RM-9 Mechanical noise

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kmanusa

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RM-9 Mechanical noise
« on: 28 Nov 2008, 06:51 pm »
Hi all, I am new here.  I just bought an RM-9 amp from a local guy here in Virginia. It is in decent shape.  I am using it to drive the mid/high section of a vintage Infinity RS-4.5 loudspeaker.  Crossing over at 200 Hz and matching the level of the RM-9 to that of my bass amp (a McIntosh MC7270) using a Bryston 10B crossover, I have managed to achieve a nice sound with this system. 

One question I have about the RM-9: it appears to have quite a bit of mechanical noise which sounds like it is coming from the power transformer.  There is virtually no hum or noise coming through the speakers, I have verified that.  I am wondering if this is a common issue with the RM-9 and whether anyone has insight into how I can eliminate or reduce the mechanical noise short of replacing the power transformer.

K.C.

  • Jr. Member
  • Posts: 68
Re: RM-9 Mechanical noise
« Reply #1 on: 29 Nov 2008, 06:01 am »
Mechanical noise ?

Maybe the transformer is oscillating ?

My RM-9 doesn't do that but I have an RM-10 that does if I push it hard.

Is the amp on an appropriate stand to isolate it ?


kmanusa

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  • Posts: 40
Re: RM-9 Mechanical noise
« Reply #2 on: 29 Nov 2008, 11:38 am »
Mechanical noise ?

Maybe the transformer is oscillating ?

My RM-9 doesn't do that but I have an RM-10 that does if I push it hard.

Is the amp on an appropriate stand to isolate it ?



Hi, I believe the power transformer may have a loose winding.  This sometimes happens to vintage gear-- over time a winding gets loose and begins to vibrate at the line frequency.  I can hear it at the listening position on the other side of the room so it is a bit annoying.  The noise is there at turn-on and as far as I can tell, it remains at a constant level whether music is playing through the amp or not.  I have tried to tighten the bolts that attach the power transformer to the top plate of the amp but it did not make a difference.  The amp sits on top of a large, very heavy wooden record cabinet.

K.C.

  • Jr. Member
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Re: RM-9 Mechanical noise
« Reply #3 on: 30 Nov 2008, 03:57 am »
Roger shows up here every couple of weeks so you'll eventually get a reply. Your assumption certainly sounds plausible.

rbwalt

Re: RM-9 Mechanical noise
« Reply #4 on: 30 Nov 2008, 03:39 pm »
Kmanusa i to had a RM9MkII that used to hum also from the transformers. it is nothing to worry about and does not affect the sound. i now have a RM9SE and it is as quiet as a mouse. where in virginia are you? i am in the Sterling, Potomac Falls area.

rob W.

oh by the way roger winds his transformers himself.

bullwnkl999

  • Jr. Member
  • Posts: 10
Re: RM-9 Mechanical noise
« Reply #5 on: 2 Dec 2008, 04:01 am »
One possible cause - if you get any direct current on the circuit, it may cause the transformers to "hum," or "buzz" if you prefer.  My RM-200 had a fairly audible intermittent hum.  Like you, it was a noise from the transformers themselves, and not anything you could hear through the speakers - they were dead silent.  Not a hum, hiss, or noise of any kind.    I finally isolated the cause to a lamp with a dimmer on it, which in one setting would make the transformer hum, and in another it didn't.  The lamp wasn't even in the same room, but was on the same circuit.  I moved it off the circuit and cured the problem.

Unplug EVERYTHING on the circuit except the amp, and see if you still get the hum.  Then you can add your other electronics one at a time and see when (if) it reappears and you have your culprit.  Someone else on the forum may have an easier way to find DC on the line ???  Any DC on the circuit will cause most toroid transformers to hum like crazy...

Good luck!

Mark

P.S.  Roger may at one point have wound all his transformers himself, but no more.  You pay a premium for that, I think about $1K.  I've never heard them, but am considering the option for my RM-200, unless I decide to bi-amp (which is more likely) my high efficiency speakers.
« Last Edit: 2 Dec 2008, 09:13 am by bullwnkl999 »

kmanusa

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Re: RM-9 Mechanical noise
« Reply #6 on: 2 Dec 2008, 01:08 pm »
Thanks Mark, I am aware of this behavior and have investigated possible causes.  I have dimmers in the house but not on the same circuit.  At any rate they are of the type that you can switch off and out of the circuit when the light is not being used.  Apparently it is possible for motors and other kinds of equipment to affect the amount of DC offset on the line too, even if they are not on the particular circuit you are using for the amp.  I'll have to shut-off all the breakers in the house except to the circuit the amp plugs into to determine if this is the cause.

I did speak with Music Reference (I believe it was Roger) yesterday by phone about this.  It turns out my RM-9 is one of the very oldest and in his estimation, it is likely that the transformer is just probably getting noisy due to age (over 23 years old).  A replacement is the only cure but they are expensive and will probably require shipping back to MR to do the work.  I decided to think it over since the amp otherwise works fine.  I think I will try to find a spot in the room for the amp where the noise doesn't carry as well and leave it at that!

Roger A. Modjeski

Re: RM-9 Mechanical noise
« Reply #7 on: 12 Dec 2008, 06:56 am »
I have developed a new way to make power transformers that makes them dead quiet and will stay that way.

Check the price list to see what I am up to with the RM-200 MK II-T transformer upgrade. They all have transformers wound by myself with these new techniques. The output transformers are better than ever and I have extended their response out to 100 KHz if I wind them.

Here's the current list and prices.  http://ramlabs-musicreference.com/pricelist.html