3€ - 12:1 Mic Out transformer
« on: March 30, 2019, 09:35:08 AM »
Hello people!

I just received this 3€ - 220-18v power transformer, which measures about 12:1 ratio.

DC resistance is 3k - 30 ohm.
I measured it and it is very flat down to 10hz, and has slight hf roll off at about 18k. It has low THD as well.

Is it a bad idea to use a transformer like this in a mic build. I mean, it could be the ultimate poor man's microphone out transformer.

It is a bit larger, but that shouldn't be a problem.

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F173371131503


Khron

Re: 3€ - 12:1 Mic Out transformer
« Reply #1 on: March 30, 2019, 10:03:54 AM »
THD's gonna depend on level.

The dual output ones do indeed sound interesting - not in the least for phantom-powered mics (take the power from the secondary "center-tap").
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Re: 3€ - 12:1 Mic Out transformer
« Reply #2 on: March 30, 2019, 10:15:08 AM »
THD is measured at pretty high injected level into the tube.

Gus

Re: 3€ - 12:1 Mic Out transformer
« Reply #3 on: March 30, 2019, 10:25:20 AM »

Using Si steel output transformer is something I have on my list of things to try for fun.

The picture looks like a split bobbin for separation of winding voltages so it wont have the best coupling.

I would drive it with a low output resistance high signal level because of the Si steel.

If you use a single triode I would try a high voltage BJT or MOSFET direct coupled (plate to base or gate)follower.


abbey road d enfer

Re: 3€ - 12:1 Mic Out transformer
« Reply #4 on: March 30, 2019, 10:27:46 AM »
My experiments trying to use power xfmrs out of their comfort zone were disappointing. The drive impedance must be quite low; if not, THD increases and frequency response narrows significantly.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Khron

Re: 3€ - 12:1 Mic Out transformer
« Reply #5 on: March 30, 2019, 10:33:48 AM »
If split-bobbin is a undesirable, that makes one wonder how small toroidal ones might fare.
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Re: 3€ - 12:1 Mic Out transformer
« Reply #6 on: March 30, 2019, 12:22:58 PM »
Soyuz uses toroidal.

abbey road d enfer

Re: 3€ - 12:1 Mic Out transformer
« Reply #7 on: March 30, 2019, 12:51:32 PM »
If split-bobbin is a undesirable, that makes one wonder how small toroidal ones might fare.
The main differences between an EI and a toroidal are:
  • Less gap, which increases the actual permeability, which, in turn allows reducing the number of turns
  • Better coupling coefficient; the difference between 0.997 and 0.999 may seem marginal, but in fact it's three times less leakage for the latter
Both give advantages to toroids in terms of THD and frequency response.
It is quite possible that what is lost in split bobbins (=> less coupling) is compensated by the continuous flux lines of toroid construction.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: 3€ - 12:1 Mic Out transformer
« Reply #8 on: March 30, 2019, 05:17:59 PM »
I don't know guys, but after a day of testing this transformer in C12 circuit with 6s6b tube against 3u audio gzt12 (12:1) i just find it to work great.

The only drawback is -3db high end roll off at 16khz starting from about 10khz. This roll off might be usefull as we all know with brighter capsules.

On the other hand it has less THD and phase shift compared to 3u audio one. Especially at LF! A bit stronger 3rd harmonic with this one, but less 2nd harmonic. And less THD altogether.

I strongly sugest trying this one out, could be i just got lucky.


Gus

Re: 3€ - 12:1 Mic Out transformer
« Reply #9 on: March 31, 2019, 01:16:28 PM »
The roll off can be used to help some capsules as you posted.

Might be interesting to try a 120VAC to 24 VAC with a circuit that can drive it.

Interesting what transformer was used
http://www.vintagewindings.com/tech%20swag/Church%20Mic%20Recreation.pdf


Re: 3€ - 12:1 Mic Out transformer
« Reply #10 on: March 31, 2019, 01:23:55 PM »
Wow, awesome document!


 

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