Aion FX Sunn Beta Lead build whine/squeal in the treble pot

[comradehoser]

Hello good people of the audio-electronic kingdom. 

Background: This is my first-time post here.  My problem child is the AionFX version of the Sunn Beta (Lead version).  It is the 9th pedal that I have built (including another Sunn Beta clone by PCB Guitar Mania).  I am currently at a beginner high-intermediate low level of understanding of pedal electronics. The intent behind the project is that the Beta pedal will be one of two boards running as a modular, pedal-format preamp running into a 100w Class D power amp in emulation of the original Sunn Beta.

The build was done with the aionfx pcb, as well as a mix of components that I had left over from other projects, Aion's Mouser BOM, and orders from Stompboxparts.com.  To my knowledge, I built it exactly to stock specs without substitutions, and tried to order high-quality components when I could choose them.

Here is the documentation with schematic: https://aionfx.com/app/files/docs/beta_preamp_documentation.pdf
I performed the recommended jumpering of IC2 pins 9 and 11 to the ground terminal of the mids pot.  Off-board wiring done with 24AWG solidcore wire (I'm trying to be more tidy), according to AionFX diagrams.

My gutshots, PCB unmoored from the enclosure for probing (please pardon my messy wiring): https://photos.app.goo.gl/JvC4RkjVkpcjhq3fA

The problem: I have run into something odd that I am at a loss to understand, explain, or find the source of, and I bring this to you because 1) I would like my pedal to run correctly throughout the range of possible settings, obviously, and 2) because I would like to understand why it's happening. 

The guitar has signal and effect as expected.  But, with the "level" pot at unity gain (~9:00) and the "drive" at about 60%, the last 10-20% of travel in the treble pot yields a high-pitched whine/squeal that becomes more pronounced when the drive pot is turned up.  Cranking the level pot brings the beginning of the noise back.  With level at 100%, the noise starts at ~40-50% of travel in the treble pot.  At lower "Drive" pot levels, gradually increasing the treble pot at the onset of the noise results in sounds or modulations that remind me of changes in radio frequency.

I searched this forum, contacted aionfx, facebook pedal building forums, and reddit for any additional info, the only thing I found is a user on facebook who just built the same version board (albeit jumpered to ground at pin 7 of the CD4069) and reports the same issue.

Troubleshooting per the forum guide:

With the audio probe, I could detect the whine/squeal noise at audible levels (but not nearly as loud as the level on output) beginning at R24, a 22k resistor, which seems to be correctly soldered and of the correct value.  The noise was also present in the bass pot, treble pot, of course, and in R29, but not in R23 (unless it is very very faint), or in c15 or or C19.  Noise was absent in all RC4558 signal out pins (1 and 7) except for IC 6, in which it is extremely present.  I also couldn't detect anything out of the CD4069. 

Let's get to the numbers.  Measured with a Mestek DM100C multimeter, pedal on and connected to 9V OneSpot wall wart measuring at 9.426 v DC at the input jack and at entry to the board:

Q1 RC4558P
1: -0.352
2: 0
3: 0
4: -8.667
5: 0
6: 0
7: -0.16
8: 9.135

Q2 CD4069UBE
1: 3.626
2: 3.631
3: 3.610
4: 3.558
5: 3.602
6: 3.753
7: 0.001
8: 7.841
9: 0 (jumpered to 11 and to ground)
10:  7.84
11: 0 (jumpered to 9 and to ground)
12: 3.624
13: 3.617
14: 7.843

IC3 RC4558P
1: 0
2: 0
3: 0
4: -8.66
5: 0
6: 0
7: -0.018
8: 9.127

IC4 RC4558P
1: 0
2: 0
3: 0
4: -8.665
5: 0
6: 0.002
7: -0.015
8: 9.130

IC5 LT1054CP
1: 9.129
2: 4.923
3: 0.001
4: -3.957
5: -8.663
6: 2.571
7: 1.431
8: 9.127

IC6 RC4558P
1: 0.001
2: 0
3: 0
4: -8.665
5: 0
6: 0.006
7: 0.618
8: 9.126

Z1 1N4742A
A: 9.131
K: 0

I'll be happy to give any additional details regarding any more of the weirdness of this phenomenon.

