Controlling volume of an amplifier..

[mister_e]

Nah.. no need for servo... there's some motorized pot and faders already available on the market. Penny & Giles are the really first that spring to mind (for faders). Almost sure that ALPS do some as well.

[abidr]

Ioannis:
I think what you have mentioned is not very difficult to achieve, but for that you ll need a bigger PIC like 16F877A and probably two ULN chips. I intend to make an input selector with a simpler PIC like 16F84A, but insted of relays I would like to use something like MPC507A or if I want to complicate circuitary I ll use something like SSM2404.
Here are a couple of PICs of the populated pre amp its a very small size PCB like 4.5x4.5 Inches.

[Ioannis]

Both chips look nice although MPC507A does not refer any distortion in audio range.

But I think the relay solution gives much better results in whole (crosstalk, distortion etc).

Ioannis

[davesatu]

Both chips look nice although MPC507A does not refer any distortion in audio range.

But I think the relay solution gives much better results in whole (crosstalk, distortion etc).

Ioannis

I agree with the posts here regarding the noise introduced by digital volume/balance controls. Have used many but mainly the Dallas DS1809 stereo chip. No matter what you do with support circuitry including the suggested bridge there is still a lot of noise if your aim is top quality sound.

So I went back to normal pots. Used Alps with motors for both volume and balance. There seems to be a move not to include a balance control for various sonic reasons. I find it essential as my recordings vary all over the place and I like the vocal "middle sweet spot". I have now settled on the circuit here - it's about try 7 I guess. Simple but good.

For my new tube pre-amp all functions and the two displays are controlled by a single 16F877 PIC. This is what it controls.

1. Ten second countdown via LED on startup to let tubes warm up prior to turning selected input on.
2. Selectable start Input default or you can code to save to start with off selected.
3. Seven push buttons for Input up/down, Volume up/down, Balance left/right plus Mute. These plus a display/buzzer on/off and standby system on/off are also available from the remote control.
4. Five stereo line inputs via relays. Three Line outputs.
5. Current Input number selected is displayed on a 7 segment LED. When the mute button is pressed the current input is turned off until reactivated. During this time the input is flashing.
6. Alert buzzer which can be programmed to do just about anything.
7. And now the good stuff. There are two other 7 segment LED's which are multiplexed to display at least at the moment a dB volume level as the default. Press a button and the current balance will be displayed. This can then be adjusted from L1-9 to R1-9 until the display says what you want. Seconds later the volume level returns.

All this is done in just one small PIC. Quite amazing. But I must tell you there are no pins left!

I spent a bit of time here to hopefully repay a little the advice received from this Forum over some years. Thanks Guys! - Happy to help if the info here is not enough.

[El_AMPo]

Been there, found this guy:

AN5262

It's a tv volume control IC. Really cheap, really nice and linear at work. Just connect it to a R2R DAC or similar and you're done (if you find the spare part that is).

[Ioannis]

TV chips are not (usually) Hi-Fi parts!

Ioannis

[El_AMPo]

TV chips are not (usually) Hi-Fi parts!

Ioannis

He didn't ask for hifi, anyway for hifi better stay with the motorized pot.
Or turn all your broadcast to digital (probably their source is digital so no point in DAC->super wire->super pot) but well audiphiles want to fight that war, i'm neutral..

[smartufo]

Ioannis:
I think what you have mentioned is not very difficult to achieve, but for that you ll need a bigger PIC like 16F877A and probably two ULN chips. I intend to make an input selector with a simpler PIC like 16F84A, but insted of relays I would like to use something like MPC507A or if I want to complicate circuitary I ll use something like SSM2404.
Here are a couple of PICs of the populated pre amp its a very small size PCB like 4.5x4.5 Inches.

Very good design Abidr.Please tell me what the IR code of your remote control (Sony,Philips..) and which compiler for your project.Thanks.