McIntosh MI254 Power Amplifier Teardown

[Chrispy]

Some of our amplifiers, and the professional amplifiers in particular, use fans which are thermally controlled. Most of our amps don't use fans. We are known for large heatsinks and beefy construction.

Autotransformers vs conventional is really apples to oranges. No particular shortfalls in either approach.

That was my general impression of a class d heat situation, thanks. On the autoformers, or autotransformers (not sure if there's a difference in McIntosh's use?), thanks, but why would there be an advantage or not using one? Does your company actually employ them in some designs? Just curious in a general sense.....

 

[Doodski]

If you look hard at the picture, that capacitor likely has a dent in the can and that is making the sleeve print look as poor as it does. (the same effect is seen over the base-crimp on the same cap) Combined with low lighting and low resolution, the cap looks like a dodgy fake. I don't think it is.

Now that I think about it I've seen a bunch of Sony ES units and the caps inside where perfect. Straight text/shrink wrap, mounted square to the PCB and all aligned perfectly with the adjacent components. I'm surprised to see this sloppy stuff in a McIntosh.

 

[Chrispy]

Now that I think about it I've seen a bunch of Sony ES units and the caps inside where perfect. Straight text/shrink wrap, mounted square to the PCB and all aligned perfectly with the adjacent components. I'm surprised to see this sloppy stuff in a McIntosh.

Maybe if they measured equally despite appearance and came with a discount? Trying to be optimistic

 

[Doodski]

Maybe if they measured equally despite appearance and came with a discount? Trying to be optimistic

A discount might actually be in order. Considering the global market $ for capacitors I would think they would be a bit more competitive and assemble the things better. Global Capacitors Market to Reach US$23.5 Billion by the Year 2027. Amid the COVID-19 crisis, the global market for Capacitors estimated at US$18.8 Billion in the year 2020. That's big big business and I imagine competitive too and so why are we getting some of the crap we are getting...

 

[MakeMineVinyl]

That was my general impression of a class d heat situation, thanks. On the autoformers, or autotransformers (not sure if there's a difference in McIntosh's use?), thanks, but why would there be an advantage or not using one? Does your company actually employ them in some designs? Just curious in a general sense.....

I believe the only company that really uses auto transformers in most of their designs is Macintosh. They have a legacy in tube power amplifiers and their transformers are renowned for their quality. So it's natural that they would use them in their solid state designs. Personally I don't think there's a need to use them because they don't really buy you anything but that's just me. They also add a lot of weight.

 

[CinDyment]

If you look hard at the picture, that capacitor likely has a dent in the can and that is making the sleeve print look as poor as it does. (the same effect is seen over the base-crimp on the same cap) Combined with low lighting and low resolution, the cap looks like a dodgy fake. I don't think it is.

Its not the indent in the can, it is how diffuse it is with the n at the end almost smeared like they are printing whatever you want at the end of the line. I have never seen that in a genuine Nichicon cap. Fake Rubycon yes.

The MFG is being done in China. I wonder who is doing the MFG.

 

[WestSideWarrior]

It would be amazing if you were kind enough to allow Amir to put the amplifier on the test bench. It is an Ncore based product, so it should be pretty good, but other companies (NAD with Purifi) have managed to provide worse results than baseline amps, so...

From this amp, we could also get an idea about the 7 channel MI347, which I think is basically the same thing in its higher power 3 main channels.

I would love to send it to Amir for measurements, but shipping is potentially risky and prohibitively expensive as I'm not residing in North America.

Another question in regards to heat: will it need fans when rack-mounted with other components?

I have the unit in an enclosed cabinet and it does get slightly warm (around 40C on the back area w/o vent grills) during extended movie sessions, but for peace of mind, I decided to put a small laptop cooler on top for extra ventilation.

 

[Doodski]

Its not the indent in the can, it is how diffuse it is with the n at the end almost smeared like they are printing whatever you want at the end of the line. I have never seen that in a genuine Nichicon cap. Fake Rubycon yes.

The MFG is being done in China. I wonder who is doing the MFG.

View attachment 194099

One would think if manufacturing technology can make and then shrink on a complete label like these kitchen cleaner bottles that a simple capacitor shrink wrap would be as perfect too. The size/proportion and container shape variation is pretty clear and I think that the shrink-wrap on the bottles is much more difficult to align and shrink proportionately. This is taking it to a level where it is art.

 

[Chrispy]

I believe the only company that really uses auto transformers in most of their designs is Macintosh. They have a legacy in tube power amplifiers and their transformers are renowned for their quality. So it's natural that they would use them in their solid state designs. Personally I don't think there's a need to use them because they don't really buy you anything but that's just me. They also add a lot of weight.

Yeah weight is one thing I've seen commented on, like in this thread which got me to wondering if a technical guy like yourself could offer some reasoning for using them particularly.

 

[MakeMineVinyl]

Yeah weight is one thing I've seen commented on, like in this thread which got me to wondering if a technical guy like yourself could offer some reasoning for using them particularly.

MacIntosh says that a reason for using them is that speakers of all impedances can get full power from an amplifier. However given that the trend these days is towards speakers with lower impedances where conventional amplifiers deliver their most power, an auto transformer doesn't seem to provide any benefit.

 

[Chrispy]

MacIntosh says that a reason for using them is that speakers of all impedances can get full power from an amplifier. However given that the trend these days is towards speakers with lower impedances where conventional amplifiers deliver their most power, an auto transformer doesn't seem to provide any benefit.

