DIYstompboxes.com

Riiiight. Had a chance to build this finally. Only a quick test but it's looking a lot better - for some reason it still doesn't like the wet side being closed, I have to leave the wet side open for the dry switch to operate correctly. If I have dry open and wet closed the dry side produces distortion (like the jfet hasn't opened fully again...).

Something weird is going on.  As far as the switching is concerned the Wet and Dry paths are essentially the same.   The only thing different is the specific JFET in each position.  So if you swap the JFETs does that move the problem to the DRY signal?   That would be an extremely good sanity check.

Another extremely good check would be to pull the JFETS and put in links.  I'd pull the JFETs out entirely.  It would be good to try one at a time then both.  See if you get the same problems.   Also see if there's a pattern.   It might be the circuit itself oscillating or acting funny.

It's usable for what I need in this form, as I can just mute the wet output in software, but ideally I'd like to figure out why it causes this problem - it'd help for future projects and also for my understanding of this stuff.

IMHO it's good to take that stance.  Weird problems often point to a bigger or more devious problem.

My guess is there's something different about the Wet circuit.  It can't be a DC issue on the Wet side.   What is feeding the Wet signal?  If you have a BBD or digital device driving the Wet side and there's not enough anti-aliasing filter there would be a high frequency modulation signal present on the wet line.  That will cause all sorts of havoc with the JFETs.   While you cannot hear the high frequency signal it can affect the circuit.

Another possible cause is the circuit feeding switch starts to oscillate when both wet and dry are active.  While it might happen more easily with a resistive mixer, the virtual ground mixer you are using is fairly immune to that effect.

There's also some slight thumps when switching, bigger cap C19 needed perhaps?

Under normal circumstances you shouldn't get thumps. It might turn out that once the weird problem above is solved the thumps disappear.   Those caps should be plenty big enough.  One caveat is if the JFET cutoff voltage "Vgsoff" or VP  is too low the JFETs will see faster transitions than the RC circuit.  In which case a larger cap might help.

What's actually feeding the Wet and Dry signals?   Knowing that might help find the crack causing the problem.

I finally found mine on my 'repair/refurbish' pile.  It's really muffled and I need to work through it.

It is muffled in bypass mode?  Could be something simple like the connectors or output electrolytic cap those would affect both modes.   If it's only the compressor then maybe the pot or the two electros going to the treble switch.

It's a V2, with Q10 and D5.  One difference is that I have D3 in mine, not a jumper.

As for your question about parts, the Diode reads 4.13v engaged.  I can take more readings if you'd like.  I didn't have time to pull it off the board and inspect the markings this morning.

The middle caps are 220pf and the lower are 470pf.

Thanks a lot for checking those.  It's actually interesting that D3 is there.  I haven't seen small incremental changes like that in the same Boss pedal before.  I've only seen difference across different Boss pedals.

I'll have to measure the zener voltage on one of my Boss units to compare the voltage.  It looks like your zener is 4.7V.

So one thing that would be cool to check is if the resistor above Q10 (near wires 2 and 4) is 100 ohm or 1K.
I've only been able to work out that the 1K changed to 100R when the diode was removed.

----------------------------------------------------
Changes to Early Units

From mid 1979 to late 1980 there were circuit changes.
Across the board there were changes around the footswitch.
By Dec 1980 all changes are in place, which lines-up closely with the release
of the PH-1R.

I suspect devices before mid 1979 had the momentary check LED:
- SP-1, PH-1, OD-1, DS-1, CS-1, GE-6, TW-1, SG-1 (just)

Footswitch Circuit Changes: (intended to be in chronological order)
- Mods to make LED come on in Effects mode, instead of only being a
   momentary battery check while the footswitch is held down.
- Changes to circuit so LED is on in Effects mode.  LED current reduced.
  The LED is wired to the flip-flop or has its own transistor.
- (not sure of order, maybe later) Zener on LED changed from 4.7V to 5.1V.
- Change 1uF cap across footswitch changed to 10n.
- 2x470pF on input of Flip-Flop changed to 2x220pF
- (together?) Remove Flip-Flop emitter diode, and,
  Change footswitch series resistor from 1K to 100R.

Actual units are likely to have these small changes in spite of what
the official Boss schematics show.  Very early Boss schematics can
be different to later released schematics marked "First Edition".
----------------------------------------------------

SPICE suggests sustained and stable 1.5Hz to 8.1Hz speed range using the following single-pot circuit and values ...






which I loosely derived from the following Fender Custom Shop Vibrolux Tremolo oscillator:




www.lynx.net/tremoloCircuits.html



you may have to use film caps for the smaller ones

and, to be clear you’d be replacing Rspeed by a 250k pot and 2k2 resistor wired in series

of course, you’ll be the first to try this out
good luck

PRR is everywhere  it makes sense now 
@PRR: i am the same guy with Farfisa organ spring's broken cart and surf bear fender tube emulation that mosfets run too hot 400mA bias(groupdiy). For the second, didnt found time yet to change R1's (IRF510) value to double or triple as you suggested so for less dissipation and still give lots of drive n drippy. will do asap and get back. As for farfisa i m thinking of using this thread's circuit as external reverb unit and experiment. Farfisa amp out (has its own built-in full tube amp) ---> Rod Elliott Sound rvrb ---> interface, dont know if it can work right though.

the pinouts aren't the same. the "l" suffix on BC series transistors indicates an end base connection, as opposed to the standard centre base connection. [I've seen only one datasheet where this does not hold.] so if your transistors are BC184l, they need leg twists to go on that board - as I understand it, from their docs, but not stated therein.

have you posted all your transitor pin voltages that we might see?

From what I've found, the BC169C has the same pinout configuration with the end base connection.

I'll take voltage measurements from the transistors and post them.

Thanks so much to both of you for your knowledge and assistance.