Tubescreamer BB mod

[lerxst88]

I have a TS9DX and I was thinking of having a switch to add in an extra op amp (either a 4558 or a TLO72) in a similar fashion to the BB Preamp. I soldered up a veroboard with the opamp stages and I couldnt get it to work. Im going to doublecheck my circuit for dumb mistakes but Im thinking the 4558 I had was burned up so Im curious if this looks like it would even work. Tell me what you think!

[slacker]

The second opamp won't pass any signal, that's probably why it's not working. You've got the signal going into pin3, but that is attached 4.5 volts, which is ground for audio signals. It looks like the 10k resistor should really be going to pin 2, that would make it work.
What is this supposed to do anyway? It's just like a preset version of the tone control.

[lerxst88]

Well from the schematics I've found, I would  assume its akin to adding tube stages to a preamp except I'm using opamps. More distortion and of course a change in tone. If it works as well as having a TS-808 and a BB preamp on a switch in one small pedal then I am one happy camper!

so basically just connect the 10k going into the second opamp to pin 2? Never knew audio signals would react that way to the 4.5v

[lerxst88]

Ok Im back and I connected that 10k to Pin 2 and it worked great! I noticed a small volume drop but it was no problem.

I re-did the circuit on perfboard so it would fit in my Tubescreamer and I could put the two on a switch. Unfortunately now im getting next to no volume and it is much raspier, like a fuzz. I have everything in the right place and socketed the IC so I know its not burned up. Any ideas?

[Taylor]

Well from the schematics I've found, I would  assume its akin to adding tube stages to a preamp except I'm using opamps. More distortion and of course a change in tone. If it works as well as having a TS-808 and a BB preamp on a switch in one small pedal then I am one happy camper!

Hmm, not sure about that. Tubes distort. Adding more tubes changes the distortion. But the opamp stages you have there do not distort, at least not in any pleasing way. I know people get all worked up about the opamps in TS circuits, but it's the diodes where the clipping (distortion) comes from. Adding more clean opamps will not change the distortion quality (unless you clip the opamps, in which case you'll get unpleasant distortion). All you have there, as slacker said, is just a preset version of the TS tone control pretty much.

I don't think this idea makes sense I'm afraid.

Looking at the BB, it's just a TS with the tone control preset, and then a Baxandall tone control. If you want to cop what this pedal does, forget what you've done above, remove that, and add the Bax bass and treble control after the stock TS tone control.

[PRR]

> akin to adding tube stages to a preamp except I'm using opamps. More distortion

Your reddish opamp stages have "NO" gain. The 2nd reddish stage is clearly a unity-gain follower (would be, if pin 3 weren't nailed to a solid DC point). The 1st stage has gain approaching 11,220/10,220 or 1.1 which is hardly audible..... and then you have the bizzare 1K input resistor.....

And a clipping level far higher than the D101 D102 stage.

So whatever comes out of IC101 just flows through the reddish stages un-harmed (clean).

> I noticed a small volume drop

....and then you have the bizzare 1K input resistor to a low point on the NFB network, which is too messy for hand analysis but probably puts about 1K of loading on the R107 1K source, dropping level in half.

> akin to adding tube stages to a preamp except I'm using opamps. More distortion

Copy the IC101 stage two more times. Change R104 C103 in all 3 stages to 22K and 22nFd to 5nFd (probably best not all the same, something to play with). Instead of getting all your grind in one grossly overloaded stage (BIG frikkin hammer), you will chip away a bit at a time (stone-carver). That's what you seem to be trying to do; it may not be what you want.