Somewhat where it makes no sense to me....it just makes the amp as limited as one of only higher impedance capabilites or? Does it make the amp capable of handling lower impedances particularly? Does it just overall limit the useful power range for a speaker via the amp? I guess I just don't understand the concept....

 

[MakeMineVinyl]

Somewhat where it makes no sense to me....it just makes the amp as limited as one of only higher impedance capabilites or? Does it make the amp capable of handling lower impedances particularly? Does it just overall limit the useful power range for a speaker via the amp? I guess I just don't understand the concept....

If anything, an auto transformer is going to slightly increase the output impedance if it is not within the global feedback loop - I don't know how Macintosh implements them. Auto transformers behave somewhat better than conventional transformers, but in the end, they're still not a direct connection from the output transistors to the speaker (but given there's only a "primary" winding on an auto transformer, this is arguable), which can introduce downsides. All that being said, I don't expect that these amplifiers would perform any worse (or better) than any other high quality amp.

 

[Chrispy]

If anything, an auto transformer is going to slightly increase the output impedance if it is not within the global feedback loop - I don't know how Macintosh implements them. Auto transformers behave somewhat better than conventional transformers, but in the end, they're still not a direct connection from the output transistors to the speaker (but given there's only a "primary" winding on an auto transformer, this is arguable), which can introduce downsides. All that being said, I don't expect that these amplifiers would perform any worse (or better) than any other high quality amp.

Thanks for the bit of expansion, altho still not sure why they're there So no particular reason to employ them, at least without specific "McIntosh" knowledge? Any audible benefits under specific circumstances (and which ones?)?

 

[MakeMineVinyl]

Thanks for the bit of expansion, altho still not sure why they're there So no particular reason to employ them, at least without specific "McIntosh" knowledge? Any audible benefits under specific circumstances (and which ones?)?

I can't think of any reason why I would employ them. They obviously have strong marketing incentives to use them, given their history.

 

[Vacceo]

I would love to send it to Amir for measurements, but shipping is potentially risky and prohibitively expensive as I'm not residing in North America.


I have the unit in an enclosed cabinet and it does get slightly warm (around 40C on the back area w/o vent grills) during extended movie sessions, but for peace of mind, I decided to put a small laptop cooler on top for extra ventilation.

Thanks for your answers! I was thinking about this amp to set it in a studio rack (esentially a table with mesh walls and fairly open, so natural airflow is there).

From your words, it seems that a mesh cabinet would even eliminate the need for fans.

 

[Surge]

I read that the MI254 has a “feature” that automatically shuts off the amp if no signal is received in 30 minutes. This seems like a stupid feature, especially when you use it for its intended purpose of driving surround speakers. The only way to turn this off is if you connect it to a preamp with a trigger input; but then that will turn off the meters, unless you use a Mcintosh preamp, or modify the trigger cable in some way — at least that’s what the other owner said.
Does anyone know more about this?

 

[CinDyment]

I read that the MI254 has a “feature” that automatically shuts off the amp if no signal is received in 30 minutes. This seems like a stupid feature, especially when you use it for its intended purpose of driving surround speakers. The only way to turn this off is if you connect it to a preamp with a trigger input; but then that will turn off the meters, unless you use a Mcintosh preamp, or modify the trigger cable in some way — at least that’s what the other owner said.
Does anyone know more about this?

Suggest asking in a McIntosh forum. Not sure this a a group that buys into Mac.

 

[WestSideWarrior]

I read that the MI254 has a “feature” that automatically shuts off the amp if no signal is received in 30 minutes. This seems like a stupid feature, especially when you use it for its intended purpose of driving surround speakers. The only way to turn this off is if you connect it to a preamp with a trigger input; but then that will turn off the meters, unless you use a Mcintosh preamp, or modify the trigger cable in some way — at least that’s what the other owner said.
Does anyone know more about this?

I guess the auto power-off feature was included as this amp could double as a multi-zone amplifier.

I connected the MI254 power control trigger with the Marantz SR6014 "DC OUT" and it seems to work just fine. The amp turns on/off with the receiver, the auto power-off feature was defeated, and the meter lights works normally.

I've heard about the meter lights/trigger issue as well. McIntosh power control triggers also control meter lights when used in conjunction with McIntosh preamp/processors. This is useful for dark theater rooms with amps on an open rack as the meter lights can be distracting.

It is possible to do a workaround by using a 3.5mm stereo aux cable as opposed to a standard (mono) trigger cable.

Fully inserting the stereo jack into the trigger input = Auto power-off DISABLED, Meter Lights ON
Inserting the stereo jack only halfway (one conductor exposed) = Auto power-off DISABLED, Meter Lights OFF

The green McIntosh logo lights can't be turned off, however.

 

[WestSideWarrior]

Whoops. Here comes the Big Mac.

 

[r042wal]

I have an MC500 (1000 watts) paired with a C48 preamp. I am so pleased with my setup I have never bother to look at upgrading. I like my vintage speakers (Celestion Ditton 66) and rebuilt the crossovers and even did a a couple of the diaphragms in the towers for the 1" super tweeter and the 2" midrange driver.

A few months ago my MC500 stopped dead in the water as my wife and I were watching TV. I took it to an authorized McIntosh repair depot about 3 hours away. He said a leaking capacitor had shorted out a circuit board trace which in turn resulted in some additional damage. He recapped everything, replace 4 transistors (not power/output transistors) and did all the panel lamps.

I'm a happy camper and love the sound.