AionFX Penumbra build problems

[benh]

Hi Folks !

I put together the kit from AionFX (I got lazy and decided not to drill my own enclusure this time so bought the full kit) and ... odd things happened :-) I was hoping for some help.

(FYI, docs and schematics are here: https://aionfx.com/app/files/docs/penumbra_kit_documentation.pdf)

Note: This isn't my first build (I did plenty, generally rather succesfully, including some I tweaked, though I freely admit having only cursory knowledge of analog electronics (especially when transistors are involved, op-amps are easier :-). I'm pretty experienced with soldering). Another note is I used lead-free solder at 320C (don't ask...). I did generally manage to keep the heat on the pads/legs on for less than 1.5s or so, the solder joints are prety clean. I *think* I didn't damage the transistors but ...

Also note: The kit came with the "old" values for R6 and LEDR but I swapped them with resistors I had matching the values in the updated doc.

Now it's a gift for my son who is a bassist. I thus haven't been able to try it out with a real bass. For now I'm using a combination of signal generator & scope and for "sound", my Korg SV2 keyboard and a small class D amp on output. The setup works with other pedals and in bypass.

Finally ALL those tests are done with the pickup sim OFF.

The first issue is obvious: As soon as the pedal is enabled (foot switch), I get a LOT of noise. Feels like white noise with an added high'ish frequency component. The TONE pot does allow a slight reduction in noise (probably that higher frequency component). It's quite loud noise, definitely unusable as is.

When I play, I can hear the instrument on top of the noise, but it's still 50% noise.

Additionally, the FUZZ pot seems to have no effect. Or rather, it depends... with PINCH all the way on one side there is a tiny bit of effect, barely perceivable, with PINCH turned up, no difference. It's basically always fully fuzzing.

Now I checked the voltages based on the troubleshooting guide in the doc at the leg of the transistors and they look fine (I skipped Q1 as I don't use the pickup sim).

I did continuity tests between components and couldn't find a fault. I tested a few caps too and they seem allright (with the value slightly varying due to surrounding circuit in some cases, but nothing dramatic).

The pots seem to be working fine based on Ohm-meter (though the PINCH pot is wired differently on the PCB than the schematic, no biggie, just the center (pin 2) is wired to pin 3 on the PCB and pin 1 on the schematic, but that shouldn't make a difference other than which direction does what.

It's possible that the transistors got somewhat damaged during soldering, though I was pretty careful and went quick...

Using a signal generator and scope too. I sent a +/-200mV (tried 500mV too) sine wave at 200Hz (tried 440Hz too) into the input jack and measured at various points of the circuit.

I can see the signal at the base of Q2 mostly clean, but can be slightly deformed (flattened at the top) with PINCH turned a good amount. The base of Q3 however shows pretty much a square wave with something like 80..90% duty cycle (ie mostly high, some dips). The only effect of the FUZZ put is, if PINCH is all the way low, it *slightly* rounds the corners of the squares but that's about it.

I can send photos probably tomorrow of the scope screen but basically like this:

_|----|_|----|_ ...

I was expecting something "cleaner" with FUZZ down and getting square-wavy as FUZZ is increased but I don't observe that.

I did tiple check that the pot seems to be working fine (with an ohm-meter). And yes, the electrolytics are the right way around :-)

Interestingly, I tried to dig out my old SparkFun Proto Pedal (basically jacks, power and a breadboard), and reproduced the circuit without the pickup sim, and with only one of the tone options (ie, not using a switch, just using the 100uF for now). I also used a C500K rather than B500K as I didn't have one, and for FUZZ a C50K wired so that the "low" part of the log uses the most of the rotation.

The results, (un?)surprisinly are ... similar ... large amount of noise (using components from my stash and brand new 2N3904's I grabbed at the local hobby store today) and the same audio and scope behaviour with FUZZ doing basically nothing.

I can post photos etc.... in the next couple of days, in the meantime, any suggestions of things to look at or try are welcome. I'm delaying the "unsolder the transistors and plonk them on little sockets" step (in case they are busted) because desoldering at 320C without damaging the PCB is a bit tricky without a pump, at least for me.

