What could be wrong with my Proco RAT breadboard build ?

[kaushikwavhal]

Yes, i am using a ESP LTD F-10 Guitar with stock pickups. One humbucker and one singlecoil.

The output is connected to VOX pathfinder 10 Amplifier.

I'll have to try turning the guitar volume down and then testing it. I will update it today.

No. My circuit is currently on a breadboard, but the output isn't satisfactorily like a distortion pedal. Something clearly seems off. I have a metal enclosure. I plan to put this thing on a home fabricated PCB and inside the metal enclosure once it works good enough on breadboard. I know there will be some stray noise and stuff on the breadboard that will go away in the metal enclosure but if you listen to the sound samples i've sent, it doesn't seem like the circuit is really working.

[GGBB]

Yes i do have one. I've traced it to pin 6 (Post-Amplification) of the opamp and pin 3 (Pre-Amp sound) of the opamp. Except the sound levels , i didn't notice much difference. The major bad fuzzy tone still exists.

Where is the last point where the sound is good? This will probably be clean guitar signal. Normally the problem lies between where the sound last stays good and where the sound first goes bad. In your case this is somewhere between input and pin 3.

Can you post pics of your breadboard so others can look for an error?

[Markw5]

I know there will be some stray noise and stuff on the breadboard that will go away in the metal enclosure but if you listen to the sound samples i've sent, it doesn't seem like the circuit is really working.

I listened to the sound file you posted. Sounds to me like you are picking up way too much noise from stray electromagnetic fields around the room.

What if you don't connect the a guitar to the input, and instead connect nothing, or maybe a resistor to ground? It probably sounds about the same as what you recorded, but without the guitar part of the sound. To emulate a guitar with a resistor, as far as impedance presented to the pedal input, the guitar might look like roughly somewhere between 5k and 250k, depending on the particular pickups, volume pot type, and volume pot setting.

You could also try shorting  the input to ground. Does that clean up the noise?

[graemestrat]

Pins 2 and 3 should be about the same dc voltage (with no ac signals coming in) so you would appear to have a problem around the feedback path (pins 6 and 2) or from pin 2 to ground.

Good Luck!!

[Quackzed]

also check that c5 c6 and c7 are oriented the right way..

[graemestrat]

Now that I think about it a bit more, the voltage at pin 3 looks too low. It should be around 4 to 4.5V. Pins 2 and 6 look ok.
So have a look around this pin.
Check that you have 4 to 4.5V at the junction of R11 and R12.
If this is ok then check that you also have 4.5v at junction of R2 and R3
These voltages should be closer to 4volts than the 2v that you are getting.
Also check that + side of c13 is connected to R12/R13 junction and not the other way around.

Don't give up!!!!

[Kipper4]

Now that I think about it a bit more, the voltage at pin 3 looks too low. It should be around 4 to 4.5V. Pins 2 and 6 look ok.
So have a look around this pin.
Check that you have 4 to 4.5V at the junction of R11 and R12.
If this is ok then check that you also have 4.5v at junction of R2 and R3
These voltages should be closer to 4volts than the 2v that you are getting.
Also check that + side of c13 is connected to R12/R13 junction and not the other way around.

Don't give up!!!!

I would think the 2+volts is meter loading, since pin 6 is at V/2.
I've been wrong before though.

[kaushikwavhal]

I would think the 2+volts is meter loading, since pin 6 is at V/2.
I've been wrong before though.

What is meter loading exactly?

[Kipper4]

Your meter is reading the voltage wrong. It is loading down I think the chances are the real pin 3 voltage is nearer to 4v5 otherwise the pin6 (output) would read less than 4v5 too.
I think the voltages are ball park.
It sounds like oscillation IIRC from the sample.
I'd go back over all connections using the schematic as a guide and the DMM set to beep and make sure they're all where they are supposed to be.
Recheck your values too.

[kaushikwavhal]

Yes, I think there was some strange readings too. While i checked the voltage at pin 6 it was proper, but when i checked the voltage after the immediate following capacitor  () it showed me 0V. I traced it till the JFET's Gate pin where it still showed 0V but the JFET's source pin (the output pin for the effect), it showed 1V.

[Markw5]

A normal voltmeter has a 10M input impedance. Measuring from a node in your circuit to ground is like putting a 10M resistor from node to ground, then measuring the voltage with an ideal meter of infinite input impedance. Therefore, if adding a 10M resistor to a circuit would change the voltage there, then so would trying to measure the voltage with a normal DVM.

[Kipper4]

its odd because the GGG rats jfet gate biasing uses a voltage divider with a voltage of ~2v8

see here
http://www.generalguitargadgets.com/pdf/ggg_rodent_sc.pdf

but I guess electro smash cant have got that wrong because many others Guss Marcov included use the same Jfet gate biasing.

