only approximate the logarithmic attenuation characteristics within a certain range, which may not meet the needs. I will test one and post the data later. In addition, carbon film has its own problems. When the requirements are not very high, the ALPS dual volume potentiometer is sufficient.

cruelfox

gmchen posted on 2019-6-3 16:55 Also, can this circuit be implemented using an R-2R network? I haven't thought about it carefully. If it can, the variety of resistors will be greatly reduced.

Yes. There is also an application of using R-2R DAC to directly control the volume, with the reference as the signal input. Because the voltage divider ratio of R-2R is linear, many bits are required to meet the changes in the minimum volume, which requires more relays.

vosrock

Finally found the teacher. This website is very convenient for calculation. I even made an attenuator with DIP switches, and the precision is very high. I wonder if the original poster has made an MCU?

cruelfox

vosrock posted on 2022-2-10 00:51 I finally found a teacher. This website is very convenient for calculation. I even made an attenuator with DIP switches. The accuracy is very high. I don’t know if the host made an MCU...

It is very simple for MCU to control several relays. The I/O port can directly drive the NMOS tube to control the relay.

The trouble is the wiring layout of the whole machine. If potentiometers were used originally, there will be a lot of flying wires to change.

wuguangyue

The original poster is asking for the URL of this calculation. I can’t open it when I copy the link?

cruelfox

wuguangyue posted on 2023-2-1 17:10 I want the URL of this calculation. I can’t open it after copying the link?

Just enter the data in the browser according to the picture.