Soundcraft EPM Balanced outputs - electronics

[jamesperrett]

All I hope now is the pics are visible, could someone let me know please.

 

I'm seeing a 404 error here.

[sunray]

All I hope now is the pics are visible, could someone let me know please.

 

I'm seeing a 404 error here.

Oh dear

 

All I hope now is the pics are visible, could someone let me know please.

 

I'm seeing a 404 error here.

Oh dear

How about now?

 

[jamesperrett]

I'd always assumed electronically balanced mean the signal was inverted with an op amp rather than there just being signal on one leg.

 

 

40 years ago you would have been right - just about every electronically balanced output drove both legs. In fact, if you look at the output circuit for an Otari MTR90 Mk2 tape machine, it looks more like a pair of power amplifiers, one on each leg, with some serious line driving capability. I would guess they were designed to drive 600 ohm inputs.

[sunray]

I'd always assumed electronically balanced mean the signal was inverted with an op amp rather than there just being signal on one leg.

 

 

40 years ago you would have been right - just about every electronically balanced output drove both legs. In fact, if you look at the output circuit for an Otari MTR90 Mk2 tape machine, it looks more like a pair of power amplifiers, one on each leg, with some serious line driving capability. I would guess they were designed to drive 600 ohm inputs.

I think even now that is still the case with some of the 'better machines'. But of course we've moved away from matching out puts and inputs and these day we rely on the gain control to put things right

 

 

And it was a cool way of getting a pair of 'buffered outputs' from a device to unbalanced inputs.

Edited June 17, 2021 by sunray

[kalmatthew]

Both images give 404s to me

[sunray]

I wonder if this works:

 

https://photos.app.goo.gl/FxQEZHSZFtYe1QpKA

[kalmatthew]

I wonder if this works:

 

https://photos.app.goo.gl/FxQEZHSZFtYe1QpKA

That's sorted it

[sunray]

I wonder if this works:

 

https://photos.app.g...QEZHSZFtYe1QpKA

That's sorted it

Thank heavens

[alistermorton]

I'm just getting 404 on those links, Ray.

 

Edit = aha, I see you've fixed it.

Edited June 17, 2021 by alistermorton

[Brian]

What sort of mains connections do these units have?

 

I have an odd situation on a setup with two items connected together where each unit has a 2-pole figure-8 mains connection. As the connectors are reversible that means that I have four possible combinations...

 

AA - terrible HF interference

AB - some HF noise

BA - some LF noise

BB - silent

 

(the exact order might be wrong but you get the idea)

 

It's down to how the items deal with any HF noise to meet EMC requirements without a real ground connection to use. Most switch-mode supplies do it by taking their 0V output line back to a point on the mains side via a capacitor. That point may be the 'neutral' line, but with a 2-pole connector that might be the 'live'. They might use a point somewhere after the incoming mains filter and rectifier. They might just pick a random point. For EMC it doesn't really matter as long as it is low impedance at RF. But it can play havoc with audio. In my setup, with those two units, there's clearly something odd going on and they aren't playing nicely with each other.

[sandall]

Thanks for that, Brian. It's something I'd never even considered. In this case the EPM comes with a 13A-IEC earthed lead, but I wouldn't know about the ATEM. Edited June 17, 2021 by sandall

[TomHoward]

Interesting, the ATEM mini in question has a SMPS wall wart down to 12V DC, 18W according to the website though I haven't checked it directly so it's not insignificant draw

I am doing a couple of channels of 1080 scaling on the ATEM as the inputs are 25 or 50fps and output is running at 30fps for Youtube so there is a lot of digital activity going on inside

[J Pearce]

We’re not getting any significant digital noise on our Atem Mini, but have found it necessary to use transformer isolaters to avoid ground loops.

 

What’s the power arrangement on your cameras? Are you building up a ground loop on the HDMI lines, that is then manifesting in audio?

 

There is a lot of processing packed into the box!

[TomHoward]

The cameras and the entire system is an absolute mess of USB power supplies, GoPros, SDI boxes, HDMI splitters to boost long cable runs, etc etc.

[themadhippy]

There is a lot of processing packed into the box!

yep

https://odysee.com/@eevblog:7/2021-02-24-Atem-Mini-Pro-Iso-Teardown:f