craigmorris74

283AV output for Passive Summing Makeup Gain?
« on: December 04, 2011, 10:07:10 PM »
I am building a couple of 283AV output sections to use as makeup gain for passive equalizers.  Will these work as makeup gain amps for my passive mixer (built from the NYDave schematic)?  Not sure if the output/input impedances will play nice.

Thanks,
Craig


craigmorris74

Re: 283AV output for Passive Summing Makeup Gain?
« Reply #1 on: December 07, 2011, 08:45:41 AM »
Bump.  Want to see if anyone's tried this.

0dbfs

Re: 283AV output for Passive Summing Makeup Gain?
« Reply #2 on: December 07, 2011, 10:38:32 AM »
Didn't neve use 1272's as bus-amps in their consoles (which were passive/ voltage-summing configs I believe)? 1272 is both sections (pre-amp & output stage) of a 283 I think. I have a pair of the LN72 boards which I intend to stuff for that same purpose. Probably set a fixed input gain and configure it with a master fader but may end up putting all of the various gain-staging controls on a panel.

Are you trying to avoid an input transformer?

Best,
jb
Music is everything!
Audio is everything else!

MatthisD

Re: 283AV output for Passive Summing Makeup Gain?
« Reply #3 on: December 07, 2011, 01:26:13 PM »

If the passive mixer output impedance is 200ohm balanced (40db loss) and you want to be able to use it with any mic pre as well as the 283 you could use a neve type mic input transformer 1:2 (+6db) added to the line stage gain that maybe enough.
If you raise the passive mixer output impedance to 600ohm (20db loss) you can use the same transformer as 2:1 and still have some gain left over.
Presumably you would run your EQ output unbalanced to the gain stage, bypassing the transformer.

To reduce cost you could try a 1:1 line output transformer at the mixer output with a 1/4 jack for unbalanced out and an XLR for balanced and keep the 283 input transformerless.
Matt

craigmorris74

Re: 283AV output for Passive Summing Makeup Gain?
« Reply #4 on: December 10, 2011, 08:57:25 PM »
Thanks for the feedback.

I think I will try to avoid an input transformer-don't need the extra expense, so I'd like to run them unbalanced, but thinking about different ways to get around that.  I'm going to make the output resistor of the summing network switchable to change output impedance from 200 to 600 ohm, depending on what amps I use for make up gain.  I calculate the resistor across the output to be about 857 ohms for 600 ohm output based on the NYD passive summing schematic.  Is this accurate?

Thanks again for the help,
Craig

« Last Edit: December 10, 2011, 10:16:29 PM by craigmorris74 »

MagnetoSound

Re: 283AV output for Passive Summing Makeup Gain?
« Reply #5 on: December 11, 2011, 04:53:02 AM »
Craig,

You have a 120k resistor loading pin U, the first stage input. Then there is a 68k impedance to ground after the blocking cap.

If you're going to go unbalanced, you can pretty much make your summing bus output impedance whatever you like (design for the least loss) and it will work fine.

Dan

I don't think people realize what an embarrassment of riches this place is   -  Paul Gold

craigmorris74

Re: 283AV output for Passive Summing Makeup Gain?
« Reply #6 on: December 11, 2011, 04:00:01 PM »
So I think I'll do 600 ohm output.  Are there any other options for going from balanced to unbalanced besides the 1:1 transformer?


 

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