McIntosh Transformer causing noise in speakers while disconnected.

[mhardy6647]

Tap the valves with a pencil.

This particular issue is arising in a 100% valve-free context. Pencil tapping's a great diagnostic tool (I usually use a chopstick ) but probably not gonna add much value here.

@ClassG33, another suggestion (very tangential to the topic of this thread but well worth passing along) from the Polk folk -- this isn't meant to be critical, but that equipment stand looks a bit insubstantial for that big momma amplifier. How much does the amp weigh and how sturdy is that "lowboy" shelf?
I will - humbly and with the best of intentions - suggest that you put that amp on a sturdy stand close to the floor.

 

[Doodski]

So moving the speakers away from the amp lowered the floor noise (noise period)?

Moving the amp to the speakers means the speakers make the sound.
Moving the amp away from the speakers stops the sound coming from the speakers.

This is where things get very strange.
The amplifier is not connected to the speakers with any speaker wire.
The sound from the speakers is coming from the McIntosh SS amp but that is without a wired connection from the amp to the speakers.
I was of the idea that mutual induction between the amp and the speakers is occurring but @Zapper a very experienced electronics engineer advised that this is not possible @ 60 Hz to have energy transfer across the large air gap between the amp and the speakers.
The hypothesis he stated is that there is some sort of high frequency RF fundamental required for energy to be transferred from the McIntosh amp to the speakers.
Then... Another hypothesis introduced into the commentary is that there is a DC voltage current coming from the wall outlet AC mains that develops a electromagnetic field around the toroidal transformer in the McIntosh amp and that enables the power transfer between the McIntosh and the speakers with no speaker wired connecting them.
The plot thickens majorly and it just gets more interesting all the time.

 

[Golf]

I have moved the speakers but haven't taken the amp off the cabinet. I can carry the center speaker in my hands, and it will produce this sound as I hold it within range of the amp. I've slid the tower speakers closer to the cabinet, and they begin to make the noise as well, again 100% disconnected.

So what about this?

• Keep the towers at a location near the amp, so that they do the hum also.
• Then, (switch off the amp and) connect the center speaker to the amp.
• Switch the amp back on and check if the towers are still humming.
• Turn up the amp’s volume a bit (without any fed signal) and check if the towers are still humming.

 

[Doodski]

@restorer-john I want to bring this thread to your attention because it is a unique issue. I am very interested to read your ideas and opinion regarding this thread. It starts out pretty simple, then gets a little technical and then really gets hypothetical. I think you will enjoy this thread. Let us know what you think.

 

[Golf]

Maybe I missed a statement from @ClassG33 regarding this. Are the devices involved fresh purchased McIntosh/B&W products or are they second hand?

 

[radix]

In regards to the proximity of the amp to a speaker, like @OldHvyMec, I have a SS Mac amp (MC2205, 200 wpc, 85lb) about 3" from an L100. Zero issue with induced noise on the speaker. Though I've never tried it without the speakers hooked up.

I'm sure McIntosh service will be very happy to help the OP and resolve the problem.

 

[Kal Rubinson]

tagging @amirm and @restorer-john @John Atkinson @Kal Rubinson and @SIY in case they have not seen this thread.

OP has a B&W center channel with zero wires connected to it. When he moves it close to his McIntosh amp, there is enough induction from presumably a magnetic field to induce the voice coils of the speakers to move, generating audible buzz… and he has the videos to prove it.

Has *anyone* ever seen/heard this?

News to me. Can I assume that the Mac is powered up? How close is close?

 

[GXAlan]

I haven't read all the pages of posts but I can say 1) that amp shouldn't be turned on without speakers connected to it 2) the amp probably needs to be serviced. If its generating enough magnetic noise to be picked up by a speaker driver it's probably not healthy for you to be near it.

I would add #1 is part of the troubleshooting. It happens when connected or not connected.

News to me. Can I assume that the Mac is powered up? How close is close?

There's a cellphone video on the 2nd or 3rd page. Yes. Once the Mac is powered up, it happens.

Close is adjacent. Copy/pasted the pic here.

Not unreasonable from the standpoint of wanting to see the meters, and not a "common" position to be that close, but not unreasonable given the layout.

But this happens with or without the speaker connected. If it only happens when the speaker is NOT connected, you might say that once you connect it, the amp itself dampens movements.

In this very specific case, though, this makes me think of all those scenarios like power conditioning, cable lifters, and what is often voodoo might be some perfect storm of environmental electrical noise.

