McIntosh MPM4000 Power Meter Review

[HaveMeterWillTravel]

real shame the full quoted price for a full width one would almost be worth it

I actually had one in the trunk of an Acura Legend driving Focal separates and JL Audio subs. Luckily I didn't have to pay retail!

I find it facinating how the electical motor power engeeneers has solved the current measurment problem in a cheap and accurate way for motor control.
Warning: reading this and your head might start to spinn: https://www.ti.com/lit/ug/tiducy7/tiducy7.pdf?ts=1738066318483

It is not only measuring the current. One also needs to know the ~instantaneous phase between it and voltage if one wishes to calculate actual "watts".
btw: I have used TI's INA series of current sense amplifiers in several designs over the years.

I am not even positive how to implement a clipping light or what have you.

I remember back in my sales days NAD and HK had clipping lights (among other I am sure) but never really thought about how the circuit would be.

McIntosh's "Power Guard" works by comparing the time waveform of the output to the input. IIRC, it's effectively around 1% distortion.

If your talking about input limiters, (the only way to prevent amp clipping) thats rare and miss leading.

But relevant to the discussion of McIntosh amplifiers.


Sorry for so many individual posts. I forgot you an quote/reply to more than one post at a time.

 

[Holmz]

View attachment 426153

I actually had one in the trunk of an Acura Legend driving Focal separates and JL Audio subs. Luckily I didn't have to pay retail!
…

I picked up some Mc Intosh amps to put into the truck (ute).
Mostly using them for status points as they look pretty nice.

 

[JimWeir]

This is a review and measurements of the McIntosh MPM4000 Power/dB vintage stereo meter. It is on kind loan from a member and costs used from US $500 to $999.
View attachment 424110
It had come out in 1997, aimed at automotive market so requires 12 volt power. As you can see in this sample though, it can be readily used in home systems with a case and external power supply.

Unlike every other VU meter we have tested so far which are just for show, the MPM4000 is supposed to be calibrated for a 4 ohm speaker. The purpose of the review then is to see if there is an impact on the fidelity and accuracy of its markings.

FYI the sample I have has very dim lighting. I suspect the originals were brighter.

McIntosh MPM4000 Power Meter Measurements
For testing, I configured the Purifi reference amplifier for 1 watt output. Here it is by itself:

View attachment 424111
As we expect, distortion is vanishingly small. Let's now connect the MPM4000 in parallel to left (1) channel:

View attachment 424112

There is no impact whatsoever which is a relief.

Now let's test for accuracy. I measured the above on the meter and it was accurate, subject to optical error. I then jumped to 10 watts and it too was accurate:
View attachment 424113

I then went up to 100 watts and it too was accurate. So mission is accomplished!

Conclusions
We have had many discussions of vintage meters on power amps being accurate (or not) in the context of new versions which clearly are not. I did not know what to expect but was pleasantly surprised to see that not only is it transparent but that it is also accurately showing power output of the amplifier.

The only negative is the astronomical pricing of it. I guess half of that is for the "status" sake.

I am going to recommend the McIntosh MPM4000 power meter if you don't have to tap into kid's college education fund to buy it!
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As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

This is still a voltage meter calibrated to read power across 4Ω

 

[Barry_Sound]

Im waiting for the review of the McIntosh lightbox that only costs 2000 dollars or so.

It's green light. What does it do? It turns green.

 

[Carl-Fosi Audio]

@Fosi Audio
@Douk Audio

Go make a budget version of this! This is what people want. No impact to audio, and calibrated output of power.

Besides the accuracy, you can see the ballistics here.

Just give us some time.

 

[Carl-Fosi Audio]

Not quite. A modern version should have an adjustment that allows you to dial in the nominal load impedance.

Sorry, I dont understand what do you mean about the adjustment? Could you please give me more details?

 

[Carl-Fosi Audio]

It was from 1964 which is even cooler. It used the 3” CRT that was used in real oscilloscopes at the time.

http://www.tubebooks.org/file_downloads/McIntosh/MI3.pdf

A company like @MAMORITAI Audio / @Fosi Audio could release a lot of vintage, mid century modern style luxury audio jewelry.

What made McIntosh great was its reliability and performance (relative to era). With that brand, they can sell based upon looks alone.

We have great audio performance today, but reliability and looks are important. Nothing better than drawing back upon the heritage of vintage classics, the same way there are vintage inspired furniture. Raphaelite has some of the nicest looking HiFi products out of China, so again, you could draw inspiration from McIntosh and it would be hard to go wrong. All of the circuit diagrams and service manuals are well documented as well, with any IP long expired.

It would be nice if you could give me some ideas.

 

[EJ3]

It would be nice if you could give me some ideas.

1 idea:
The MPM4000 active meter circuity allows direct readings of power output from the power amplifier it is connected to.
The meter scales, both wattage and decibels,
are accurately calibrated when there is a four ohm impedance loudspeaker connected to the power amplifier the MPM4000 is monitoring.

That would be a very good thing, I think.

 

[Holmz]

1 idea:
The MPM4000 active meter circuity allows direct readings of power output from the power amplifier it is connected to.
The meter scales, both wattage and decibels,
are accurately calibrated when there is a four ohm impedance loudspeaker connected to the power amplifier the MPM4000 is monitoring.

That would be a very good thing, I think.

Maybe - better than a wild guess I suppose.
But the speaker impedance is generally “all over the shop” .

