noisy plates, tracking down any hum and buzzes

[pucho812]

Trying to work out where we are getting noise from when using our studio plates. This has been a problem  well before I was working here and now that I am, I am  trying to work out  all the buzzes and hums. Luckily this is the last of the punch list stuff.  For starters  our plates are located in their own box  in a separate room behind the control room. The box is just a wood frame with drywall around it and a door. It houses our 2 X plates in their own wood frame boxes which sit decoupled from the floo.  They are on a different electrical circuit and have about 30-35 feet or so of balanced snake cable between the patch bay in the control room .  One has emt solid state electronics, the other has martin sound electronics.  The plate with EMT electronics has a light hum, and it can be heard if I crank  up the monitors to full. I assume this is normal for a plate that old that has seen little servicing. nothing that can't be addressed in time.
  The Martin sound electronics have large amount of hum.  I have swapped power  around with marginal success, meaning I ran a power extension cord from the control room power circuits  and connected to the plate with a reduction in buzz but still low frequency hum.  I have tried  running  audio cables directly from the control room to the plates and still had issues.  I have confirmed  the patchy connections are solid  and working as they should.
The Martin sound plate electronics had recently been serviced and given a clean bill of health by the manufacture.
So as I read and comb over Bill Whitlock,  does anyone have any ideas of things I can try out?

 

[ruffrecords]

First try an isolating transformer on the balanced outs and ins just to verify if it is  a hum loop or not.

I cannot remember if EMT plates have piezo or electromagnetic pick-ups but either could be susceptible to hum fields. Try rotating the plate to see if the hum changes.

Cheers

 

[gridcurrent]

They are on a different electrical circuit

should be on the same electrical circuit.

a healthy solid state 140 has virtually no hum.

the pickups are crystal, few problems,
never observed a hum issue with them even with the  tube electronics.

 

[pucho812]

First try an isolating transformer on the balanced outs and ins just to verify if it is  a hum loop or not.

I cannot remember if EMT plates have piezo or electromagnetic pick-ups but either could be susceptible to hum fields. Try rotating the plate to see if the hum changes.

Cheers

space does not permit that but we will give it a go.

should be on the same electrical circuit.

a healthy solid state 140 has virtually no hum.

the pickups are crystal, few problems,
never observed a hum issue with them even with the  tube electronics.

Yes they should be, time to make that happen. The EMT version is usable and hum is noticeable when monitor pot is full throw. the martinsound  version is unusable as the hum and buzz is dominant.  This is after it came back from their shop after getting fixed. 

 

[VertigoRecording]

Take the Martech electronics out of the Plate and set it on the floor away from the wooden box. I know the wires aren't super long but the mechanical noise from the power transformer makes everything hum. Give it a try.

 

[pucho812]

will do that tonight 

 

[pucho812]

with the electronics out of the unit, there was no change in hum or buzz.  But good idea though, the only electronics for the Martin sound  are in their own chassis that is sealed.  We did try a grounding adaptor 3 prong to 2 prong and had the units  on the different circuits and while the unit was not free from hum and buzz it drop considerably so clearly there is a ground loop in the electrical between circuits.  So we are going to move the emu's electrical to be on the same circuit and sub panel as the control room.  Then work on the audio wiring. I didn't do the wiring but I have been cleaning up issues  as time permits. 

more over I noticed the power transformer in the Martinsound has a nice hum to itself when connected

 

[gridcurrent]

with the electronics out of the unit, there was no change in hum or buzz.  But good idea though, the only electronics for the Martin sound  are in their own chassis that is sealed.

no ideal what is sealed but the electronics following the piezo pickup is a 351 followed by a complementary pair.
that design  including the 3  diode drops between the transistor bases is a martin theme.
looks to me that some or all the eq is in that circuitry.
if so,  move the psu external , scrap that sealed thingy, fabricate a pro quality output stage with an output transformer of your choice.  install a XLR pin 1 lift switch.
plenty of good support on this diy forum.

We did try a grounding adaptor 3 prong to 2 prong 

that should get some of our resident posters' heart-rate up a notch.

 

[pucho812]

Was for test purposes only, not long or short term solution.

We have discovered group loop between rooms, we also discovered the martech electronics have a hum in their power transformer. Time to tighten up the lams and reduce that to see where it gets us