Aion Oceanid (Cornish OC-1) unwanted amplification

[mrtzly74]

Hello,

unfortunately i have a problem with my aion oceanid build. I built the pedal exactly as described in the documentation except for two capacitors C7 + C18. I substituted these with "Styroflex" capacitors of the same value. (This shouldn`t make any difference?).
The pedal works as it should except for there is amplification with all knobs on zero

(so the signal is louder when the pedal is turned on). As far as I can tell all the other functions are working therefore there is an increase of compression, volume and "blend" when turning the knobs up.
Also it doesn`t make a difference if i switch the pedal to true bypass instead of buffered bypass (with that mini slider switch).

Name of the project: Oceanid Optical Compressor by Aion Effects (Cornish OC-1 clone)
https://aionfx.com/app/files/docs/ocean ... tation.pdf

Attached is a pic of the pcb.

I contacted Kevin from Aion FX earlier and he suggested to post in this forum. That's what he said concerning the problem:
"But, it's not something I've heard before so unfortunately I don't have any suggestions, other than that it's probably outside of the envelope detector section and in the main signal path."

Here are some voltages i measured across the pcb.



Out of circuit battery voltage: 9.62 V

Voltage at the circuit board end of the red battery lead = 9.46 V

Voltage at the circuit board end of the black battery lead = 0.00 V

Q1 (2N5088)
C = 9.12 V
B = 5.15 V
E = 4.73 V

Q2 (2N5088)
C= 7.41 V
B= 0.62 V
E= 0.07 V

IC1 (TL072)
P1 = 4.57 V
P2 = 4.57 V
P3 = 4.15 V
P4 = 0.00 V
P5 = 4.14 V
P6 = 4.56 V
P7 = 4.57 V
P8 = 8.30 V

IC2 (TL072)
P1 = 4.55 V
P2 = 4.55 V
P3 = 4.54 V
P4 = 0.00 V
P5 = 4.13 V
P6 = 4.54 V
P7 = 4.54 V
P8 = 8.26 V

IC3 (LM358N)
P1 = 0.00 V
P2 = 0.02 V
P3 = 0.02 V
P4 = 0.00 V
P5 = 0.00 V
P6 = 0.02 V
P7 = 0.00 V
P8 = 8.81 V

IC4 (LM358N)
P1 = 0.03 V
P2 = 0.03 V
P3 = 0.03 V
P4 = 0.00 V
P5 = 0.07 V
P6 = 0.07 V
P7 = 0.61 V
P8 = 8.80 V

D1 (1N5817 Schottky diode, DO-41)
A (anode, the non-band end) = 9.31 V
K (cathode, the banded end) = 9.04 V

D2 1N914 Fast-switching diode, DO-35
A (anode, the non-band end) = 0.00 V
K (cathode, the banded end) = 0.02 V

D3 1N914 Fast-switching diode, DO-35
A = 0.00 V
K = 0.03 V

Z1 (LM4040-5.0)
1 = 0.00 V
2 = 4.99 V
3 = 0.00 V

[idy]

Schematic seems to be cut off in the original doc, can't see the far right. Here is the volume control, it changes the gain of an opamp that mixes clean and compressed. It does not look like it wold ever cut the output below unity, so you can't cut the volume below what goers in. I think.

I would verify the Resistors around that volume pot (R13, 15, 15, 20) and the soldering and value of that pot.

It is also possible that something is bad in your setup: bad cable, other effect etc, and that adding a buffer defeats that "drag" or loading on your guitar. A buffer will make a terrible signal chain behave better and sound louder... Make sure you are testing: known good guitar-known best (short) cable- effect-known best (short) cable, amp.

[idy]

 schematic partial

[antonis]

Let us see..

[aion]

Let us see..

FYI, this is the trace schematic which may or may not correspond to the PCB... the circuit is the same, but the schematic numbering may be different and the Oceanid has a true-bypass option that the original does not have.

[mrtzly74]

Thank you so much for chiming in. I checked the resistors around the volume pot and they all seem fine. The volume pot has a value of 96,3 kOhms (measured whilst in the circuit). May this affect the gain in any unwanted way? What in the circuit could cause an amplification? Unfortunately i don't understand too much of the circuit..

I don't think it is a setup (cable, other effects, etc.) problem since i tried it many times with different setups with the same result.. 

[ElectricDruid]

This links works for me for the docs:

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

Nothing very obviously wrong from the voltages. The LM358 stages looked weird at first, but then I realised they're the envelope follower and they're referenced to ground. So you wouldn't expect to see anything unless you're feeding it with a signal generator or something.

[idy]

So maybe you want to alter levels somewhere. That is a pretty fancy mixer Opamp: the clean signal has already been inverted, so it goes into the inverting input, and the compressed signal goes into to non-inverting.