That said, my meter routinely shows 1/2 W, which is probably about close to being right.

 

[A Surfer]

I can't help but think that really VU meters are unlikely to be very useful even if calibrated. I suspect that they are more eye candy than anything.

 

[Multicore]

Sorry, I dont understand what do you mean about the adjustment? Could you please give me more details?

Of the old McIntosh unit tested in the OP Amir wrote:

Unlike every other VU meter we have tested so far which are just for show, the MPM4000 is supposed to be calibrated for a 4 ohm speaker.

A modern design that does what the old McIntosh does, I would suggest allowing the user to adjust the speaker impedance calibration so that it displays the correct power in Watts for 4 ohm, or 6 ohm speakers or whatever the user has.

 

[Carl-Fosi Audio]

1 idea:
The MPM4000 active meter circuity allows direct readings of power output from the power amplifier it is connected to.
The meter scales, both wattage and decibels,
are accurately calibrated when there is a four ohm impedance loudspeaker connected to the power amplifier the MPM4000 is monitoring.

That would be a very good thing, I think.

So copy MPM4000?

 

[MediumRare]

I can't help but think that really VU meters are unlikely to be very useful even if calibrated. I suspect that they are more eye candy than anything.

I use my Mac meters all the time. Most important is for quick level setting when listening. It’s amazing how often the ear acclimates to loudness and one can’t objectively tell how loud it is playing. Also, when I want to listen very loud (especially highly dynamic music like classical) it’s useful to see when I’m approaching but not hitting clipping. I’ve found there is a sweet spot in my room where modes are under control and the loudness of each track varies, so seeing when the meters move out of that range can clue me to it before my ears can tell. Also helps for troubleshooting etc etc.

 

[Multicore]

I can't help but think that really VU meters are unlikely to be very useful even if calibrated. I suspect that they are more eye candy than anything.

Eye candy is half the game. A lot of people are into gear for the looks. But eye candy married to measurably correct performance, well, that's the best! I don't much care for bouncy needle meters but even I was impressed with the calibration as shown in Amir's photo:

 

[Holmz]

I can't help but think that really VU meters are unlikely to be very useful even if calibrated. I suspect that they are more eye candy than anything.

True - but it is pretty noice to look at.

 

[Sernyl]

I have the Fosi. Only for switching ...and fun.
I'd like to have same sort switcher for my HF rigs & antennas.
(Needles could have different purpose, of course)

 

[A Surfer]

Not saying that I don't love eye candy of all kinds, I certainly do. I wouldn't go out of my way for VU meters though, and if implementing them in typically lower cost gear increased the selling price, I would wonder why.

I absolutely get why premium priced gear should have those extra tasty treats incorporated into their designs, but budget friendly gear? I guess if the price increase was modest why not.

 

[ban25]

Not saying that I don't love eye candy of all kinds, I certainly do. I wouldn't go out of my way for VU meters though, and if implementing them in typically lower cost gear increased the selling price, I would wonder why.

I absolutely get why premium priced gear should have those extra tasty treats incorporated into their designs, but budget friendly gear? I guess if the price increase was modest why not.

If you don't care, why post in the thread?

 

[A Surfer]

If you don't care, why post in the thread?

Bored, free speech. That kind of thing. Plus I do sort of care. I grew up with VU meters. Felt I had the right to contribute in my own way to the discussion.

 

[GXAlan]

So copy MPM4000?

You have to decide the identity of Fosi and the identity of MAMORITAI.

The Toyota Century SUV and Porsche Cayenne Turbo GT are both ~$200K luxury products and both pinnacles of their respective genres, but also different in their clientele. Moving up, you can buy a Rolls Royce or a Ferrari or Lamborghini. All premium products with different.

Think McIntosh vs Accuphase vs Esoteric vs Marantz 10 series in terms of look and feel.

1) The Fosi Audio typography is a bit plain. Perhaps having an artist create a new logo a la KIA motors or even Lexus or Audi would be an interesting option to reduce visual clutter. The musical note logo is nice and you may find that to be a better showcase for Fosi and sufficient badging.

2) If you look at McIntosh and Accuphase, the actual axis of the meter is hidden. Fosi does this with the linear grids, but this looks cleaner to mask it off.

3) The Fosi, going from 100 to 200W reports a +4 dB gain when it really should be +3dB gain, right?

You can compare the McIntosh’s power output which is labeled in orders of magnitude versus Accuphase.

For a speaker level product, it would be nice to have an option of 2/4/6/8 ohm calibration which you could choose. Alternatively, just pick 4 ohms.

For a line level product, it would be nice to voltage be displayed. 4V unbalanced peak and 8V balanced peak.

4) If you can have peak hold capability, that is a nice feature that is on the official McIntosh gear.

5) I don’t think you need speaker switching. People can get the LC30 if they want that and just want pretty lights. This could be wired in parallel, to minimize any impact to the fidelity of the speaker itself.

6) For line level product, you do need passthrough and ensure that it is clean.

7) RGB LEDs may not be necessary since the color gamut tends to be poor. I would pick a warm front lit display like Accuphase if you want to harness the “Fosi Orange” or adopt BMW amber, but I think the McIntosh teal is popular for good reason. Classe and Audio Research do fine with white.

More important than the color would be the ability to choose brightness. off-low-medium-high. Low should be the lowest possible display that doesn’t cause flickering. Imagine watching a movie. High should be visible during daytime.

If you have the evenness of McIntosh meters, you could do off and on only…