Pete Cornish - OC-1 Optical Compressor [traced]
- aion
- Solder Soldier
Information
All right, the legendary Mystery Pedal™ is finally done!
I traced the Cornish OC-1 Optical Compressor over the summer and today I'm ready to share it.
Pete claims this is an all-original circuit design, and fortunately I can confirm that it's not quite like anything I've seen before. The audio path is pretty simple, but the sidechain has a few unfamiliar tricks, perhaps taken from an obscure op-amp application note someplace.
In any case, though, it sounds great!
Schematic: The unit traced was from 2014. There are no known circuit revisions since that time.
Full tracing journal here:
https://aionelectronics.com/blog/tracin ... ompressor/
Imgur gallery with 50+ photos including X-rays:
PCB available here:
https://aionelectronics.com/project/oce ... ompressor/
I traced the Cornish OC-1 Optical Compressor over the summer and today I'm ready to share it.
Pete claims this is an all-original circuit design, and fortunately I can confirm that it's not quite like anything I've seen before. The audio path is pretty simple, but the sidechain has a few unfamiliar tricks, perhaps taken from an obscure op-amp application note someplace.
In any case, though, it sounds great!
Schematic: The unit traced was from 2014. There are no known circuit revisions since that time.
Full tracing journal here:
https://aionelectronics.com/blog/tracin ... ompressor/
Imgur gallery with 50+ photos including X-rays:
PCB available here:
https://aionelectronics.com/project/oce ... ompressor/
- Attachments
-
- cornish-oc1-trace-schematic.pdf
- Cornish OC-1 Schematic (PDF)
- (311.59 KiB) Downloaded 259 times
- guiddruid
- Breadboard Brother
IC3A/IC3B looks like the "precision full wave rectifier" circuit from Horowitz & Hill (don't have my copy to hand, but IIRC this is it; https://en.wikipedia.org/wiki/Precision_rectifier), but with D2 connected on a separate op-amp. Seems to me this should be functionally equivalent. Not sure what (if any) advantages this would bring. [edit] Sorry, D2 is also backwards compared to that circuit, and the signal is going into inverting input of IC3B. Not sure if that's then achieving the same result. [edit yet again] Nope. I don't understand how IC3B functions at all with pin 5 connected to GND. If it were connected to Vb, I think it would work as a "perfect" diode, preventing that node from dropping below Vb & would also bias that node in the circuit.
IC4B/Q2/Z1/R37 looks like an opamp current source, converting the voltage at IC4B + to a current through the LED. Again, I'm pretty sure this is in Horowitz & Hill; https://en.wikipedia.org/wiki/Current_s ... nt_sources
IC4B/Q2/Z1/R37 looks like an opamp current source, converting the voltage at IC4B + to a current through the LED. Again, I'm pretty sure this is in Horowitz & Hill; https://en.wikipedia.org/wiki/Current_s ... nt_sources
- bajaman
- Old Solderhand
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Don't forget - the LM358 is a single supply optimised dual op amp and does not require a half bias voltage to function in this application
cheers
bajaman
cheers
bajaman
be kind to all animals - especially human beings
- guiddruid
- Breadboard Brother
But the only way to forward-bias D2 is for pin 6 to go below GND. Even if that were possible, with the supply rails on IC3 being +Vc/GND, I don't see how the input circuitry in the opamp can work.
- andy-h-h
- Breadboard Brother
Information
Finished a vero layout for this, will give it a run on the weekend and post if it goes well. I'm pretty happy with my bajaman optical limiter, so see how it compares.
- andy-h-h
- Breadboard Brother
Information
Yes it did go well - just waiting on an NSL-32 to confirm 100% (should arrive this week). It sounds good, I was using a different vactrol, which was working, but not quite right (compressing, but not enough).tubegeek wrote:Didn't go well? Curious about this one. Thanks!andy-h-h wrote:Finished a vero layout for this, will ... post if it goes well.
This is the layout I used.
Hi guys,
Based on this schematic I've drawn a PCB for this compressor, it's still unverified and unfortunately I'll not be able to build it untill april, any attempt to check it will be reward with many thanks and infinite love
I know it's not really tidy but I've done my best, red sign are top wire bridge, the only thing not included is the buffer.
Let me know if it works.
EDIT: I forget dimensions are 52x84mm (pdf are 1:1 and don't need it).
regards
luix
Based on this schematic I've drawn a PCB for this compressor, it's still unverified and unfortunately I'll not be able to build it untill april, any attempt to check it will be reward with many thanks and infinite love
I know it's not really tidy but I've done my best, red sign are top wire bridge, the only thing not included is the buffer.
Let me know if it works.
EDIT: I forget dimensions are 52x84mm (pdf are 1:1 and don't need it).
regards
luix
- Attachments
-
- OC1-BOTTOM.pdf
- Bottom view ready to be printed, 1:1
- (92.34 KiB) Downloaded 140 times
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- OC1-BOTTOM_MIRROR.pdf
- Bottom view mirrored and ready to be printed, 1:1
- (92.64 KiB) Downloaded 128 times
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- OC1-TOP.pdf
- PDF with transparent background.
- (147.53 KiB) Downloaded 109 times
you can find some of my creation on instagram @ luixanalogdevices
I have an order on jlcpcb of my drawn of tube driver tou find in the last page of apposite thread... So if you can upload the gerber file, I'll order it and I'll verify within 1 weekluix wrote:Hi guys,
Based on this schematic I've drawn a PCB for this compressor, it's still unverified and unfortunately I'll not be able to build it untill april, any attempt to check it will be reward with many thanks and infinite love
I know it's not really tidy but I've done my best, red sign are top wire bridge, the only thing not included is the buffer.
Let me know if it works.
EDIT: I forget dimensions are 52x84mm (pdf are 1:1 and don't need it).
regards
luix
You can try but I think I've not respected the DRC rules, I've designed it for photoetching process.
- Attachments
-
- Cornish OC-1.rar
- gerber files
- (172.96 KiB) Downloaded 137 times
you can find some of my creation on instagram @ luixanalogdevices
Maybe i can modify it... Thank you very much bro!!!! So let's try to do it togetherluix wrote:You can try but I think I've not respected the DRC rules, I've designed it for photoetching process.
STOP! I found an error, the anode of the zener diode is connected to V+ instead of GND, I'll correct quickly.
The top layer is essentially the same, I've updated gerber and bottom.
The top layer is essentially the same, I've updated gerber and bottom.
- Attachments
-
- OC1-BOTTOM_MIRROR.pdf
- pcb bottom mirrored
- (92.81 KiB) Downloaded 175 times
-
- OC1-BOTTOM.pdf
- pcb bottom non mirrored
- (92.46 KiB) Downloaded 164 times
-
- OC-1_gerber_V1.rar
- Gerber file with mod
- (86.33 KiB) Downloaded 139 times
you can find some of my creation on instagram @ luixanalogdevices