Boss SD1 slightly popping while switching

[ct_anthony]

Hi all,

I have a problem with a Boss SD1. It is slightly popping (a slightly not to aggressive fooop noise) when switching form bypass to active. It is only noticeable when using the pedal as a booster into high gain (Crunchbox in this case). I've checkt several new production units and all behave the same. There is no AC on the audio line, power supply  is all battery. I'm pretty sure it is something related to the SD1. The popping occurs even when the volume is turnend down to zero. In contrast a Boss OD-2 is complete inaudible when doing the same.

Anybody else noticed this about the SD1? Logically I think that the bypass is switching to fast (but its supposed to be the same than in the OD2)... any tips about what to try/check/mod ?

SD1: Schematic: http://www.hobby-hour.com/electronics/s/schematics/boss-sd1-super-overdrive.gif

Regards, anthony

[antonis]

If it also happens when inserting Input plug, I'll suspect the absence of Input pull-down resistor (Output is OK via R17..)

If not, is probably an LED caused pop which is easily cured by adding a relatively small resistor (i.e. 330R) between R30 & GND and a 10μF capacitor between those two resistors junction point and GND..

P.S.
I have some reservations about DC offset of Level pot..

[anotherjim]

Level pot returns to Vref, all should be good assuming that caps are all good - I think it's safe to assume they are for now.
I think it's significant that it still happens with the Level control turned off.

I'm thinking that maybe it is due to the status LED current, but your Crunchbox may be feeling it via power supply ground coupling. How is the SD-1 powered? Try a battery in the SD-1.

[ct_anthony]

Hi everbody,

Everything is powered via its own 9v battery, the "pop" or better "fooop" is there when I go into "any drive channel"... I think it may be the LED. Will disconnect it and check again... but it might take some time to do it. Need more time for preparing a gig currently

Regards, anthony