Melcor (Navy) 5 Compressor Unit AN/GSA-33 - AM1910/G modules

[beezer4]

Have you increase capacitance?

I was checking on extending bandwidth on my Tri-Tronics CAA/FAA, by replacing transformers on input / output. Another person had tried that on a forum and said the circuit became unstable. The restricted bandwidth was part of the reason for stabilization. His comment was it would need a redesign when opening up the bandwidth. Could just be an excuse but lm passing it on.

How do the ones that work sound. The tri-tronics sounds lowfi which is cool for trash & thrashed sound but not good for hifi IMO.

I have increased capacitance, which has increased the frequency response. I adjusted C215 and C216 up. The two modules that do work properly sound nice. Agree they have a lo-fi vibe, but test pretty flat 20-20k. Decent amount of harmonic distortion. It's good to call out the input and output transformers do test flat 20-20k.

What's interesting is I have made the same modifications and capacitor changes to all modules and only 2 are experiencing this oscillation issue. I'll try some of the recommendations above and report back on any progress I make.

Thanks everyone for the thoughts and insight. Appreciate the collaboration.

 

[mjrippe]

And thank you for doing all the work! When I get around to mine I'll be re-reading this thread for sure.

 

[beezer4]

UPDATE: Turned out to be a couple things causing the oscillation. Once I fixed that the noise floor jumped up, but alas all is solved now. Here's what I ended up doing:

• These two fixed the oscillation
  1. Removed the center tap from the input and output connectors and ran that terminal on the connectors to chassis.
  2. There was some redundant grounding on the boards and the transformers, removed what was unnecessary and move grounds to a single point.
• After I made these modification the noise floor jumped up one of the modules. I ended up replacing almost all the resistors on the input board as they had drifted substantially
• Now all the modules sound great, flat basically 80-18k with a little roll off at both ends

I ended up using parts and a PCB from one of the modules, so I converted that module into an API style 2520 preamp. I leveraged a "Gain PCB" from JLM Audio, a Flickinger style opamp and the original input/out transformers from the module. Added stepped gain, output level, pad and phase reversal. It sounds pretty dope.

All in all, this was a pretty intense project chasing down the issues, but turned into a solid 5 channel mic pre with compressors on 4 channels. Line level duty will require lower levels from the DAW or an inline pad, but they also function good as mic pres on loud sources or with condenser mics. The compression is pretty apparent, but sounds solid on heavy or lo-fi drums. I bet it's be great on guitar or a distorted vocal. If anyone is interested in hearing them, I'd be happy to run some of your stems through it.

Here are some pics.

 

[lassoharp]

Fazer said: "I believe their for compressing voice transmission so as to be heard during battle."


With the sonic aesthetic of many of todays top pop radio mixes in mind, that's the best ad copy description for a squash box I've ever heard! I may borrow that one!

 

[mjrippe]

Nice work James! I actually got the ebay notification before I saw it here
Very good idea turning the "parts" unit into a preamp, rather than a blank panel or empty slot.

 

[beezer4]

Here is a quick example of the unit on drums in a small tight drum room:

 

[TwentyTrees]

Oh, that is just brilliant. Great work, I'm so happy to see this all came together! And it will certainly turn some heads in the rack!

 

[mjrippe]

In the video, are you using them as pre and comp or just comp? It sounds like better fidelity than I imagined!

 

[beezer4]

In the video, are you using them as pre and comp or just comp? It sounds like better fidelity than I imagined!

Running line level out of Pro-tools and using them as just a comp. I’m hoping to record some demo tracks next week using them as a pre and comp. Probably more drums, guitar and bass.

 

[fazer]

They do sound good. Nice job on the retro restoration.