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.

 

[kike]

Thank you for the answer.

The whole point of making external power supply is that the manufacturer chose the wrong transformer and the unit overheated, and eventually regulators fail.

I am not expert in electronics, I built couple diy stuff and I thout that this is not a big problem to do

One of mine fail that way so I choose transformer with lower voltage.

I made a small box with cheap standard transformers (2x18V, 6V). I don't need phantom power, but a small 2x30V will also fit inside this box.
I haven't found a transformer that fit inside the Behringer case, so I went this way and it's rather easy. The box powers two Behringer.

This is where I got he idea.

 

[kike]

Nice job.

Although if anyone were to add phantom, I'd suggest 2x22V or 2x25V, since 2x30V is too high. The 6V transformer is going to cool down the unit considerably. the 2x18V is still higher than needed, though slightly gentler than the 2x20V original. You could almost certainly get away with 2x15V I reckon, that too would cool down the unit, and render the 7815, -and particularly the 7915- less prone to failure.

-You know, the secondary may even be un-windable... I have a dead tranny here that I can try it on... I'll give it a go. I wonder how many turns you'd have to remove from the 12V secondary? -Half of them should be plenty, and would more or less halve the heat generated from the 5V rail.

Keith

Is there advice to fix the problem I have.
Witch transformer to buy?
More amps is better of should i need to look for something else

Again, thanks for the time

 

[ccaudle]

Witch transformer to buy?

If not changing any of the rest of the power supply design then an 8V transformer of suitable current rating would be optimal.
8V nominal would be 7.2V AC RMS at the lowest specification line voltage, which would be around 10V peak. Based on the 'scope measurements you posted there is about 2V ripple before the regulator, so that would be 8V minimum at the input to the 7805. That is high enough that the regulator does not drop out of regulation.
At nominal line voltage the input voltage would be just over 11V peak and 9V minimum, and at highest spec line voltage (230V +6%) the regulator input voltage should be 12V peak.
You would still need to verify if the heatsink is large enough for dissipating that amount of power.
The first post in this thread indicated that the factory transformer measured 11V RMS under load, but it is not clear if that is a transformer rated at 11V, or a 12V transformer which was optimistically rated or used at a higher current than intended.
I am not sure how easy it would be to find an 230V to 8V AC rated transformer, but unless someone can show differently I think that would be the optimum to reduce power consumption while still meeting spec at 10% low line voltage.

Note that 2V ripple seems high, so it is worth checking whether the capacitors are in spec. If they have dried and are lower capacitance than specified, then simply replacing the capacitors might decrease the ripple enough that the transformer you have will work.

 

[kike]

Thank you very much.



There are no heatsinks on 5v regulators, there are three of them in one unit, only on 15v regulators

 

[kike]

Is this one ok

Or can i buy two 6 volts an connect each unit on his own trafo

I will change capacitor either way