Pete Cornish - OC-1 Optical Compressor  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.

Pete Cornish - OC-1 Optical Compressor  [traced]

Postby aionios » 15 Nov 2019, 22:21

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:
cornish-oc1-trace-schematic.png


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:
https://imgur.com/a/sjtezCB

PCB available here:
https://aionelectronics.com/project/oce ... ompressor/
You do not have the required permissions to view the files attached to this post.
Aion Electronics - DIY PCB projects for classic and obscure circuits

For this message the author aionios has received thanks: 15
guiddruid (16 Nov 2019, 11:04), Intripped (16 Nov 2019, 09:43), lietuvis (17 Nov 2019, 12:45), lohstah (16 Nov 2019, 18:35), Manfred (15 Nov 2019, 23:30), marmaliser (18 Nov 2019, 10:38), modman (28 Nov 2019, 08:57), mr coffee (01 Jan 2020, 00:50), roseblood11 (03 Dec 2019, 02:50), Zokk (16 Nov 2019, 13:44) and 5 more users
aionios
Breadboard Brother
 
Posts: 105
Joined: 22 Mar 2012, 01:12
Location: Des Moines, IA
Has thanked: 7 times
Have thanks: 151 times

Re: Pete Cornish - OC-1 Optical Compressor

Postby guiddruid » 16 Nov 2019, 11:03

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
guiddruid
Breadboard Brother
 
Posts: 88
Joined: 14 Aug 2009, 13:18
Has thanked: 9 times
Have thanks: 5 times

Re: Pete Cornish - OC-1 Optical Compressor

Postby bajaman » 18 Nov 2019, 21:25

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 :wink:
cheers
bajaman
be kind to all animals - especially human beings

For this message the author bajaman has received thanks:
bmxguitarsbmx (19 Nov 2019, 03:02)
User avatar
bajaman
Old Solderhand
 
Posts: 4381
Joined: 26 Jun 2007, 22:18
Location: New Brighton, Christchurch, NZ
Has thanked: 467 times
Have thanks: 1666 times

Re: Pete Cornish - OC-1 Optical Compressor

Postby guiddruid » 18 Nov 2019, 21:58

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.
guiddruid
Breadboard Brother
 
Posts: 88
Joined: 14 Aug 2009, 13:18
Has thanked: 9 times
Have thanks: 5 times

Re: Pete Cornish - OC-1 Optical Compressor

Postby Ben N » 21 Nov 2019, 10:33

How about a roll-your-own vactrol--will that work?
Ben N
Resistor Ronker
 
Posts: 347
Joined: 12 Dec 2008, 04:34
Location: Israel
Has thanked: 25 times
Have thanks: 15 times

Re: Pete Cornish - OC-1 Optical Compressor

Postby Agent86 » 22 Nov 2019, 22:35


For this message the author Agent86 has received thanks:
Satch12879 (25 Nov 2019, 15:09)
Agent86
 
Posts: 9
Joined: 22 Dec 2008, 14:37
Has thanked: 0 time
Have thanks: 1 time

Re: Pete Cornish - OC-1 Optical Compressor

Postby andy-h-h » 28 Nov 2019, 10:24

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
 
Posts: 47
Joined: 22 Jul 2017, 04:54
Has thanked: 10 times
Have thanks: 16 times

Re: Pete Cornish - OC-1 Optical Compressor

Postby tubegeek » 09 Dec 2019, 04:39

andy-h-h wrote:Finished a vero layout for this, will ... post if it goes well.


Didn't go well? Curious about this one. Thanks!
tubegeek
 
Posts: 1
Joined: 15 Dec 2011, 04:37
Has thanked: 2 times
Have thanks: 0 time

Re: Pete Cornish - OC-1 Optical Compressor

Postby andy-h-h » 09 Dec 2019, 08:09

tubegeek wrote:
andy-h-h wrote:Finished a vero layout for this, will ... post if it goes well.


Didn't go well? Curious about this one. Thanks!


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).

This is the layout I used.
You do not have the required permissions to view the files attached to this post.

For this message the author andy-h-h has received thanks: 4
Cigla tel. (31 Dec 2019, 14:39), Manfred (09 Dec 2019, 10:34), modman (20 Jan 2020, 20:46), tubegeek (12 Dec 2019, 18:12)
andy-h-h
 
Posts: 47
Joined: 22 Jul 2017, 04:54
Has thanked: 10 times
Have thanks: 16 times

Re: Pete Cornish - OC-1 Optical Compressor

Postby luix » 27 Jan 2020, 14:20

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 :D

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 do not have the required permissions to view the files attached to this post.

For this message the author luix has received thanks:
stefanogueli92 (27 Jan 2020, 17:28)
luix
 
Posts: 10
Joined: 17 Mar 2009, 02:56
Has thanked: 0 time
Have thanks: 4 times

Re: Pete Cornish - OC-1 Optical Compressor

Postby stefanogueli92 » 27 Jan 2020, 17:31

luix 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 :D

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


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 week
stefanogueli92
 
Posts: 17
Joined: 28 Jan 2019, 14:20
Has thanked: 10 times
Have thanks: 2 times

Re: Pete Cornish - OC-1 Optical Compressor

Postby luix » 27 Jan 2020, 20:41

You can try but I think I've not respected the DRC rules, I've designed it for photoetching process.
You do not have the required permissions to view the files attached to this post.

For this message the author luix has received thanks: 2
modman (27 Jan 2020, 22:23), stefanogueli92 (27 Jan 2020, 22:21)
luix
 
Posts: 10
Joined: 17 Mar 2009, 02:56
Has thanked: 0 time
Have thanks: 4 times

Re: Pete Cornish - OC-1 Optical Compressor

Postby stefanogueli92 » 27 Jan 2020, 22:22

luix wrote:You can try but I think I've not respected the DRC rules, I've designed it for photoetching process.

Maybe i can modify it... Thank you very much bro!!!! So let's try to do it together

For this message the author stefanogueli92 has received thanks:
modman (27 Jan 2020, 22:23)
stefanogueli92
 
Posts: 17
Joined: 28 Jan 2019, 14:20
Has thanked: 10 times
Have thanks: 2 times

Re: Pete Cornish - OC-1 Optical Compressor

Postby luix » 28 Jan 2020, 10:39

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.
You do not have the required permissions to view the files attached to this post.

For this message the author luix has received thanks:
stefanogueli92 (30 Jan 2020, 10:50)
luix
 
Posts: 10
Joined: 17 Mar 2009, 02:56
Has thanked: 0 time
Have thanks: 4 times


Return to Boutique Stompboxes dissected...

Who is online

Users browsing this forum: eric_obrien and 5 guests