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Old 20th September 2003, 12:56 AM   #1
Salsero is offline Salsero  United States
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Post unbalanced to balanced converter

Hey Guys,
I am considering my first DIY audio project. I think I want to build an unbalanced to balanced high quality converter to connect my McCormack micro line drive (unbalanced output) to the balanced input of my Odyssey Stratos Amplifier. I saw some op-amp inverter circuits and others using transformers. Does anyone have experience with this? Any schematics or kits available? Any feedback will be appreciated.
Salsero
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Old 20th September 2003, 01:04 AM   #2
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Have a look here.
http://sound.westhost.com/project35.htm
Certaintly worth a look...lolx
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Old 20th September 2003, 01:51 AM   #3
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You might want to look a the SSM-214x series that AD makes. They sound ok, a little rolled off on top. Relatively inexpensive solution.

Another option is a transformer. Expensive, but they have the advantage of galvanic isolation. I've used both Jensen and Lindahl. You can order from Jensen dircet, and Lindahl has a distributor in the US.

In any case, I suggest visting Jensen's site to read the excellent papers that Bill Whitlock has written on high-performance interfaces. That should give you lots of food for thought.

Jocko
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Old 20th September 2003, 02:03 AM   #4
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Quote:
Originally posted by Jocko Homo
Another option is a transformer. Expensive, but they have the advantage of galvanic isolation.
Hey Jocko,

How about one of these.
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Old 20th September 2003, 02:21 AM   #5
SY is offline SY  United States
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Ah, the transformer in a parakeet coffin.

Salsero, I'd go for the transformer if money is not a consideration, an SSM chip if it is. And when you're ready to do it with discrete parts, I've got an interesting circuit.
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Old 20th September 2003, 02:42 AM   #6
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Quote:
Originally posted by roddyama

Hey Jocko,

How about one of these.
Hehehe. Alas, even I wouldn't recommend that as a solution here. Jensen's input transformers don't have fully balanced outputs. You could balance them with a bit of extra capacitance on one leg, but even then, the 2.34k output impedance wouldn't make for a very good line driver.

The better solution would be an output transformer like the JT-11-DMCF or the DMPC (a PC mount version of the DMCF). However there is one caveat; if the output stage that will be driving the output transformer is capacitor-coupled, because of the small primary inductance, you need a pretty big cap (200-300uF) to prevent low frequency resonance.

se
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Old 20th September 2003, 02:44 AM   #7
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Originally posted by SY
Ah, the transformer in a parakeet coffin.
Liar! There are TWO transformers in that parakeet coffin I'll have you know.

se
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Old 20th September 2003, 02:48 AM   #8
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Originally posted by Steve Eddy


Liar! There are TWO transformers in that parakeet coffin I'll have you know.

se
Yeah, not enough room left for the poor dead bird:
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Old 20th September 2003, 02:52 AM   #9
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Actually perhaps a better solution if one is going to use transformers is to use a pair of input transformers driving the Odyssey's unbalanced inputs (preferably building them into the chassis if possible) and leave the McCormack unbalanced.

Even when fed from a wholly unbalanced source, a good input transformer like the JT-11P-1 will give you 100dB of common-mode noise rejection. Which is far better than most any electronically balanced input can give you when fed from a balanced source under realworld conditions.

With the 11P-1, there's only about a 7dB difference in common-mode rejection between a balanced source and an unbalanced source.

se
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Old 20th September 2003, 02:53 AM   #10
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Salsero,

I don't want to post just to give you bad news, but the XLR jack on the Stratos isn't really balanced. It's wired with only two pins in parallel with the RCA jack. Sorry.

Mike G.
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