amp input: potentiometer, capacitor

[autir]

Hello all, I am new in here :-)

I have a question regarding the Pentawatt class AB models from ST (TDA2003, TDA2006, TDA2030, TDA2040, TDA2050). I want to include a volume control in the input, but I have 3 questions:

1) What type of pot do I use? logarithmic or linear?
2) How do I calculate its value?
Where do I place the capacitor?

Thank you in advance.

[J M Fahey]

Hi. You have two groups there:
The TDA2003 is meant for split supply and self biasing, so its +input (where you apply signal) *must* be DC isolated by a capacitor.
If you use from .47uF up to 10uF you'll certainly use an electrolytic, its "+" end should point towards the IC.
All others are just "big/beefy Op Amps" and must be biased accordingly.
For volume pots, Log will work much smoother than Lin.
Without too much math, a 100K Log will be fine.

[autir]

Thank you for your reply.

Without any complex math, is there a hard and fast rule to relate the "correct" value of an input pot to the input resistance of a chip? What about opamps with very big input resistance?

Is there a resource online describing it with complex math? :-)

[phatt]

Use a bigger value pot.  Durh!!!  it should be obvious.
BTW, You just got the best answer you could ask for from JMFahey,,, now if you want to spend the next mindnumbing 4 years
at teck colledge just to get the maths sorted then go for it mate,,,
Meantime 5 minutes work to swap out a couple of pots will tell you the right value.

In the case of your situation  ( I Assume ?*)   You are taliking about a  * Master Volume for a *PowerAmp module*?
Then most are not ever high enough Imp to cause concern.
So take a 100k pot and don't concern yourself with trivia maths that is niether here nor there.
Phil.