[eh la bas ma]

hi, welcome,

I am probably just as knowledgable in electronics as you are. But I have 1 or 2 ideas you can try :

From instructions, p.7 :

"Thanks to Brad from Nerd Knuckle Effects for diagnosing the issue and running noise tests to determine
the optimal way to disable the CMOS gates. At max volume & gain with all tone controls at noon, the
noise was measured at -36.1dBV when gates were tied to ground and -34.1dBV when tied to VB, so we
opted for ground in version 1.1."

I guess your noise is the one mentioned above, probably coming from IC2.

I would try an other CD4069 in IC2, , the one from your Guitar Mania build for exemple. First without the v.1 fix, and with the fix. It is said that the chip will get hot, but won't overheat without the fix, let's see if the noise remains...

If it doesn't change anything, I would try to connect gates to VB, just in case : C35 + side, instead of the mid pot. On schematics, IC2 Pin 14 seems connected to VB too, but I wouldn't touch it, to avoid more unexpected issues from IC2.

[comradehoser]

Hey, thank you much!  Does FR=le beau pays?

OK, will try your suggestion, I have an extra CD4069, and at least I can see if it's a different noise.  I forgot to say, I checked CD4069 and couldn't find the whine either.

Report: ohhhh, no, no, no.  Without the fix, that was just a festival of craptastic fizz.  And still had the squeal to boot.

Just so I don't do dumb stuff, can you elaborate on what you mean by "C35 [capacitor 35] + side"?

Just as a general update of things I tried, I replaced R24 on the off chance it was defective, and it didn't do a thing.

[eh la bas ma]

Hey, thank you much!  Does FR=le beau pays?

yes, by the way, have you ever tasted natural white wine from Anjou ? good stuff, "natural" means no chemicals. They're using what they call "noble rot"... that's why it's so good...

Just so I don't do dumb stuff, can you elaborate on what you mean by "C35 [capacitor 35] + side"?

Instructions say you can connect the CMOS chip either on ground, or to VB. If I understood correctly, Aion suggests to choose ground because they noticed less noise on their build, but maybe VB will work better on yours...
Electrolytic capacitors are polarized, positive side has a + sign on the pcb. I suggest to try connecting IC2 pins 9 and 11 to C35 square pad :



That way these pins will be connected to VB instead of ground.

But i am assuming the noise comes from IC2,  and maybe this is wrong.

From your pictures, I'd say your soldering skills are very good, but you never know...maybe you have a bad solder joint somewhere, sometimes they look good but they aren't.

Did you go on the hunt for shorts ? And try to reflow all suspicious soldering pads ? the pads connecting the main board to the footswitch are looking a bit suspicious to me, for exemple, but that's probably not the issue. I would reflow every pads, just to be sure, and clean the tiny spaces between pads on every IC's sockets, going quickly with the iron to avoid overheating the board.

Maybe a long shot but I see you have some of those yellow caps.

I do too and someone on this forum told me once they were "microphonics" or something, meaning they are noisy, not to be put on the signal path.
But i am not sure if yours are the same. Can you show their specifications ? like where you got them and what kind of caps are they ?

Edit : remember to take every heat-sensitive parts off the board if you use your soldering iron near them (only ICs in your case).

Edit 2 :

ohhhh, no, no, no.  Without the fix, that was just a festival of craptastic fizz.  And still had the squeal to boot.

Well, from what I can understand p.7, the v.1.0 version is supposed to work without any fix, the fix only prevents the chip from getting a bit hot, and that's all.

[comradehoser]

Non, je ne peux pas dire que j'ai goute le vin Angevin--mais c'est aussi vrai que je suis plutot biere que vin.  Par contre, les petits vins et alcools esoteriques, j'adore explorer--tel le vin jaune de Franche-Comte. (desole, pas d'accents).  Pour le vin de pourriture noble, le Sauternes est assez spectaculaire, aussi.  Vous venez d'Anjou, donc?  Ma famille est du cote au nord de Cognac, plutot la Charente Limousine, si vous connaissez le pays la-bas (bravo le pineau).

OK, back to English for the electronical benefit of all.

Thanks for the idea on soldering to VB.  I will check it out, as it's a very easy thing to test anyway.

Yes, I definitely reflowed the board and I try to be very meticulous about things as I'm soldering and I will check for possible shorts and poor joints after every component.  The only other thing left is my off-board wiring--this doesn't sound at all like ground-related noises I am familiar with, but who knows.  I will try to post a recording, if I can.