 

[OldHvyMec]

I know there is huge desire (hope is a better word) that some weird thing will fix it. But there is a point you know
the power amp has a problem. Because no one has had it happen and MANY people have Mac/B&M combos
its got to be the amp if every speaker in that room will act that way. Did they have an MRI machine that went
haywire above your apartment? Is Tesla in the building? Did Magneto escape or did they ever catch the guy?
Is floor 13 missing on the elevator selection but actually there?

Are you on drugs or worse not on drugs making this up, humming in the background? LOL Is your partner
messing with you. Mine will move a speaker just to mess with me. I'm wondering?

All kidding aside, the amp? Get anything, anywhere and see if it goes away, a stereo amp will work fine.
I've know of at least 6-8 mac amps failing more than 1/2 were vintage valve, 3 or 4 were SS.

I've actually seen more drops or shipping stuff than anything. Glass mainly but the corner drop and tweak
is common because of weight. Freight only for me. If its' 5K or more, strap it to a pallet I don't care if it's
5 lbs. It's safer. All my newer Mac gear was sent by pallet double boxed, labeled as GLASS, Handle with care!

Good luck, NC500oems are pretty amazing, and amazingly inexpensive. 2k or less for 3 channels and a
great backup amp or bi-amp once the old Mac is up and running.They are like TT one is never enough.
I'm not sure you can have to many, maybe.

Regards

 

[restorer-john]

@restorer-john I want to bring this thread to your attention because it is a unique issue. I am very interested to read your ideas and opinion regarding this thread. It starts out pretty simple, then gets a little technical and then really gets hypothetical. I think you will enjoy this thread. Let us know what you think.

Observations:

They're mobile phone microphones, recording a bass-challenged centre speaker, so the fundamental (60Hz) would be hardly audible. We are likely mostly hearing the 120Hz and other harmonics.

The power transformer is a large toroidal, likely mounted vertically in that cover/case, which is unusual may be a factor.

If it's audible on the centre speaker drivers, it's measureable. Put your DMM on AC and hook it to the centre speaker LF terminals on the back of the speaker. Bring it close to the amp.

Edit: I've reproduced this phenomenon and solved the mystery!

Standby for pictures.

 

[Doodski]

Edit: I've reproduced this phenomenon and solved the mystery!

Standby for pictures.

I'm in a holding pattern!

 

[GXAlan]

Edit: I've reproduced this phenomenon and solved the mystery!

Standby for pictures.

@amirm when this is done, this needs to be front page discussion! This is science applied to audiophile voodoo.

 

[Doodski]

@amirm when this is done, this needs to be front page discussion! This is science applied to audiophile voodoo.

Please do not do that. I am embarrassed at some things in this thread. sigh* LoL.

 

[Doodski]

If it's audible on the centre speaker drivers, it's measureable. Put your DMM on AC and hook it to the centre speaker LF terminals on the back of the speaker. Bring it close to the amp.

I don't suppose you have a very high input impedance spectrum analyzer to view that stuff do you? That would be amazing.

 

[restorer-john]

What you'll need:

• Decent size vertically mounted toroidal transformer with attached power supply, preferably CT split rail (not nnecessary but I wanted a rectifier, duals caps etc). I had a Definitive Technologies subwoofer I bought for parts with such a bracket. Still on the plate amp.

• A random centre speaker, but decent. The OP's is an expensive B&W. (Preferably with a reasonable crossover, particularly for the bass/mids/treble- this is an important clue)

• A DMM and a couple of leads. (that is not a reading BTW)

• A random woofer inductor and a few random electrolytic/film caps maybe

• Optional: audio analyzer to look at the spectrum.

Basically, we have inductive coupling from the giant McIntosh toroidal to inductors in the loudspeaker crossovers, which will be 2nd order networks or higher. The other thing with expensive speakers, is they of contain large and high quality inductors of all different values in various configurations. Plenty end up across the drivers themselves or in series with resistors in parallel configs.

I'd say the McIntosh toroidal is mounted with it's internal bracket mounting-bolt facing horizontally to the left of the amplifier. The random toroidal I have here is only about a ~300W unit and virtually unloaded, so the huge McIntosh, idling 5 channels and all the other circuitry will have a much greater effect at a greater distance.

I can't make videos/recordings with sound right now as we have gale force winds drowning out my 'hum' (and making me really angry), but it's quite audible in the centre speaker with a small woofer inductor acting as a pickup coil at 7" away from the barely loaded transformer.

I'll get a few recordings when this wind dies down.

 

[GXAlan]

Basically, we have inductive coupling from the giant McIntosh toroidal to inductors in the loudspeaker crossovers, which will be 2nd order networks or higher. The other thing with expensive speakers, is they of contain large and high quality inductors of all different values in various configurations. Plenty end up across the drivers themselves or in series with resistors in parallel configs.

