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substitute a resistor in place of a potentiometer?

Started by fivestring, March 02, 2014, 06:52:03 PM

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fivestring

Hey, noob here. I have a basic question about builds that are not from this site. I hope I don't get chewed out for this, but after browsing diy forums, this one has so far been the most active and helpful to me.
So here's my progect-
I am trying to install a simple 9v amp http://www.runoffgroove.com/ruby.html
and a distortion effect http://www.diyguitarpedals.com.au/shop/boms/7_Min_Fuzz_Schematic.pdf
inside a cigar box guitar. The idea is to have a simple, travel, jam guitar that you can switch on and plug any speaker or headphones into.
My goal is to make the guitar as simple as possible to play with minimal switches and controls.
I want only a volume pot for the amp and an on/off switch for the fuzz. My thought was that I could put a resistor in place of the fuzz pot at the right level to get the distortion effect at the same volume as the clean tone.
Is this possible??
I have already built the 2 components with some success, I am still trying to work out the cracks and buzzes. 

RobA

I can't get to the schematic to the fuzz right now, because the server won't respond. In general, it would be possible to put resistors in place of the sections of pots to set the fuzz level and the volume level to match the output levels together. But, I'd need to be able to see the schematic to be sure of how it would go together.

Does the fuzz normally have two pots or is there just one?
Affiliations: Music Unfolding (musicunfolding.com), software based effects and Rock•it Frog (rock.it-frog.com), DIY effects (coming soon).

RobA

I've been able to get to the sight now and see the schematic. So, I take it that is the output volume pot on the fuzz that you want to set. The easiest way to do that might be to replace the output pot with a 100k trim pot. That way you could set the volume level to match the clean signal fairly easily and then leave it set to that level.

Assuming that you don't want to do the trim pot, you need to use two resistors to replace the volume pot. The volume pot forms a voltage divider on the output signal, so, you need one resistor to hook up to the output from C2, and the other to hook to ground. You then bring those two resistors together at the free ends and hook your output to that center point. The complication then is that you need to figure out what values to use. That's going to depend on the output level of the clean signal. It would probably be easiest to do that by using a 100k pot and then measuring the resistance between the pins, center-to-top, and center-to-bottom, and then get resistors that are as close as possible to these measured values.
Affiliations: Music Unfolding (musicunfolding.com), software based effects and Rock•it Frog (rock.it-frog.com), DIY effects (coming soon).

fivestring

Yes, the fuzz output volume. I've ordered the trim pot, that seems like an easier way to go than trial and error with resistors. Thanks for the help!