Schematic Request: Melcor CL-20 limiter (photos added)

[soundguy]

Anyone have a schematic for a melcor CL-20? I have one of these limiters, hooked it up, sounds really nice, however would like to modify it for attack and release adjustability. Its a real simple diode bridge limiter with only three opamps in the circuit, would be super easy to diy it seems. Cant find documentation for this anywhere though.

dave

 

[rafafredd]

I was always curious about this circuit, but also couldn´t find any info.

Would it be feasable to reverse it?

 

[soundguy]

it would be easy as pie to build one of these assuming there isnt some complicated process in regards to matching the diodes. Ive already spent three hours trying to trace the circuit, its simple as hell but Im not very good at drawing an easy to read schematic from something like this, so its taking me a crazy amount of time to draw it out and dont have too much time as it is now to devote to this, kinda working on this in my spare time away from more pressing things. Would be excellent if someone had a schem laying around, would be so much cooler to put the effort into racking this up instead of writing the circuit down. Guess we'll see how it goes, hopefully someone out there has a schematic.

dave

 

[Family Hoof]

Dave, holy shit you have 3000 posts! Are you going to be in the city tomorrow? Work was canceled so I could spend the day tracing it.

Diodes have to be matched for forward voltage drop if you want a balanced bridge. This is not a big deal. Whether or not there was any other trimming or AOT (apply on test) components involved is the more pertinent question me thinks.

 

[soundguy]

Im in the city, limiter is in nj.

cool how things work like that...

dave

 

[chrissugar]

Hey Dave,

Put the PCB on a scanner and make some hi rez pics with the components side, and I will try to help the reversing. Also I can produce some gerbers for a possible project.
If you have them, you can send me an email or upload somewhere.

chrissugar

 

[clintrubber]

Just curious & not knowing this unit at all, does this circuit use anything 'special' besides the DOA's & matched diodes ? Does it use any iron ? Any elaborate switching ?

Or just throw a few Melcor-PCBs and some R & C & Q & D at it and it's OK ?

Thanks,

Peter

 

[clintrubber]

Just curious, how alike or unlike is it to this one ?

http://www.danalexanderaudio.com./ApiInfo/525Cschem.jpg

http://www.groupdiy.com/index.php?topic=61&highlight=api+525

 

[soundguy]

here are some photos if anyone wants to try to trace it. Im guessing the attack and release is set by the cap and resistor under the top opamp.

the top panel pot is the threshold, the bottom panel pot is the makeup gain, the trimmer to the rigth of the bottom left opamp is the DC offset trimpot, the trimmer above it is in the feedback loop for gain, the trimmer closest to the meter is a meter cal and the one next to it Im not too sure what it does. Its sort of like an attack control but Im not sure thats what it does. When I turn it, it sorta sounds like the attack changes, sorta sounds like the threshold changes however the meter readings dont change. Cant quite figure what that pot does however it does have a useful audio effect and will likely bring this to the front panel when I rack it. what do you think?

The bottom left opamp is the input buffer, the bottom right is the output driver it seems and the one on top is in the sidechain. Below the wire hanging off the meter is a transistor.

dave

 

[peter purpose]

Dave... any movement on this?
If not, then squirt over the high res versions of those pix and I'll have a go.

peter

 

[soundguy]

no, none at all, bigger fish to fry right now. Thing sounds really nice though.

dave

 

[peter purpose]

Dave.... kindly dig out those hi res pix, so I can have a pop at reversin it.

peter

 

[dogears]

Bumping this zombie thread. I have some nice photos to work from for the circuit, but it would be nice to have some guidance.

Anyone got a schematic of a CL-20? It looks like an earlier version of a 525. No transformer in the side chain, though.

 

[mjrippe]

If you have nice photos of the PCB from both sides I might take a crack at drawing it.