Behringer ADA-8000 owners: PLEASE READ!!!

[Matador]

It may not be a ground loop, it may be that the current draw of multiple units drag down the secondary voltage enough that the regulators drop out of regulation, which will indeed turn them into 120Hz (100Hz) hum generators.

A voltmeter across pins 1-3 of the positive regulators (or 2-3 of the negative ones) will tell you if this is happening: these regulators need 2-3V worst case across them minimum in order to stay in regulation.

 

[kike]

If this is the case, what is the cure?

 

[Matador]

If this is the case, what is the cure?

I would confirm that's what's happening first! It's pretty easy to test if you have a VOM.

 

[kike]

The pins on 15v regulators gives approximately 9V when all three units plugged, 10V when only one

The pins on 5v regulators gives 2V when all three units plugged, 2.7V when only one.

I have oscilloscope, can I check something with that?

Edit:

I have played with an oscilloscope.
Don't know what I am doing but still...

The voltage on 15V regulators is flat but on 5V regulator has a small oscillation when i plug all three units


The input stage of 074 opamps output pins doesn't do anything

 

[ccaudle]

That is the output of the 5V regulator? Definitely quite a bit of 100Hz ripple.
What do the 5V power supplies feed in that unit?

 

[kike]

Ad da converters, i think. And optical adat in an out
But now i see that there is only 2.5 volts on that picture. I will check

 

[ccaudle]

But now i see that there is only 2.5 volts on that picture

Not correct. The sensitivity is 1V per (large) division. It is faint, but I have highlighted the ch 1 reference point here (the ch2 reference point seems to be off the screen).

 

[kike]

Yes, i have checked, it is 5V. But there is a ripple

 

[ccaudle]

Yes, i have checked, it is 5V. But there is a ripple

So the next step is to check the input to the 5V regulator. Nothing obviously wrong with 12V (at least no noise, so assuming that is actually 12V, since the trace isn't scaled to have the reference point on screen to verify).

 

[kike]

This is when nothing pluged in to transformer

This is when unit is pluged in


This is when probe is on gnd and rectifier diode



This is when all three units

 

[ccaudle]

Somehow you managed to show everything except the one suggested measurement.

 

[ccaudle]

Sorry, I think I may have misinterpreted. When you say the probe is on the rectifier diode, do you mean the junction of D10 and C1, so effectively the input to the 7805?
I find your terms of where you probe vague, it would be helpful to point out a specific node on the circuit you are probing to be less ambiguous.

But that waveform described as probe on ground and diode looks like the output of a diode with no bulk capacitance. With a 1000uF capacitor it should be mostly DC with just a slight ripple (unless there is a huge current draw). The scope was a little hard to read, but I think it should be right around 10V DC and dropping down a bit based on current draw. Should definitely be enough to keep a 7805 in regulation.

What is the current draw on the 5V analog supplies?

The power supply circuitry in each ADA8000 is all stock, all you did is take out the original transformer, and put two transformers in an external box which has a set of wires to the existing power supply circuit in each of three ADA8000 units?

 

[kike]

Sorry, I think I may have misinterpreted. When you say the probe is on the rectifier diode, do you mean the junction of D10 and C1, so effectively the input to the 7805?

Yes, the probe is there. Sorry. I am not native english speaker so i write short as possible.

The power supply circuitry in each ADA8000 is all stock, all you did is take out the original transformer, and put two transformers in an external box which has a set of wires to the existing power supply circuit in each of three ADA8000 units?

And yes to that

What is the current draw on the 5V analog supplies?

I don't know.

And i noticed when i hold 5v wire on transformer with aligator probe when unit is not plugged in, i hear slight buzzing on my studio monitors.
Other probe is not connected

 

[kike]

I am sorry, this is new readings
Input regulator


Output regulator


I have uploaded a little video

When the usb of the soundcard is connected (rme digiface) the ripple jumps
When disconnected ripple disappeared for few seconds and then gradually turns on

When i turn the laptop off it is the same like i disconnect usb

Rme is usb powered

Laptop is on the battery, nothing is plugged in in it except for rme, only this power supply is plugged in in wall outlet and oscilloscope
I even turn the lights off, to check

 

[ccaudle]

OK, this is not complicated.
A 7805 regulator has a 2V dropout voltage, meaning that once the input voltage is below 7V the regulator cannot regulate at all, the input voltage variations are passing directly through to the output. If you notice in the datasheet all the performance data is measured with an input voltage of 10V. A minimum input voltage of 8V should be OK, but really the minimum input voltage, meaning at minimum AC line voltage (meaning 207V in Europe, 230V nominal -10%).
You can see clearly on your scope picture (and I have highlighted to make it even more obvious) that the input voltage falls below the minimum dropout voltage.



The points where the input voltage falls below that 7V line I have marked correspond with the points in the output 5V that have the drooping response.
The transformer you chose for the 5V supply is not appropriate, it needs to be higher voltage (and rated appropriately to supply current to the multiple units).

When I asked earlier what was the current draw for the 5V supply your reply was that you don't know. That indicates that you do not have enough basic information to choose an appropriate transformer, so as a bare minimum you should measure the current consumption of the different power supplies, and check the original transformer to see how it was rated to make sure that you do not purchase another inappropriate transformer.
Presumably you should double check that the higher voltage transformer is appropriate as well, it is possibly barely functioning properly.