Potentiometers

[blyloveranger]

Originally posted by Peter Daniel
You might use R1 or not, it's not really critical, with a pot I'm usually not using it.

When you are referring to R1 here, do you mean the R1 on the first schematic shown is not needed, i.e. the one with a 25k log pot? Also in another thread someone asked

What if one does not have any input cap or input resistor, just a pot and a shunt resistor? any problems there?

and the response was

Yes, there is a potential for problems. The DC impedance, looking back from the opamp input (which is a source of leakage current) to the audio source, will be all over the place. That will affect the DC offset, because the leakage current will induce a different voltage depending on the position (resistance) of the pot. Even though this voltage is small, it is amplified by the gain of the opamp.

So I am trying to figure out whether a cap and a shunt resistor is needed, if I am using a pot? Since by this quote it seems that he feels that they are important. Is it one of those things where I am just going to need to build it to see?

Patrick

[homer09]

From what ive read, it seems that having an input resistor is "safer" for your amp/source/speakers. But its not really necessary if you dont have any major dc offset problems without it. Peter i believe suggests to not use it if possible because he designed a minimalist GC, so one less component in the signal path could only help (if there arent other consequences of course).

if you are using a pot, then there is some resistance in the signal path anyway (except at max volume of course) so you should not need the input resistor. If you are building a true amp (no volume control) than an input resistor is probably necessary.

any corrections welcome from the more experienced

What i would like to know is what causes DC offset to increase or decrease when you change volume. How is DC offset related to input resistance? maybe with answers to those questions, i will be able to decide what value of linear pot to use in the fake lawing setup. And if the input resistor is still necessary in that case.

[edjosh23]

Would putting a greater value resistor is R2 decrease dc offset, if one cannot find what is causeing the problem, which is of course better?

Thanks,

Josh