I'd expect 0v after a cap since caps block DC.
I'll breadboard the jfet buffer later and report back.

Am I mistaken then MarkW5 ?

[kaushikwavhal]

I'll breadboard the jfet buffer later and report back.

Does that mean i can eliminate the circuitry after pin 6 for time being till i resolve this issue ?
Can i just use the pin 6's output to my 6.5mm Jack ?  Which will then go into the amp.

[Kipper4]

Sure Stick your audio probe before or after the 4u7 (c7) cap and see if the problems before or after.

[Kipper4]

with the N channel jfet buffer set up on the breadboard (J201)
D +9v
G 0v
S 0v75

[GGBB]

its odd because the GGG rats jfet gate biasing uses a voltage divider with a voltage of ~2v8

see here
http://www.generalguitargadgets.com/pdf/ggg_rodent_sc.pdf

but I guess electro smash cant have got that wrong because many others Guss Marcov included use the same Jfet gate biasing.

I'd expect 0v after a cap since caps block DC.
I'll breadboard the jfet buffer later and report back.

Am I mistaken then MarkW5 ?

See R10 and R16 below.

Original RATs bias the gate to ground via 1M resistor. G ~ 0V.

Turbo RATs bias the gate to 1/2 Vin via 2M2+2M2 voltage divider. G ~ 4.5V.

IMO you may encounter issues depending on your FET if you bias the gate to ground. I prefer biasing to Vref using a 1M or 2M2 resistor - much like the biasing of the op-amp.

[Markw5]

its odd because the GGG rats jfet gate biasing uses a voltage divider with a voltage of ~2v8

see here
http://www.generalguitargadgets.com/pdf/ggg_rodent_sc.pdf

but I guess electro smash cant have got that wrong because many others Guss Marcov included use the same Jfet gate biasing.

I'd expect 0v after a cap since caps block DC.
I'll breadboard the jfet buffer later and report back.

Am I mistaken then MarkW5 ?

The difference in FET biasing could have some effect on how the pedal sounds in some operating conditions, but would not seem to account for the reported problems. I still think the sound sample seemed to be picking up too much stray noise. I would try some experiments like moving the circuit around, away from any computer, florescent lights, etc. and seeing if anything changes. Also, try turning down the guitar volume pot and see what happens. Sometimes changing things in the environment can give useful clues. Other than that, the real solution is to look at it with a scope. Even with a scope, it might be necessary to shield the circuit a least partially in order to get clean enough signals to look at clearly. Same goes for measuring voltages, a DVM besides being a 10M resistor, also has some unspecified input capacitance. Sometimes you need a scope to see if the DVM is changing the circuit operation. Also, if the circuit is oscillating at some high frequency, a DVM may give erroneous readings because it wasn't designed to work properly with RF or near RF going into the inputs.

[LightSoundGeometry]

its odd because the GGG rats jfet gate biasing uses a voltage divider with a voltage of ~2v8

see here
http://www.generalguitargadgets.com/pdf/ggg_rodent_sc.pdf

but I guess electro smash cant have got that wrong because many others Guss Marcov included use the same Jfet gate biasing.

I'd expect 0v after a cap since caps block DC.
I'll breadboard the jfet buffer later and report back.

Am I mistaken then MarkW5 ?

See R10 and R16 below.

Original RATs bias the gate to ground via 1M resistor. G ~ 0V.

Turbo RATs bias the gate to 1/2 Vin via 2M2+2M2 voltage divider. G ~ 4.5V.

IMO you may encounter issues depending on your FET if you bias the gate to ground. I prefer biasing to Vref using a 1M or 2M2 resistor - much like the biasing of the op-amp.

is there a different path for sw1 and sw2 on this schematic? I had to ask because it looks like its going to the same path lol . I always get messed up on the swith paths for some reason ..im not good with relay either !

[Markw5]

If the failure was due to improper placement, it should have been rectified when i rebuilt the circuit. I am getting the same output in both the builds.

Also the input wire to the circuit is isolated to a great extent. I suspect the problem lies in some faulty resistor or capacitor.

Are there pictures available of the build or builds?

[GGBB]

is there a different path for sw1 and sw2 on this schematic? I had to ask because it looks like its going to the same path lol . I always get messed up on the swith paths for some reason ..im not good with relay either !

FS1a and FS1b are the two poles of the DPDT true bypass switching in the original RAT (no LED). FS2a and FS2b are the two poles of the DPDT true bypass switching in the RAT2 and Turbo RAT which have a status LED implemented using "RAT bypass" which is similar to the famous millennium bypass. Purple = original, green = RAT2 etc. Note that modern RATs (since ~2002/2003) of all flavours now use 3PDT bypass switches so the wiring sans LED is the same as FS1.