Cheers,
Ben.

[benh]

Another observation ... I did all the testing without the pickup sim as I was trying to reason about a simpler circuit... However, with the piano as input, the pickup simulator turned on seems to improve things somewhat ! A tad less noise (still plenty but ...) and the FUZZ pot is now actually doing something, which is ... a surprise.

With PINCH, FUZZ and TONE all the way left, I get something almost clean. No noise when idle and a light fuzz when playing.

turning TONE right causes noise but only when playing a note. Not fuzz, but some kind of higher freq noise superimposed with the note.

now, with TONE kept right (ie, noise when playing), turning PINCH right slightly (about 1/5th of the way) and I'm now getting that noise even when not playing, but turning it *further* and the noise goes away again. It's always back when playing though.

turning FUZZ right has a similar effect, noise starts happening around 1/4 of the way (when not playing) and becomes louder as I turn it further until it's really loud.

Any idea ? Could be something with the tone part of the circuit ? The LOW switch doesn't affect the noise behaviour.

[antonis]

Hi & Welcome..

Your ascertaiments are quite right..!!
(it's a heavy fuzz..)



You can see that FUZZ pot does nothing while PINCH pot widens (almost doubles) positive waveform..

[aion]

High level, here's a live read of my sensors going off as I read through the post:

"I haven't tried it with a real bass, but used a keyboard" - if there are unexpected results, I always look for unusual or uncommon inputs and make sure those can absolutely be ruled out as being the issue. Signal from a non-guitar source would definitely be an unusual input.

"This setup works with other pedals" - this circuit in particular is unique... Zvex circuits are very primitive in their design compared to most other types, getting most of their sounds from abusing transistors in creative ways, as opposed to intentional tone shaping with filters and clipping. Because of this, one of their signature characteristics is that there's a lot of knob combinations that don't work at all, or sound really bad. The Fuzz Factory is exponentially worse. But it's definitely in a category of its own and I would not be surprised if it behaved very differently than most other pedals.

"It works much better when the pickup simulator is on" - i.e. when the signal is more like a guitar.

I don't at all mean to be pedantic so hopefully it doesn't come across that way. These are the parts that stand out to me as big clues.

For this circuit in particular, I would avoid drawing any conclusions about whether it's working right until you can play it with a real bass, or just an electric guitar if that's available. Then compare it to the demo video or to YouTube demos of the Woolly Mammoth and see how it stacks up. It sounds like it may be working as designed, but not working as expected - which for Zvex circuits are often two different things!

[benh]

Thanks ! I get it about the source and the oddity of the circuit, I'll try to "borrow" a guitar or bass in the next couple of days.

That said, with the pickup Sim, it does seem to sound like it should with the piano, it's actually quite nice, except for that noise, which happens even when not playing anything at all

I just want to check if that's expected... It kind of sound like an AM radio tuned to no station, it's fairly loud. My second post explains how the noise relates to the pots. It's especially strange how it comes and goes with PINCH... Almost feels like it hits some kind of resonant freq range that makes it pick up RF noise.

If that's normal with this pedal then all good. If unclear I'll so some recordings to clarify once I have a proper string instrument connected :-) it's definitely much louder noise than the usual noise one gets from high gain pedals.

[benh]

For this circuit in particular, I would avoid drawing any conclusions about whether it's working right until you can play it with a real bass, or just an electric guitar if that's available. Then compare it to the demo video or to YouTube demos of the Woolly Mammoth and see how it stacks up. It sounds like it may be working as designed, but not working as expected - which for Zvex circuits are often two different things!

So I tried it with a variety of instruments (passive bass, active stingray, and a cheap fake strat) and it's indeed night & day :-)

It's working great. Now, I was using a bass amp, it's possible that the weird noise still happens with some setups and is just low-passed out by the amp, but it's fine. The sound is great. In fact even the active Stingray doesn't need the pickup sim to sound good.

Sorry for the false alarm !

And praise for the quality of your kit ! From the really nicely coated and printed enclosure to the good quality components, the really nice IO board, use of connectors etc... it's the highest quality kit I've built so far !