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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 6th Apr 2019, 5:18 pm   #1
stuart_morgan_64
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Default What are these transformers?

Can anyone advise what these maybe or from? Thanks
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Old 6th Apr 2019, 5:20 pm   #2
M0FYA Andy
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Default Re: What are these transformers?

Microphone transformers?

Andy
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Old 6th Apr 2019, 5:37 pm   #3
John10b
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Default Re: What are these transformers?

Thatís what I thought Andy, could they have come from or be used in a mixer deck?
Cheers
John
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Old 6th Apr 2019, 5:51 pm   #4
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Default Re: What are these transformers?

If you can find any legible details on them (manufacturer's name and/or part number) then it's worth checking whether they can be re-purposed as step-up transformers for moving coil phono cartridges. If so then they might be worth money.

Cheers,

GJ
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Old 6th Apr 2019, 7:16 pm   #5
Ed_Dinning
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Default Re: What are these transformers?

Also very useful to reduce hum on sensitive input circuits, much beloved by the BBC.

Ed
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Old 6th Apr 2019, 8:13 pm   #6
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Default Re: What are these transformers?

Could also be line isolating/matching transformers for things like 600 Ohm phone lines etc.

The first step is to use an audio generator and scope to measure the ratio(s) and then measure the bandwidth.

David
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Old 6th Apr 2019, 11:29 pm   #7
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Default Re: What are these transformers?

DONT test them with an ohm meter!!!

IF they have mu-metal cores ( and I suspect they do) you will permanently magnetise them making them worthless and useless as they will saturate more easliy in one direction than the other.

If you want to test them use a sine wave generator set to a very low output to start with and observe the outputs with an oscilloscope

Joe
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Old 7th Apr 2019, 1:30 am   #8
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Default Re: What are these transformers?

Certainly audio matching or isolating transformers, and it looks like you have at least two different types. Can you make the markings more legible, on those that have them?

If you can measure the ratio and inductance of the windings it will give an idea of their use, and working impedances.
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Old 7th Apr 2019, 6:58 am   #9
Craig Sawyers
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Default Re: What are these transformers?

They look like they could be one of many varieties manufactured by Sowter

http://www.sowter.co.uk/pro-audio-transformers.php

Craig
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Old 7th Apr 2019, 9:18 am   #10
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Default Re: What are these transformers?

I've seen similar transformers used for impedance-matching dynamic microphones, in an old valve PA amplifier. I was surprised to see replacements were still available -- but not as surprised as when I saw how much for! You might have a veritable little treasure trove on your hands there.

With the current interest in analogue recording studio equipment, somebody might well want them off your hands and in a mixing desk they're restoring .....
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Old 7th Apr 2019, 9:41 am   #11
stuart_morgan_64
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Default Re: What are these transformers?

Hya..Thanks for the comments. I have a signal generator and scope so will have a look later. The comment re ohm meter, that is something i hadn't thought of.
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Old 7th Apr 2019, 9:58 am   #12
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Default Re: What are these transformers?

I wouldn't have thought a modern digital meter would put out enough current to magnetise a transformer core permanently, but mu-metal is funny stuff.

Would that mean it would be a bad idea to try to use an electret microphone into one of these transformers? Since the DC blocking capacitor on the output would have to charge through the transformer primary winding .....
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Old 7th Apr 2019, 10:52 am   #13
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Default Re: What are these transformers?

Its normally accepted that one DOES NOT use DC currents into a transformer with a Mu-Metal core!!
I will most likely be shot down, BUT please check transformer basics.
Electret condenser microphones ?? WHY would anyone want one in the first instance?? Bass boomy, treble screetchy, PERFECT for digital!!.
A half decent dynamic is far more desirable, and doesnt require ( 48 volts, no less) biasing voltages, nor does it kill superb little microphone coupling transformers of yesteryear.

Just my two bobs worth

Joe
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Old 7th Apr 2019, 12:21 pm   #14
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Default Re: What are these transformers?

Transformer cores can be de-magnetised. Hit them with a big AC signal and then smoothly and slowly reduce it to zero. There is no need to dump the transformer or to dismantle it and anneal the lams.

If you use an audio sig gen to test one, don't just break the connection or switch off abruptly, diminish the signal gently to zero. Abrupt starts and stops of AC actually contain DC transient components.

Condenser microphones are very good indeed. There are some superb condenser mikes and recordings made with them. Some even include valves, if that is of any importance. And plenty of polarising voltage is helpful. Electrets are less high-faluting but are permanently polarised, and the only power needed is for a high impedance buffer after the capacitor. They can live with lower phantom voltages.

With care, condenser and electret mikes, transformer cores other than mumetal, transistor and digital circuitry can all be made to work very well indeed. Don't judge the whole just because there have been some grotty examples. There are some people around who can design things properly.

David
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Old 7th Apr 2019, 6:05 pm   #15
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Default Re: What are these transformers?

I think they may also have been used as baluns, to match a balanced mic circuit to the unbalanced amp input.
Alan.
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Old 7th Apr 2019, 6:13 pm   #16
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Default Re: What are these transformers?

RS do something similar

https://uk.rs-online.com/web/p/audio...rmers/2106352/
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Old 7th Apr 2019, 10:01 pm   #17
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Default Re: What are these transformers?

Quote:
I think they may also have been used as baluns, to match a balanced mic circuit to the unbalanced amp input.
Yes they were. I had a 70's "Zoot Horn" studio mixer that had them on every mic channel
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Old 8th Apr 2019, 3:27 am   #18
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Default Re: What are these transformers?

The examples shown in post #1 only show four wires. I don't think you can use them for balanced inputs. ( I may be wrong). To me they look like input transformers that feed directly into a grid, base or gate connection. With or without decoupling caoacitors.

Joe
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Old 8th Apr 2019, 10:51 am   #19
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Default Re: What are these transformers?

Quote:
Originally Posted by joebog1 View Post
The examples shown in post #1 only show four wires. I don't think you can use them for balanced inputs. ( I may be wrong). To me they look like input transformers that feed directly into a grid, base or gate connection. With or without decoupling caoacitors.

Joe
Assuming that it is a single primary/single secondary, yes they would work perfectly well with either a balanced or unbalanced input, the benefit in either case being earth-loop removal and improved common-mode rejection. Perhaps Joe, you are thinking of the centre tapped primary variety? Not often seen these days.
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Old 8th Apr 2019, 7:59 pm   #20
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Default Re: What are these transformers?

Sometimes referred to, back in the day when most had centre taps, as "floating" rather than "balanced".
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