Aion Oceanid Troubleshoot - Signal, but no compression

[Quiddel]

Hello everyone,

First post, as googling and research couldn't help me. Now, I would need some help with troubleshooting the Aion Oceanid optical compressor. This is the documentation:

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

The pedal is built as documented, no mods. I do get proper signal both in true and buffered bypass and also engaged, but I do not hear any compression happening. In what I assume is the wet side of the blend pot, the signal is way louder, so the volume make up works well. It's just not compressing. Of course I did the obvious, I desoldered the vactrol twice to double check (put it in also in reverse, which just made it distort horribly once the input sound was above a certain threshold, independent of any knob position). My vactrol is marked NSL-32 and on the side NSL-7053, thus I am convinced dot = cathode (-).

A bit of background, I built about 30 pedals and two tube amps so far and lots of other DIY audio things.

Thanks a lot everyone!

Matthias

Here are my measured voltages:

Input voltage
9.0V

Vactrol (LED side)
(+ square) 8.5V
(- round) 7.1V

Q1 (2N5088)
E: 4.5V
B: 4.3V
C: 8.7V

Q2 (2N5088)
E: 0V
B: 0.5V
C: 7.1V

Z1 (LM4040CIZ-5.0)
Left/Right pin 0V
Middle pin 5V

IC1 (TL072)
Pin    Voltage
1    4.3V
2    4.3V
3    2.2V
4    0V
5    2.1V
6    4.3V
7    4.3V
8    7.9V

IC2 (TL072)
Pin    Voltage
1    4.3V
2    4.3V
3    4.3V
4    0V
5    2.1V
6    4.3V
7    4.3V
8    7.9V

IC3 (LM358N)
Pin    Voltage
1    0.08V
2    0.02V
3    0.01V
4    0V
5    0.0V
6    0.01V
7    0.0V
8    8.5V

IC4 (LM358N)

Pin    Voltage
1    0.01V
2    0.01V
3    0.01V
4    0V
5    0.0V
6    0.01V
7    0.05V
8    8.5V

[antonis]

Hi Matthias & Welcome ..

IC1 pin 3 & 5 and IC2 pin 5 low voltages can be justified due to loading by your DMM's low impedance..
Q1 Voltages aren't correct..
(Emitter should stand about 600mV lower than Base..)

Main suspect is IC4B bias configuration..
(you should read "some" voltage on pins 5, 6 & 7..)
Start measurements from Zener diode Cathode (R35/R36 junction) and downwards..

P.S.
And, of course, pictures of your build..
(we have a very  crabby moderator - but he's sleeping now 'cause he lives down-under..)

[new tube]

Yes, that is probably the problem of this compressor. It behaves more like a boost. So it went in the drawer. A lot of people on the internet find it difficult. The sound samples are not convincing either.

[Quiddel]

Thanks a lot for your help! I will have some time tonight and measure starting from Z1. One thing I noticed when inspecting this part of the circuit is that I do have a 10k trimmer, and not as recommended a 20k trimmer in my build. I got my kit from Musikding and forgot to check the trimmer value before. The documentation mentions a that the trimmer in the traced original was dialed to 5.5kOhm, so this might not be an issue, but we'll see.

Regarding the photos, I have uploaded them in my original post. Do they have to be approved by a mod?

Thanks, Matthias

[new tube]

Why do you have the vactrol soldered on the opposite side to the components. The dot is the cathode, are you correct?

[ElectricDruid]

Why do you have the vactrol soldered on the opposite side to the components. The dot is the cathode, are you correct?

From the Build Doc:

DOCUMENT REVISIONS
1.1.0 (2020-02-22)
Moved optocoupler to the bottom side of the PCB to make more space for the DC jack.

[aion]

Try desoldering one leg of the resistor side of the vactrol and then use a DMM to measure resistance between the two legs as the signal increases. That will tell you if it's at least attempting to reduce the signal level.

If there's no resistance change, it could be an issue anywhere in the trigger section or just with the vactrol itself - but it will at least help narrow things down a bit.

[Quiddel]

Thanks, ElectricDruid. That's indeed the reason.

So, I worked my way down from Z1. The Bias used to be set to max resistance, so I now dialled it to about 50% (which should be in range of 5kOhm. IC4 now has higher readings for Pins 5-7:

IC4 (LM358N)

Pin    Voltage
1    0.01V
2    0.01V
3    0.01V
4    0V
5    0.04V
6    0.05V
7    0.54V
8    8.5V

Nothing else changed voltage wise. I checked all voltages around IC4 and Q1 and they are roughly what I expect coming from VD.

To be fair, I am questioning whether the compressor is indeed working as it should, and I am just expecting too much. With the trimmer on 5kOhm I do hear some compression, and it's also visible in the waveforms. You do hear the compressor shaping the attack (see attached image of gain matched waveforms). However, I do not hear (or see) the gain reduction lifting off when the note rings out, thus not increasing the sustain.

In a nutshell, even with the compression pot on full, I would not call that obvious compression.

Now, is this just the circuit as it is supposed to be? Am I expecting too much? Or is something wrong? Would somebody see a way how I could increase the gain reduction? My workflow normally is to dial in too much compression and then take it back until I like it. This approach does not work here. :-(

Thanks again for the help so far! Does anybody have practical experience with the Oceanid/OC-1 and can share some insight how much compression I can expect from that circuit? I intend to use it for bass by the way.

EDIT: Just saw your reply too late aion, I'll do that just to be sure. However, I do see some compression happening, so it seems to work in general. (Let me also use the occasion to thank you for your amazing projects, the documentation is amazing! This is neither my first not my last aion pcb for sure! :-) )

Thanks a lot for all your help,

Matthias

[Quiddel]

New post to keep the thread transparent.

Okay, I feel a bit ashamed. I dialled back the compression pot a bit and now I do get proper sustain. It seems that actually everything is (and was) working as it should, I just expected a way more audible compression in extreme settings, especially for the attack. It is rather slow, which is not surprising for an opto compressor to be fair. When doing the initial biasing, I ended up leaving the bias trimmer on a non-optimal position and that brought me here ultimately.

The compressor is described as "transparent" and I have a feeling that's what it is. Unfortunately I did not find any audio samples with bass and I did not have anything to compare it with.

So I guess I fixed the issue by just adapting in my head without soldering anything? At least shows that I manage to solder properly...

Thanks again for your quick help and input!

Matthias