Chasm Reverb, Bypass Drain

[Groovenut]

I think the real anomaly might be the working pedal. In my tests, the brick pulls 60mA typ and 100mA max, which lines up with the spec sheet. A load that size across the 33R is going to drop voltage 1.98V @ 60mA and 3.3V @ 100mA, that's about the voltage drop you are actually measuring in the non-working circuit.

Just my thoughts...

[samhay]

Some bricks can draw as much as ~ 100 mA. This will drop 3.3V over a 33R resistor, which may be what you are seeing.
What happens if you temporarily short the 33R resistor?

[italianguy63]

Some bricks can draw as much as ~ 100 mA. This will drop 3.3V over a 33R resistor, which may be what you are seeing.
What happens if you temporarily short the 33R resistor?

Just did that actually.. voltage raised up 2V.  I will go see if it will operate...

[italianguy63]

I'll get back to you... Not sure if it is working-- but maybe.  I have a new issue.  I have had the PCB out of the enclosure so many times now I may have hosed something up.  It seems to be switching now (at least on the not-engaged) side.  Not fully on the engaged side, but it does not look like I am passing signal anymore.  I will have to tone it out again.

This "may" have it.  At least the voltages have come up where they should be it seems.

I'll report back in the future.  Thanks again..

MC

[italianguy63]

Guys--  I think I am going to have to punt on this one now...

I have soldered and unsoldered the JFETs so many times the traces are lifting, and the board is bodged up.  I will just order a new one from Rob, and start over...  I think the issue may be resolved, however.

Samhay & Law, when I get the new board, will it be OK to omit R22?  (33ohm).. and just jumper it?

This pedal is a Xmas gift for my GF's brother.. I really want it to look nice inside.

MC

[Groovenut]

Guys--  I think I am going to have to punt on this one now...

I have soldered and unsoldered the JFETs so many times the traces are lifting, and the board is bodged up.  I will just order a new one from Rob, and start over...  I think the issue may be resolved, however.

Samhay & Law, when I get the new board, will it be OK to omit R22?  (33ohm).. and just jumper it?

This pedal is a Xmas gift for my GF's brother.. I really want it to look nice inside.

MC

It should be fine to omit R22. It provides filtering for the incoming DC. IMO, it's not really needed so much. The opamps provide plenty of power supply ripple rejection and the 5V regulator has plenty of filtering for the brick.

[samhay]

Yes - the 33R probably does more harm than good. I don't include an equivalent in my PT2399 or BTDR designs.
Rob - no harm leaving this design in, but might want to add a note to the build doc that suggests using a jumper unless power supply node is objectionable.

Lawrence - sorry for ignoring you yesterday. seems I missed your post.

[italianguy63]

Thanks guys.  I'll report back when I get the rebuild done...

MC

[deadastronaut]

cheers sam, i'll make a note of that . 

[flanagan0718]

Hmm, I had the same issue with a chasm (not DA's pcb) as well. I wondering that 33 ohm resistor is acting up with my brick as well. I'll have to give it a shot tonight. I'll socket it and jam a 0 ohm in there and see what it does. My guess is that it'll start verbing.

[Groovenut]

Yes - the 33R probably does more harm than good. I don't include an equivalent in my PT2399 or BTDR designs.
Rob - no harm leaving this design in, but might want to add a note to the build doc that suggests using a jumper unless power supply node is objectionable.

Lawrence - sorry for ignoring you yesterday. seems I missed your post.

No worries Sam. I didn't take it as a slight, just a matter of post timing I believe.

I still think the more interesting question is why Marks other build works with the voltages he posted ? Unless the brick on his other one is pulling very low current, those voltages should be the same the problem build. It would appear to be breaking Ohms Law [emoji2][emoji851]

[samhay]

Indeed, I have puzzled that too.
There are quite a few of the circuts that do work, so there must be quite a few bricks that only pull 60mA-ish. With a 9V supply, I guess this won't quite drop the supply low enough to cause the voltage regulator to crap out (although must be (very) close).

[rafikian]

Hi everyone !
this is the first time I post sth here,  I have read all the thread and :
I had the same experience as all of you guys:
voltage drop to 7V when soldering the brick & audio leakage through effect path
the leakage issue is more serious than voltage drop because even with VC@7v I can still have 4.8 v @ the regulator output AND the brick is working.
so after destroying the first board with the repetitive soldering/un-soldering  I got a new board and socket all trannies. so the the leakage was caused by the 2N7000 which didn't shut off (ground) the effect portion correctly.
this is done, everything seem to work perfectly oscilation swirch and all the rest but, in bypass mode, when maxing the mix and the volume knobs, i can hear a slight hiss, i guess that the brick hiss even with no input. does anyone with a working pedal has the kinda thing ?! 

[italianguy63]

Still waiting for my boards to cross the big pond.  Should be here shortly, and I will build one out again quickly, and can report back.  My working pedal is gone to the new owner already.

I plan to replace the 33R resistor with a 680uH choke.  That should be about 7.5 ohms.. I will report back how that works out.

MC

[italianguy63]

this is done, everything seem to work perfectly oscilation swirch and all the rest but, in bypass mode, when maxing the mix and the volume knobs, i can hear a slight hiss, i guess that the brick hiss even with no input. does anyone with a working pedal has the kinda thing ?! 

Hey Rafikian-- got my 2nd one up and running tonight.  Yes, with everything cranked, I hear a slight hiss too...

Report:  I swapped R22 (33ohm) for a 680uH choke (from Tayda).  Rebuilt the PCB and dropped it in.  Worked right out of the gate!

Sorry, I did not yet take the time to measure what the voltage drop of the choke was-- but assuming it runs about 7.5ohm, I am expecting about a .5V drop.  As long as those JFETs switch correctly, I could give a rip.  I don't want to tell you how many 2N5457's got murdered in the troubleshooting of this thing.

I didn't bother with the VOM, because really, I just want to be done with this build!!  Set me back a lot of time... it happens.

Thank you again Rob (BTW, got both boards, thank you), Samhay, and Groovenut.  You guys rock!

I will post a pic of it in a day or two-- it came out sweet.

MC

[deadastronaut]

Cool, glad you got it sorted man...

[rafikian]

thanks for your reply italianguy, I will try to post some pictures too