Aion effects "Convex" - clone of the Dinosaural OTC-201 Opticompressor

[LaceSensor]

Ive had a Dinosural OTC-201 for a long while now - really an amazing compressor.
When I stumbled across Aion doing a PCB I felt somewhat duty bound to build it and do a side by side
Nice story about the reverse engineer here: https://aionelectronics.com/blog/tracing-journal-dinosaural-otc-201-opticompressor/

Suffice to say I can cop all the sounds of the original. I am somewhat partially convinced that the pot tapers arent the same
My clone gets louder more quickly, in a comparative fashion turning up the level and sustain knobs. However, the levels match up at the extremes, so I beleive the pot values are accurate.

Overall, great project. Id have loved to have availed of  Aions fixing and enclusure kit, but alas out of stock. It did mean that I could use a really nice silver hammered paint enclosure I have been stashing for oooh 7 years...!

Enjoy pics.

[LaceSensor]

In fact I have just looked it up from the part code on the visible pot I can see on his trace (no time to take mine apart right now)

The 10k (Balance/Volume) control should be Log (!)

The part code is 91A1A-B28-D15L
https://uk.farnell.com/bourns/91a1a-b28-d15l/potentiometer-10k/dp/9357823?scope=partnumberlookahead&ost=91A1A-B28-D15L&searchref=searchlookahead&exaMfpn=true&ddkey=https%3Aen-GB%2FElement14_United_Kingdom%2Fw%2Fsearch

[aion]

Oh wow, thanks for catching that - yes, "D15" on the pot code definitely refers to audio taper.

I'll see if I still have the Sustain pot handy to check the code on that one since it's obscured by the pics. Did the taper seem to match better on the Sustain control or did it feel off as well?

[LaceSensor]

I think the sustain taper is ok
I can take my OTC apart and check the pot codes

It's really quite noticeable on the level / balance pot

I would recommend testing and perhaps then changing the BOM

Ian

[aion]

Thanks. I'm going to try to find the parts for mine and verify as well. I'll update the BOM for the Balance control in the mean time.

[LaceSensor]

Cool. I tried today and I cannot get my OTC PCB out of the case - I think the jacks get soldered in once the assembly is in place
I dont want to risk forcing anything really - so apologies but I cant check

[somnif]

Cool. I tried today and I cannot get my OTC PCB out of the case - I think the jacks get soldered in once the assembly is in place
I dont want to risk forcing anything really - so apologies but I cant check

I know its not optimal, but you can test the taper fairly easily. Given its in-circuit the numbers may be wonky (don't have the schematic in front of me) but test its resistance at 0, check its resistance 10, and check its resistance in the middle.

If its resistance at 5 is halfway between 0 and 10, its a linear taper (or W taper, admittedly). If its 10% of full, its log taper. If its 90%, its rev-log.

[LaceSensor]

Cool. I tried today and I cannot get my OTC PCB out of the case - I think the jacks get soldered in once the assembly is in place
I dont want to risk forcing anything really - so apologies but I cant check

I know its not optimal, but you can test the taper fairly easily. Given its in-circuit the numbers may be wonky (don't have the schematic in front of me) but test its resistance at 0, check its resistance 10, and check its resistance in the middle.

If its resistance at 5 is halfway between 0 and 10, its a linear taper (or W taper, admittedly). If its 10% of full, its log taper. If its 90%, its rev-log.

Good idea

The readings I get are

Sustain
0% - 0
50% - 8.9k
100% - 108k

Balance
0% - 0
50% - 8.2k
100% - 8.3k

Not sure its working great for the Balance, but I already know thats meant to be a Log pot from the potentiometer code.
Would seem the sustain pot might also be intended to be a Log pot, based on the in circuit reading however.

[aion]

I was able to find the original pots and can confirm that the Balance pot is indeed 10kA and the Sustain pot is 100kB.

Here are the codes -
100k: 91A1AB28B20L
10k: 91A1AB28D15L

Thank you for noticing - I don't think anyone else would have ever caught it without an original to compare to!

[LaceSensor]

I was able to find the original pots and can confirm that the Balance pot is indeed 10kA and the Sustain pot is 100kB.

Here are the codes -
100k: 91A1AB28B20L
10k: 91A1AB28D15L

Thank you for noticing - I don't think anyone else would have ever caught it without an original to compare to!

No worries glad to have helped you out.
Great project -  so good that I sold my original (!)

[aion]

Great project -  so good that I sold my original (!)

Well, that's just about the ultimate compliment! Good to hear