Normalizing balanced/unbalanced signals

Hi All.

I have just started thinking about the in/out circuitry on a simple VCA design and I have, but I can’t quite get my head around it. I don’t usually work with balanced signals anywhere in my chain so please bare with me.

I was thinking about using something similar to Gyraf’s SSL compressor circuitry using standard op-amps, but I need the signal to be normalised to 0dB (from input to output) regardless of wether the in/out signal is balanced or not.

In my head I see a 6dB loss at the input when plugging in an unbalanced signal/cable, and another 6dB loss at the output if I plug in an unbalanced cable. So we are talking about 12dB loss if I use unbalanced signals. Are there any circuits out there to mitigate this loss when an unbalanced signal/cable is plugged in?


Here again a brief explanation of the two possible scenarios:

Scenario one:
Balanced TRS in/out plugs, interfacing with other balanced gear.

Scenario two
Unbalanced TS in/out plugs, interfacing with other unbalanced gear.

thanks!

Take a look at cross-coupled outputs at the end of this article https://www.rane.com/note124.html, you can also use a good old transformer instead.

+1 on the tx boost.  You get galvanic iso out of the bargain and excellent cmrr on the outs as well.

user 37518 said:

Take a look at cross-coupled outputs at the end of this article https://www.rane.com/note124.html, you can also use a good old transformer instead.

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Thanks this looks interesting! I saw your other thread on MCI cross-coupled outputs. Did you ever find a stable reproducible circuit that worked?

This is a semi-commercial idea and Transformers are unfortunately far out of the budget range.

Do you know about anything that would solve the problem on the input side?

boji said:

+1 on the tx boost.  You get galvanic iso out of the bargain and excellent cmrr on the outs as well.

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see above

electric_diaries said:

Are there any circuits out there to mitigate this loss when an unbalanced signal/cable is plugged in?

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THAT (http://www.thatcorp.com/) is the way to go. 1200 and 1646. Properly implemented, you,ll never look back. No noise or stability issues, indifferent to balanced/unbalanced connections.

abbey road d enfer said:

THAT (http://www.thatcorp.com/) is the way to go. 1200 and 1646. Properly implemented, you,ll never look back. No noise or stability issues, indifferent to balanced/unbalanced connections.

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These chips did cross my mind, but I wondered if there was a cheaper alternative. Could be the way to go here though.

Do you know if the 1250/1290 series will also handle my normalising issue? I had a quick look through the data sheets but couldn't find the relevant info. CMRR isn't really a huge deal for me, because the cable length will almost always be under 2 meters on the input and output.

electric_diaries said:

These chips did cross my mind, but I wondered if there was a cheaper alternative.

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There are, but they suffer of compromised performance and are more complicated to optimize.

Could be the way to go here though.

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I don't think you will regret it.

Do you know if the 1250/1290 series will also handle my normalising issue?

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Neve 1290 is already transformer balanced so don't need additional circuitry to be compatible with either balanced or unbalanced connections.

CMRR isn't really a huge deal for me, because the cable length will almost always be under 2 meters on the input and output.

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CMRR can be an issue even with very short cables because of possible ground loops.

abbey road d enfer said:

Neve 1290 is already transformer balanced so don't need additional circuitry to be compatible with either balanced or unbalanced connections.

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I meant the THAT1250 and THAT1290 (this is a stereo design).  Do you know if they will handle my normalising issue?

electric_diaries said:

I meant the THAT1250 and THAT1290 (this is a stereo design).  Do you know if they will handle my normalising issue?

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Yes. Note the 1290 is available only in a 16-pin QSOP package (SMD), which may or may not be an issue.