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Still Switching (sort of Tapdancing really...)

12/14/1999 10:08 PM
Still Switching (sort of Tapdancing really...)
I found a SD-1 schematic including the switching part. Would it be easy to use that for switching? I thought that R.G. said something like "these CAN sound very leak-free". Would it do any good (then you might not need any relays nor expensive footswitches)?
12/15/1999 1:58 AM
Don Symes

Point to it so we can all see. (please)
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12/15/1999 11:32 AM

Oh, of course, sorry ;-)  
I found it at Plate-To-Plate:  
It looks very open in structure..
12/15/1999 11:59 AM

I mirrored it for the moment, just in case you can't get on the site...:  
Kind regards,  
12/15/1999 8:38 PM
Don Symes

Well, the actual switch part has issues, as noted below, but the part of the circuit from the footswitch up through teh cross-coupled NPN transistors (and associated components) is something you DO want.  
This setup is a cheesy form of flip-flop that debounces a momentary switch into a 2-state one. Each closure of the switch causes one transistor to turn ON, which turns the other OFF. The LED stuff over to the left probably acts as a power-up reset so it always starts in a known (OFF) state.  
The transistors are generic - use whatever's handy and has the capacity to operate your signal switch of choice - relay or 4053. BTW you'll only be using one of the two outputs, pick the one that starts in the BYPASS condition for whatever you choose to switch with.  
Have fun!
12/20/1999 11:01 PM

>>The LED stuff over to the left probably acts as a power-  
>>up reset so it always starts in a known (OFF) state.  
That's what I meant with the Ds-1 stuff somewhere else on the list here: Boss changes specs all the time. "Never change a winning team" he? or as they say "You can always tell a classic, it's one impossible to improve on..." Sorry, but my newer Ds-2 always start in the on position when powered! Some years ago ALL my Boss pedals started in off, as far as I know. Well, never mind about that. So my Ds-1 is most likely different from the earlier one I liked so much (more).
12/15/1999 12:24 PM

There's a problem with JFET switches if you're using a single 9V battery. You have to guarantee that the JFET is completely OFF with just -4.5V of VGS (not to mention the signal itself - if you have say 2V peak to peak then the JFET has to be off with -2.5V). You'll need to get FETs with low pinchoff voltages, perhaps select them, to get low leakage. Or you can use two 9V batteries and use "normal" FETs.  
Also, since the FETs are in series with the signal, in order to avoid unwanted distortion you need to feed the switcher from a low impedance source and send it to a high impedance load. The BOSS unit uses transistor buffers for this.  
Yet another problem you may have with FET switching is capacitive coupling that will let high frequencies bleed even if the FET is off.  
You may want to try optoFETs like it was suggested on a channel switching thread sometime ago.
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