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pftrvlr 29th April 2009 03:59 AM

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?

dsavitsk 29th April 2009 05:28 AM

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.

pftrvlr 29th April 2009 05:38 AM

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.

analog_sa 29th April 2009 07:43 AM

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?

dsavitsk 29th April 2009 09:29 AM

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.

AJT 29th April 2009 10:08 AM

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...

pftrvlr 29th April 2009 08:17 PM

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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