Using a TDA1524A for volume and tone control

[DaveParker]

Sirs.
Problem
I have a small pocket computer which I attach to a guitar amplifier for use in a small hall to play music.
I need a volume control and tone control to fit alongside my PDA so that I don't have to use the volume and tone controls on the amplifier, which is remote from where I sit.

My solution is to use the TDA1524A device to fit in line using the attached circuit.
I have a circuit which seems to be easy enough for me, with my limited knowledge, to construct.
However, the circuit needs a 50k linear pot for the controls.
I can't seem to get a slider pot for that value from my usual supplier ... would 100k create a problem for the circuit?
Could I strap a 100k resistor in parallel with a 100k pot without losing too much of the linear requirement?

2nd problem, I can't seem to find a 22nf capacitor .... would a 15nf be a suitable replacement.
I don't know sensitive this circuit might be to these changes.

Any advice would be greatly appreciated.

 

[keith1200rs]

The tone control inputs can take up to 5uA maximum. I would tend to favour a lower rather than a higher value than 47k. Can you get 20k?

I cannot see a 22nF on the circuit. Do you mean 22uF? If so, 15uF will be fine - bit of bass loss maybe. You could use a larger value rather than smaller one.

Keith.

 

[DaveParker]

Many thanks Keith, for responding to this enquiry.

It is typical of me to get mixed up with my pico, nano and micros.
You are, of course, correct,... and I don't have a problem with that now!
So that is one that problem sorted! .... thank you.

The variable pots that I can find are only 10k or 100k.
Whilst there are thousands of choices for rotary pots, there seems to be a shortage of choice on the slider types ... at least at a price that makes the project cost-effective.
Is the paralleling of a 100k resistor with the 100k slider a non-starter?

 

[keith1200rs]

Putting 100k across the pot won't help. It is supplying current into the control pin that matters. I think I would be tempted to go for 100k. If there seemed to be anything funny happening then I would probably add two 47k resistors to each pot - one each from the wiper to the two ends. It would mess up the linearity a bit but I don't suppose you are writing calibrated dB markings on the slider!

Keith.

 

[DaveParker]

Many thanks Keith.

I hadn't realised that 100k across the slider wouldn't work..... I thought it would bring it down to 50k, but with a funny old gradient.
I am glad I asked.

I will try as you suggest.
First with the 100k, which I have, then try the 47k to the slider if that doesn't seem to work.

I don't often get a chance to try out this electronics hobby of mine ... but when I do I get a great buzz of anticipation when I start again.

Thank you for your advice ... I am happy to give it a try now.

Excellent!

dfp

 

[keith1200rs]

There is something **broken link removed**about changing the "law" of a pot which is the usual reason for adding a resistor or two (scroll down the page to near the bottom - figure 8)

Keith.

PS.

It all depends on what you mean by "across the slider". As it is a slide pot, I assumed you meant across the ends. The place you need to add resistors is from the wiper to one or both ends.

 

[DaveParker]

Keith. You are correct. It was my intention to strap the 100k resistor across the ends of the resistive track. It had not even ocurred to me to strap it to the slider. I'm am now trying to get my mind round the mathematics of your solution.

I really do appreciate your time spent on my problem. Thank you.

P.s. I couldn't find anything below which helped.

 

[keith1200rs]

I subtly put the link on the word "here" in my earlier post so you wouldn't spot it. The links don't show up very well with the forum colour scheme.

I will post it again: **broken link removed**
Keith