Hi, I am having problems with my rat clone from ggg.
The volume and tone seem to work but I only get a faint guitar sound through the effect. It is clean. When I max the overdrive, the sound just dissapears. I suspect the problem is around the ic and I would like to debug it.
I searched the archives for voltage values but couldn't find them. Can anyone post'em ?
Thanks

Mine seems to be working well, built it last week. I'll try and post some numbers late tonight (assuming I remember). Mine does however, have a bit too much gain, but I think that's unrelated to the build, just the pickups on my guitar being a bit overzealous.

Unfortunately, I don't have the one that I just finished building. It went to my cuz as a belated X-Mas gift.
It worked fine, but as Martin noted, it has a bit too much gain; maxxed out it sounds almost like a fuzz. Built it using SmallBear's LM208 IC.
Other than that, it worked fine. I wired it up with a SPST toggle to switch out one diode, and it got louder in that position. Sorry I couldn't be more help.

I could use the pin voltages also.

Take some readings on your ckt and post them...I, or someone even 'better' than me [at reading into Pinv's] for preblem solving may be able to see something...

Right Pete, i'll do this when I get home. Now I got to get to that meeting  :evil:

My pin voltages with 4558:

1- 7.2
2- 0
3- 0
4- 0

5- 8
6- 9
7- 0
8- 0

The only substitutions are the IC, 2N5458 with 2N5457, and an electrolytic 1uf cap.

I tried some other ICs yesterday, but I get the same result, no audio. LED works  but is dim when switched.

If this is like a standard 8 pin IC wiring for Opamp...
 Well if its a single OA like 741 pin 7 should have PS ..like 9v
 If its a dual pin 8 should be getting 9v.
 Is this a PCB or perfboard build?

now I see..dual OA yes should have 9v at pin 8...I would go through with a DMM and chech wirings around the OA pins...
 Check continuity with beep setting of the pin 4 and the battery clip ground same for pin 8 and battery clip +

The LM208/308 is a single OA, no? It should be getting full supply voltage (+9V) on pin 7, not pin 8 which would be for a dual opamp setup.

Wait. Xlrator - 4558 is not an acceptable substitute if you're trying to go pin for pin with the LM308. Are you making this thing with JD's layout or perfing it? If you want a chip sub for the 208, try an LM741 or TL071 instead.

Here's the single opamp pinout:

Here's the dual:

(Hard to read kinda but its v+ on pin 8, v- on pin 4, + ins on 3 and 5, - ins on 2 and 6, outs on 1 and 7)

O.K.  I put a UA741 in there and it works.  :lol:  I think it sounds better than the built in dirty channel on my amp.

I etched the layout from JD.

Now somewhere in the forums I read that all opamps use the same pinout? Is this only in the case of single - single and dual - dual.

All is good now.

doublepost

Glad you got it working.

I think in general most dual opamps have the same pinout, and most singles have the same pinout, but very different from one another! Never hurts to look up the specsheet and be sure. Also the schematic on Jd's site has the pin numbers listed on the opamp symbol. Easiest thing to do is trace where your V+ enters the board, and check which pin that goes to. Make sure the correct pin is getting the supply...It's slightly more confusing for the Rodent (Rat), since the V+ from the battery/wall wart goes through a 47 ohm resistor and isn't *directly* connected, but it's still an easy sanity check.

Thanks all for the helpful info.

Sorry to steal your thread Martin.

Ok, here's the meat:
p1 7.7
p2 4.2
p3 2.1
p4 0
p5 0
p6 4.3
p7 8.5
p8 4.3

So this is quite different than Xlrators'

the difference is that mine still doesn't roar.

any thoughts ?

QuoteSorry to steal your thread Martin.

no hard feelings, i don't think this is really mine anyway, it belongs to the "community"  

Here's mine, FWIW - I am certainly not the authority on this design:

1: 8.6
2: 4.6
3: 4.15
4: 0
5: -.1
6: 4.6
7: 9.25 (wall wart supply V = 9.38 ) edited - dumb automatic smilies
8: 4.6

Most of them seem to be differences due to the supply voltage (I assume youre using a battery) but that pin 3 looks suspicious at roughly half my measurement. I would suggest checking resistor values and connections leading up to this pin (Starting at the input and working towards the opamp). Looks like there are only 5 components between the input and pin 3 (the noninverting input of the opamp) so it shouldn't be too hard to pin down if that's the problem.

Here's my question - am I understanding this correctly? The 9V source becomes the V+ for the opamp. In order to bias correctly, 4.5V is generated from the 9V source, and this is coupled to the AC signal (input from the guitar). This 4.5V acts as virtual ground to the opamp, causing actual 0V ground to appear to the OA as -4.5V. So Martin's pin 3 above is (in terms of the virtual ground of this circuit) kind of like -2V? Am I getting this?

Oh, and I think pin 3 should be a bit higher anyhow, I swapped in a higher value resistor to deal with my too outputty pickups.

Thanks Samuel. The pin 3 also looks suspicious to me. I'll work on this. For your question: It seems reasonable to think the way you do but what would the negative voltage be needed for ?

Now my rat works well!

Fixed this tonight. I had to change R1 from 1M to 100K. The voltage drop was too steep due to this resistor. Also, there seems to be an error on the wiring diagram. (see GGG) The Gain pot is wired in reverse (assuming it is seen from the back)

Anyway, i'll get my buddy's original rat2 and compare them next week.

Thanks to all the great folks on this forum!

Sweet. Glad you got it working. I noticed the backwards gain pot, but I just assumed I had goofed and wired it backwards.