When we talk about bi-wiring (not bi-amping) and all this talk about back EMF, etc. -- one consideration is that once you actually connect the speaker to the binding posts, the back EMF effect is lower. That's audiophile handwaving. Is there a difference? Or is it different since the inductive coupling is at the crossover level instead of the voice coil level?

Since "shielded" speakers only shielded the drivers and not the crossovers, they would be subject to this as well?

The other thought is that it's not only the toroidal transformer, but the crossover board, right? Because if the inductors are oriented in a different way inside the center channel (or you had a LCR which works vertical or horizontal...)?

 

[Doodski]

What you'll need:

• Decent size vertically mounted toroidal transformer with attached power supply, preferably CT split rail. I had a Definitve Technologies subwoofer I bought for parts with such a bracket. Still on the plate amp.

View attachment 358037

• A random centre speaker, but decent quality like the OP's. (Preferably with a reasonable crossover, particularly for the bass/mids/treble- this is an important clue)

View attachment 358038

View attachment 358039

• A DMM and a couple of leads. (that is not a reading BTW)

View attachment 358040

• A random woofer inductor and a few random electrolytic/film caps maybe

View attachment 358041

• Optional: audio analyzer to look at the spectrum.

Basically, we have inductive coupling from the giant McIntosh toroidal to inductors in the loudspeaker crossovers, which will be 2nd order networks or higher. The other thing with expensive speakers, is they of contain large and high quality inductors of all different values in various configurations. Plenty end up across the drivers themselves or in series with resistors in parallel configs.

I'd say the McIntosh toroidal is mounted with it's internal bracket mounting-bolt facing horizontally to the left of the amplifier. The random toroidal I have here is only about a ~300W unit and virtually unloaded, so the huge McIntosh, idling 5 channels and all the other circuitry will have a much greater effect at a greater distance.

I can't make videos/recordings with sound right now as we have gale force winds drowning out my 'hum' (and making me really angry), but it's quite audible in the centre speaker with a small woofer inductor acting as a pickup coil at 7" away from the barely loaded transformer.

I'll get a few recordings when this wind dies down.

So... The 60 Hz or 120 Hz has enough energy to jump the air gap. I like this very much.
I have a question regarding the fundamental frequency.
Is it 60 Hz or 120 Hz?
It seems to me that the massive capacitance value smoothing caps after the bridge will prevent 120 Hz from being the fundamental and any induction must come from both the combined energy of the primary and the secondary inductors which are @ 60 Hz.
Does a power OFF with discharge @ the McIntosh toroidal and then a power ON create a high current surge resulting in a high instantaneous peak of electromagnetic energy to the speaker creating a higher peak sound output?

This does not explain the 40 Hz fundamental that was measured by @mhardy6647.
That is still up for debate as is the 120 Hz fundamental indicated by @Golf's software analysis.

 

[Doodski]

I can't make videos/recordings with sound right now as we have gale force winds drowning out my 'hum' (and making me really angry)

I'll get a few recordings when this wind dies down.

I live in The Great White North renowned for extremes of weather and yet your weather is way nastier and regularly pesky. Plus you have toxic reptiles and bugZ! I like it where I am...

 

[Doodski]

talk about bi-wiring (not bi-amping) and all this talk about back EMF

the back EMF effect is lower

The back pressure per say is reflected back to the amp as a load resistance varied by the inductive reactance and capacitive reactance of the load (Z load @ speaker). The combination of the output impedance (Z output @ amplifier) and the load impedance creates a voltage divider that makes the frequency response non linear.

That's audiophile handwaving. Is there a difference? Or is it different since the inductive coupling is at the crossover level instead of the voice coil level?

The second question is answered with, the inductive energy transfer is occurring all through the speaker to varying degrees dependent on the shape of the electromagnetic field around the toroidal transformer @ the McIntosh amp. The entire wiring assembly of the speaker is saturated with electromagnetic energy and the saturation of everything causes the energy transfer to occur.

 

[DanielT]

Exciting this.

It's just a matter of trying to find the source. Mix more speakers into the whole thing and experiment with them. Preferably one more amp. Experiment with different combinations. Move the stuff around physically and see what happens, change rooms, change houses and test. All to see when the phenomenon occurs.
Is the same sound heard with headphones?If you put a powered off tablet tablet/laptop on your amp, do you hear the sound from your tablet's speaker?...And so on. There are lots of different things that the OP can try.

See if you can record how loud it sounds and at what frequency or frequencies the phenomenon occurs.

Edit
Note. I change my mind DO NOT put a tablet /laptop on the amplifier. Who knows what could happen then.