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Old 20th December 2004, 05:50 PM   #1
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Default Using microphone transformers as phase splitters .

Hi There,
A friend has just given me a pair of microphone transformers. I was toying with the idea of using them as phase splitters in a simple push pull amp.
Unfortunately the ratio is the wrong way round with the primary at 50kohm and the secondaries at 600ohm (giving a ratio of 9.13:1). This would mean amplifying any signal by an extra margin of 10x just to get back the original signal. Also these are only really mean't for very low voltages so pumping 10Volts into them might present an issue. Also in order not to put them under strain the recieving output tube would have to have zero grid leakage.
Am I barking up the wrong tree, or do you think theres legs in this one ?

Shoog
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Old 20th December 2004, 07:02 PM   #2
HDTVman is offline HDTVman  United States
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The turns ratio is not a problem. Just apply signal to the 600 ohm side and the 50K side will output the signal stepped up (reverse the connection of primary and secondary). Where you will have trouble with this is that those transformers can't handle the DC current on the windings. You may be able to use them in a parafeed circuit though. Check out Tubecad journal. I know that he has talked about parafeed there.

Later BZ
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Old 20th December 2004, 07:15 PM   #3
Zhan is offline Zhan  Belgium
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Should not you use it as an autotransformer to do the phase splitting job if it has two identical primaries?
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Old 20th December 2004, 08:11 PM   #4
moamps is offline moamps  Croatia
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Default Re: Using microphone transformers as phase splitters .

Quote:
Originally posted by Shoog
...... Also these are only really mean't for very low voltages so pumping 10Volts into them might present an issue.....
Correct.
Microphone transformer can't handle high voltage (especially LF spectrum) with reasonably small THD.

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Milan
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Old 20th December 2004, 08:30 PM   #5
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Pffbbt. I used a pair for my WOT headphones amp, works fine (well, if I had the PSU around anymore ). I intend to use one some day for input isolation on a line-op zero bias 6V6 PSE amp on the drawing board.

Tim
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Old 20th December 2004, 09:02 PM   #6
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Quote:
I was toying with the idea of using them as phase splitters in a simple push pull amp.
Ummm..... I did this on a Lundahl and I got away with this because Lundahl trannies are well made and matched within winding although the step up was wrong......
When the ratios' are more reasonable.... Things can go adrift capacitively at the HF end.....due to different placement of the windings thus phase errors creep in causing considerable top end THD with push-pull circuits.
This simple technique was used alot in earlier HP class B amps to get the desired o/p drive swing often with lousy quality 5-10% THD....only suitable for tannoy systems at showgrounds .

www.sowter.co.uk also does the real thing which might be more suitable.
rdgs
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Old 20th December 2004, 09:12 PM   #7
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I have a bunch of transformers from 150/600 ohm to 15K or 15K to 15K or 150/600 to 150/600. They aren't designed to handle any current and very low voltage. Best bet is to sell the transformers on ebay and purchase the correct ones for your usage. Just my .02
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Old 21st December 2004, 02:53 AM   #8
adason is offline adason  United States
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you can use those mic trafos as step up for mc cartridges of medium and high output
some, like benz micro silver like it, some dont
some require much lower input resistance
anyway, you can have high quality no noise first gain for phono with mic trafos, just improvise, otherwise they are not suitable for higher than few milivolts, after few hundred mV you get iron saturation and nasty distortion
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Old 21st December 2004, 05:30 PM   #9
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Hi there,

Thanks for all the replies. You prity much highlighted all my concerns. This one will have to go by the board, I was only searching for a use.
Unfortunately if I do sell them on Ebay, I will have to give the money back to the man who gave them to me.
It might be worth incorperating them into a phono amp (I have a great opamp one at the moment - the VSPS), but have the tubes lying around to build the Thorsteons simple valve circuit.

Shoog
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