What could be wrong with my Proco RAT breadboard build ?

[LightSoundGeometry]

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.

okay i see it now. it just has both on schematic for reference ; not that it has to switches.

[graemestrat]

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

Sorry for my late reply - pc is down so have to use the one at my local library!!!!

OK it isn't too hard to calculate the meter loading effect.

First we know that the input z of an lm308 is 30meg worst case. Assume (note!!) that the meter used has an input z of 10 Meg.
We know that the battery volts was 8.4V

So now we look at the resistances from r11 and r12 through r2 and r3 to the parallel combination of lm308 and meter (10meg in parallel with 30meg).

My scratchings make this about 3.7 to 3.8 volts, which is still nowhere near 2v.

Of course if the meter used has a lower input z than 10meg then that could explain the low reading but since we are dealing with a fault that is sort of working and not a complete failure then I would be looking for marginal type problems. eg weird things like reverse polarity electro's etc.

You know I was just wondering if you have tried replacing the op amp - it could explain this low volts reading as well??

[kaushikwavhal]

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?

I'll click and upload few pics and another sound samples today with more isolation.

[kaushikwavhal]

You know I was just wondering if you have tried replacing the op amp - it could explain this low volts reading as well??

Yes, i've tried with two LM308's and one NE5534. All sound the nearly same.

[Markw5]

Regarding opamp voltages, if the opamp is good, then if the two input pins are not within about 1mV or less of each other (whatever the offset voltage and currents would require, but very close to the same voltage), then the output should be saturated as close as it can get to the power supply rails at one extreme or the other. It should not be somewhere in the middle of its range unless there is some external source holding it there while it current limits. That's simply a consequence of the very high gain of the opamp amplifying the voltage difference at the inputs. In that case, if the opamp is saturated or somehow clamped, then there should not be any audio coming through at all.

If the opamp was wired up with positive feedback resulting in hysteresis, then you could get a situation where a guitar signal could cause it to flip back and forth between being saturated in one direction or the other. Since this circuit operates from 9v, it might be possible that 6.5 volts at the output would be as saturated in the positive direction as it can go. If playing guitar causes it to flip back and forth between two saturated values, then that would suggest a positive feedback path. Checking the wiring, and/or observing with a scope should clarify whatever is going on.

[GGBB]

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

Bump.

[PRR]

> I would think the 2+volts is meter loading
...the input z of an lm308 is 30meg worst case.

> if the opamp is good, then if the two input pins are not within about 1mV or less of each other

For the second reason, the "30Meg" of a LM308 is not involved. Under feedback it will be "infinite" for all practical purpose.

BUT-- if you only have one meter, measure one pin, then the other, you generally WILL measure a difference. You are measuring "two different circuits", with an added 10Meg here or there. With two meters you can watch the OUTput and see it change with meter loading. (You can also measure both inputs at once, but this may pull the opamp out of its operating zone.)

The '308 is biased from 50K divider, another 1K, but mostly with a 1Meg or 2.2Meg resistor. Classic electronic VTVMs and DVMs are 10meg (or 11Meg) input on DC range. 10Meg hung on 1Meg is about 9% error, "4.5V" sags to 4.1V. With 2Meg bias, sag some more, 3.7V.

BUT I have been seeing "general purpose DMMs" with 1Meg input, or some odd value in that range. Klein CL1000 (a fine electrician's DMM) is 8.5Meg input.

The 1Meg version with 1Meg meter, or the 2.2Meg version with ~2Meg meter, does give near 2V.

[kaushikwavhal]

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

Bump.

Here are the pics of the build. Sorry for the delay.

http://i.imgur.com/fARCttZ.jpg
http://i.imgur.com/6OGS5yL.jpg
http://i.imgur.com/3Q1gBDz.jpg
http://i.imgur.com/QBVlviC.jpg
http://i.imgur.com/hdI5jiP.jpg