Tubescreamer help

[adding_to_the_noise]

This doesn't seem to be the problem, anyone else have a suggestion?

[Transmogrifox]

I'm not somebody else, but I do have few more ideas. 

1)  Measure the voltage between pin 1 and 2.  If it isn't real close to 0, then that tells us there's a problem in the feedback loop (that is, negative lead on pin 1 and positive lead on pin 2). 

2)  take your audio probe, and stick it on pin 3.  If there's a significant volume loss there, then the problem is somewhere between the input buffer and bias network.

3) take the diodes out of the circuit and see if the voltages change.  That would be another feedback loop problem.

Basically what it comes down to is that it's not possible for you to get undistorted sound through a Tubescreamer with the feedback network properly hooked up if you have full volume at the input of the clipping stage.  If you can use your audio probe to verify that there is guitar at about the same volume on pin 3 as there is at the input jack, then you're lying to me that the feedback network is correctly hooked up.  But who knows, maybe the op amp went unstable at an ulrasonic frequency due to a layout issue (and this is not a joke, either).  If the wires on your breadboard are only as long as necessary, and output wires don't cross output wires, or run parallel for a certain bit, then you're probably ok with the stability issue.

I hope that gives you some more ideas.  I can sympathize--it sometimes can be really frustrating when something so simple just won't work and I have rebuilt it several times and tried everything I or anybody else can imagine.  It usually ends up being something really simple.

The good in it is that you have already learned a lot from the number of ideas you have tried.

[adding_to_the_noise]

Sorry about that, I didn't mean to say that you couldn't suggest anymore Thanks for the great help you've been giving me and you seem to really know your stuff. Well, I'll have to take some time to check all these problems you're suggesting-with work and everything- I'm sure you can sympathize with that too. I just finished drilling the box today so hopefully I can get this circuit working sometime in the next century. I wasn't expecting to have this many problems with this circuit but I guess it's par for the course. Since I have some time before I can check this, can you specify exactly which parts of the circuit you are referring to, i.e. Feedback network, clipping stage, input/output buffer? Thanks so much again for all your help.

[Transmogrifox]

No apology needed.  You didn't hurt my feelings   

Anway,

with the feedback network properly hooked up if you have full volume at the input of the clipping stage

I guess that is quite a bunch of geek talk there.   I'll try to explain what this stuff is that I'm referring to:

Input Buffer
This is composed of the .27uF capacitor, 2.2M resistor, 510k, 1k, 10k resistors, Q1 and the 1uF capacitor.  The purpose of this group of parts is to present a high impedance input to the guitar, and a low impedance output to the opamp.  The capacitors block DC voltages to keep it from interfering with different parts of the circuit.   The gain (amplification) through the buffer is unity, or no amplification.  It's actually about 0.98, but for all practical purposes, what is seen at the input gets "copied" to the output.  If this stage were not here, then a BJT opamp such as in this circuit would load down the guitar pickups at higher gain settings for the pedal.  The buffer is able to drive the load while keeping the input impedance high on the guitar side (I hope the redundancy doesn't confuse you).

Clipping Stage
IC1a, 10k, 4.7k, 51k resistors, 500k pot, D1,D2,D3, 0.047uF capacitor and 51pF capacitor. This clump of components amplifies the signal by a factor that is adjustable between approximately 10 and 100.  When the signal level gets above the forward voltage of the diode, then it limits the output from getting any larger.  This is called "clipping" as it essentially "clips" off the tops and bottoms of the waveform.  The more you amplify the signal, the more of the wave gets clipped (do refer to GEO Technology of the Tubescreamer).

Feedback Network:
4.7k, 51k resistors, 500k pot, D1,D2,D3, 0.047uF and 51pF capacitor.   These components take a portion of the output and feed it back to the input.  Notice it feeds back to the op amp inverting terminal.  This is called negative feedback.  It kinda "fights" the input, so the more you feed back the more it wants to prevent the op amp from amplifying.  If you didn't feed anything back, you'd have a square wave fuzz because the gain would be so high the op amp would be banging from rail to rail every time the signal crossed 0.  The pot allows you to adjust how much of the output is fed back to the input. 

I could keep explaining, but I'd be rehashing everything that RG covers in his Technology of the Tubescreamer article.  He has done an excellent job of breaking it down into functional stages and explaining what each block does.  I strongly recommend reading it. 

Here's the link:
http://www.geofex.com/Article_Folders/TStech/tsxfram.htm

[adding_to_the_noise]

Sorry I haven't posted in a while guys, but I finally got the tubescreamer to work about a week ago thanks to all your help! Does anyone have any good tone mods that they have added to their tube screamer rigs? Is it possible to get more gain from this circuit?