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Altec 1566a Output Wiring Impedance
Old 3 days ago
  #1
Here for the gear
Altec 1566a Output Wiring Impedance

I'm getting an Altec 1566a here (with the output transformer) and I'm a little confused by the output wiring.

Here's the manual, which lays out the options nicely, but I'm not sure what the best one is for my home studio:
http://www.vintagewindings.com/gen%2...66A-PreAmp.pdf

The input the wiring is obvious, since my mics are all in the 150 ohm range, I'll use the 120/200 ohm input to wire my XLR input. But I'm not sure about the output.

Should I go with 600 ohms? It'll be going balanced into A/D (ESI [email protected]) or to an outboard compressor (Aphex 661). Any benefit to using the unbalanced direct out wiring?

TIA
Old 3 days ago
  #2
Lives for gear
Normally, the standard would be to use balanced wiring. The since the inputs its feeding are much higher impedance than the transformer, there's a slight s/n benefit to using the 600 ohm tap.

HOWEVER, if your studio cables are very short, there's a theoretical advantage to using the unbalanced direct out (assuming you strap the subsequent inputs to match). With a very short cable, you don't need the CMNR of balanced wiring. And direct output will eliminate the tiny bit of distortion and low-end rolloff a transformer contributes.

UNLESS it hums. If you've got a ground loop, go back to balanced wiring but disconnect the shield connection.
Old 3 days ago
  #3
Here for the gear
Excellent, thanks!
Old 2 days ago
  #4
Lives for gear
 
emrr's Avatar
If it works for you unbalanced, it also eliminates the roughly 14dB of gain lost in the output transformer. The actual amount will differ depending on the way the cathode follower output interacts with the load you feed it to.
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