Boss sd-1...how to fix bleedthrough when bypassed?

[wampcat1]

any help appreciated!

Brian

[petemoore]

You're getting efkt coming through with bypass?

[wampcat1]

yes, when using fairly hot guitar pickups, with the pedal bypassed, and the gain knob all the way up.

Brian

[Mike Nichting]

Hey brian,
had this same problem~!! I had the help of a very intelligent individual on this forum but I can't remember who it was, sorry~!!
anyway, I changed a couple of resistors and got rid of the bleed through. This doesn't work all of the time. Boss admits this problem and said they would have to re-engineer the pedal to fix it and they're not doing that anytime soon.
But here are the resistor values I changed: R11 and R14 are 22k. I changed those to: 1K. They are right beside each other so it's not hard to do.
If that doesn't work I'm sure someone with crazy electronics knowledge can tell you how to get deeper with it but those 2 resistor changes worked for me.

Good luck,
Mike Nichting

[petemoore]

I can only really guess that it could be in the bypass switching [I hope that's vague enough, cause I'm not familiar with these]. Boss often uses an eletronic bypassing switching method, I don't know of any other way signal could get into the ckt if the switch is working properly.
 Maybe you could audio probe it near the input, with it bypassed, and see if you can tell how the signal is getting in there.
 I think it is likely in the electronic switching.

[Mike Nichting]

I meant that the mod doesn't work all of the time on eahc different persons pedal. Mine works fine though after changing the resistors.
Check this out, a buddy of mine has a Marshall amp that he uses this SD1 with and he modded a cap on the volume control of the amp and that got rid of the feedthrough on his SD1.
Go figure :-)

If you really like the pedal and want to keep it try changing the resistors I told you to. If that doesn't work maybe think about putting it in a box with a DPDT switch and true bypass. A thought anyway.

[wampcat1]

thanks guys-I appreciate the help!

Brian

 

[Gringo]

My metal zone does that (bleedthrough) when the battery is about to die. Does yours bleed all the time?

Good luck man.

[GFR]

The JFETs used for electronic switches need a negative Vgs to be "OFF".

In a Boss pedal, you've got a 9V battery (less as the battery discharges), minus 0.6V of the diode for reverse polarity protection minus another 0.6V of the diode for "ground loop breaking" if you're using an adapter.

The d and s of the JFET are at 1/2 Vcc, so it's ~ 4V or less. The flip-flop that drives the g to turn the JFET ON/OFF doesn't go to 0V but to ~0.2V.

So you need a JFET that can be turned OFF with less than ~3.8V (minus the voltage swing at the output).

With hot pickups, high gain, the voltage swing at the d/s makes it even worse, say if you have a 2V negative peak  at the pedal output, you need a JFET that will be REALLY OFF (not "almost off") with only ~1.8V or less.

Possible solutions are replacing the JFETs with selected ones (hard to find and to select), or increasing your power supply voltage, or converting it to true bypass (you can build a "A/B" box and use it to switch the pedal, so you don't need to mod it).

[Ryan_77uk]

Some SD-1's require a 9v 200mA PSU and some require a 9v 300mA PSU (my SD-1). I have a high-output pickup and haven't noticed any bleed, I don't think. You might want to try using a 300mA 9v PSU.

That should work right?