McIntosh Transformer causing noise in speakers while disconnected.

[Doodski]

Your local mains frequency is 50 Hz? Would be interesting to see any difference based on the fact that ClassG33’s is 60 Hz, I believe.

This... Is a very interesting part. To see what the crossovers and whatever do to the AC mains frequency.

 

[Brian Hall]

This... Is a very interesting part. To see what the crossovers and whatever do to the AC mains frequency.

This is like binge watching a series on NetFlix and finding out the last episode has not been released yet.

 

[Blumlein 88]

Sometimes with big toroids they use a copper or steel flux band. It fits around the toroid, is not directly connected to it. This had to have continuity all the way around. I wonder if this amp has one which is soldered or connects at some junction and that junction has broken loose or was not made when it was manufactured. I think I'd contact McIntosh first. Otherwise you need something to contract/give a lower reluctance path for the magnetic field. Mu Metal is optimum, but just mild steel might work. If you could get a sheet of steel, or iron it might reduce the size of the field. Just slide it underneath the amp and see if you can get closer to the amp without the noise from one of your speakers carried to and fro. Maybe even a large cast iron skillet under it just for a test. Most cooking pans are aluminum and wouldn't work very well. They'll work to stop an electrical field if grounded, but not magnetic.

Also toroids don't usually have a big field, that is one reason to use them. They will spew harmonics if they are being used close to saturation however and throw quite a field that way up into harmonics of the power line frequency. I'm pretty sure McIntosh wouldn't release such a design unless there is some issue with your particular amp. Maybe an error in the winding when it was made.

A mounting issue could be the problem. Here is an example of improper mounting. This would be okay if the upper mounting bracket were insulated from the chassis. Perhaps your amp has some non-metal washers or insulators that were left out or have shifted allowing continuity where there should be none. That likely would cause increased fields and harmonics in the field.

 

[mhardy6647]

The other interesting thing to consider is the induced signal in the speaker from the Mac's transformer could be very partially fed back to the input via the NFB loop and it could be modulated somewhat, depending on the fluctuations in the field due to currents flowing in all the channels whilst playing robust content.

I don't blame the McIntosh at all and it's not faulty IMO. Plenty of amplifiers have stray radiated fields from large transformers. Back in the vinyl and tape deck days, much time and effort was spent by me and millions of other audiophiles, carefully arranging HiFi components to ensure their transformers didn't induce noises in EQs, cassette decks and turntables. Knowing where the transformers were and moving things from right to left in cabinets, spacing and order of stacking was extremely important. But to get it in a unconnected loudspeaker is pretty awesome in my book.

You should simply move the amplifier to the other side of the cabinet, that will cut down the noise significantly I would expect, as the TXF is further away from the speaker and its internals (depending on where the inductors are inside), or preferably into its own cabinet or stand. You bought a beast of an amp and its letting you know that. I think you should also reach out to McIntosh service department and relate your experience- see what they have to say.

I remember once, years ago putting a loudspeaker on top of an amplifier I was testing and heard what I thought was a buzz in the unconnected speaker. I blamed the magnet assembly and the top panel of the amp and promptly forgot about it. I'll bet it was the same thing, but I dismissed it at the time as "impossible".

I've definitely had sensitive headphones that have picked up radiated mains and the concept is the same- but they were terminated.

Your experience, @ClassG33, encouraged me to investigate and work out just WTF was happening in your case.

If anyone wants some analyzer FFTs of the induced mains in the centre speaker drivers, from the toroidal in my pics I can do that in the morning? It is just a proof of concept that it could happen and be audible, not indicative of the OP's actual severity.

Sorry to get all internet-y... but this, times 10^6.

 

[restorer-john]

What is the input impedance of your spectrum analyzer? Just curious.

The QA-403 I'm using now for audio spectrum analysis, is 100kOhm- single ended, 200kOhm differential. It can do up to 384k FS for the A/D (~180kHz BW).

 

[OldHvyMec]

I'm pretty sure McIntosh wouldn't release such a design unless there is some issue with your particular amp.

This is the answer, just send it in. Mcintosh amps do not do this normally and I've seen and owned a lot bigger amps from Mac
than this one. 4 MC1.2 and 2 MC611 all sided by side. Quiet as a mouse, running 3 bi-amped speaker and a TT as a primary.
Streaming was an afterthought.

Macs don't make noise, cabling and broken equipment does.
BTW I have a MC225 that has all but one original 12AX7 tellie and NOTHING has been touched. Is is combined with a rebuilt
Samra C20. It is as quiet as my Nords idling with the same speakers. They are not a noisy amp at all.

MX110z, Mc225, Mc240, Mc275; One of two sets. I sold one set in 2022. They don't make noise, but they
sure sound good. Infinity RS4b, wonderful combo with any of those amps.

May your Amp be healed by the Amp Gods. McPassZilla (Like Zeus)

Regards

 

[Doodski]

The QA-403 I'm using now for audio spectrum analysis, is 100kOhm- single ended, 200kOhm differential. It can do up to 384k FS for the A/D (~180kHz BW).

