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Old 27th October 2013, 04:43 PM   #1
Corpius is offline Corpius  Netherlands
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Default Single ended to balanced conversion

At the moment I'm designing a balanced DCB1. While most of my gear has balanced in and outputs, some have only single ended outputs. For that reason I want to add some single ended inputs to be balanced DCB1. I'm looking for a good way to achieve this, without using expensive transformers.

After some reading on the web I came across this article from Walt Jung
http://www.analog.com/library/analog...h6_final_I.pdf
Look at page 67.
The schematic on that page shows an op-amp circuit used for single ended to balanced conversion. It does exactly what I'm looking for, but if I was to use such an circuit I'd like to use it with better op-amps, so if I change the OP275 for TI's LM4562 would the circuit still work?

Perhaps there are other (better??) ways or circuits to achieve single ended to balanced conversion?? Perhaps other op-amps that are better suited for the job, anything... I'm open to suggestions.
I'm looking for a high fidelity solution with reasonable pricing.
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Old 27th October 2013, 05:19 PM   #2
raul_77 is offline raul_77  Europe
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Perhaps the more easy can be the use of especifics IC's, as the INA134 and the DRV134:

http://www.ti.com/lit/gpn/ina134

http://www.ti.com/lit/gpn/drv134

Some examples:

Electronique - Realisations - Symetriseur audio 006

Electronique - Realisations - Desymetriseur audio 005
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Old 27th October 2013, 08:18 PM   #3
Corpius is offline Corpius  Netherlands
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Interesting little IC. Especially that almost no other components are needed and all precision resistors are included in the device itself. Any (soundwise) comments on the DRV134's performance?
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Old 27th October 2013, 08:51 PM   #4
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What do you hope to gain by adding more amplification stages? If the source is single ended, adding more stages to convert the source to balanced will not improve anything.
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Old 27th October 2013, 11:24 PM   #5
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I have converted my system to balanced {sowter transformers} and several other peoples systems; I did not think it would improve the Audio but it certainly makes them much quieter. another advantage is the better XLR connectors and you can run much longer leads.
My friends and Myself think it has made a big difference; mine is very minimal but one friend has everything balanced; cost a lot using transformers.
Phil
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Old 28th October 2013, 08:19 AM   #6
Corpius is offline Corpius  Netherlands
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Quote:
Originally Posted by Frank Berry View Post
What do you hope to gain by adding more amplification stages? If the source is single ended, adding more stages to convert the source to balanced will not improve anything.
Adding more amplification stage is not the goal, I'm just looking for a way to let the balanced DCB1 take both balanced and single ended inputs and output the signal to balanced outputs. I clearly see the benefit of balanced lines, so that's no point of discussion to me. Besides most of my gear has balanced in and outputs and I'd like to use these.
Now back on topic; The only outputs will be balanced outputs for now, but maybe I will want to add some single ended outputs to make it a bit more versatile. That would mean that there must also be some sort of balanced to single ended conversion, but that is easier to achieve imho. So the big question is how to let the balanced DCB1 take both balanced and single ended inputs and output the signals to the balanced outputs in a way that does degrade the signal integrity as little as possible, but at a reasonable price.

These are the schematics for the balanced input --> buffer --> output

Click the image to open in full size.
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Old 28th October 2013, 09:09 AM   #7
tinitus is offline tinitus  Europe
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if I'm not mistaken, you can just connect negative input to ground to create single ended inputs
(but don't how it will interfere with balanced input attenuator)

if you use a multipole input selector it might be able to do the switching
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Old 28th October 2013, 09:27 AM   #8
Corpius is offline Corpius  Netherlands
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That's how you can connect single ended outputs to a balanced amplifier. The output will not see ground if I connect the negative input to ground because the buffer is in between.

I was planning to use a single relay to control the MUTE circuit of a single balanced channel. I could use two relays of course. When using a single ended input I can short the buffer's (negative) output to ground. This way the amplifier will also see ground. I think that this is what you mean, right?
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Old 28th October 2013, 09:30 AM   #9
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by Corpius View Post
That's how you can connect single ended outputs to a balanced amplifier.
is that not what it is
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Old 28th October 2013, 09:39 AM   #10
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by Corpius View Post
I was planning to use a single relay to control the MUTE circuit of a single balanced channel. I could use two relays of course. When using a single ended input I can short the buffer's (negative) output to ground. This way the amplifier will also see ground. I think that this is what you mean, right?
hmm, not sure, maybe

I meant that a multipole input selector might do double function and simultaniously switch to SE convertion when selecting to those sources

but yeah, maybe a simple relay is easier

on second thought, maybe it would wise to cut ground input as well as signal input for all sources, so that only the active input is grounded
(might take care of possible chassis/ground loop issues)
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