Discrete electronic unbalancing stage ???

It is not clear to me why you think that a discrete solution is easier than a bit of voltage dropping--likely you'll end up with a discrete opamp and that's definitely more hassle.

Dropping voltage from 60 V to 30 V or 36 V needs a resistor, a zener and an electrolytic capacitor, not a fancy full-blown LM317 supply.

Alternatively OPA551 may be your friend. Or a transformer...

Samuel

Just run it unbalanced. Common to input sleeve, lift the shield. No technical need to add active electronics.
Mike

Or configure an opamp with a few discretes around it (above & under) for increased supply voltage capability.

Jensen and Sowter make something that would work for you..... CJ would love it!

Just run it unbalanced. Common to input sleeve, lift the shield. No technical need to add active electronics.

Click to expand...

What works very well for unbalanced outputs connected to balanced inputs doesn't work well the other way round. Depending on output stage topology you might end up with gross distortion--at best you'll have at least one (if not two) orders of magnitude less CMRR than with a proper balanced input.

Or configure an opamp with a few discretes around it (above & under) for increased supply voltage capability.

Click to expand...

This works well for noninverting configurations but is more difficult for a differential amplifier if one is not about to exceed the linear CM range of the opamp.

Samuel

Butta,

have you looked at the Nelson Pass opamp doc on http://www.passdiy.com/legacy.htm . He has several designs that run on +32/-32V rails. You could use the JLM method of turning a single + rail into a +/- (in his case 48V into +/-24V).

No idea if the opamps sound good, if the CMMR would be up to snuff or if the PSU idea is really viable but the pdf is a great read anyhow.

cheers,
Ruairi

[quote author="Samuel Groner"]

Or configure an opamp with a few discretes around it (above & under) for increased supply voltage capability.

Click to expand...

This works well for noninverting configurations but is more difficult for a differential amplifier if one is not about to exceed the linear CM range of the opamp.

Samuel[/quote]

There is that dual inverter differential topology
(dont have any link, but I guess you people know what I am
referring to)

cheerz

ypow

Based on the responses, will look into the nelson pass opamp. Would like to keep the monitoring path transformerless.

Click to expand...

If you dislike distortion (that's how I read you're intention to avoid transformers) the Pass stuff is definitely the wrong thing for you. It will distort more than a good transformer.

I still don't understand why you absolutely want to avoid the easiest solution of just dropping the voltage or using a high-voltage IC but anyway: a good high-voltage DOA could be built based on the 990 by replacing all small signal transistors (including input pair) with 2SC2240BL/2SA970BL, MPS8099/MPS8599 or any other general-purpouse high-voltage complementary pair. The output transistors should become MJE172/MJE182 or BD139/BD140. No other changes needed.

There is that dual inverter differential topology. Don't have any link, but I guess you people know what I am referring to.

Click to expand...

That one: balfig12.gif? Doesn't adress the problems I've mentioned at all--or do I miss something? The problem is that both CM voltage and output voltage needs to be within the supply rail for linear operation. For any differential reciever this cannot be guarateed as common mode voltage (which hopefully doesn't make it to the output) can be completely different than differential voltage.

Samuel

[quote author="Samuel Groner"]
That one: balfig12.gif?
Samuel[/quote]

Nope, like this one
balfig13.gif
but using both amps as inverters. That is, Cold goes to R1, stick another 1K
resistor at A2 negative input and bring Hot to that resistors. Connect positive
inputs of both opamps to ground or whatever mid voltage point you need.

cheerz
ypow

[quote author="Samuel Groner"]

Just run it unbalanced. Common to input sleeve, lift the shield. No technical need to add active electronics.

Click to expand...

What works very well for unbalanced outputs connected to balanced inputs doesn't work well the other way round. Depending on output stage topology you might end up with gross distortion--at best you'll have at least one (if not two) orders of magnitude less CMRR than with a proper balanced input.
[/quote]

I have not experienced this. Disagreeable output topologies are few in most recording studios.
I have installed scores of Hafler, Crown, etc. type unbalanced input circuit amplifiers in rooms with all types of balanced monitor sources. There have been few interface issues, and, nuff' respect, but no one has ever asked me to improve the CMRR by any fraction of a magnitude.
The few outliers would be machine room runs over 75 feet, GML or other custom consoles, and just plain garbage equipment. Most outlier solutions used a high quality isolation tranny.

Mike

[quote author="sodderboy"][quote author="Samuel Groner"]

Just run it unbalanced. Common to input sleeve, lift the shield. No technical need to add active electronics.

Click to expand...

What works very well for unbalanced outputs connected to balanced inputs doesn't work well the other way round. Depending on output stage topology you might end up with gross distortion--at best you'll have at least one (if not two) orders of magnitude less CMRR than with a proper balanced input.
[/quote]

I have not experienced this. Disagreeable output topologies are few in most recording studios.
I have installed scores of Hafler, Crown, etc. type unbalanced input circuit amplifiers in rooms with all types of balanced monitor sources. There have been few interface issues, and, nuff' respect, but no one has ever asked me to improve the CMRR by any fraction of a magnitude.
The few outliers would be machine room runs over 75 feet, GML or other custom consoles, and just plain garbage equipment. Most outlier solutions used a high quality isolation tranny.

Mike[/quote]

When you connect the output like this, aren't you shorting one of the balanced line drivers from the signal source?

Just connect the tip and common from the output to the unbalanced input. You will still lose 6dB of signal and CMRR, but at least you aren't shorting the output of your line driver.

[quote author="gswan"]

When you connect the output like this, aren't you shorting one of the balanced line drivers from the signal source?

Just connect the tip and common from the output to the unbalanced input. You will still lose 6dB of signal and CMRR, but at least you aren't shorting the output of your line driver.[/quote]

This was addressed by "Disagreeable output topologies are few in most recording studios." Of course "few" doesn't mean they don't exist.

The audio in balanced outputs is most accurate + relative to - output. There very well may be CM errors wrt grounds.

JR