View attachment 358418

Thannk you @restorer-john.
Veryyy Nice! For those that geek out on metering gear here are some details about it.

QuantAsylum QA403 Audio Analyzer​

QA403 Audio Analyzer

29-Mar-2024: The QA403 is back in stock and orders can be placed, but fulfilling orders may take up to 5-10 days. Elektor and Saelig should have stock next week. 26-Feb-2024: The QA403 is sold out until the end of March. We'll resume orders in the middle middle of March once the delivery date...

quantasylum.com

 

[radix]

Guess I don't know haha!

I guess my goal here is to determine if this is indeed a problem - I am gathering that it's 95% sure to be a problem, based on experience from other people much more intelligent then me, plus the fact that I have listened to, setup and worked on many systems with McIntosh amps of even higher toroidal power (MC611, MC462), tube amps like the 275, ma352/252, etc.that have easily been within a foot of other B&W speakers, and do not have this issue. Also other brands with powerful toroidal amps, and never had the issue.
I consider the possibility of "maybe I just didn't notice at the time?" However this is too loud not to notice.

I have had this setup with an Arcam AVR20 which is toroidal, albeit lower power...

Did you ever call McIntosh support to see what they say?

 

[peng]

Sorry you're correct this uses toroidal transformers

That's not relevant, it can have toroidal transformers for power supplies and can still have autoformers for output impedance matching, though in this case the OP said there were no autoformers used in this amp.

 

[peng]

So it is normal for the amp to create a brief noise within itself?

The brief surge is coming straight from the amp itself, not the nearby speakers. It is less then 1 second, then is silent. The tone SPL from the speaker is constant from the moment it picks it up.

It is normal, for a short duration only, could be as long as 100 ms, though normally shorter. This amp has inrush current limiter anyway so it really wouldn't make much of a noise even for that short duration.

 

[RayDunzl]

I didn't see anyone take the MP4 into Audacity, clip out the extraneous noise, save as WAV, and drag into an REW RTA.

Gives a clearer picture of the buzz

 

[Doodski]

It is normal, for a short duration only, could be as long as 100 ms, though normally shorter. This amp has inrush current limiter anyway so it really wouldn't make much of a noise even for that short duration.

Hi @peng. How do you know it has a inrush current limiter. What is used to make a inrush current limiter?

 

[peng]

@DavidShe . How would I go about that? Sounds risky lol

No risk at all, as the speakers are not powered, and are no connected to the amp so no risk to the amp either. If the terminals are shorted, the noise should be reduced, it won't solve anything, just confirming something we already know.

 

[radix]

Hi @peng. How do you know it has a inrush current limiter. What is used to make a inrush current limiter?

It's in the 255 manual. Someone posted that earllier, but here's the figure again.

There's the manual

 

[peng]

Has the OP contacted Mc about the issue yet? I am sure they have a better idea about what's going on, than what we have been speculating.

 

[Doodski]

It's in the 255 manual. Someone posted that earllier, but here's the figure again.

View attachment 358470

There's the manual

OK. Thank you very much. Is a inrush current limiter a single component or a assembly of components making a circuit. I'm very curious because this device has such a high capability for inrush.

 

[peng]

OK. Thank you very much. Is a inrush current limiter a single component or a assembly of components making a circuit. I'm very curious because this device has such a high capability for inrush.

No idea how it's done, can't tell by just the block diagram. As always, there are different ways.

 

[EDMoser]

I just disconnected a bookshelf speaker here in the music room and put it right on the transformer of a QSC GX5 power amp, and sure enough I can hear a very faint buzzing sound from the woofer. The buzz is very faint and is gone completely moving the speaker just a few inches from the transformer.

 

[peng]

I'm very curious because this device has such a high capability for inrush.

Not really that high, the amp is rated 200 WX5 and the power requirement is only 120 V at 10 A.
Assuming McIntosh would take a very conservative approach in their specifications, I would guess the transformer would probably be around 1200 to 1,500 VA inrush current could be as high as 60 times for such toroidals, though more likely to be between 10-20 times rated current.

Bottom line, it won't be worse than the likes of Parasound A31, 51, or comparable ATI, Outlaw, Anthem, Bryston, Monolith class AB amps.

 

[ClassG33]

This is the answer, just send it in. Mcintosh amps do not do this normally and I've seen and owned a lot bigger amps from Mac
than this one. 4 MC1.2 and 2 MC611 all sided by side. Quiet as a mouse, running 3 bi-amped speaker and a TT as a primary.
Streaming was an afterthought.

Macs don't make noise, cabling and broken equipment does.
BTW I have a MC225 that has all but one original 12AX7 tellie and NOTHING has been touched combined
and with a rebuilt Samra C20. It is as quiet as my Nords idling with the same speakers. They are not a noisy
amp at all.

MX110z, Mc225, Mc240, Mc275; One of two sets. I sold one set in 2022. They don't make noise, but they
sure sound good. Infinity RS4b, wonderful combo with any of those amps.

May your Amp be healed by the Amp Gods. McPassZilla (Like Zeus)

Regards

If you have the same thing, and do not have this issue, that is telling.