[sdiy] CGS30 BPF modded for guitar use

Dave Kendall davekendall at ntlworld.com
Sat Nov 13 21:43:41 CET 2010


Hi all.

Mad idea I know, but it's a request from a guitarist mate. I want to 
find a way to mod this circuit  
http://www.cgs.synth.net/modules/cgs30_bpf.html
for use in a guitar stompbox. FWIW, I believe the circuit to be the 
same as, or a near clone of the roland SH5 BPF.

As noise levels are not critical for his intended use, for power, I 
guess I could use a resistor divider with a 9V battery to, generate 
±4.5V, with the centre tap to GND on the PCB, and something like a 47uF 
cap between the centre tap and 0V on the battery (which is now -4.5V on 
the PCB)

I 'll need to attenuate the level after the effect, which will have 
quite a lot of gain, in order to approach unity gain at the output.  
Question is, keeping a 1K output impedance, how could I alter values in 
the circuit to achieve this? I don't understand the circuit , and I 
guess I could always do the obvious, and use a voltage divider at the 
output using the 1K final output resistor as one half, and a pot or 
fixed resistor to GND as the other half of the voltage divider, but I 
suspect that might have a big effect on the output impedance - I don't 
know if that's a real problem or not. The output will directly drive a 
guitar combo input.

Would such a voltage divider make potential problems for a guitarist?

Any thoughts welcome.


cheers,
Dave




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