Author Topic: DIY ProCo Rat problem  (Read 6090 times)

Dendrikas

DIY ProCo Rat problem
« on: September 09, 2012, 06:12:42 AM »
Hello, i have decided to build a proco rat clone, based on this schematic :

http://analogguru.an.ohost.de/193/schematics/Proco_TheRat-1986.gif

I have designed PCB by myself, soldered everything, plugged it in. Schematic works, but the gain control is somewhat bad.
Starting from 20%, distortion is too muddy, compressed and unpleasing. And overall the character of the sound is ugly compared to other original or diy rats.

On my circuit i used LM308N as opamp and the transistor is 2n5457, instead of 2n5458. Clipping diodes are 1n4148. All other parts are the same as in the schematic. Some capacitors may be quite old.

I have measured the voltages on the IC and it showed strange results.

Voltage across the supply pins is +9v

LM308 :
1. +6V
2. +4.5V
3.  0V (the hand of the analog multimeter quickly jumps up to +1V and comes back to 0V, strange)
4.  0V
5.  0V
6.  +4.5V
7.  +9V
8.  +0.8V

Voltages above were measured after changing voltage divider resistors and capacitor from 100k,100k,1mF to 10k,10k,47mF, as suggested in another schematic

the 1 , 3 and 8  voltages seems to be abnormal, as i have read that pin 1 should be around 8.5V, pin 3 around 4.1V and pin 8 around 4.5V.

Please advise me, what components may need to be replaced or what may be wrong. Thank you.
« Last Edit: September 09, 2012, 07:12:23 AM by Dendrikas »

GGBB

Re: DIY ProCo Rat problem
« Reply #1 on: September 26, 2012, 12:10:47 PM »
I would go back to the original voltage divider, and if you want to be truly faithful to the original Rat specs, get rid of R2.  As for the tone problems, it may be your 'quite old" caps.  Aluminum electrolytic caps degrade over time.

bukas

Re: DIY ProCo Rat problem
« Reply #2 on: February 14, 2013, 08:26:51 AM »
I would go back to the original voltage divider, and if you want to be truly faithful to the original Rat specs, get rid of R2.  As for the tone problems, it may be your 'quite old" caps.  Aluminum electrolytic caps degrade over time.

agree, i have seen this in many DIY projects resistor connecting signal line and fx ground, it only creates buzz and has no other purpose, add 1 diode between C12 and C13 solder to gnd pointing V rail, and distortion pot is backwards xD
« Last Edit: February 14, 2013, 08:31:18 AM by bukas »

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Re: DIY ProCo Rat problem
« Reply #3 on: February 14, 2013, 10:47:03 AM »
it only creates buzz and has no other purpose

It is a pull-down resistor.  It allows the input capacitor to discharge while the pedal is bypassed in order to prevent any audible popping when the circuit is engaged.  Most of my pedals have them and they normally do not cause any problems.

Quote
add 1 diode between C12 and C13 solder to gnd pointing V rail

This diode is already present in the circuit as D3.

Quote
and distortion pot is backwards xD

It looks right to me.