Electronically balanced in/out – design topologies?

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pepe

Active member
Joined
Aug 31, 2006
Messages
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Location
Halmstad, Sweden
Which topology should I go for when implementing electronically balanced in?
I’ve seen different solutions like JLM Hybrid Opamp and Gyraf SSL, but are there any significant advantages with each method (transient response etc.)?
I’m also wondering why several designs use electronically balanced in but transformers on the out (I'm thinking why not likewise go for the electronic route on the outs).
 
[quote author="pepe"]Which topology should I go for when implementing electronically balanced in?[/quote]

I dont know

[quote author="pepe"]
I’m also wondering why several designs use electronically balanced in but transformers on the out . [/quote]

AS I see it, ALL gear should be transformer coupled on the input, impedance balanced at the output. Not as common as youd think although I believe alot of manley gear was built this way.

if you see a transformerless input/ transformer output they were either delibrately going for coloration or were misguided in their attempts to achieve best performance.

mike p
 
Which topology should I go for

Well, you've opened a can of worms there pepe.

The reason why a well designed transformer input or output is so desirable is because not only is it balanced, it is also earth free.
Particularly transformer outputs - you can connect them to balanced or unbalanced inputs without level shifts, you can run long lines with good isolation and no RF problems and they do tend to have a good sound! (depending on the design).
The big problem is cost and size, because for reasonable LF performance the transformers need to be fairly big.
Electronically balanced inputs are fairly good with the much-used active differential op-amp (and also the 'instrumentation amp' design).
Active balanced outputs are a different matter.
The circuit of the GSSL for instance will result in a 6dB level drop if plugged into an 'unbalanced' input and will mean that one of the op-amps is driving into 100R.
Some people use a cross-coupled design on their output which can drive balanced or unbalanced loads.
Special attention to earthing has to be observed when hooking up active balanced in and outs to avoid earth loops.
It's possible you might get better transient response with electronic designs. I remember bypassing the transformers on a Studer multitrack many years ago and it sounded considerably better. But I think that was more down to the fact that their transformers weren't great and they had padded down the signal to get get reasonable LF distortion.
Hard to draw an absolute rule to these things, but generally it's the size and the cost that stops a lot of people using transformers.
 
[quote author="pepe"]Which topology should I go for when implementing electronically balanced in?
I’ve seen different solutions like JLM Hybrid Opamp and Gyraf SSL, but are there any significant advantages with each method (transient response etc.)?
I’m also wondering why several designs use electronically balanced in but transformers on the out (I'm thinking why not likewise go for the electronic route on the outs).[/quote]

There are several good topologies that have been discussed here in the past. Count on throwing at least two or three opamps at it, to do it well.

JR

PS: Some people like the sound alteration caused by transformers. YMMV
 
This list has been going and active for such a long time, I'm starting to find my searches turing up 400 results. It can be a bit daunting sometimes.
good collection of links here.
Kelly
 
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