Debugging a SD-1

[Renegadrian]

I got a SD-1 from a guy with modding wills, he just managed to destroy some tracks of the PCB and also changed parts without clue...(started as a SD-1-ts808 conversion but he went further...) - I managed to put all the missing pieces, try to save the broken tracks and some...

Original circuit...


Made some changes, following some info I found googling around, and here in the forum obviously

r2   1m
r5   22k
r6   2.2k
r16   100r
r17   10k
c2   100n
c3   100n
c8   100n

Signal goes, both bypassed and on, but the effected sound isn't as it should be...gain pot is not effective, volume and tone works...the sound is more or less at unity with pots on ten...

Voltages...
IN from wall wart 9.71 V
pin 1 5.90 V
pin 2 5.90 V
pin 3 5.84 V
pin 4 0
pin 5 4.36 V
pin 6 4.84 V
pin 7 5.90 V
pin 8 9.71 V

[Guitarfreak]

Sounds like something that happened with my SD-1 at one time.  Make sure opamp pins 6 and 7 are not bridged with solder or a component leg.

[Renegadrian]

thx for the reply, I edited my post including the voltage readings, I guess it's not the same case, else they'd read the same voltage, right?!

[flintstoned]

What's going on in that clipping circuit? Has r5, d4-6 been "modded"?

[Renegadrian]

As you can read above, r5 has been lowered from 33k to 22k - diodes are untouched...

[ayayay!]

but the effected sound isn't as it should be...gain pot is not effective

It's there somewhere.  Check continuity on wires 2 and 3.  Check continuity between pins 6 and 7.  Check voltage on both sides of R5.  Unsolder the Gain pot and measure Ohms.  Check continutiy between R5 and the Vref side of C3.  Check continuity between all diodes.
I'll bet you have a destroyed track somewhere. 

[Renegadrian]

Sometimes things are easier than expected, and funny too...not thinking about a couple of hours of checking every frekin' component on the board...I had lug 1 of the gain pot touching to tone pot body...that shorted it...now it works at it should, nice overdrive and the mods sound fine!!!

now, what about R5?! someone went down to 10k, someone went up to 100k...I tried 22k as it is in a TS...But I guess it's not that different from the original 33k...

[ayayay!]

R5 is all about taste.  The larger it is, the more saturated the gain sounds, but really there's not THAT much room to play with.  More than 100k sounds like poo.  1k sounds weak and wimpy on the lowest settings. 

[newfish]

Hi!

Love the SD-1.  Great 'string point' for overdrive.

I'd leave R5 as 'stock' 33K, and concentrate on the R6 / C3 path.

My SD-1 has a SPDT switch between these stock values (4K7, 0.047uF), and a 'hot-rod' mode (1K and .224uF).

It goes to eleven...

C6 can also be removed to add more 'push', too.

Hope this helps.

Cheers!

[Electron Tornado]

Hi!

Love the SD-1.  Great 'string point' for overdrive.

I'd leave R5 as 'stock' 33K, and concentrate on the R6 / C3 path.

My SD-1 has a SPDT switch between these stock values (4K7, 0.047uF), and a 'hot-rod' mode (1K and .224uF).

It goes to eleven...

C6 can also be removed to add more 'push', too.

+1

You can also try increasing C1 to 0.1uf.  There is also plenty of space for a toggle switch if you want to mod the clipping diodes.

Did the changes to R2, R16, and R17 have much effect on the sound?

[Renegadrian]

Did the changes to R2, R16, and R17 have much effect on the sound?

I don't know, I found it non working and began modding and repairing at the same time...it sounds good but I cannot make a comparison with the stock...