SOLVED Aion's Beta preamp : Treble pot issue

[eh là bas ma]

Hello,

I am having a hard time debugging this circuit, although it should be quite simple, I hope.

I am building the Sunn Beta Lead/Bass preamp. I'd like to have both versions on one board, so I opted to add two extra 4PDT toggleswitches to be able to change 7 values in the circuit.
Musikding sent me one of the old boards, so I did the "version 1.0 C-MOS fix" as instructed.

https://aionfx.com/app/files/docs/beta_preamp_documentation.pdf

The only issue I have is that the Treble pot is acting strangely in the last few bits of the last quarter of rotation. It's happening in a narrow spot, just before being set fully CW. There is a slight increase of volume, just before the signal fades and is covered by white noises. In other words, all controls are ok except the treble control when it's set fully CW. Almost the whole rotation is fine, and the pot does what it's supposed to do.

Both Lead/Bass toggleswitches sound like everything is working fine. However I had a doubt about how to wire R23 to the toggleswitch : one side is grounded, so i am not really sure if my wiring is allright.
For every components on the toggles, I found the pad with the incoming signal, wired a blue wire going to the middle 4PDT terminal. Then, both Lead and Bass components soldered at the outer terminals, with their remaining led connected with a wire soldered to the output pad. For R23 it's the grounded pad, I hope it's correct ? I tried to invert both wires for R23, and didn't notice any change.

I wonder what could cause the Treble pot to go off the rails in the final part of its rotation ?

What's happening, according to the schematics, when the Treble is set fully CW ?



Every help and every suggestions are welcome !

Edit : just found out that a famous builder has a similar issue on his build (v1.1) :

Aion Beta Bass preamp

The beta preamp can be built for either guitar or bass with only a few component changes, this one being the latter. I've been playing it unboxed for a few weeks and finally came to the conclusion that it needs to go on my board. I actually kind of avoided this project for a while because I...

forum.pedalpcb.com

 

[eh là bas ma]

10k resistor between Treble pot lug 3 and its pcb pad fixed it.

Still wondering what was happening, there were really weird noises... fast popping and decaying white noises, like the thing is blowing up....

 

[jesuscrisp]

I remember having some weird issue with the treble being fully turned up as well, while everything seems OK. Will check back when I test what it was again.

 

[martin76]

10k resistor between Treble pot lug 3 and its pcb pad fixed it.

Still wondering what was happening, there were really weird noises... fast popping and decaying white noises, like the thing is blowing up....

Having the same Issue, may i ask if you could tell me how you did that 10k treble mod? Whats the Lug3 on the pot? did you solder parallel or in series?
Another Issue, when i unplug the 9Volt DC and plug it right back in, the Pedal just produces white noise and dosent work. Waiting 20 sec and replug the 9volt and the Pedal and its working great again ... very strange ... made a short videoclip - any ideas?.

thanks a lot!
regards from austria
martin

 

[eh là bas ma]

Having the same Issue, may i ask if you could tell me how you did that 10k treble mod? Whats the Lug3 on the pot? did you solder parallel or in series?

Weird noises appear at the end of the Treble pot rotation ? Some part is pushed beyond its max specifications, it sounds glitchy and terrible.

The idea is to limit the Treble pot's range, in order to always have a bit of resistance at one end of the rotation. On my build, the guitar signal is still good at 10k, noises appeared between 8k and 0k resistance. We don't want the pot to reach these values. We install a permanent resistor in series between the pot and the board, so there is always some resistance. A 10k allowed me to eliminate the noises and keep 90% of the rotation, more than enough Treble range on tap. I guess this value can change on every builds because of parts tolerance.

If you want to keep it fast and simple, try 8k2 or 10k, see if it works. If it doesn't, try 15k, etc.

If you want to eliminate the noises and keep as much treble as possible :

You can set your treble pot at the most precise position right before the noises appear. Lock this position on the pot with tape, unsolder the pot, measure with a multimeter the resistance between pot lug2 and lug3. This will tell you which resistor value you need to add in series between the pcb pad 3 and the Treble pot lug3.

