Balancing minidsp 2x4 hd

So I bought a minidsp 2x4 hd dsp processor and was toying briefly with the idea to use this for Pa system tuning, equalization, crossover duty etc.
https://www.minidsp.com/products/minidsp-in-a-box/minidsp-2x4-hd

Problem is the outputs are unbalanced.

I have a couple of edcor wsm 10k:600 and also 600:10k transformers lying around doing nothing, would these work? Im thinking 4.1:1 stepdown from foh mixer xlr outputs into the dsp and then 1:4.1 stepup on the outputs, or will the impedance reflected to the minidsp output stage be to low when connected to your average pro  amplifier balanced line input for it to drive the output correctly?

The specs for the minidsp are as follows:
Analog audio input Unbalanced stereo (2 channels) analog audio on RCA connectors
- Max input of 4V or 2V RMS, jumper–selectable
- Input impedance: 10kΩ
- THD+N: 0.003% (RCA to USB)
- Dynamic range: 103dB
Analog audio outputs Unbalanced analog audio (4 channels) on RCA connectors
- Max output: 2V RMS
- Output impedance: 560Ω
- THD+N: 0.001% (USB to RCA)
- Dynamic range: 103dB

Im mainly asking since i already have these transformers lying around if it would work ok. If not, maybe point me in the right direction. I could always build something with drv134/drv135 or opamps aswell I guess. Thanks for any advice!

The best way to find out is to try it! ;D

The 2V output level should drive almost any power amp directly, albeit unbalanced.

The Owner Manual clearly shows it used this way.

Thats good to know! However if i have ~50meters of multicable returns from foh to amplifiers unbalanced, it could be a problem, im guessing...?
/J

Jonkan said:

Thats good to know! However if i have ~50meters of multicable returns from foh to amplifiers unbalanced, it could be a problem, im guessing...?
/J

Click to expand...

You need to use proper 3 circuit (+.-. and shield) XLR wiring.  2V is enough level to drive most PA amps to full scale.

Connect the single ended output to XLR pin 2 (+), output ground to pin 3 (-), and pin 1 to chassis ground.  Most amplifiers will have a decent input differential circuit.

2V does not provide much headroom, but should work well enough to make noise.

JR

> ~50meters of multicable

5,000pFd of capacitance. Source is 560 Ohms. This works out to 59KHz at -3dB, 30KHz at -1dB. If you can actually hear the -0.5dB at 15KHz, surely that box can EQ it up?

The unbalanced is not ideal but I have run full unbalanced long distances at power-amp input level without harm.

JohnRoberts said:

2V is enough level to drive most PA amps to full scale.

Click to expand...

Gotta disagree with that one, JR.

Most(?) pa companies have standardized on amps set to 26dB gain, 20X voltage in-out. That works out to 2V in,  40V out.

At 8 ohms load,  200 watts. My ears are bleeding.

Gene

The output impedance of the MiniDSP is 560 ohms.
Clearly, you can't drive a xfmr. It will make some noise, but not pretty.
The MiniDSP balanced has an output Z of 1120 ohms.
It's ok if you drive a single amp via a short cable. For any serious environment, you should use a THAT 1206/1646 combo.

I think the original idea was to use a 10K/600 transformer to drive the line.
IMHO driving a 10K transformer impedance from a 560 ohms source is not a problem.
A bigger problem might be the low(er) level on the long line and two transformers in the path.
But I would also prefer the unbalanced option!

Gene Pink said:

JohnRoberts said:

2V is enough level to drive most PA amps to full scale.

Click to expand...

Gotta disagree with that one, JR.

Most(?) pa companies have standardized on amps set to 26dB gain, 20X voltage in-out. That works out to 2V in,  40V out.

At 8 ohms load,  200 watts. My ears are bleeding.

Gene

Click to expand...

OP should check actual voltage gain of amps he plans to use.

He needs to be able to drive the amp to full clipping. In fact if the amp has clip limiting and he wants to get any use of that he needs to drive it past clipping.

I repeat 2v does not provide much (any?) headroom, but will make noise. (not enough to hurt Pinks ears.)

Many(?) amps provide more than 26dB of voltage gain.

JR

RuudNL said:

I think the original idea was to use a 10K/600 transformer to drive the line.
IMHO driving a 10K transformer impedance from a 560 ohms source is not a problem.
A bigger problem might be the low(er) level on the long line and two transformers in the path.
But I would also prefer the unbalanced option!

Click to expand...

The other way round! 10k:600 at the input and 600:10k at the output.
Using a 10k:600 at the output would limit the level to about 0.5Vrms.

Yes, that is exactly what I was saying!  ;D
(His idea was to keep the signal balanced, although at low level, and restore the level at the end of the line with a 600/10K transformer.)

RuudNL said:

Yes, that is exactly what I was saying!  ;D
(His idea was to keep the signal balanced, although at low level, and restore the level at the end of the line with a 600/10K transformer.)

Click to expand...

And I still say it won't work, bedause the 560 ohms impedance of the processor will have a hard time driving the 600 ohms winding.
A 600 ohms winding need to see about 60 ohms source impedance for correct operation; otherwise LF attenuation and LF distortion occur.

Is it out of the question to replace the silly 560 ohm output resistors with something more sensible, perhaps in the 50 ohm region?

abbey road d enfer said:

RuudNL said:

Yes, that is exactly what I was saying!  ;D
(His idea was to keep the signal balanced, although at low level, and restore the level at the end of the line with a 600/10K transformer.)

Click to expand...

And I still say it won't work, bedause the 560 ohms impedance of the processor will have a hard time driving the 600 ohms winding.
A 600 ohms winding need to see about 60 ohms source impedance for correct operation; otherwise LF attenuation and LF distortion occur.

Click to expand...

The idea wasn't 560Ω-->10K:600Ω-->long line-->600Ω:10k-->bringing load? In that case the 600Ω winding is being driven by the other 600Ω winding driven by the 560 across the transformer, so about 150Ω. Depending on the specific transformer that may not be a problem I guess.

JS

joaquins said:

The idea wasn't 560Ω-->10K:600Ω-->long line-->600Ω:10k-->bringing load?

Click to expand...

No. Read the OP: " Im thinking 4.1:1 stepdown from foh mixer xlr outputs into the dsp and then 1:4.1 stepup on the outputs,"

Thanks for all the help! Im thinking of maybe doing some that 1646 1206 chips on breadboard. I also just remembered i have some edcor xs1100 lying around. http://www.edcorusa.com/xs1100

Would it be possible to use these on inputs, or outputs? Im guessing the minidsp outputs wont drive these very well either, but it does say: "Primary (Input)
Designed for a low impedance source, such as an operational
amplifier or transistor with a maximum input voltage of 7.5Vrms"
On the edcor website... Thoughts?
/J

Jonkan said:

Thanks for all the help! Im thinking of maybe doing some that 1646 1206 chips on breadboard. I also just remembered i have some edcor xs1100 lying around. http://www.edcorusa.com/xs1100

Would it be possible to use these on inputs, or outputs? Im guessing the minidsp outputs wont drive these very well either, but it does say: "Primary (Input)
Designed for a low impedance source, such as an operational
amplifier or transistor with a maximum input voltage of 7.5Vrms"
On the edcor website... Thoughts?
/J

Click to expand...

What they mean is "the very-low-impedance output of an opamp or SS amplifier under heavy NFB".
This transformer may be usable as an input xfmr, under the condition that it's driven by a low-Z source, which you can't always guarantee. The MiniDSP has a 560r resistor in series with its output stages; it may be possible to short them, so they may be capable of driving this xfmr. I don't know what type they are.