transformer hums - how to get around them?

[The Tasmanian]

This has been on my mind for years..
There has been a few times when I have had transformer hum from units being on top of each other in a rack.
2 x vintage Sta-levels for example needed to be moved apart by 150mm - no problem they are old men that cant be too close together - or they will fight!
Even my Retro Sta level does it too when it is too close to other equipment - like a Purple MC77 on top makes it hum.

The big one that bothers me the most is my Chandler Passive TG channel - especially if I wind some low end in on the EQ - the hum comes up - so I have to pull it out of the rack at times.
I don't have endless rack space to be able to put spaces between everything.
Is there some sort of metal material that I can put between 2 units that will stop the hums from the transformers interacting ?

[rick]

sure you can wrap them in mu metal - its designed for the job

its not cheap though ... as in "really" not cheap

the real solution is to make all power supplies external like they were way back when , go all digital .. rob a bank and buy serious mu metal shields
or move then apart till they dont talk to each other .

i have a collection of mu metal transformer shields , i have been known to hand a few out from time to time .
but i think i will wait till the new place is finished before i do so again
interesting topic though

[Ben M]

Hey Chris

You might be able to make a bigger sheet out of these sheets.

http://cgi.ebay.com/New-MuMetal-Ultrape ... 500wt_1156


or have a metal guy make some covers out of them...they may need to be wrapped in another material to stop any sort of contact.

[The Tasmanian]

Never heard of Mu - only the Vari Mu!
The thing about the Chandler is its power supply is no where near the unit.
So maybe the transformers inside the unit are picking up hum from other units power supply's nearby?

[Chris H]

One thing to look for is some gear has the power supply on the left and others on the right. It's less likely to be a hassle when you put the outboard with gear that has the power supply on the same side.
That's what I've heard.........might be internet rumor. Can anyone confirm?

[Ben M]

Hi Chris

I forgot to mention this sort of stuff;
http://don-audio.com/trafo-shielding

We need to reduce the magnetic field..captain! (Scotty voice)

[Linear]

Interesting thread.

fortunately I don't get any hum from bits of gear being too close to each other. I would recommend that you think carefully about rack placement, ie having the internal power supplies lining up if possible. ie pop the lid, make a note of where each transformer (mains or audio) is and put corresponding units on top of each other. most of the time the IEC lead is on one side (with the transformer inside close to the connector), and the output trannies are on the other.

if this is too hard/doesn't work, then next step I think I'd be taking the transformer out of the case, mounting it into a little metal box (jaycar has loads of different sizes) and reconnecting via a multipin connector.

if you weren't confident with this, then I'm sure a tech would be able to do it without too much fuss. I'd estimate it'd take a couple of hours at the most.

Chris

[The Tasmanian]

Thanks Ben - that's a good headstart - I may have to vari those mu sizes!
Chris1 - the left side/right side PS, I've thought about in the past - it makes total sense : with the 2 x Sta levels as the PS's are directly above one another.
I just checked the retro and MC77 and they do have the PS's on the same side - so maybe this is true - but the chandlers supply is not near the unit.
Chris2 - its only the odd units that hums - usually older stuff (LA2a's may have given me these problems in the past too from memory)
Its happened in other locations/racks before too.
It would be good for Rob to chime in here cause he is the official Chandler repair man - so maybe he knows whats inside them and why this happens on a unit with external supply.
If it is related to the supply's being on the same side then I can reshuffle my racks, but still the Chandler question remains.
Maybe it has inductors that pick up magnetic fields from the PS's ?
Thanks guys
Chris3

[Ben M]

This is like a Chris convention....
If we're talking chandler... the power supply is away on a 5 pin lead. Which should just leave the internal components.
Ultimately... you either move the units or shield them. I would rack the problem units separately Chris. Like the other side of the room separately.
Or give them to me... aand problem solved.