The Treble pot's lug 3 needs to be desoldered from the pcb. One end of the extra resistor is soldered to the unsoldered pot's lug 3, the other end is soldered to the pcb pad 3.

Edit : I tried to connect this 10k resistor earlier on the signal path, to keep the pot soldered on the pcb, but it didn't work, the issue was still there.

I hope this is clear ?

Edit 2 : about the DC 9V observation, it's probably a capacitor taking some time to unload and reload ? Although, your soldering looks a bit casual, if i may be so blunt ? Probably better than mine, but still... We can't underestimate the value of a good soldering joint, right ?

 

[martin76]

Thank you very much, works! Yeah! You are right about my soldering - i'm still learning - today i resoldered all joints.
About the DC 9V thing i dont have any clue ... do you have the same issue?
thanks again and take care
martin

 

[AdrianSunn0)))]

Having the same issue with the treble pot, at about 3 o clock on the treble pot, there is uncontrollable noise/oscillation that takes over my entire signal. My circuit is REALLY noisy all around, but also its extremely high gain so im not super surprised. Tried to add small pf capacitors over a few gainstages feedback loops but it did not tame the noise from the gain.

Also tried to solder a 10k in parallel with lug 3 of treble pot to the next connection point, and didnt help. I will try in series next by desoldering lug 3.

 

[eh là bas ma]

I will try in series next by desoldering lug 3.

I had to desolder it. No way around it.

See reply #5 for all the details.

 

[comradehoser]

Having the same issue with the treble pot, at about 3 o clock on the treble pot, there is uncontrollable noise/oscillation that takes over my entire signal. My circuit is REALLY noisy all around, but also its extremely high gain so im not super surprised. Tried to add small pf capacitors over a few gainstages feedback loops but it did not tame the noise from the gain.

Also tried to solder a 10k in parallel with lug 3 of treble pot to the next connection point, and didnt help. I will try in series next by desoldering lug 3.

Yep--same with me, oscillation in the last 10% of treble pot with gain up, both beta lead and bass versions. Glad to see there is a fix. [edit:] actually this isn't a fix of the oscillation per se, it's limiting the pot from getting to problematic range. It's the same as not turning the pot all the way, no?

 

[Mentaltossflycoon]

Yep--same with me, oscillation in the last 10% of treble pot with gain up, both beta lead and bass versions. Glad to see there is a fix. [edit:] actually this isn't a fix of the oscillation per se, it's limiting the pot from getting to problematic range. It's the same as not turning the pot all the way, no?

That's why I didn't bother with it. I don't desire anything close to a dimed treble pot out of this pedal. I used this pedal quite a bit before hearing about this issue. If I never noticed it in the first place it's not really an issue for me. I'm also an antiperfectionist so there's that...

 

[eh là bas ma]

It's the same as not turning the pot all the way, no?

Yes it is.
I had help from diystompoxes's kind forum members to find the issue. Aion's pcb designer said (reply #10) :

"I've heard a couple reports of the treble whine on 10, but it definitely doesn't happen all the time (certainly not on mine) so it's possible it's related to power filtering or wiring or something, possibly component tolerances as well, or something rig-dependent. When volume or an EQ control is on 10, it's more likely to bring out stuff that wouldn't happen in normal use since it's running at the edge of its max performance."

Aion's Beta preamp : Treble pot issue

Aion's Beta preamp : Treble pot issue

www.diystompboxes.com

On my build the noises were very loud and annoying, it was beyond "the edge of max performance". The kind of noises that makes me worry for the guitar amp's speaker.
I didn't want to take any chances that these noises appear if the High control is accidentally turned fully CW.
I'd rather have usable and friendly controls that are effective through the whole rotation. Something that startles me with sudden crazy popping noises isn't good enough as long as i can fix it, and i am also far from being a perfectionist.

The Treble pot has a lot of range. With the 10k resistor, it's not dimed at all, i just avoid the unusable zone at the end of the rotation.