ProCo Rat project debugging

[dbalu]

Hello all,
I have recently built a Rat clone based on gaussmarkov.net/wordpress/circuits/rat/
Modifications to the original circuit was using a NE5534 IC instead of the one mentioned on the site and using a 33pF cap instead of 30pF. All of the modifications are due to lack of parts in my area.
On the first look everything seemed ok, so I fired up the amp to test it. Unfortunately there was nothing coming out from the amp, so i tried pushing gently some components, wich made the pedal work for a few seconds and then it stopped with a squelching sound. Realizing there were some bad soldering joints I carefully remade the soldering work and also compared my project with one of my friend's clone which works. The voltages on the IC pins were almost the same, except pins 5 and 7. I have a high reading of about 9,2 volts on pin 7 (voltage in) compared to 0.03 reading on the working rat clone. Also I have a 3-4 volts reading on pin 5 (datasheets says it's COMP pin) compared to 0.06 volts on the working clone, all voltages are measured compared to groun. I checked the voltage imput line on the circuit and everything seemed okay.. Could anyone please help me with debugging the circuit?

[T-Dub]

Hmmm, does that IC need the compensation cap?
Did you use a PCB or vero? I'd start tracing your voltages back from the power supply section because it seems something is stopping the juice getting to the chip. Any pics?

[dbalu]

I did everything like the project page said, nothing additional except what I mentioned, my friend used the same components and his effect works. I traced the vircuit and the only direct component in the path of 9v to the ic power in is a 47 ohm resistor, which can be seen also on the diagram on the site. I will provide pictures as soon as I get home.

[bluebunny]

There's something wrong with your readings (or the way you're taking them).  The almost zero volts on the "working" pin 7 is wrong: it's the power for the op amp and should be close to the battery voltage.  The 9.2V you see on yours is correct.

From what I recall, the LM308 is "essential" for the RAT.  Not sure how true that is...  And its pin 5 is "NC" (no connection), which is different to the NE5534.  (The cap substitution will make no difference, btw.)

Go check out the "DEBUGGING" thread at the top of this forum and follow the instructions.

[GGBB]

 +1 to bluebunny.

Also, the 5534 is not a direct replacement for the LM308 in this circuit. Pins 5 and 8 should be used for the compensation cap, not pins 1 and 8. Pin 1 is for offset voltage adjustment, which I'm not sure how to use nor what would happen when connected to pin 8 via a cap. So move the 33pF cap from 1-8 to 5-8, or for testing just remove it entirely, and leave pin 1 unconnected. Also, as the 5534 has a higher slew rate than the LM308, and the purpose of the compensation cap is to lower slew rate, you should try a bigger compensation cap with the 5534 - say 100pF or so (experiment).

[dbalu]

The 30p cap is between the 2 balance pins on the ne5534, found online that this ic works with the configuration (my friend's project uses the same IC). I will have to remeasure the two effects once again side by side, maybe there was an error while measuring the voltages on the working effect (judging by bluebunny's statement that Vin=9.2 is okay). Pin 5 is not connected to the rest of the circuit, by design, but still gives me a reading of about 3 volts. Is this ok?

[bluebunny]

Pin 5 is not connected to the rest of the circuit, by design, but still gives me a reading of about 3 volts. Is this ok?

It's irrelevant.  Don't worry about it.

[dbalu]

I managed to solve the issue, pushing the 100p cap (C4) made the pedal work. Squelching still heard, due to the pot wires, (pictures coming tomorrow if still wanted). I guess it's a bad joint due to the legs being too far apart for the holes.

[GGBB]

The 30p cap is between the 2 balance pins on the ne5534, found online that this ic works with the configuration (my friend's project uses the same IC). I will have to remeasure the two effects once again side by side, maybe there was an error while measuring the voltages on the working effect (judging by bluebunny's statement that Vin=9.2 is okay). Pin 5 is not connected to the rest of the circuit, by design, but still gives me a reading of about 3 volts. Is this ok?

I suggest you read the datasheet for the 5534 - pins 5 and 8 are for compensation - not 1 and 8. I'm not saying it won't work with the cap connected that way, but it won't be working as a compensation cap, which is an important part of the RAT circuit.