Replacing broken volume control with digital volume control

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Hi all,
I have multichannel solid state amplifier, but the right channel volume control (potentiometer) was broken.

I can not find the part for replacement, so I want to replace it with digital volume control.

My plan is using the left channel potentiometer as a control for new digital stereo volume control.

Please help me, I need circuit diagram for this,

thankyou in advance.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Using a pot to control a digital attenuator is far from easy, I don't know how you would do it without purpose writen code to interface it to a "one off" purpose built attenuator...

You could use it to control an analogue VCA (voltage controlled amplifier) though, but surely fitting a conventional replacement pot is far far easier.
Digital control usually requires either a rotary encoder for control or up/down buttons. All the original pot can do is generate a variable resistance (or voltage) and nothing more. What happens if the good side of the pot goes faulty?

Is the original motorised ? Photos ? Make model etc ?
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
The current is just ohms law.
A 5 volt supply
A resistor to limit current (stated as 24 to 100ohm)
The volt drop across the LED... say 2 volts.

So we 5-2 =3volts.
3 volts across 24 ohm is 0.125amp. As the pot is turned from zero resistance that current will burn the resistive track at the ends.

Why can you not just fit a normal pot... what's the problem. Must be far easier than all this.
 

tomchr

Member
Paid Member
2009-02-11 12:58 am
Calgary
www.neurochrome.com
Replacing the pot with another logarithmic/audio taper stereo pot is by far the easiest solution. The Alps pots are quite nice.

If you insist on using a digital solution, I suggest that you replace the pot with an encoder, use a volume control IC (like the Texas Instruments PGA2320) and use a micro controller to read the encoder and control the volume control IC.

~Tom
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Thank's Mooly,
The problem is, all the 7 channel using 1 pot rod and motorized, so if I replace 1 of the pot, I must replace all and to make it worse the part is not available...
How about using transistor as buffer to limit the current across the pot?

If there are 7 separate gangs to the pot... and that's how it reads... then with the greatest respect I do not think you realise how difficult and complex this would be. You would never match the characteristics of an LDR/or Digital arrangement to the others.

Post a picture of it all... and the make and model :)
 
You can buy a ladder type attenuator kit. It has a pot option: a PIC reads pot's positions and translates it in decibel steps. A stereo ladder attenuator with 4 switchable inputs costs around $50. One of advantages is precision tracking between channels.

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Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Nothing to suggest really... I think trying to source a replacement is the only viable option.
With the greatest respsect do you realise how big a task trying to integrate something like a totally different control system into a commercial product is ? What about maintaining remote volume operation from the same handset... yes it's all do able but it's a monumental task.

It would help to see picture of this thing (the pot). How many gangs etc. Have you tried Yamaha direct for spares... in different countries ? Similar models that use the same pot ?
 
It's really quite easy. Pic any AVR, PIC, etc with an analogue input. A few lines of code and a simple interface to any number of the many available electronic pots. All in a day's work and voila :) Provided, of course, your time is free and you have some basic knowledge of microcontrollers.
 
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