I'm not sure if the noise is from IC2, as I remember checking the outs on the CD 4069, and couldn't hear it.  I just don't understand why it would start at R24 as it doesn't really seem to be a particularly complicated place where things are coming in to mess up the signal or amplify lurking noise frequencies.  Something coming from the charge pump, maybe?

The yellow caps are mostly 100nf MLCC or smaller pf value caps obtained from Mouser and specified in Aion's layout and BOM.  I don't know if they are particularly microphonic and have never heard/observed that, but what do I know?

I don't know about the precise reasons for the jumpering fix, but I think they were experiencing noise issues, and IC2 with all pins in socket was pretty horrible sounding--maybe it was a bad IC? but I think it's more probable that it was the problem they were trying to fix.  It also didn't heat up noticeably, so maybe that's a clue, I don't know. 

[duck_arse]

also welcome.

most all IC's will upset when any/some/all their pins are connected to some voltage outside the limits defined by their supply pin conections. in the case of the 4069, ground and VB. it doesn't really matter what the value of VB is, within the chip max values, obvs. and THE RULE of cmos ic's is ALWAYS always terminate unused input pins to a logic level. your logic levels here are 0/low/ground and 1/high/V+ supply, in this case VB. either of those must be safe to connect to, by definition. so, really, don't be traipsing that terminating wire all over the board, take it to the only 2 safe pins on the board, either pin 7 or pin 14 of the 4069.

because you have 4 of the invertors in that package biased to their linear regions in order to do amplifyings, the IC will draw more current than if it was doing ordinary logic 1 and 0's, so it can be expected to get warm even when working correctly. measure the voltage across R34 [from end to end, polarity not important] and apply Ohm's law for the current drawn.

it might be an interesting exercise to audio probe all your IC supply pins, because you are expecting clean DC on all of them, so any noise might be a useful pointer to your problem.  check very carefully the two diodes at pin 7 IC6, make sure they are pointing correct ways. as for that "LEVEL" pot configuration, I've not seen it before, dunno quite how it works. but it looks suspiciously close to your R24.

[comradehoser]

Roger, wilco on the three things and will report back.

I suspected the charge pump because the whine, but I subbed it out with the Guitar Mania pedal's known functional LT1054, and I have the same problem.  Also subbed all of the RC4558s and the CD4069 to no effect. 

[comradehoser]

Report:  soldered terminating wire to pin 7 per aion recommendation.

voltage across R34 was 1.177.

Audio probed all of the RC4558 voltage supply pins (8 and 4).  Quiet.  Verified that no whine present in CD4069.  The only place where I could find a similar noise in amplitude and similar frequency was pin 7 of the charge pump, LT1054.  I can't tell where it goes in the schematic.  I assumed it was a dead terminal.

In unscientific fashion (because I did a bunch of stuff and didn't test in between), I also twisted the ground and 9V supply wires, reflowed all of my grounds and any solder that looked remotely funky.  When I had the whole circuit out of the enclosure for audio probing, I thought I had something reasonable: no squealing except at everything-dimed levels and when the guitar was muted. 

But when I remounted in the enclosure the result was.... the same.  So maybe to do with offboard wiring or some interaction with the enclosure?

The pedal is very temperamental.  Sometimes the squeal is much louder; at one point, I had nothing but hiss.  Obviously it's due to poking around and moving stuff, but there is something I am not grasping about this because I can't make sense of what I'm observing.

[eh la bas ma]

When I had the whole circuit out of the enclosure for audio probing, I thought I had something reasonable: no squealing except at everything-dimed levels and when the guitar was muted. 

But when I remounted in the enclosure the result was.... the same.  So maybe to do with offboard wiring or some interaction with the enclosure?

I can't really see on your pics...is there some isolating material on the pots to prevent them from touching the pcb and the jacks ?

If not, some plastic tape or even a piece of cardboard will do the trick.

If that's not the issue, can you post a pic with everything in the enclosure ?

Edit : looks like you made a mistake drilling the holes for the jacks, I guess you forgot about the pots when you did the first ones  ().

Are we sure there's enough room in there for the jacks, without touching the back of the enclosure  ?

[comradehoser]

Yes, the pots have dustcovers on them.

You are exactly correct on the drilling.  I was like "oh, I'll drill the jack holes offset so that the 9v cable has more room."  I actually did it to 4 pedal enclosures 

The jacks sit slightly proud, but I rotated them so that the grounds, if anything, will make contact.

