my latest build.. having some problems with it

[Keven]

hey! i just finished building a runoffgroove tube reamer for fun. the circuit seemed interesting and i was curious to see how it sounded.

i built it with a RC4558P opamp i had spare. i have a LF358P laying around i'll try swapping around, and i have some power diodes i may try for the clipping section.

now, if you schematic gurus, don't mind, please enlighten me.

http://runoffgroove.com/tubereamer.html here's the schematic.



the build works. no parts were subbed. with the gain off and the volume at 7-8 o clock. i get alot of drive anyway, it's like i could do away with the whole clipping section. i'm thinking something's driving the opamp into distortion, but looking at the schematic, should it? if it's normal behavior, it's fine, i mean, i like the idea of having an OTT overdrive to bring out during recording sessions.

it also really squeals when turned up higher, which could be a side effect of too much gain into either of the opamp stages...

the circuit itself has alot of gain. man... and way too much treble, i should swap a cap or two to tune the treble response to what i like...but if the opamp is driven into distortion for no reason and it shouldn't, i better fix that first.

any assistance? the thing works real well, but it feels like i should limit the range of my knobs to get something remotely usable.

[Keven]

update. i removed the clipping diodes and it's clipping real bad either way. something must be really driving my opamps into distortion. maybe a short circuited resistor.

i'll do some trouble shooting at home tommorow. but which resistor sets the opamp gain? I'm thinking the 1M which goes to Vref, or maybe the 1k before U1b

[Deadstar]

Could be that, you got a multimeter should be easy enough to see if that is your problem.

Otherwise, are you absolutely sure you've got all the right resistor/capacitor values in the right place, cause if your grounding too small a signal level that'll overload the opamp.

Also depending on the particular diodes your using they may have a fairly low clipping threshold which will make the drive and tone completely different, this is one of the most major changes you can make to an overdrive pedal. Though if I remember my info about screamer clones there should be a degree of the dry signal through this which causes a slight phase shift and tightens up the low end i.e. the secret of the tube screamer.

The squealing is a bit odd, you may possibly have something touching if you have done this on perf board check all the copper is cut clean so none of the paths are crossing.

I'd offer more advice but I've not done any pedal building in a while - pics might help.

[Keven]

well, i completely removed the clipping diodes and it still clips, with quite a bit of high frequency content. like a tube amp dimed into home audio speakers. and the volume isn't on at all. there is definitely something up with the build.

[jpfamps]

Sounds like you have way too much gain.

You also need to work out which one (or both) of the op amp stages has too much gain. My guess is that it is the second stage.

You can reduce the gain of the 2nd stage by decreasing the value of the 51k resistor (try flying a trim pot). You can reduce the gain of the first stage by increasing the value of the 2.7k resistor, although this will affect the frequency response somewhat, and you will need to reduce the value of the 220n cap according to maintain the same frequency shaping (the value of R x C should remain constant).

Hope this helps.