help: TS808, no distortion (but gain works)

[rody82]

Please help, i've built the Ts808 (tonepad layout), with these mods:
cap 0,047 -> 0,1
cap 51p -> 56p
25k tone pot (the others are as on the schematic)
drive section resistors: 51k -> 47k
input cap: 0,027 -> 0,022
diodes -> 1N0007 & 1n4148 & jumper, (tried 3 1n4148 too with same results)
resistor 2M2 -> 3M3 near the input
tone caps : 0,33 tant. (not 0,22)

used 2N3904 trannys and a JRC4558D chip.

It sounds very good to me, but when everythings at max there's only an almost unaudible overdrive. (its there though,
but maybe its just my amp). Turning the drive pot makes the sound louder though...
Any ideas?

[Mike Burgundy]

Jumper? What's that jumper? That's the first thing that popped out - if you hav a jumper across the diodes, this will not allow the diodes to do anything to the sound at all. The other changes don't have an impact on distortion as you describe it?
hih
Mike

[rody82]

Well, look at the tonepad schematics. You have to put something into the D3 slot, else one of D2's legs will be just floating.
Anyway, first i was trying without the jumper, then i've realized the mistake. Interestingly, nothing really changed.

[MikeH]

I'd say to make sure that the resistor that goes from pin2 to vref (via the .047uf cap) is 4.7k, not 47k.  That resistor controls the gain, I believe.

[Steve C]

Is the pedal really loud with the knobs all the way up?  If so, it's most likely a problem with the diodes make sure the orientation is correct on them, if using two they should both be pointing in opposite directions.  Triple check everything off pins 1 and 2 of the IC.  Check all you solder joints again.

[Mike Burgundy]

Okay, my bad. The TS is such a well-known circuit that additions to it sometimes cause Pavlovian reactions.
Still, this does look like that's the area to look at.
Is the circuit very loud but still cleanish compared to bypass - so it's a booster?
That would indicate some problem with the feedback/clipping loop.

[rody82]

thanks, i'll check theese out when i get home. I didnt wire it up for bypass, its wired
for always on for testing purposes, but i think its definitely loud when crancked up. Seems to be a booster.
I think the problem must be somewhere near the diodes, because changing them doesnt
really change anything. i'll check that area first.
That 4k7 resistor is ok, (first i was trying with 2k2, same results)
I thought it was the value changes, but i see now that its probably something else...

[eetfuk]

I havent looked at the schematics for some time, but IF the diodes are not connected, or short circuted it will not clip(unless the gain is to high..nevertheless)
This is based around the dual op amp think, and i believe that lack of voltage gain earlier in the circuit is the reason from a theoretical standpoint.
I did not account for you to make any mistakes.

[rody82]

I've noticed that turning the drive pot works like a tone control... is that normal?
(checked that 51p cap, put 56p and 47p there, nothing changed)

[Mike Burgundy]

double check continuity between the diode legs and pins 1 and 2 of the opamp.
Then, lift one leg of both diodes, and test them in both directions with your DMM.
My guess is they're busted (non-conducting in any way), or there's some kind of wiring problem and both connections to the diodes are open.

[rody82]

hmm.. my post i wrote yesterday disappeared..
The problem was that i used 0,001 cap instead of 0,1 in
the clipping section. 
Now i have tons of distortion. Waay too much!! Now it sounds
a bit dull. With an 1n cap there was almost no distortion and the
gain worked like a tone control but it had a dinamic, brilliant,
nice tone. Lowered the cap back to stock 47n but i'm still no satisfied.
I wanted distortion, now i have too much 
help!