McIntosh Transformer causing noise in speakers while disconnected.

[Zapper]

am convinced it is a distorted 60 Hz waveform

I agree, that's the sound coming from the speakers. But is it what the EM field is? It could also be a higher frequency AM modulated at 60Hz and harmonics.

Speakers usually have multiple current loops through the crossovers, with large air core inductors that can turn AC EM fields into AC current. So there is a mechanism to convert EM field to sound with no wires attached. It would take a very strong field however.

 

[JustJones]

 

[mhardy6647]

Can you run an FFT on that? The spectral information would be useful to us and to McIntosh.

I'd like to think so... gimme a minute.

 

[ClassG33]

I agree, that's the sound coming from the speakers. But is it what the EM field is? It could also be a higher frequency AM modulated at 60Hz and harmonics.

Speakers usually have multiple current loops through the crossovers, with large air core inductors that can turn AC EM fields into AC current. So there is a mechanism to convert EM field to sound with no wires attached. It would take a very strong field however.

You nailed it. This is my ascertation as well, which is why my first question was "what am i dealing with scientifically"? The Tweeter is also affected, and produces its own noise, so that makes sense.
It's basically like a Microphone: takes the sound of your voice into a magnetic coil and converting it into an electromagnetic signal - except this is working on the opposite direction where the electromagnetic field is a particular multiple of harmonics, picked up through the air by the speaker crossovers, and outputs the harmonic associated with each driver's crossover....

When I say it like that, this makes me strongly feel like the amp should NOT be producing such an EM Field. My speakers are not the least efficient, but they are certainly not all that sensitive..

 

[mhardy6647]

SMPS? PWM?

Switch-mode power supply and pulse-width modulation. (EDIT: oops, @Doodski had you covered!)
The former is a way to make high-efficiency power supplies, rather than simple, brute force "linear" power supplies that transform (change the voltage), rectify (convert to DC), then filter the 60 Hz (or 50 Hz, depending on where one lives) AC from the wall outlet to get DC.

PWM is a high-efficiency way to (among other uses) amplify AC signals (such as music waveforms). For audio amplification, it's known as "Class D".

 

[Doodski]

PWM is a high-efficiency way to (among other uses) amplify AC signals (such as music waveforms). For audio amplification, it's known as "Class D".

In the case of a switch mode power supply the controller IC for the switch mode power supply by using feedback and timing components (Resister and cap etc.) in the peripheral circuitry of the IC outputs a pulse width modulation of a varying frequency square wave that switches the power FETs that control the primary of the step up transformer. So PWM is used for class D and switch mode power supply operation.

 

[JustJones]

I assume you bought this new. I'd send it back informing them of the problem. Looks like toroidal and McIntosh autoformers in the power supply. This amp is made for AV installation

Edit: it's class A/B amp.

 

[ClassG33]

In the case of a switch mode power supply the controller IC for the switch mode power supply by using feedback and timing components (Resister and cap etc.) in the peripheral circuitry of the IC outputs a pulse width modulation of a varying frequency square wave that switches the power FETs that control the primary of the step up transformer. So PWM is used for class D and switch mode power supply operation.

Mcintosh does not say specifically but they call it a Switching Amplifier. So it would either be Class A/B or Class G.

 

[ClassG33]

I assume you bought this new. I'd send it back informing them of the problem. Looks like toroidal and McIntosh autoformers in the power supply. This amp is made for AV installation.

Brand new.

There is no autoformer on this amp though!

 

[mhardy6647]

mmm... I'm a babe in the woods vis-a-vis doing meaningful spectral analysis with Audacity.
Does this help any? Sorry!

 

[mhardy6647]

There is no autoformer on this amp though!

That's why you can move it without an engine hoist!


There's an old MC-2100 in my basement. Gravitational potential energy is why it stays down there.

 

[Doodski]

mmm... I'm a babe in the woods vis-a-vis doing meaningful spectral analysis with Audacity.
Does this help any? Sorry!
View attachment 357724

Can you zoom in for more resolution of the waveform timing details. What we need is the time interval for a complete 360 degrees of the distorted sinusoidal waveform and that time duration will give us the frequency.... 1/T = F

 

[mhardy6647]

The sound of that sample reminds me of an AC "vibrator" type motor -- like an old electric razor or hair clippers.

 

[Sokel]

mmm... I'm a babe in the woods vis-a-vis doing meaningful spectral analysis with Audacity.
Does this help any? Sorry!
View attachment 357724

Why do I get a different one?

(that's after the 25 sec where the buzz is audible)

 

[JustJones]

Brand new.

There is no autoformer on this amp though!

Aren't the photos from the manual showing in my previous post. Those 6 big things are the autoformers

 

[ClassG33]

Aren't the photos from the manual showing in my previous post. Those 6 big things are the autoformers

It's just the capacitors.

 

[JustJones]

It's just the capacitors.

Sorry you're correct this uses toroidal transformers

 

[ClassG33]

Can you zoom in for more resolution of the waveform timing details. What we need is the time interval for a complete 360 degrees of the distorted sinusoidal waveform and that time duration will give us the frequency.... 1/T = F

Let me take a better sample with less noise from my movements. Give me an hour or two and I'll report back with a clean sample.

 

[Doodski]

It's just the capacitors.

That and for autoformers to emit a massive EM field they need lotsa current and that means the audio amp section would be amplifying in a big way at the unity gain stage and that would mean connecting the amp to speakers would be catastrophic. As @ClassG33 operated the amp successfully that means the unity gain stage is not conducting en mass unless a audio signal is present.

 

[mhardy6647]

Can you zoom in for more resolution of the waveform timing details. What we need is the time interval for a complete 360 degrees of the distorted sinusoidal waveform and that time duration will give us the frequency.... 1/T = F

That I can do.