SD-1 bypass issue

[B9 Robot]

I just completed all of the mods on my SD-1 listed on the Fuzz Central site except I used an OC44 transistor for D6 instead of the 1N34A germanium diode listed. (I had the OC44 and it was too low gain to be useful for much else.) I must say that the sound has improved greatly. All of the harshness of the stock pedal is now a thing of the past and it has a lot of smooth and harmonic distortion available. I only noticed one negative and it could be due to something I have done wrong. When the pedal is bypassed, I can still hear the overdriven signal in the background. It is faint but still noticeable. I can probably get away with using it live with no problem but it is audible enough that I would not use it in the studio. I changed R2 to 620K which I thought was supposed to improve the bypass, but it has seemed to have got worse. Has anybody else experienced this? Is it normal? Is there a remedy for this? Any help or comments will definitely be appreciated.

Thank you,

Todd

[Fret Wire]

The SD-1 does that sometimes. The jfet is not shutting completely off (leaky). Assuming nothing else is wrong, change both R11 (22k) & R14 (22k) to 1k for both. That should do it.

[timrand]

Hey

I have been tweaking this pedal for a while lately. The C6 cap removed definately takes the cushion in front of the speaker effect away.

I have found that the assymetrical clipping I like better but I recently added 51pf cap across the diodes and found it smoothed out the sound.

Replaced .027 C5 with .047 metal film

However I am still finding the unit to honky.

[MartyMart]

Thanks Fretwire, thats a great tip, both my SD-1 mods sound "leaky" when bypassed.
Are there any side-effects to this ? could the JFET just be swopped out?
Thanks, Marty.

[Fret Wire]

No side effects. You could just replace the jfet. Depending on it's specs, it may, or may not, happen again. The resistor change is the easy, first step to try for a slightly leaky jfet. It's one of the differences between the SD-1 and the TS-9, which almost never has this problem. Of course if the jfet is completely on or off, then you have to replace it.

[MartyMart]

:? Just swopped out the R11 and R14 resistors, its reduced the break through distortion by about half, still a bit there though!
Could i go lower with the values? 750R  ??
Thanks,
Marty.

[Fret Wire]

You can pull the 1k's and replace with jumper wire. If it still bleeds through, it's jfet replacement time.

[B9 Robot]

Thank you Fret Wire! I will have to stop by the "Shack" today and get some 1K resistors. I hate to pay their prices but I don't have any more 1Ks left and I don't think 99 cents is too awful to get my SD-1 in tip top shape.

Thank you timrand for suggesting additional mods. I will definitely look in to these. Right now though, I am still blown away with the Fuzz Central mods. Mine does not sound honky at all IMO. I already have an SD-1 converted to TS-808 specs, so I wanted something a little different with this one. I am using a dual SD-1 set up currently. The 808 is set for just a little drive and the Fuzz Central is set for over the top driven leads. Both of them together is awesome!!! With my single channel, non-master volume amp; this set up gives me great flexibility. I would highly recommend it.

Thank you all.

[timrand]

What amp are you running ?

[B9 Robot]

I am using a Blues Pearl Verbrasonic. It is like a Fender Super with reverb. 35 watts, two 10" Jensen C10Q's, 5AR4/GZ34 rectifier, two 6L6 power tubes and a built in 3-knob reverb. Unfortunately, as word has it, the builder of these amps has got into some trouble and the company is out of business. Occasionally one will show up on Ebay, but not too often. They usually can be had for a good price if you can find one. It is also PTP and totally hand made. I'm quite happy with it, but I would still like to get my hands on a reissue JTM45 head and mod it as close as I can to original specs.

Have a great day,

Todd