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G1176 with dual VU's

Discussion in 'DIY Pro Audio Forum' started by chrisv, Mar 6, 2003.

  1. chrisv

    chrisv Guest

    Hi guys,

    For my 2nd G1176 i'm using a pair of VU's from a Tascam M600 console. It looks as though it has a buffer built in to the small PCB attached to the VU's.

    My question is this - would there be any problem in having both the gain reduction and output level on simultaneously - ie defeat the meter switch and have two VU's?

    I can't see this being a problem but thought i'd check here first.

    Also is it worth trying to use the buffer amp on the VU's? It would be a bit of a pain as it runs on 16V rails.


  2. Kev

    Kev Guest

    I don't see any problem with the basic idea.

    I don't think you need a buffer amp on the Gain reduction part.

    A buffer might be nice on the output as it will degate the distortion argument But the dual rail might be a problem.

    But is it worthwhile ?
  3. Swedish Chef

    Swedish Chef Active Member

    Pro Audio Dabbling & Production
    London, UK
    Home Page:
    Kev. Omly 3 more posts and yet another landmark will have been reached! Particularly pertinent to this thread... ;)

    As to the buffer plus minus 16V. As the inards of the 1176 are so small in size leaving lots of room, and the required p/s relatively simple, just for the anorak value I would be tempted to do it. Just think of the impressed looks from clients when you explain the lengths you've gone to to eliminate distortion, and improve on the orig design... :D
  4. ssltech

    ssltech Guest

    ...Of course you could just AC couple the input to it, and regulate a 0V/16V/32V from the 1176's internal supply... Could be used as a "ground-shifted-up-16V" supply. -personlly I think this would be fine.

    I was thinking myself that the few mods that I'd like to do to my MC76's (once they're built & working -naturally!) would be to a unity gain install meter buffer before the +4/+8 switching (daughter card, powered exactly as described) and to interrupt the detector signal by lifting one end of R78 at it's junction with R23 (MC76 component designations... the junction of the "Output Level" control and the resistor feeding the "ratio" switch array)... then taking the signal from R23 through a unity-gain balanced driver to a male XLR on the back panel. -A female XLR right next to it on the back panel would feed a unity gain differential receiver, and the output of that would go back to the detector by returning to R78. The balanced driver/diff. receiver would be on a small daughter card, powered in the same "ground-shifted" manner.

    This gives you a correctly balanced sidechain insert. -Myself, I don't like adding sidechain in/out switches on the front panel if you're trying to make the unit look authentic... I think the MC77 looks slightly less attractive with those switches on the front panel! -If you're wiring the unit to a TT patchbay that has normalling contacts available, that's how I like it. -Just patch it and it's done! -Un-patch it and it's undone!

    -If you're making something like a G1176, there's perhaps less of a "spoiling the established look" issue but that's a personal thing for me! -Of course if there's no normalled patch, and no easy rear access to the unit, a front panel switch (single pole changeover... disconnecting the return of the diff. receiver from R78 and reconnecting R23 to R78) will do the job.

    The other thing that I did to a UREI 1176 that failed during a session about 10 years ago (Back in England) was when the stud diode failed short-circuit, taking the power resistor with it... -(all the shops were closed, and I didn;t have a stud zener to hand...) -I made a series regulators with a few zeners (that added up to about 31 Volts) a medium value resistor (a few kilohms) a high-gain NPN, -BC109 I think it was- and a power NPN transistor.. probably an MJ3055. ...well it got the unit back working again in about 15 minutes, and the session carried on... I intended to order the correct parts and restore it back to original spec, but then I notices how much cooler it ran than it's (same manufacturing date) neighbour...

    I think I'll put some slightly less "stone-age" voltage regulation on mine, too! -Hey, the whole simple series regulator cost less than a replacement stud diode...

    I forget how Jakob did the supply regulation in the G1176... I'm going to take a look next thing!


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