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Old 20th October 2005, 07:04 AM   #1
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Default Unbalanced to Balanced Line Level XFMR

I'm looking for a single ended to balanced output line level transformer for a studio RIAA preamp project. I know about Jensen and Lundahl, but there is another inexpensive manufacturer that has been mentioned on this forum that isn't cropping up in my searches. Can anyone else help me out? BTW - yes, I know all about SSM2142s and DRV134s - I want to try an absolute minimalist approach this time around, and eliminate any possible ground loops while I'm at it.
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Old 20th October 2005, 07:37 AM   #2
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Default Re: Unbalanced to Balanced Line Level XFMR

Quote:
Originally posted by wrenchone
I'm looking for a single ended to balanced output line level transformer for a studio RIAA preamp project. I know about Jensen and Lundahl, but there is another inexpensive manufacturer that has been mentioned on this forum that isn't cropping up in my searches. Can anyone else help me out?
Sure. That would be CineMag.

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Old 20th October 2005, 08:23 AM   #3
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I made it with DRV134 - cannot recommend this monolithic circuit.
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Old 22nd October 2005, 04:26 AM   #4
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I got in touch with Cinemag, and am looking at the CMOB-4 transformer. My final choice will depend on the input impedance of the A-D I'm driving (the studios have digital boards).
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Old 22nd October 2005, 06:12 AM   #5
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Quote:
Originally posted by wrenchone
I got in touch with Cinemag, and am looking at the CMOB-4 transformer. My final choice will depend on the input impedance of the A-D I'm driving (the studios have digital boards).
That can work.

Though is there any reason you can't use an input transformer on the A-D?

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Old 22nd October 2005, 06:23 AM   #6
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Same thing really... The A-D (studio type) wants a balanced input anyway, and there's room in the phono preamp box.
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Old 22nd October 2005, 06:37 AM   #7
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Quote:
Originally posted by wrenchone
Same thing really... The A-D (studio type) wants a balanced input anyway, and there's room in the phono preamp box.
Well, what I was getting at is that a good input transformer will give you better common-mode noise rejection when fed from an unbalanced source than typical electroincally balanced inputs being fed from a balanced source.

Also, you have to be careful with output transformer vis a vis any output coupling capacitance from the stage driving them which can interact with with the output transformer's primary inductance (which is typically significantly lower than the primary inductance of a good input transformer) and cause low frequency peaking and resonance if the output coupling capacitance isn't large enough.

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Old 22nd October 2005, 07:31 PM   #8
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Ill keep your comments in mind. Next step will be to buy a couple of CMOB-4s and check them out with a sig gen and a buffer similar to what I'll use in the final circuit.
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Old 22nd October 2005, 08:06 PM   #9
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Quote:
Originally posted by wrenchone
Ill keep your comments in mind. Next step will be to buy a couple of CMOB-4s and check them out with a sig gen and a buffer similar to what I'll use in the final circuit.
Okie doke.

If they're going to be driving much higher than a 600 ohm load you may need to add an RC snubber on the secondary to prevent any high frequency resonance problems.

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