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Studio Hums 'cause it doesn't know the words...

There was a studio in Coraopolis, PA that I was sort of involved in. A local band sort of rented it from a local business guy and he ended up with a partner - Bill. Long story short, a lot of political upheaval and such...

But I was doing some tech work there They had an old Amek 2500 console and a vintage A80 Studer. I recall Blues Travelers and Hootie & the Blowfish being there two different times when I was doing some repairs. Hootie was cool, But I recall Blues Travelers kicking everyone out for their rehearsal.

"You too hippie - gotta go!" as I had the master module out trying to figure out why the logic rail went dead. "Ok cool...." I stated  as I was putting my tools and test gear away. While pulling my tool cart out of the control room I mentioned, "Good luck - BTW - the console's dead..."

A quick aside with the head Blues dude and his manager - "OK you can stay..."  "Really?" I thought. "Gee, thanks..."

Anyway as you can see in the pic's the equipment was long in the tooth, even back in the early 90's. That's my first born when he was about a year old at the Studer and old Amek...

I recall that with the old gear, any guitar or bass brought into either the main studio or the upstairs MIDI-room was affected by an atrocious hum.

In fact, the old A80 MKii Studer 24tk  would hum on repro during mixdown  unless you moved it to a certain angle and adjusted the head shield to a 45 degree angle. I didn't know at the time what caused it, we guessed it was something to do with the large power lines located along the building.

I also had recently proto-typed a bass guitar preamp and installed it in one of my basses, an old BC Rich Warlock that used to pick up everything from hum to radio stations near my house. After installing my prototype, I took it to the studio, which we were refitting with a new Studer A827 and AMEK Rembrandt console. To the amazement of the entire staff, I was able to turn the amp to max with no hum or buzz. The amp was turned up so far that just touching my A string with my left hand caused the amp to go into clipping/protection. I was able to walk around the entire main room with no change in the noise floor.

This is the New Stuff ...

So they suffer a lightning hit and I get called in. The partner of the owner wants to just replace the gear. They get hold of a new Amek Rembrandt with Neve EQ; he was working for Harmon/Amek at the time - got invited to meet him at AES - but that's another story. They also bought a new Studer A827 - the last of the multitrack analog decks that Studer would ever make.

Here's some pic of the new design I did. Made it into Mix magazine I'm told...


After installing the bulk of the wiring audio , and having the local electrical contractor finish the new service entrance (3PH 208 wye),  and overseeing the room refit I had to leave Pittsburgh due to my day job ( I was  the founder a communication electronics firm - my lab:  ).

I got a call a few weeks later. Seems that when Studer/Revox finally came to the studio to commission the new 24-track, they encountered more hum and buzz than the old A80 had. After repeated attempts to get Studer to help they told the owner, Bill, that he should have done an EMF survey before building the studio there. He reminded them that it was an existing facility but their only offer was to mu-metal the head stack cover and repro head wiring.

When Bill called me ( I had since moved) , it was so bad I heard the hum over the phone. He had the guys there from Duquesne Light (the local utility) and AMEK. I asked him if it was only in repro and he confirmed my theory; there was a serious EMF field being impressed across the room and the new 24-tracks repro head stack. I told him to try and isolate the old building power from the new studio power service we'd just installed.

Well, Duq Lite brought in a mobile generator along with the VP of Engineering. Even with all the power to the building cut at the utility pole and just the console, monitor amps  and Studer on, there was still an atrocious hum - just in repro mode. The guys from Duq Light were stumped. Their milligauss meter showed that the field seemed to emanate from the floor in front of the console. They couldn't understand how, since all of the power for the building was off. They gave up.

Later that day Bill calls to tell me what happened. I told him to check and see if there was a ground wire in the basement, tying the old service to the cold water pipes which came in from the other side of the building.  Poor Bill was so distraught he was ready to do anything. In fact he'd just bought $3k worth of mu-metal sheets in a desperate attempt to line the ceiling in the basement.

So Bill went downstairs, told me that yes indeed there was a bare copper wire going between the old service and the pipe near the water meter. It was traveling across the beam, right about where the Duq Light guys measured EMF.

So I’m on the phone, can easily hear the hum in the background. I told him to cut it at the cold water bond point; when he did, I could hear that the hum had changed harmonic content  but was still there.  When he got back on the phone he mentioned there was a definite difference in the hum, and that when he cut it, it melted the dikes.

I hung up. Within the hour, Bill called me all excited.  No more hum.

He said he went down after talking with me about 8:30PM, shut off the water before the meter, and with rubber gloves, grabbed a hacksaw and cut the pipe right after the meter and inserted a plastic section of pipe.  He stated that when he finished the first cut, the hack saw blade melted to the pipe coming out of the water meter. I asked him to grab a DVM from the shop and see what the voltage was across the plastic pipe. About 60-80VAC... I told him he’d better call the power company back…

When  the VP of Duquesne Light came back he again measured the floor in front of the console – no more EMF. As they were inside one of the DL techs came in with a stick mounted version of the milligauss meter and mentioned that the sidewalk outside was now showing an increase in EMI. He also mentioned that as he was outside, a man approached from the VFW across the street and mentioned, " I saw your Duquesne Light trucks and have a question - last night about 9PM all my lights in the hall during bingo got real dim..."

Seems the building across the street had an open neutral, caused by a lightning hit,  and their neutral current was actually going down the bonded ground in their box, across the street to his studio via the  bonded pipe and finding its way to his grounding system via the building metal. These buildings were older and it was typical to bond the neutral and safety in the mains panels. The VP confirmed this by talking the gauss meter out on to the sidewalk where the water service came in.

Some of the strangest shit I've ever had to troubleshoot...

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