Have electrical tape on the back of the enclosure.  Pedal squeals with or without it on.

Here are pics (on and squealing): https://photos.app.goo.gl/CMDqNndKRgyCQ44H9

If it is of any importance, I'm using a little Orange Crush 12L as my test amp.

[edit: decided to change the test parameters:]
Squeal issues:
Single coil different/less than humbucker/two single coils selected

Orange 12L Crush (solid state): Present

Silverface Twin Reverb (tube): Present

Sunn Sonaro Bass head (tube) and 2x15 cab: Present

Nux MG-30 multi-effects pedal with cab-only IR and with/without preamp: You can detect it as background/residual noise, but out-and-out squeal/whine NOT present.  However, with the squeal muted a bit, it is a noisy AF pedal.  Lots of ground noise that is affected by touching the enclosure.

Could it be the presence of another preamp that is the issue?  Unfortunately, none of my IRL amps have a bypass effects loop to test the idea.

[eh la bas ma]

Lots of ground noise that is affected by touching the enclosure.
(...)
Could it be the presence of another preamp that is the issue? 

I doubt it 's related to an other preamp, you can test it by connecting headphones to your build, instead of an amp.

The fact that the enclosure is sensitive like this, points toward a ground issue, or a short somewhere.

You can do a continuity test, with your DMM, on all your grounds locations, and check if everything is ok.

Probably nothing, but on your second pic, looks like one side of CD4069 isn't correctly inserted in the socket.

I guess you already reflowed all the pots pads, and checked carefully the R24 aera for shorts.


As your audio-probe test indicates something happening at R24, I would give a closer attention to this location, check all the grounds with a continuity test, reflow all pads. Still on continuity mode, check all connections  between components according to the schematics, etc.

On the other hand you noticed that the circuit is "temperamental". Once everything is inside and screwed to the enclosure, if you shake it a bit you can hear some variations in the sounds or in the squealing ?

This would indicate a loose wire or some unstable connection from a bad solder joint, could even be some piece of hair or some dust somewhere on the board. You can clean the pcb with a dry toothbrush.

An other test could be to feed the circuit with a battery, and not with your usual power supply. To check if there is a bad interaction there.

[comradehoser]

Salut l'ami!

Yup, forgot to say that I did check every ground point in the circuit and in the wiring.  Everything checked out. Is it possibly the fact that I'm using solidcore vs. stranded wire?  Just shook it about while in squeal mode.  No audible changes.

Can you tell me what you see for CD4069?  It's in there pretty much as far as it can go.

I did indeed reflow every solder point, including pots.  The only thing I didn't resolder were the in and out wires.

That's a good idea on the battery.  Will do. 

The temperamentality is not readily explainable to me.  I just don't get why sometimes it works better than other times.  It's been a bit random and all over the place because I am not getting the something that is causing this.  Poking in the charge pump with the audio probe and inadvertently bridging pins reliably shut the pedal down and it would pop back up after a while. But other than that, I don't know.

I feel very much like your signature quotation, there.

[eh la bas ma]

I feel very much like your signature quotation, there.

Indeed ? i thought it was a bit too much. I ll keep it for a while then.

Can you tell me what you see for CD4069?  It's in there pretty much as far as it can go.

Zooming in on the CD4069, I thought... Probably just an optic illusion...sorry.

On Aion's Spectron, I had one weak trace, the current couldn't pass between 2 components, and I had to solder a jumper to get a connection. Then it worked.

My point is to check that the parts are really connected as they should, according to schems. Especially in the R24 aera. For exemple, R23 should ring with R24, BASS lug 3 should ring with R29, and R29 with TREBLE lug 3, and so on...

I highly recommend building the Spectron, by the way.

LT1054 may be a suspect, but I wouldn't touch it with the DMM, unless you know exacly what you are doing. I'd be more confortable taking it off and checking the socket's connections, power supply unplugged, looking for shorts or bad connections.

Edit : You can try your charge pump in your guitar mania build to make sure it's working.

[comradehoser]

Alright, I will check continuity.  But it seems like this isn't a matter of go/no go continuity/no continuity, but something in the degree of connection or what the parts are doing too much or too little of.   

I actually did the opposite and swapped in the 1054 from the GuitarMania pedal.  As usual, no effect.

