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Halp!

I'm Building a dual pedal with a Lil pony and Mimosa Jr in a single enclosure. Got the mimosa working but after i built the lil pony I got the following issues:
Fizzy distortion sound especially as the note decays

Tons of headroom until you tune the volume up to about 75% then it starts to feedback and squeal like crazy.
Distortion knob adds what sounds like under biased fuzzy fizz till about 75%, then if I play hard the volume ducks and eventually the pedal starts to self oscillate with a thumping sound.

Ive gone through and checked every solder joint, reflowed them and tested with a multimeter for continuity. checked all the wiring to the pots looking for shorts.
the symptoms happen even when pcb is out of the enclosure.

The voltages on the ics are:
starting on pin 1 of IC1: 0v 0v 0v 8.6v 0v 0v 0v 9.35v.
IC2: 0v 0v 0v 8.6v 0v 0v 0v 9.35v.

some pics for reference

I think you triple posted by accident, so I deleted the other two posts—but if there was anything in them that isn't in this one, just let us know.

A few questions:

1. You mentioned the Mimosa Jr. worked on its own. Did you test the Lil Pony on its own as well? It's definitely best practice to get everything working separately before you combine them. If you haven't done this, please do this first so we can rule out any interaction problems between the two circuits.

2. It looks like you have an order flipper toggle in the build. Does the problem occur in both orientations?

3. How are you powering this pedal? Charge pump circuits like the Pony family of effects often do not respond well to certain power supplies, notably the 1Spot.

_________________
Scott

My band, Austin Hollow

I did try the pony on its own and isolated the power from the mimosa same issue
I noticed weirdness with a 1spot so I switched to a boss power supply and also a voodoo labs iso 5
Regarding the order flipper, yes the issue is the same in both positions.

I’m noticing on my voltage readings that the tl 072’s are not seeing the 16v on pin 8 but instead are seeing 9v not sure why that would be as it seems the numbers on my charge pump are pretty close no?

Also I think my charge pump voltages got cut off..
They are: 9.36v, 5.62v, 0v, -3.4v, -8.6v, 4.5v, 5.98v, 9.36v

Thanks for catching the triple post. Not sure how I did that haha

Pretty sure the pin 4 values that you reported are -8.6V (which is correct), not +8.6V.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Yes I think you are right it’s -8.6

So if my charge pump numbers are right any thought about why i wouldn’t see 16 v at tl072s

It's not supposed to produce +16V. It's only supposed to produce -9V

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Your TL072 pin voltages are correct for the Little Pony. It uses the -9v output of the charge pump but not the +16V, opting instead for the (nominally) +9V of the power supply. The voltage doubler capability of the charge pump is not used in this circuit to save space on the already crowded PCB, since it would require two more diodes and another electrolytic cap. But the resulting ~18V differential is used in both of the TL072 dual op amps. This differs from the full-size Silver Pony circuit where IC1 operates with an unaltered 9V voltage differential while IC2 uses a ~25V differential via the full charge pump capability. Just a slightly different implementation.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

I see, that’s good to know. So that being said where should I look next. The volume and drive controls are basically unusable above 50% plus the distortion def doesn’t sound right. I’m hopeful to get this pedal working properly.

It's hard to say when you've got it boxed up like that. I'd start by working on it ala carte without the flipper switch. If it starts to self-oscillate when you turn up the volume, maybe you have a feedback loop.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

I did try isolating it from the mimosa but didn’t take it out of the order switch. It squeals with the volume up and self oscillates with the drive up. I’ll try totally taking it out of the case.

Update!

I took the order switch out of the pedal. The volume doesn’t squeal anymore. The volume and treble pot both function great and the boost capabilities of the pedal are awesome but the distortion still isn’t right.

As I turn the drive knob up I get a crackly fizzy drive blended with the clean until about 75 - 80 % when it ducks in volume after hitting a note. Above that it goes into an uncontrollable distorted thumping. It only goes away if I turn the knob back down. Thoughts?

Please disconnect the drive pot's A2 wire from either the main PCB or daughter board (just one of the other will suffice). Does that get rid of the self-oscillation?

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Finally just got back to this after traveling for a bit!

Removing the A2 wire doesn’t get rid of the oscillation.
Tho it slows the thumping. When I touch the removed wire to the pad where it was soldered to, the thumping frequency increases.

There's a 1k5 resistor on the left side of the board between two caps just above the OUT eyelet. Pull one end of it from the PCB and see if that stops the oscillation.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Pulled that resistor and the oscillation stopped!

If you look at the schematic, you'll see that R11 is part of a feedback loop between R17/18 and C2/4. It's actually supposed to create a tiny amount of self-oscillation. I can't tell you why yours in self-oscillating too much. Maybe you have a short somewhere in the path that is bypassing the R12/C8 low pass filter? You should follow that trace on the pcb very closely and see if you see anything weird.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Went through the pcb again looking for shorts but couldn’t find any. Reflowed solder on anything that looked suspect but Same issue still present, also there is a very fuzzy clipping sound when the gain is turned up before it gets to the oscillation. Sounds ok with the resistor pulled but very saturated. Checked to see if I had any components mixed up but everything seems as it should. Not sure what to try next.

I went through the pcb again cleaning any extra flux with isopropyl .. I also installed sockets for the op amps same issues .. any one have any idea what I should try next?

Have you tried it totally ala carte from the mimosa yet? I would try removing the TL072 chips and adding sockets. If you're not going to put it in the smaller enclosure, then you should be safe to use sockets. We don't use sockets in the kit because the added height doesn't fit in the small enclosures. Anyhow...the purpose of sockets is so that you can easily try a new set of TL072. That's pretty much the only other suggestion I have.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Ok I socketed both op amps .. tried another set of TL072’s tried a set of 4558’s as well. Checked every trace in the feedback loop, pulled c8 to make sure it wasn’t shorted to ground or reversed, Checked values of R5, R11, R12, Cleaned everything thoroughly, totally isolated the jack’s and power from the mimosa.
Still getting a fizzy distortion in the back ground, a squeal when all knobs are up, a feedback oscillation /thump when r11 is connected. Not sure what to try next.