Replacing broken volume control with digital volume control

[Gunawan W]

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]

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 ?

 

[banana]

I agree with Mooly, it will be difficult to use a volume pot to control digital attenuator. I have made it by feeding the pot with 5Vdc, and then encode the pot voltage by an ADC. The whole thing is quite clumsy. See link below.

http://www.diyaudio.com/forums/chip-amps/107196-bananas-pre-inelegant-way-contrl-vol.html

 

[Gunawan W]

Thank's Guys,
I searched the net, and I find more simple solution using optocoupler like this:
DIY "Lightspeed Attenuator" - Passive LDR Volume Control (audio optocouplers)

what do you think?

 

[Mooly]

Thank's Guys,
I searched the net, and I find more simple solution using optocoupler like this:
DIY "Lightspeed Attenuator" - Passive LDR Volume Control (audio optocouplers)

what do you think?

It needs a dual pot... and yours is broken

 

[h_a]

All the original pot can do is generate a variable resistance (or voltage) and nothing more.

No problem with that, use ADC to get the position/direction.

But, of course, I agree with Mooly, it's a not so easy task, even more so for commercial multichannel amp with little space left.

 

[Gunawan W]

How about this schematic? it use single pot....

diyparadise - all about volume control...

 

[Mooly]

How about this schematic? it use single pot....

diyparadise - all about volume control...

Who are you trying to convince...

How much current is going to flow via the pot wiper at the end of it's travel. I'll let you worki it out... I wouldn't count on the remaining good side of your pot staying good for very long though

 

[Gunawan W]

Hi Mooly,
I don't know how much current...
I only knew that the right channel was broken, maybe it was because my daughter turn it at max at one time when I turn it it on... the amp is 100 watt per channel.

thank's

 

[Mooly]

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.

 

[Gunawan W]

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?

 

[tomchr]

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]

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

 

[BobEllis]

Hi Mooly,
I don't know how much current...
I only knew that the right channel was broken, maybe it was because my daughter turn it at max at one time when I turn it it on... the amp is 100 watt per channel.

thank's

Are you sure it is the pot and not the right channel amp? What are the symptoms that make you think the pot is broken?

 

[Speedskater]

From the description of the failure mode, I too doubt that the problem is the pot.

 

[Gunawan W]

Hi Mooly,
it is Yamaha DSP A-970, I can't take picture, because the unit still at my friend.
Hi Bob,
yes it is broken, I already tested it.

 

[Wavebourn]

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.

 

[Mooly]

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 ?

 

[analog_sa]

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.

 

[farjon]

What about this?

audioPT - Pré-amplificador audioPT 1

You can translate it on Google.