The choices would be lowering the volume of one or both of these signals before mixing, or the volume at the mix.

The blend know seems to vary to level of the clean part.

When the blend is all the way clean, and the volume down, you are still getting a boost?
If so, then we might want to find a way to reduce the clean...

There are a lot of resistors setting gain around those three opamps. There is also the brute force method: increase R22. If it was 10k you would be cutting output by about 1/2. Try a pot or trimmer...?

[mrtzly74]

Thank you so much again guys!

Yes i was thinking about dropping the level too. Preferably without altering the tone in any way because i really like it. It is just a too big of a volume jump when i turn the pedal on. And yes, that is also with all knobs on zero (which should mean "blend all the way clean"?
So maybe it would be better to alter the clean signal?

If i was increasing R22 and therefore reducing the signal before it goes to the output, is there any likely sound change? And if so, in what way?
I will try a trimmer after R22 tomorrow.

Do you think the volume pot value of 96,3 kOhms (should be 100kOhms) has anything to do with this problem? I was wondering because the circuit seems to be very "picky" with resistors since it uses some of the rather uncommon 91Ohm ones. But again my knowledge of the function of the circuit or any particular resistors is very limited..

[antonis]

Do you think the volume pot value of 96,3 kOhms (should be 100kOhms) has anything to do with this problem?

Nahhh...
3.7% it's a nice tolerance for pot..

[idy]

Changing R22 should not affect your sound at all, just drop the output.
The cap before is monstrous so that no realistic change in what you are driving will cause a loss of bass. Theoretically you will add a slight bit of noise... always a cost. You probably won't hear that below... several hundred k?

R22 and R21 make what you call a voltage divider. If they are equal you will get half the voltage. If R22 is larger than 10k you will cut more and more. You may find that cutting by half is not that much; our hearing is more log that linear. Try a 50k pot maybe.. find the value that's right.
If you want to get fancy you could solder a new value R in place of 22, or just leave your little trimmer.

[mrtzly74]

Okay i will definately try a 50k ish pot later! And yeah if i find the right value i would want to get fancy and solder a new resistor in.
But i have to say the problem still makes me wonder because it must be (?) a problem somewhere else in the circuit that causes that excessive volume?
Whats the matter with R16 and R22? Why are they 91 Ohms? As is understand it, as you said, R22 and R21 form a voltage divider to give you just the "right" amount of volume that should give unity gain with all knobs on zero.

What is amplifying the signal in the circuit? Could these 2n5088 be part of the problem (maybe a exceptionally high hfe value)
I have to say though the volume increase is not dramatic, but very noticeable. It bugs me that something is not right and my only option is to use the "brute force method" as you described it earlier..

I will check all the resistor values up next. I think one time in the past i already reflowed all the connections with fresh solder.
Can a faulty cap cause such a problem?

Edit:
Okay i checked all the resistor color codes once again. Everything seems to be fine!

[new tube]

Try short pins 1 and 2 ICA1 or resistor R12. Gain= 1

[mrtzly74]

Hey thanks for chiming in.

Try short pins 1 and 2 ICA1 or resistor R12. Gain= 1

Is this safe?

[new tube]

Yes

[mrtzly74]

okay i tried shorting pin 1 and 2 of IC1 and it did the trick.
But whats the matter with that? What does shorting the pins do?

[FiveseveN]

https://www.electronics-tutorials.ws/opamp/opamp_3.html

[mrtzly74]

Thank you! So with shorting the pins i have set the gain of the first stage to 1 (=unity). But why is this unequal 1 in the first place?

Kevin from Aion once told me "It should be fully transparent and unity gain with all knobs on zero, since it's just passing through a few unity-gain buffers with no filtering or coloration."

And sound coloration wise, is this method preferred or altering R22 at the output?

[antonis]

okay i tried shorting pin 1 and 2 of IC1 and it did the trick.

You turned IC1A into a buffer (voltage follower) of unity gain..
(previously it had a gain of X2 - see link posted above by FiveseveN..)

But it affects both clean & wet signals..
If this is OK with you, you can delete all circuitry from R7 to C8, saving you a lot of items & space..
(about 40R Q1 output impedance shouldn't be a problem..)



Or you can retain initianl circuitry and tweak R12 value for desired output level..

[antonis]

And sound coloration wise, is this method preferred or altering R22 at the output?

R22 does nothing, on its own..
(its right leg is floating..)

What it might prevent is IC2B possible heavy loading (output shorted) or oscillation (large capacitive output load..)

It froms a LPF with next stage shunt input capacitance, for sure, but its low value in conjunction with unknown (usually small) succeeding capacitance puts it out of game..

P.S.
Consider its existence owed to "good design practice"..