SD-9 Almost there !!!

[MartyMart]

:? Hey guys, this is a learning curve and a half !   so . . . . .
Followed RDV's "FET" pinout lead and swopped the FET's around on the board ( sorry if this is basic stuff for most of you ! )  before i had NADA  now i have Distortion when engaged, but a little "thin" sounding and not much volume, when "Bypassed" i now have "full on Distortion" just like the pedal should sound, interesting eh ??.
Does my logic follow then that One of the FET's is now the wrong way around?
Or is it nonsense and there's more to this.........??
As i said "Almost there"   but where is that ??
( please dont forget i'm a bit of a novice, though i have done some fantastic mods)
Regards, Marty.

[RDV]

I have looked for a full schematic of the SD-9 on the web so I could better help, but have not been successful. It's probably identical to the same era Tube Screamer switching-wise, so a look at a full TS-9 schem is probably going to help the most. I've never had to try to fix the switching on one of those, luckily I haven't had that problem. Here's a full TS-9 schem:
http://www.diystompboxes.com/cgi-bin/webbbs_scripts/webbbs_config.pl?noframes;read=122

Good Luck

RDV

[Dan N]

I spent $8.00 for an SD9 "service manual" off the web.

Recieved a very crap xerox! Can't hardly read the darn thing!

Yea, probably the same switching as the TS9 etc...

[TheBigMan]

Similar to the TS-9, but I don't think it's the same.  :?

I've been tracing out the bypass path in mine to fix the same flaw (no clean sound in bypass) and have traced it to a non switching FET.  The bypass signal runs through the input and output buffers like in the TS, but also gets buffered through the second half of the 4558.  Pin 7 of the 4558 goes through a cap to the switching FETs.  The one controlling the distorted signal is switching fine, the one controlling the clean signal is not so in bypass mode there is a little bleedthrough of the distorted signal and nothing else.  Strangely enough the voltages at the FETs are the same for both, and I replaced both as well so I don't understand why one is switching and the other isn't.  Might try dropping in some different FETs, in the meantime I've got a datasheet on the SK30A to read.  :roll: