Boost into Ruby question

[dennism]

I like the way it sounds when I put a Tube Screamer in front of my Ruby amp, so I decided I would build an overdrive circuit right into my little cigar box amp.   I used the Electra for my overdrive and a toggle DPDT to add the Electra in front of the Ruby or bypass it for just the Ruby.

Here's my issue.   With the Electra on and turned all the way up, it's just too much gain, it goes into squealing wall of sound feedback.   Turn the Electra down about 1/3 of the way and it sounds killer.   I'm using a 100K log pot for the Electra.    How can I get the Electra to sound killer over the full range of the pot?   In other words, "turn it down" a bit.   I'm thinking I need to put a resistor in series with the Electra volume pot, but I have no idea what value to use.

Thanks for any help you can give me.

[deadastronaut]

hmmmm...maybe a 150k on outer lugs to knock it down to around 60k...IIRC ths is what i did to a delay to squeeze a little more time out of it before breakup instead of using a 47k/50k pot....

[dennism]

Ok, so I'm thinking that when a pot is turned all the way up to max, the resistance is zero?   And I want to find a way to make it actually be some amount of resistance more than zero when it's turned up all the way.   That's what I'm trying to figure out how to do.

[Gurner]

Ok, so I'm thinking that when a pot is turned all the way up to max, the resistance is zero?   And I want to find a way to make it actually be some amount of resistance more than zero when it's turned up all the way.   That's what I'm trying to figure out how to do.

The way you'd do that, is to put a resistor in series with your pot ...cos even then when the 'wiper' is at zero resistance...the resistor preceding it will drop some signal voltage across it. Depending on the value of your pot & depending how much you want to reduce the signal dictates the resistance. If you are using 100k pot, a 47k pot will reduce the signal voltage by about a third when the wiper on the pot reads zero resistance (ie pot at max)

[dennism]

Thanks Gurner, that's what I was thinking about doing, putting a resistor in series with the pot.   I just had no idea what value resistor to use.   I'll try the 47K you suggested tonight.

[Gurner]

Thanks Gurner, that's what I was thinking about doing, putting a resistor in series with the pot.   I just had no idea what value resistor to use.   I'll try the 47K you suggested tonight.

this may help...

http://www.electronics2000.co.uk/calc/potential-divider-calculator.php (top calculator)


R2 to all intents & purposes here will be your pot...so set it to 100k (if that's what your pot value is) , enter V1 as your anticipated AC signal input voltage (if you don't know what that is, could could set it to say 1V...it doesn't really matter, but setting it to 1V makes it easy to see how much your voltage will be impacted by R2 at the ouput), then by tweaking the value R1 up and down, you can see how much your voltage will drop at the output when your pot is at max.