Balanced and Unbalanced signals in a Control Room Monitor - diyAudio
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Old 22nd March 2012, 12:54 PM   #1
dashbad is offline dashbad  Singapore
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Default Balanced and Unbalanced signals in a Control Room Monitor

Hi, long time lurker first time poster here so please be gentle. I have searched on this query and not found a great deal of info on balanced/unbalanced conversion inside a unit. Most posts focus on interconnection of different units. While I know the principles are the same the application is stumping me a little.

I am planning a control room monitor to switch 3 sets of inputs and 3 sets of outputs using relays with a passive attenuator between the input and output. The passive attenuator runs in a stereo balanced configuration. I also want to run 2 headphone outputs from the pre-attenuator signal. 1 of the inputs and one of the outputs is unbalanced

Hopefully the image below explains things more clearly:

Click the image to open in full size.

I have assumed that I will need to convert the unbalanced signals to balanced and vice versa if I want to include unbalanced ins and outs on the units. As I am keen to use high quality components I am opting to use transformers for this purpose. The headphone Amps also take an unbalanced input so I have dedicated transformers to take the balanced input signal and converted it to unbalanced for the headphone amps.


1. Does this topology make sense - I appreciate it is expensive. Should I consider an alternative method to using transformers to convert between balanced and unbalanced that would still maintain signal quality?

2. Do I need to place a buffer between the input signal and the headphone amps or is it ok to route the signal to the attenuator and HPA's in parallel?I've been looking at a BUF634 for this. Is this required or recommended?

3. In terms of grounding I intend to ground all input and output shields to the chassis at the jack and signal grounds from PCBs using a star ground. Is this sensible/required? Is there an issue also connecting the unbalanced signal shields to this ground?

Any other feedback would be most welcome.

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Old 22nd March 2012, 03:48 PM   #2
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Osvaldo de Banfield's Avatar
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Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
Hi. Why not to use unbalanced in all circuit up to the final stage, keeping in mind each transformer adds hum and distortion?
Osvaldo F. Zappacosta. Electronic Engineer UTN FRA from 2001.
Argentine Ham Radio LW1DSE since 1987.
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Old 23rd March 2012, 01:14 AM   #3
dashbad is offline dashbad  Singapore
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Originally Posted by Osvaldo de Banfield View Post
Hi. Why not to use unbalanced in all circuit up to the final stage, keeping in mind each transformer adds hum and distortion?
90% of the time I will be using the balanced ins and outs so I wanted to keep this signal as clean and untouched as possible (I am interfacing primarily with balanced gear).

Converting the balanced ins to unbalanced and vice versa would cut down on components but the balanced signal would always be going through a conversion. I am less concerned with quality for the unbalanced ins/outs as these are for convenience.
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