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Old 21st June 2008, 07:02 AM   #101
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if you are going to build a balanced - > unbalanced converter you might be better of making something stand alone so you retain most of benefit of the balanced connections.

http://www.jensen-transformers.com/an/an003.pdf

Take a look at section 3 for some suggestions. You could build one of these interfaces in a shielded box and run short interconnects to you pre-amp RCA's. Probably not very cost effective however!!


The other alternative that might be worth looking at is one of the THAT1200 or 1240 balanced line receivers. You can get them from the following online store.

http://www.ka-electronics.com/that1200/that1200.htm
http://www.ka-electronics.com/that1240/that1240.htm

http://www.thatcorp.com/Balanced_Line_Receivers.html
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Old 21st June 2008, 03:17 PM   #102
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Nelson has mentioned several times, that his BOSOZ/balanced line stage preamp makes an excellent balanced to unbalanced converter.

I ran a balanced DAC to a BOSOZ to an unbalanced amp for a couple of years. Worked out great and give me many hours of listening fun, while I built my balanced amp.


-David
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Old 21st June 2008, 04:36 PM   #103
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I don't think the BOSOZ will have CMRR with a single ended output. It says says that PS noise won't be rejected with a single ended output.
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Old 21st June 2008, 10:21 PM   #104
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Once you have converted to SE you have no CMRR regardless of which method you use to convert. What is important is the CMRR of the balanced portion of the balanced -> unbalanced stage.
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Old 22nd June 2008, 04:21 AM   #105
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So with the BOSOZ there will be CMRR of the balanced signal from the source but the unbalanced output will not have CMRR of the BOSOZ power supply ?
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Old 22nd June 2008, 05:35 AM   #106
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You are misunderstanding I think.

The balanced signal will reject noise that appears equally on both "hot/in-phase" (+) and "cold/out-of-phase" (-) signals at the point that it is converted to SE. So, if there is noise contributed by the PSU it will be rejected to the extent that it appears equally on hot and cold signals. This works because the unbalancing process re-inverts the out of phase cold signal at the same time inverting any added noise, then sums it with the hot signal. The out-of-phase noise on the cold cancels out the equal in-phase noise on the hot. Once the signal is converted to SE there is no way for noise added to the signal to be rejected. The PSU CMRR is a red herring


this doc might make more sense than my lame attempt at explaining?
http://www.tracertek.com/docs/balanced.pdf
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Old 22nd June 2008, 07:12 AM   #107
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That's what I thought, but in Nelson's article about the BOSOZ he says that when using the single ended output there will be no CMRR from the PSU.
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Old 22nd June 2008, 07:35 AM   #108
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Can you give me a reference for NP's comments regard the PSU? He is very precise in his wording, so I'd like to read what he said.
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Old 22nd June 2008, 08:07 AM   #109
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http://www.passdiy.com/pdf/balzenpre.pdf


Page 2 paragraph 7
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Old 22nd June 2008, 08:11 AM   #110
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Ok... found.

Quote:
The supplies will be regulated, but the filter will remove stray and
residual noise at the output of the regulators. The circuit itself will reject
supply noise through balanced operation, but this does not help when
using a single phase of the output. Passive supply filtering improves
both balanced and non-balanced operation.

The only noise that will effect the SE output is whatever noise is left on the dc lines after the regs and passive supply filters.

If you are really concerned you could either try NP's suggestion in the final para:

Quote:
As an alternative to having to use the balanced
output only, you can replace the resistors R3, R4 and R5, R6 with 40 mA
active constant current sources. This will restore the 80 dB CMRR
figure for unbalanced output.
or think about putting together a complete balanced chain.
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