value of gain pot on DOD overdrive

[PRR]

> Does it make no difference at all if the two resistors are 2x22k or 2x10k? I understand the pronciple behind the voltage divider, but is the current going to change and does it make a difference?

The divider values should be much higher than the source, much lower than the load.

Here the source is a battery, under 100 Ohms (plus the 100 Ohms in the circuit), though we should not push that.

The load is one op-amp input pin. We can peek at the specifications, but we also see a 470K-1 MEG resistor before it gets to the opamp.

Already we know that 100 Ohms would be mighty low and 1 Meg may be awful high.

We could go 1K+1K to 100K+100K.

10K or 22K makes no real difference. 47K would be fine. 5K would work well also, but increases battery drain for no good reason.

Higher is slightly better because, with the 10uFd, this is also an R-C filter to reduce power supply garbage. If we went to 1K we might need 100uFd to get the same filtering. If we went 47K we could maybe use 2uFd. However caps from 22uFd to 2uFd are all about the same price. This again says 5K to 50K, anywhere in there.

On a well-used electronics work-bench, you poke in the corners and find two orange-stripe (10K-99K) resistors of the same value. It's like a carpenter who needs two equal spacers, but does not care if they are 1-inch or 3-inch: he will shuffle his scraps until he finds two sticks the same height, not silly large or small.

[feddozz]

The divider values should be much higher than the source, much lower than the load.

This sounds like impedance high at the input and low at output.
When designing a circuit is this principle roughly reflected across the circuit (with due exceptions)?

And BTW my DOD 250 is finished, apart from the bottom cover, but that's another story. I opted for a single effect pedal. No bazz fuss. The only switching I added was in the clipping diods. I have the option for 2 red LED back to back or 3 1N4148 for asymmetrical clipping.
It worked straight away, after noticing I connected the jacks the wrong way round .

[PRR]

> sounds like impedance high at the input and low at output.

Correct.

This is generally a good design guide.

Roughly like:

Don't balance your elephant on a fishing pole (wobbles or collapses)

Don't pour a 20-ton foundation for a small dog-house (waste of concrete)

10 pounds or 20 pounds concrete for the small dog-house foundation is probably all the same (don't worry too closely).

[feddozz]

Thank you all for the help and interesting discussions