Build - Quad GSSL turbo/ssc/cavendish for API console

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TubeMonkey

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Jan 24, 2014
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149
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Nashville, TN
additional photos: https://imgur.com/a/nuiwf

Alright guys, I'm really bad about sharing my projects, so I figured this would be somewhere to start.....

This is a dual stereo compressor for the front and back bus of my 1974 API console which I'm currently modding extensively. I knew I wanted a master bus compressor, and since this is a quad console I decided to do four channels, a pair each for the front and back quad bus.

I really wanted to go all out with this thing so here whats in there:

2x GSSL pcb with DBX 202c gold bars
2x Super Side Chain pcb
2x Expat turbo pcb
2x Expat VU meter driver pcb
2x Expat Cavendish pcb with 2503 Litz transformer from Jeff

Because i was limited to the physical dimensions of the console I had to get inventive with layout, eventually I fit everything in there, but it was damn close. I only had one layout mistake when assembling, but was able to fix it by removing the corner of the top Cavendish pcb to accommodate the schadow switch.

There is a LOT of wire in this thing. doing this again I imagine it may have been less work to design a new PCB in eagle to save the P2P work... but then again I always loved looking at the mass of p2p wires in things like the fairchild 670.  Got it all wired together to find two problems, one being the solder pads on the Super Sidechain pcb aren't the best quality, causing no continuity on one of the sidechain returns. (what process are these boards made from? I want to try to avoid them in the future) and solder bridge between two pins on my DIP8 jumper cable.  Once I fixed those two issues this thing is sounding great!

In the console the mode switch will control a T-bar relay which will switch the compressor from "2+2" mode to "1+3" mode. in the first mode all four channels go where you would expect them. In "1+3" mode, however,  the first channel of each stereo compressor will be used for the Left and Right of the front bus, while the back bus will be hard bypassed. This will basically create an unlinked stereo compressor. I wanted this as an option, but was aware of the constraints of the GSSL sidechain.  There is also a secret switch when in "2+2" mode to make the compressor a true quad compressor with both stereo sidechains linked. I doubt I will ever use this.... but it's there.

I repurposed a few comments off of my console including the Vemaline knobs from the submaster trims, which I removed in order to fit this compressor, and the schadow switch.  This helps me match the aesthetic of the 45 year old console. The meters were an ebay find and are of the same era... I've never seen another "reverse" vu meter of this style so when i saw the pair I snatched them up. This way the meters can throw down like the TG limiters. 

Interfacing is on a DL connector (Pro tip... Just buy the f**king crimper.)

That's it! More console mods to come

-EB

edit - finished photo added. more pics in the album l
 

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home_listening

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Joined
Jul 21, 2012
Messages
80
That is phenomenal!

With those discrete opamp boards, are the feedback resistors for the opamps still on the original pcbs or are they also moved to the new pcb?
 

TubeMonkey

Well-known member
Joined
Jan 24, 2014
Messages
149
Location
Nashville, TN
The main pcb maintains the feedback resistors. The 5532s are dual amps, but only the input is fed tot he 2520's so i guess the circuitry for the second amp is dead on the main board, as well as anything else from the output of the 5532's until the output header of the main board. I've left all components in as it was actually very useful in troubleshooting to stick the 5534's and 5532's in first to make sure everything on the main board was working properly. Then I replaced with the jumpers to add the Cavendish board and test that.

-EB
 

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