Maybe I should just chalk it down to it being a relatively high gain pedal and use it in the parameters it's comfortable playing within.

Still, it would be nice to have a 100% functional pedal and understand what is going on.

I will try to post audio if I can.

[eh la bas ma]

An audio sample might help more experienced forumites to find the issue.

There's also the possibility that you made a mistake populating the board.

In such cases, downloading a free software can help you read the resistors markings :

http://www.atlence.com/resistor/index-fr.html

Edit:

When I had the whole circuit out of the enclosure for audio probing, I thought I had something reasonable: no squealing except at everything-dimed levels and when the guitar was muted. 

But when I remounted in the enclosure the result was.... the same.  So maybe to do with offboard wiring or some interaction with the enclosure?

If there aren't any noises anymore out of the box, it should be a very good sign that the circuit is fine. Then it's surely a simple mistake when you install the circuit inside it...

For exemple, in my experience, pots can behave oddly when there is too much tension after being screwed onto the enclosure. Better to solder them last, only once they are already screwed inside the box, thus avoiding unnecessary tension on their lugs and on the board.

May I suggest to slowly fit the circuit in the box while listening to it, in order to hear when the squealing appears ?

[duck_arse]

here's something - pull IC6 from its socket, power on and audio probe pin 6 for squeel. vary the level pot, too.

[comradehoser]

duck_arse: will do.  Do you mean to power and probe pin 6 the chip independently of the circuit, or probe the pin 6 socket?

eh la bas ma: I forgot to say I did check all of the component markings, including the resistors--everything checks out so far.  I am wondering how you determine the direction of reading other than having the brown tolerance band at right?

on the fitting and pots--that is an interesting idea and I will try it as well as seeing if I can reproduce the lower noise out of the box.  I have to add that in my audio probing I actually clipped the grounds to the enclosure.  Maybe it is the pot?

I will try to record and post audio later tonight if I can figure out how to do so.

[anotherjim]

What's going on with the 4069? I see a jumper from the +power pin 14 to pins 2 and 4. Those pins 2 and 4 are outputs... are they not? Wiring outputs to any supply is not a good idea, it should only be done for inputs.
Ah, but... is the 4069 in backwards? It's just that I see what looks like the pin1 ID notch at the top of the picture but I think in the build doc it should be at the bottom.

[comradehoser]

Aaahh, anotherjim--well, unfortunately if it were only so simple!

It's just poor photography on my part.  Here it is in the middle of disassembly--what you are seeing as the orientation notch is just a molding dimple, unfortunately: https://photos.app.goo.gl/GW6aGUQ5jPUPLP2t9

Further developments:

Resolving to be more scientific, I took the board out and audio probed the signal in the squeal range as I unbolted each pot and jack. When the input jack rested on the enclosure (grounding itself) and I touched the tip flange of the jack, the squeal all but substantially disappeared.  Touching the output jack, squeal; touching both jacks, lower squeal, but squeal. 

And then a while later, the squeal happened regardless of what I touched, and was everywhere--all ICs.  I think this is called gaslighting or witchcraft or possession. The pedal is just trying to drive me crazy.

Partly a grounding issue, maybe?  I am actually thinking the ground noise from touching the tip input partially cancelled the squeal, as it tends to be displaced by signal:

The squeal is present and strongest when the guitar is muted, or with no input at all, i.e. no cable plugged into input at all.

And for duck_arse, I pulled IC6 and at that point, no squeal in pin 6--or anywhere else, actually, so maybe this is gain-related(?)

I also tried replacing IC6 with another RC4558 and a TL072--no change.  As soon as I populate IC6, we are back in squealandia.

[anotherjim]

Well, so it does sound like it's a stability problem with some stray feedback going on from output to input.
Listing some things...
Sometimes it helps to use screened hookup wire to the in and out jacks or at least just for the input jack.

I don't see a schematic for the switch PCB. I think Aion get it right and do use the middle contacts of the 3PDT for the LED indication but if they haven't it leaves input and output on directly adjacent contacts and that makes a feedback path via capacitive coupling.

I'm not sure I like the output stage, I think it might suffer from a phase shift with that Level control feedback taken from the final output. Difficult to do with a PCB build, but what happens if you take the Level pot out? Also, the feedback resistor R32 has no accompanying feedback capacitor (notice many of the opamps in the scheme do). Try 100pF across that R32.