AMI 'Spirit of 76' Compressor Build

[andrewsrea]

Thought I'd share my take on a UREI 1176 studio compressor for guitars and other instruments, called 'Sprit of 76.'

It can get traditional compressor sounds. However, using the 'blend' allows to get a BIG natural sound with added sustain and a hint of 'squish.' Expensive audiophile components keep it clear and quieter than traditional pedal compressors. The circuit board pic below shows it in test phase with TL072 ICs, which were replaced by Brown & Burr OPA1678 ICs & NOS Central Semiconductor 2N5457 transistors.

[mozz]

I know it's a big board. Every time i find a board i like, it ends up being sized for 125B, then i look around and all I have are 1590b boxes. I could get 1590b from Ali express, if i bought 12 it was $5 each for painted. Sure the price has gone up now. Got a bag full of TL074 quad op amps, found no projects yet but i am sure they are out there.

There is a small circuit you can build to measure the fet's, just went through that measuring some J10X, 2SK's. I know for phasers it's best to match them. Depends where in the circuit they are.

[tlarson58]

However, using the 'blend' allows to get a BIG natural sound with added sustain and a hint of 'squish.'

Loves me some sustain and a hint of squish.

[deeaa]

Looks impressive...I've used rack compressors quite often in amp loops etc.

I usually go for a sustained light squeeze. The release is key for those. Low threshold and mix and soft knee just to bring up nuances. This likely reads very strange for anyone not savvy in studio tech I think

Sent from my M2103K19G using Tapatalk

[Rollin Hand]

Looks impressive...I've used rack compressors quite often in amp loops etc.

I usually go for a sustained light squeeze. The release is key for those. Low threshold and mix and soft knee just to bring up nuances. This likely reads very strange for anyone not savvy in studio tech I think

Sent from my M2103K19G using Tapatalk

Yep, pretty much.

[andrewsrea]

There is a small circuit you can build to measure the fet's,

Exactly what I did to match the 2N5457 FETs, which activate the compression circuit. The control signal gets split with one half going through an inverter, then the parallel AC signal (one 'push' and one 'pull') goes through a BAT143 diode to convert it to DC, through the attack and release controls, then actuates the FETS, which leak the original signal to ground based on compression intensity. The FETs are in a Darlington pair, so I am not sure how important it was to match them, but I was able to quickly trim it to a nice setting.

I originally used MMBF5457's (SMD) and they did pretty well, but for some reason the 2N5457's sounded better. Not sure if that was a placebo effect or what.

[mozz]

Think I am going to build a dynacomp, haven't used a compressor in a long time. Just found these at the hamfest. Now to source 2SC1849 Panasonic like the original MXR.

[andrewsrea]

I have a MXR Dynacomp from January 1980 (block Logo). To which the original CA30380 was incredibly noise and finally gave out a few years ago, to which I bought a NOS RCA from Small Bear and it was about 25% of the original noise floor. I'd love my MXR if it had an in-phase 'blend' with the unaffected signal.