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Old 4th February 2011, 12:08 PM   #1
steevo is offline steevo  United Kingdom
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Default line level unbalanced to balanced converter

Has anyone got a good high performance circuit for converting standard line level unbalanced signal into a balanced signal. Or maybe a PCB layout for a circuit.

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Old 4th February 2011, 12:27 PM   #2
Boofers is offline Boofers  Canada
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Here is an interesting circuit that will convert unbal to bal.

http://passdiy.com/pdf/balzenpre.pdf
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Old 4th February 2011, 02:39 PM   #3
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One of the CCS variants of the BOSOZ or the UGS found in the pass forum would be good if you have the room or are looking for a preamp that will drive a balanced out. The CCS ends up giving the BOSOZ better tracking between the two output signals. There is an X-CCS-Cascode-BOSOZ variant.

DRV134 pcb or something of your own if you need to add SE to balanced into another component. The DRV134 uses Pass super-symmetry.
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Old 4th February 2011, 03:39 PM   #4
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Why not use a transformer,nothing else needed
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Old 4th February 2011, 04:40 PM   #5
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Quote:
Originally Posted by themadhippy View Post
Why not use a transformer,nothing else needed
That would be my recommendation as well.

Here's an example:

JT-11P-1 as "Phase Splitter" With Symmetrical Outputs

See the schematic on the right. Also note that the primary and secondary have been flipped around, i.e. the secondary is used as the primary and vice versa.

The same can be done with a CineMag CMLI-15/15B which costs less than the Jensen 11P-1.

se
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Old 4th February 2011, 04:59 PM   #6
LAJ is offline LAJ  United States
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Default Probably need level conversion too.

Standard line level for unbalanced is about -10dB. Balanced line level is +4dB. So you should need a gain of 14dB.
I did this using a 5532 op amp (balanced supplies). Make one op amp your gain stage and feed the inverting input of the second op amp (configured for unity gain). Take the outputs of both op amps for your output.
There are commercially available products that do this called the Matchbox that radio and TV stations use.
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Old 4th February 2011, 05:41 PM   #7
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Quote:
Originally Posted by LAJ View Post
Standard line level for unbalanced is about -10dB. Balanced line level is +4dB. So you should need a gain of 14dB.
Outside of professional audio, there's very little that adheres to those "standards." For that matter, even in professional audio there's considerable variance.

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Old 4th February 2011, 06:12 PM   #8
AndrewT is offline AndrewT  Scotland
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Hi Steve,
the Cinemag CMLI15/15b is used as a balanced to unbal at the receive end.
Are you confirming that by swapping it around it works as a transmitter from unbal to balanced?
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Old 4th February 2011, 06:32 PM   #9
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Quote:
Originally Posted by AndrewT View Post
Hi Steve,
the Cinemag CMLI15/15b is used as a balanced to unbal at the receive end.
Are you confirming that by swapping it around it works as a transmitter from unbal to balanced?
If by "transmitter" you mean an output transformer, then no, I wouldn't recommend using the 15/15B as an output transformer.

But as an input transformer, converting an unbalanced input to balanced, then yes, swapping the primary and secondary achieves just that.

Technically you could get away without doing that. Just that the primary is symmetrical and therefore balanced. However because of the winding techniques used, the secondary has a slight capacitive imbalance. It's probably not enough to really lose any sleep over though. SY has used them this way with good results.

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Old 6th February 2011, 08:38 AM   #10
Francec is offline Francec  Australia
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I use and can recommend the PCBs offered; simple, use to use and work well.

Balanced Transmitter and Receiver II

Frank
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