Damaged interface through bad studio grounding?

[Neutrino]

I had to send in my UA Apollo 8 audio interface for repair for the second time after the monitor output and some mic inputs started producing noise and finally died. The service technician told me that most likely the damage was caused by a discharge voltage spike from some of the equipment connected to the interface. He told me to check the grounding of all my studio equipment to avoid such damage in the future. I would appreciate help with that.

When building the studio (single room) I payed extra attention to grounding and implemented a star grounding scheme. Moreover, all my equipment runs through (one of two) Furman power conditioners. Mainly, I have a PC, an additional AD converter and a 500-series rack with a bunch of DIY preamps and a patch-bay hooked up. I have some DIY microphones as well. I checked the DC voltage of all gear housings and some connectors to mains ground and everything was below 1 V. I suppose there is a more systematic way of troubleshooting this. Any tips are welcome.

 

[Bo Deadly]

I checked the DC voltage of all gear housings and some connectors to mains ground and everything was below 1 V.

1V? All grounds should be near 0V. In practice you might see a few 10's of mV maybe but you shouldn't see anywhere near 1V. That would suggest the resistance between grounds is relatively high in which case a high voltage transient will not be shunted as expected and the limits of input protection circuitry could be exceeded.

Of course I have no idea what your setup is so this is just theory. But if I measured the resistance between two ground points anywhere in my gear and it was more than 10 ohms, I would be be concerned. Use a meter to check resistance between ground points.

Although measuring resistance with a meter will not tell the whole story. There can be significant differences in ground potentials for other reasons such as strong electromagnetic fields. Generally that sort of thing shouldn't be a problem unless maybe you're using strangely long cables and you're next to an AM radio tower or under high tension power lines.

Otherwise, just start with taking some resistance measurements with a conventional DMM. Start with distant points were a long cable runs to your "star ground" and then back over another long cable maybe with different pieces of gear on the ends.

However, be aware that oxidation on surfaces can significantly impact low resistance readings. So you might need to work at getting a stable reading.

 

[Rob Flinn]

A client of mine had a similar issue with 2 apollo intefaces in a system both of which were new.. The service centre also tried to blame the studio wiring. In this case it wasn't the wiring it was the units.

 

[Neutrino]

1V? All grounds should be near 0V. In practice you might see a few 10's of mV maybe but you shouldn't see anywhere near 1V.

I wasn't clear in my post. The multimeter reading is fluctuating in the mV range even when not connected to anything. So, it is max. a few mV when measured between two ground points. When one end is not connected the reading can go higher than that, but I guess that has nothing to do with the grounding itself, but is rather a limitation of the multimeter.

 

[sahib]

........ The service technician told me that most likely the damage was caused by a discharge voltage spike from some of the equipment connected to the interface. He told me to check the grounding of all my studio equipment to avoid such damage in the future. I would appreciate help with that.........................

Is the service tech able to tell you that the unit has protection against such spikes in its inputs and outputs?

 

[Bo Deadly]

When one end is not connected the reading can go higher than that, but I guess that has nothing to do with the grounding itself, but is rather a limitation of the multimeter.

If one end is not connected, that is basically an antenna which will not yield a meaningful voltage measurement.

 

[Neutrino]

Is the service tech able to tell you that the unit has protection against such spikes in its inputs and outputs?

I guess so. But apparently, the protection, if present, was not sufficient in my case.

 

[moamps]

....The service technician told me that most likely the damage was caused by a discharge voltage spike from some of the equipment connected to the interface. He told me to check the grounding of all my studio equipment to avoid such damage in the future....

This device was supposed to be designed to survive such excess situations, do not believe the person who tells you in advance that you are guilty of what the malfunction happened.
Especially if the malfunction occurred both on the inputs and the monitor out. How could your active speaker damage monitor out of the Apollo? Not at all.

 

[pucho812]

Having been a service tech at a known audio company in the past, it is very easy to claim it was anything and everything else other then the unit for a fault. Reality is even the best designed and manufactured units can develop a fault. It happens and no one wants to admit we have a fault in our unit.

 

[Tubetec]

Monolithic corporations dont tend to take criticism well .
No need to name names ,
Its getting hard to tell nowadays , faulty by design or built in obsolescence , stuff just isnt made to last anymore . You take a tube radio from the 50's , if it was stored in good conditions you could well plug it in and get sound out.
Fast forward 70 years from now , theres little chance of an old SMPS doing anything other than blowing its load spectacularly if you plug it in . Ive heard it said analog sound reached its zenith sometime in the mid 70's , the sounds from bands like the Floyd and Zeplin , they still measure up . Ok stuff now is made more cost effectively ,thats means a better bottom line , but the truely iconic pieces of audio gear never fall out of fashion .

 

[Neutrino]

Well ok, maybe you guys are right. But the Apollo is 7 years old and the fault happened twice within the last two years. Could be bad luck. It could be build for obsolescence. But it looks suspicious to me and I want to make sure that there is everything OK on my side. In particular, because I have lots of DIY gear hooked up to the Apollo and it’s not unlikely that there is a problem with that gear.

 

[ccaudle]

bunch of DIY preamps and a patch-bay hooked up.

Any chance you are switching mic inputs with phantom power turned on? That can put some big (48V at substantial current) spikes through inputs. Although that would generally be spikes in the preamp input stage, if the Apollo is used for line level input only then less likely that would cause a problem for the Apollo.

 

[Neutrino]

Any chance you are switching mic inputs with phantom power turned on?

By "switching mic inputs" you mean (un-)plugging microphones to the inputs with phantom power turned on? It is possible that I did that in the past.
I use both the Apollo mic preamps as well as line inputs.

 

[ccaudle]

By "switching mic inputs" you mean (un-)plugging microphones to the inputs with phantom power turned on?

Yes, but especially if those inputs are connected through the patch bay. With a TRS connector the tip connector always slides across the shield and ring connector at each connection and disconnection. If the phantom blocking capacitors get connected in a way that discharges them at different times you can get a big pulse at the input stage.
See these papers for more background information:
48V Phantom Menace paper by Hebert and Thomas
48V Phantom Menace Returns paper by Bortoni and Kirkwood

Without knowing your exact situation I don't know how likely that is to be the cause, but seeing "preamps" and "patch-bay" in the same sentence puts that at the top of my suspicion list.

 

[Neutrino]

Yes, but especially if those inputs are connected through the patch bay. With a TRS connector the tip connector always slides across the shield and ring connector at each connection and disconnection. If the phantom blocking capacitors get connected in a way that discharges them at different times you can get a big pulse at the input stage.
See these papers for more background information:
48V Phantom Menace paper by Hebert and Thomas
48V Phantom Menace Returns paper by Bortoni and Kirkwood

Without knowing your exact situation I don't know how likely that is to be the cause, but seeing "preamps" and "patch-bay" in the same sentence puts that at the top of my suspicion list.

Thanks for the pointer. In my setup only the preamp outputs are routed via the patchbay. The inputs go to a separate panel with XLR connectors only. So this is then unlikely to be the issue.