Some Transformer Questions
« on: June 28, 2020, 02:53:05 PM »
Hi All,

I work at a recycling center and I pulled these HS-66 transformers out of a blown BGW amp and also rescued this A20 before it was sent to the great scrap pile in the sky.

I was wondering if it would be possible to use any of these as a passive gain transformer for an SM7 a la something like a cloudlifter or soyuz launcher in terms of gain?  I am reading some about transformer impedance and such but I thought I would ask here as well.

The A20 has XLR pig tails and is wired for 200 to 200ohm making it an isolation transformer I think.  What ratio would be the best for input gain from an SM7?

has anyone built a multi transformer color box or anything like that?  Just wondering what a fun use of these would be.  Thank you.
« Last Edit: June 28, 2020, 02:57:16 PM by rChrome »


Re: Some Transformer Questions
« Reply #1 on: June 28, 2020, 03:53:02 PM »
Those are nice transfomers. Great find.

But you're not going to be able to get much gain out of them. If you drove 62.5 and make 600 out, that's an impedance ratio of 9.6 so square root of that is a gain of 3.1 which is only 9.8dB.

Those transformers are designed for input / output line matching. Although since virtually all line inputs are 10K now, they're really probably only useful as an output transformer. The impedances are right for a mic input but without shields and such they're not ideal for that. An op amp with some decent power like an NE5532 or RC4580 can drive 600 ohms very well. Then you can select a tap to get different levels out with a significant increase in current. That's where these would shine.

The pair on the right would make an excellent hi-fi headphone amp. Just get an RC4580 or two NE5534 and drive the primaries wired for 600. Then wire the headphone jack to the 62.5 ohm taps. That would make just about the purest headphone amp you could hope for. Load the secondary with 100 ohms or maybe lower to try to provoke "color". Then listen to Dark Side of The Moon while drinking a Tab.


Re: Some Transformer Questions
« Reply #2 on: June 28, 2020, 04:10:10 PM »
uhhh.....everyone wants those Triad for Pultec clones.....do that or sell them.   

If you use them as a step-up (not much at all) for a mic into a pre, you are LOWERING the impedance the mic sees, which can cause loading effects that undo what you're trying to do.    Good for a line in or out, or for a mic splitter.   

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde


Re: Some Transformer Questions
« Reply #3 on: June 28, 2020, 06:55:41 PM »
Thanks for the quick responses and setting me straight on what these are best for!  I am mostly itb and tho I would love a pultec clone I have other gear that I need much more before outboard EQ or musical headphone amp so I suppose I will post these for sale.  Thanks!


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