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Author Topic: Fixing old ADR Gemini Compact compressor  (Read 805 times)

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van Sinn

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A few notes on fixing and modding an old ADR Gemini Compact compressor/limiter.

Brief info
This is a dual channel device which can work either as a compressor or limiter, separately on each channel.
It's an old thingy; back then called a prosumer device. I have no specs on it, but can say it's completely quiet, at least in my own non-pro studio.
The two channels are fully separate, and as such can be used for independent processing of two separate signals.
A stereo link button, when activated, links the two sense circuits so both channels will 'do the same', thus making it a rue stereo device.
Both channels features selectable compress or limit, 1.5:1 or 3:1 compress/limit, slow/fast, input gain and release pots. The latter, when turned full down, clicks to Auto mode, where it'll sense/track dynamics as-it-comes from the source/instrument.
A common section has punch-in/out for each channel, and Stereo Link buttons.

Usability
As said, it's very quite - I can't hear a thing ;)
It does soft-knee compress/limiting to the point of being very little noticeable, as in hardly any pffhumps head when acting on level changes.
It is really neat for adding just density, rather than the harder breathing more direct compression.

PSU repair
Now, mine decided to go defunct. Turned out the four rectifier diodes were bust, same to the voltage regulator (78 type), and the larger capacitor seemed semi-shorted; at least I could hardly get any measurement on it using an RCL meter.
I replaced the four 4001 diodes with, IIRC, 4002 fast-recovery diodes, replaced the 7834 regulator, replaced the capacitor, and all was swell again.

Front pots mod
Two of the four front mounted potmeters, the ones for Input Gain, were mounted backwards, and must be operated with a screwdriver. This is to make sure the audio engineer, when reaching for the Release controls, doesn't by accident touch the delicate in/out balance during a performance.
This is rather useless in a studio setup, so I unsoldered the pots, carefully folded back the mount flanges on these non-standard potmeters, and re-soldered them back in, now facing forwards.
Careful when you bend those flanges back! They're made from soft metal, but still.. just do it gently and all will be well.
I didn't have suitable knobs to match the two originals, but found four large really old-school knobs ;)

Rear connector mod
Rear mounted in/out connections are via some rather crappy RCA/phono white-metal sockets, which hardly goes through the circuit board to ensure mechanical stability from just hte solder, and further, there's no relief to the bow, so when connecting, plugs must be carefully wiggled on to avoid breaking a solder joint.
Now, the good designers of the Gemini had of course laid out the board to accept circuit-mount jack sockets!  I replaced the RCA thingies with some jacks I had left over anyways.
Do notice that some jack sockets are a touch short on the flange to box distance. If so, do remember to add a thin washer, or you'll create mechanical tension when tightening the nuts.

Below some almost-self-explanatory pics.
The jacks.jpg shows one jack installed next to three RCA's still in place.
The pots.jpg shows two pots at slightly different angles reinstalled with corrected flanges.
Forgot to add circles around the components on the psu pic; oh well, use your berth-given hardware stereo-zoom..
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