Tube Amps / Music Electronics
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|7/11/2000 3:36 PM|
||DF-2 switching conundrum: the flip-flop flaps|
Terry Moxness from Calgary asked me about a switching problem he is having with his Boss DF-2 Feedbacker/Distortion. I have one of these too, and have looked at the schematic, but it goes outside the perimeter of my expertise, so I am foisting it on the more diligent of you, as an intellectual exercise.
The DF-2 is a very standard 2-diode fuzz whose design is essentially a BMP with one transistor gain stage and one op-amp gain stage, and clipping diodes only in the 2nd stage, and a BMP-style tone control. It also includes a parallel path with a 4046 PLL chip that produces a steady tone whose frequency is synced to the fundamental of what you are playing (*See below for some curious design tidbits if you like octavers).
Stepping on the footpedal turns it on and off, as per usual on BOSS pedals. If you step and HOLD, however, the indicator LED flickers, and the "feedback" signal is brought in. This is true at any point. So you can go from OFF to FEEDBACKER, from OFF to DIST, or from DIST to FEEDBACKER.
The schematic shows a 4001 and a few transistors used as an exotic flip-flop to engage the relevant FET's usually employed by BOSS for signal switching.
What Terry got in his box was this: You could go from DIST to FEEDBACKER and back again, but it wouldn't go to OFF/BYPASS. Clearly the switch itself works, but one of the 3 possible states remains unrecognized.
(*Much to my surprise, the DF-2 is actually an octave *divider*. "What!?" you say. How could it be an octave divider if it produces overtones? Curious thing, that. The VCO syncs to the fundamental being fed in, but it outputs a much higher tone. That tone, in turn, goes through a 4013 flip-flop and gets divided in 2 then in 4, JUST LIKE a Bluebox or any other run of the mill octave down effect. These "octave and two below" tones are then mixed in your desired proportion, and blended in with the regular fuzz when you hold down the pedal. If one could figure out a way to output a lower frequency from the on-board VCO, then your DF-2 "feedback" tones could actually be a surly growl that fades in when you hold down the pedal. Neat!!)
|7/11/2000 4:20 PM|
You can get the schematic as a 2-part zip-file at:
It's a bit grainy, but still legible. The first jpg contains the relevant information in the lower left-hand corner.
|7/12/2000 2:24 AM|
Where did that diagram come from?
are others available? (looking for CE2 chorus)
|7/12/2000 1:16 PM|
Somebody sent it to me a while back. I *think* it was our esteemed Brazilian colleague, Guillherme (aka GFR), but I may be wrong. I lost the file that was sent, and had to rescan the printout I had (thankfully) made. Hence the grittiness. Sorry, not much else from that line that isn't already posted in the usual places.
|7/12/2000 3:56 PM|
Thanks for the reply Mark.
|7/11/2000 6:15 PM|
||Re: DF-2 switching conundrum: the flip-flop flaps|
Looking at th schemo, Q4 controls the bypass circuit. This is true because Q1 is the input buffer and its output feeds many circuits including C21 (1uf/50v Electrolytic). The cathode of D6 should change states and I believe it will because you mention that the Distortion portion works with the switch. This tells me that it is successfully switching Q3 in the distortion section. I would suspect Q4 or Q5. Maybe Q5 is shorted on all of the time and the clean signal is getting drowned out by the FX signal.
Hope this helps,
|7/11/2000 9:17 PM|
The first thing that stands out is the use of two 2.2uf 35v electros bottom left of the schematic under SW LOGIC I can not make out the #s c55?,c56?. I would just replace them and see what happens. I would also look at the .047uf debounce cap I have repaired a dod that had the green mini fuse/resistor looking type of ceramic cap that went bad. I will try to work out the logic but first guess is a timing problem.
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