Volume Control

RustyH

Senior Member
Can anyone help in how I would add a volume control to this circuit

I bought a amp module that uses this IC, but could really do with volume control on it

TDA7850H.jpg
 

BeanieBots

Moderator
Assuming that a PICAXE will be controlling it, there are a few options.
An I2C controlled potential divider chip at the front end.
A FET forming the lower part of a potential divider with RC'd PWM controlling its gate voltage.

Assuming standard audio frequencies and no other information besides the series 0.1uF input cap, to be safe on the side not loosing too much bass response, I would towards a lowish source impedance of around 2k for any front end method of potential division. (ie 2k POT [log type for audio])
 

John West

Senior Member
Assuming manual control of the volume, as in BeanieBots' second suggestion, I'd replace the .1 uF caps with 10uF (nonpolarized) ones to help ensure good bass.
 

RustyH

Senior Member
Gulp......

I was hoping it was going to be a simple addition of a POT or something!!

I was planning on doing this with out a PICAXE if possible.
 

BeanieBots

Moderator
Gulp......

I was hoping it was going to be a simple addition of a POT or something!!

I was planning on doing this with out a PICAXE if possible.
What did you expect from a PICAXE forum? A non PICAXE solution!
A simple (log) POT would do the job for a simple manual volume control but it has to be assumed on this forum that you are after a PICAXEable solution.
As mentioned, bear in mind your source & input impedances for the frequency response you need. You will need to know the amp input impedance to know if it is worth going with JW's cap change suggestion but I'd probably do it as a matter of course anyway.
 

AllyCat

Senior Member
I was hoping it was going to be a simple addition of a POT or something!!
Hi,

The implication from the diagram is that you need to control four channels, but four-gang pots are not particularly available, nor cheap! Also note the reference to a "Log" pot to achieve a subjectvely linear volume characteristic.

Do you also want/need "Balance" (Left/Right) and/or "Fade" (Front/Back) controls? If so, there are probably many dedicated/custom ics which can do the job.

However, if you want to Do It Yourself "on the cheap", then an audio attenuator can be made with "variable resistors" of various types, such as MOSFETs or Light-Dependent-Resistors. My first remote-controlled "Quadraphonic" audio controller used 4 torch bulbs (before the days of LEDs) illuminating 4 LDRs (to give the above-mentioned Volume, Balance and Fade controls).

Cheers, Alan.
 
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