Rat Clone Issues

[GreySuits]

I built a Rat clone using an OP07CP.  It sounded great for about a week and then it lost all of it's power.  The effect still clicks on but I now get a very weak in distorted signal (like it's not getting enough power).  At first I thought I had a bad connection from my DC jack into the PCB (when I wiggled the wire it would some times kick on).  So I swapped the wire and resoldered the connections and nothing.  I swapped out the J109 and still had the same issue.  Finally, I swapped out the OP07 and it clicked back on for a second, then it died again.  I have also tried multiple DC adapters and that does not seem to be the problem. 

Any ideas?

[bluebunny]

Voltages around your active devices?  (Basically, the "Debugging" thread.)

[antonis]

Voltages around your active devices?

(if any..) 

Does your PS get warm ..??

[GreySuits]

Voltages around your active devices?  (Basically, the "Debugging" thread.)

IC
1: 8.93
2: 4.51
3: 2.19
4: 0
5: 0
6:4.51
7: 9.03
8: 8.92

J201
G: 0
S: 0.56
D: 9.03

[GreySuits]

Voltages around your active devices?

(if any..) 

Does your PS get warm ..??

Nope

[antonis]

Just to have a reference..
(ignoring compensating capacitor pins 1 & 8..)




Voltage on pin 2 should be the same with pin 3..
2.19V could be down to partially shorted C6 and/or C5 in relevance with Distortion pot setting,  BUT, in such a case, voltage on pin 6 shouldn't stay on 4.51V..
(for a 4.51V on pin 2 it should be ok but for present voltage it should almost be hitting the positive supply rail..)   

You can check for the above with pot set at its extreme ends while measuring voltage on pin 2..
If you get different voltage readings on pin 2 then check for DC gain (other than unity, due to C5 & C6) inside NFB loop..
(something forms a DC path from pin 6  to GND via R5/C6, R4/C5 AND pin 6 is somehow shorted to VB..) 

Additionally, voltage on JFET Source should be about double, for 2N5457 & 10k Source resistor - in case you've altered device type & resistor value I can't figure the "right" voltage..
(clipped signal voltage, after Si diode pair, is about 600 - 650mV so on negative waveform is marginally additionally clipped..)

[GGBB]

Sounds a lot like bad solder joint(s) or broken traces. Can you post pics? Try using an audio probe to trace the signal path and find out where it dies.

[duck_arse]

I built a Rat clone using an OP07CP.

Any ideas?

more information, please. show us the actual circuit diagram you built to, if you would. and as GGBB says, photos please.

[GreySuits]

Here are pictures:

[GreySuits]

Just to have a reference..
(ignoring compensating capacitor pins 1 & 8..)




Voltage on pin 2 should be the same with pin 3..
2.19V could be down to partially shorted C6 and/or C5 in relevance with Distortion pot setting,  BUT, in such a case, voltage on pin 6 shouldn't stay on 4.51V..
(for a 4.51V on pin 2 it should be ok but for present voltage it should almost be hitting the positive supply rail..)   

You can check for the above with pot set at its extreme ends while measuring voltage on pin 2..
If you get different voltage readings on pin 2 then check for DC gain (other than unity, due to C5 & C6) inside NFB loop..
(something forms a DC path from pin 6  to GND via R5/C6, R4/C5 AND pin 6 is somehow shorted to VB..) 

Additionally, voltage on JFET Source should be about double, for 2N5457 & 10k Source resistor - in case you've altered device type & resistor value I can't figure the "right" voltage..
(clipped signal voltage, after Si diode pair, is about 600 - 650mV so on negative waveform is marginally additionally clipped..)

I'm getting the same voltage on pin 2 regardless of distortion setting (around 4.8v) and on pin 3 (around 2.4v).

I looked at the soldering for caps 5 and 6 and did not see any potential shorts.  Is there a way to check for this with a multi-meter?

[Slowpoke101]

The most likely reason for you measuring 2.4V on pin 3 is that your meter is loading the circuit. Pin 3 is supplied through a 1M resistor going to Vref (4.8V or so ) and your meter has an input impedance of 1M. This makes a voltage divider which produces 2.4V when you measure it. So there may be nothing wrong around the IC but the J201 fet's voltage seem odd. Remove the J201, rotate it 180 degrees and plug it back in. Test and take some voltage readings. If still no joy,, consider making an audio probe and see where the signal goes wrong.

[antonis]

I'm getting the same voltage on pin 2 regardless of distortion setting (around 4.8v) and on pin 3 (around 2.4v).

My bad..!! 
(mismatched your initial pin 2 & 3 voltage readings.. - forget everything mentioned by me above..)

Still holds JFET Source low voltage reading so do what Ian proposed..

[GreySuits]

So it turns out that the input cap had a bad Solder joint