[Milo]

1st cow: Why do they only calculate the magnetic permeability of a metal to 5 decimal places?"
2nd cow: "Mu"

[rick]

long before my stuff hums i hear it sounding and react differently depending on where in the rack it sits

i spoke to rob squire about this kinda sheepishly once in case he thought i had finally lost it
and his response was
- parphrased
" i am not at all surprised the amount of coils tubes and transformers in your rig they must be all reacting to each other all the time - but remember your not a usual case though"

[rob]

I've just stepped off a plane flight back home following a weeks holiday. I was making some notes on the long flight for the next OTB article for Audio Technology mag. Writing about noise and in amongst my notes was some stuff about radiated noise, transformers etc etc. Then checking in with TR I find this discussion. Syncronicity!
I'll just address the question about the Chandlerfor now, but this will lay out the general principles anyway.
The clearest way to think about this is to consider that you have transmitters and receivers. Mains power transformers are good transmitters, mains cabling carrying heavy currents are weaker transmitters. Audio transformers and inductors are good receivers, other parts like transistors, capacitors and circuit traces are poorer receivers.
Some bits of gear, say a Pultec have a transmitter and recievers in the same box and so careful layout, shielding and orientation of parts is required to minimize any hum in the audio output.
The Chandler has a remote PSU, but it is full of inductors and so is still a receiver of radiated hum from any other transmitter near it. The only practical solution is to do as you have been and experiment with placement. Remember Magnetic fields weaken as per the square of distance, so sometimes moving something a few centimeters can make a significant difference as also can rotating offending units a few degrees . . . . . But this is doesn't work so well in a rack layout!

[Ben M]

Chris...if it turns out that the proximity of the chandler PS is the problem. You could extend the 5 pin PS cable so the PS unit is a bit further away.

Just thoughts...

[rob]

To be a bit clearer the Main audio unit is full of inductors, not the PSU. It will be other units mains transformers that are radiating into the Chandler.

[rick]

Back to moving them or stumbling across a cheap supply of mu metal rolls
maybe we could raid some Russian nuclear submarine wrecking yard
and do a group buy ..?

[Ben M]

maybe we could raid some Russian nuclear submarine wrecking yard
and do a group buy ..?

Postage for a russian sub would be a killer.

[The Tasmanian]

Thanks Rob - that was what I was starting to think - the inductors are like guitar pick-ups in a sense.
So I shall move the chandler unit away from all the powersupplys of other units, and then make sure that the remaining rack stuff is not interacting - that ones easy!
and yes Rick - I may rack the chandler with MU sheets on top and bottom.
Russian subs would be on ebay in this day and age - surely?

[The Tasmanian]

This is a fun topic, its been bugging me for years.
The first time this happened to me was when my tech informed me if I put a huge (10 RU) Neve power supply on ONLY the audio rails of the quadeight - I would get a much faster slew rate and a much bigger/better sound.
After being told this a few years before, when I had a custom built 3ru powersupply built (over powered) that only powered the stereo mix bus on the quadeight -
The results were gobsmaking !! massive change in the stereo width, huge improvement on frequency response, and a very noticeable tightening up of the bottom end.
So - I said yeah - lets chuck an oversized Neve PS on steriods, that only deals with the audio power requirments.
And again - this difference was outstanding , with the slew rate of the individual line amps and mic pre's/EQs - this console was on fire - so hotrodded in the power department (Power supply's were always was the week link with the these consoles - IE underpowered)
Once my tech left, I tidied up everything to try to get it all a touch more compact and neat. -
I moved the neve power supply about 150mm closer to the console.
The next day I was recording a session and I had massive hum coming through the mix busses to multitrack.
Had to can the session and get the tech back - after may hours of searching - we moved the neve powersupply only 150mm and - bingo - no hum. It was radiating into the solder tracks on the motherboard and bleeding into all 24 mix busses.
So its been on my mind...for years - its nice to hear your great descriptions Rob - really look forward to that article.

[13thbeach]

Here ya go....someone chase this one up.

http://newsblog.projo.com/2008/12/for-sale-old-ru.html

[HA_DA_JA]

Cheap option
http://www.goldmine-elec-products.com/p ... er=G16600A

[Drumstruck]

Hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm