Hiss in Trident 80 Monitor summing amps

[radardoug]

So its got nothing to do with the Trident? And you are making UNBALANCED connections? No surprise here!
ONLY USE BALANCED CONNECTIONS with sheild grounded at ONE end!!
You have been wasting our time.

 

[RFSiesta]

So its got nothing to do with the Trident? And you are making UNBALANCED connections? No surprise here!
ONLY USE BALANCED CONNECTIONS with sheild grounded at ONE end!!
You have been wasting our time.

Oh come on. Wasting your time? You obviously don't see the problem. (The Trident, by the way, has ONLY unbalanced outputs).
EVERY amplifier for guitars, keyboards, bass etc. has unbalanced inputs, every guitar, floor effekt etc. has both unbalanced inputs and outputs.
I've seen hundreds of locations, stages, rehearsal rooms, studios. Most don't have the problem we have here: We need to have a system that is not humming if a keyboard player wants to connect his keys to two different amps at one time. Or a guitar player who uses a PSU with connected ground.
This works in 90% of surroundings, it should work in ours: It's a professional studio.
If we need connections between floors or rooms that go more than 3-5 meters, we can always use transformers, but it definitely should not be necessary for short distances - and it is not a good idea for hi-Z sources like guitar pickups.

 

[radardoug]

I have also seen thousands of music locations. Pretty much every time you try and connect two instrument amps together you will get a ground loop. With guitars, the guitar is only grounded via the cable to it, but single coil pickups will pick up hum fields.
The severity of the loop will not always cause problems, but will always be there.
If you are running the Trident with lots of unbalanced connections, then you will have problems. You obviously have no understanding of the problems created by unbalanced wiring. I suggest you do some study.

 

[RFSiesta]

Just don't get involved if you dislike the discussion.

Pretty much every time you try and connect two instrument amps together you will get a ground loop

That's the definition of a ground loop, yes. Doesn't mean that it has to produce a lot of hum if the loop is quite small. And I know a single coil picks up hum    It's not more in our place than anywhere else.

If you are running the Trident with lots of unbalanced connections, then you will have problems.

A Trident 80B has ONLY UNBALANCED OUTPUTS, and only mic in, line in and monitor ins are differential amplifiers. All insert sends and returns are single ended. If you do not know the desks inside, I can send you the schematics for studies.

We try to balance as many connections as possible with trafos, I also balanced my multichannel monitoring system with 20 impedance converters followed by THAT1646 output driver ICs in a diy box, and then split everything between the studio rooms - works well. It's just not always possible - for reasons of complexity in our case.

We have hum issues with the studer as well, even if it's only connected via the patchbay to microphones.
NO ground loop, but I am certain the hum has the same reason like our GL hum.
The same desk did not hum in the last location I had.

And - YES, of course we connected the desk to monitors ALONE first. It starts to hum if you connect a microphone over the patchbay, even if the pb has no connection to ground.

 

[radardoug]

I know Trident desks well, I have worked on them.
Everything you say points to your location as a problem.
If it all worked fine at a different location, what does this tell you?

 

[RFSiesta]

I know Trident desks well, I have worked on them.
Everything you say points to your location as a problem.
If it all worked fine at a different location, what does this tell you?

That we have a problem and want to fix it. And it's not the devices, as has been stated ten times before. Because they work in other locations. You are going in circles.

 

[radardoug]

Its not me thats going in circles. The fact is, if your environment is unsuitable for the equipment, then its just not going to work.
We have now established, after much misdirection by you,  that your environment is unsuitable. You will have to move or put up with the problems.

 

[RFSiesta]

Its not me thats going in circles. The fact is, if your environment is unsuitable for the equipment, then its just not going to work.
We have now established, after much misdirection by you,  that your environment is unsuitable. You will have to move or put up with the problems.

Please, could someone else comment on this.
We are technicians, I'm not so superspicious as to see our location "haunted" just because we have difficulties finding the flaw. If there is a technical problem, it's usually fixable. If not, please give me any evidence. There are no unavoidable magnetic/electric fields that make the problem, like a television station or a transformer close to the building.
In two days we have a grounding specialist, he will first fix our faulty earth rod and add a new one. Let's see what happens!

 

[RFSiesta]

THREAD CLOSED.

Here are the results: We solved our initial problem with the mixer.

The problem was an oscillating circuit in the correlation meter sub-pcb. This could be from some modification a previous owner made, seemingly to make reaction time faster. A couple of caps have been removed and/or bridged:
The circuit oscillated at +-18V full rail voltage (!) in all kinds of frequencies between 500Hz and HF depending on surroundings, this led to coupled currents into ground and power rails - and ultimately to noise and stuff we had in the summing amps for the 24ch. monitor and the master section.

Still we have some hum issues all around the studio:
Since hum is a completely different kind of problem, this might become the topic of a different thread.
As has been stated often enough, hum obviously occurs in ground loops - this is only partially what seems to be the case at our studio, and it's a bigger problem than we are used to from other locations. Hum level is not changed by using completely different positions of ground, this does not point to a typical hum loop. As I've understood, it would be dependent from the actual impedance difference and therefore change with cables and distance between sockets.
It looks like there are still other reasons...

Of course, we will not break down the studio and quit, we can get rid of 90% by using ground lifts and transformer coupling in some places, we already did a lot of such measures with success.

WHAT STAYS: hum on the summing amps of both mixing consoles, Studer 089 and Trident 80, at -60 to -75 dB from nominal level. Sums up to a bit more than we are willing to accept if we use the monitor split section for mixing subgroups, which we do.
It's almost certainly from the same source, but we did not yet figure it out. Disconnecting the whole trident patchbay does NOT solve the problem.
There will be a last comment, as soon as we found a solution.

Thanks for support,
cheers Richard

EDIT:
We have a second ground rod now. It's going 7.5m, resistance has reached a bit over 30Ω instead of 80 from only the first one. Our dirt seemingly is NOT loam like in most areas of the city. That is what the electrician concluded. We didn't touch ground water, which rises and falls in Styria quite a lot with the amount of precipitation. But it is a lot better than before.
GUESS WHAT - GOOD NEWS!
Hum got down 15dB at least! So the better our earth system, the better our hum specs. In this particular environment.
So what we thought at the beginning seems the right direction. It's dependant from the quality of our ground.