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Line output transformer question
Line output transformer question
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Old 29th April 2009, 04:59 AM   #1
pftrvlr is offline pftrvlr  United States
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Default Line output transformer question

I am building a tube mic preamp with a 12au7 SRPP output. I am planning to use a 1:1 turn ratio line out transformer. I feel that I should get one with 10K:10K impedence ratio, but will a 600:600 also OK for this application?

How is the impedence of a transformer determined? Thought it is determined by the actual load impedence, right?
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Old 29th April 2009, 06:28 AM   #2
dsavitsk is offline dsavitsk  United States
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Default Re: Line output transformer question

Quote:
Originally posted by pftrvlr
I am building a tube mic preamp with a 12au7 SRPP output. I am planning to use a 1:1 turn ratio line out transformer.
Why? I am all in favor of transformers, but this is one place that it doesn't make much sense.
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Old 29th April 2009, 06:38 AM   #3
pftrvlr is offline pftrvlr  United States
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Default Re: Re: Line output transformer question

Quote:
Originally posted by dsavitsk


Why? I am all in favor of transformers, but this is one place that it doesn't make much sense.
Why not? Gyraf mic preamp uses a 2:1 transformer in the output.
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Old 29th April 2009, 08:43 AM   #4
analog_sa is offline analog_sa  Europe
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Default Re: Line output transformer question

Quote:
Originally posted by pftrvlr

How is the impedence of a transformer determined?

By the primary inductance.

What is this transformer going to actually do?
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Old 29th April 2009, 10:29 AM   #5
dsavitsk is offline dsavitsk  United States
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Default Re: Re: Re: Line output transformer question

Quote:
Originally posted by pftrvlr
Why not? Gyraf mic preamp uses a 2:1 transformer in the output.
A 2:1 gets you better current drive, lower Zout, and less gain. A 1:1 gets you an expensive part and higher distortion for your trouble.
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Old 29th April 2009, 11:08 AM   #6
TonyTecson is offline TonyTecson  Philippines
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Line output transformer question
Default Re: Line output transformer question

Quote:
Originally posted by pftrvlr
I am building a tube mic preamp with a 12au7 SRPP output. I am planning to use a 1:1 turn ratio line out transformer. I feel that I should get one with 10K:10K impedance ratio, but will a 600:600 also OK for this application?

How is the impedance of a transformer determined? Thought it is determined by the actual load impedance, right?
they are not the same, the 10k line traffo will handle substantialy more voltage than a 600 ohm one...ohm's law is right at work here..

while the two will have the same turns ratio, the 10k one will have about 4 more turns than the one turn of the 600ohm ones...
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Old 29th April 2009, 09:17 PM   #7
pftrvlr is offline pftrvlr  United States
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The transformer will generate balance output to feed into a DAC for recording. I assume the input impedence of the DAC pretty high. Think 10K load is what the mic preamp will see?

I may just get a few of different transformers and see how they all play out.
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