McIntosh Amps - Can they Double Down?

damacman

Resident Psycho
This topic is oft discussed - even here in the Mc forum within various threads.

McIntosh amplifiers are offered in two varieties - those with Autoformers and those without (Direct Coupled). The specifications of the Direct coupled amplifiers can be compared to competitive products with ease. However, the specifications of the Autoformer equipped amplifiers can be difficult to compare to competitive products if you don't understand what you're looking at.

For example, consider the following specifications for any number of 300wpc McIntosh amplifiers with autoformers:

300W per channel into 8 Ohms
300W per channel into 4 Ohms
300W per channel into 2 Ohms

Now, let's consider the specifications of Brand XYZs, 150W per channel power amplifier:

150W per channel into 8 Ohms
300W per channel into 4 Ohms
Not rated at 2 Ohms

First and foremost, any audio engineer worth his salt knows full well the capabilities of the parts within a given amplifier. When designing an amplifier, two of the top priorities are reliability and longevity. Those are a function of the overall design - not any one component. So, great engineers go out of their way to ensure the components themselves are always within a safe operating area (SOA). Go outside of that, even with a single device - from a single transistor all the way to the power transformer - and the amplifier won't live long in the hands of the customer.

In electronics, there is no such thing as a free lunch. All audio amplifiers generate heat as a byproduct of operation. For a Class AB power amplifier, 30-40% of what the amplifier draws from the AC outlet is converted to heat due to efficiency losses. Heat is the number one killer of electronics, so the design that manages that best is also the one that typically lasts the longest.

To that end, McIntosh realized from the onset that they could dramatically improve the reliability of solid state amplifiers by using autoformers to couple them to the loudspeakers. Here in 2017, when it is still possible to purchase an 50 year old MC2505 that still works, we realize fully that they were correct.

Quite simply, the autoformer allows the McIntosh customer to get the claimed output power into any impedance load the amplifier has taps for. This allows the amplifier to remain within the SOA, regardless of the load connected.

Let's look again, at the above specs. Notice that the McIntosh offers two benefits over the competitive amp:
- double the power at 8 Ohms
- rated to operate safely at 2 Ohms

Now, the price of admission with a McIntosh autoformer equipped power amplifier can be higher due to the additional parts cost of the autoformers but I prefer to look at this as an initial cost difference, not a long term cost difference.

So, does the competitive design actually double down? Not unless the laws of physics have changed. Due to efficiency losses, this is not possible. Sure, the amplifier may indeed make (or even exceed) the 300W per channel claim at 4 Ohms. But, the real story is - does it make only 50% of that power at 8 Ohms? The answer is no - it will always make more than the claimed 150W. So, on the bench, the numbers may look like this:

225W per channel into 8 Ohms
330W per channel into 4 Ohms

So, really what you have here is an amplifier that exceeds its published specifications (never a bad thing) but doesn't fit the marketing claim that it Doubles Down. Which sounds better? [Keep in mind that audio is a hobby that is fully governed by the laws of physics, but marketing trumps that every time as most customers don't have the depth of understanding to sort fact from fiction.]

Now, on the bench, McIntosh amplifiers on average make 30%+ more output power than claimed so if we're taking real power vs. real power, the McIntosh amplifiers always do quite well in direct comparisons. And the McIntosh power amplifier owner enjoys the maximum power the amplifier is capable of in the SOA, even at 8 Ohms, where the competitive amplifier owner has to run the amp at 4 Ohms to realize that. Keep in mind that what McIntosh considers the SOA for a given design is quite conservative to what other manufacturers consider the SOA.

So, can the McIntosh amplifier deliver more power at 4 Ohms, or even 2 Ohms than what the specifications provide? Yes, absolutely. Connecting a 4 Ohm load to the 8 Ohm tap will provide less than double* the output power and connecting a 2 Ohm load to the 8 Ohm tap will provide less then quadruple* the output power as compared to the published specifications.

*limited by efficiency losses as noted above, as well as current limiting schemes employed by the engineers to keep devices in a SOA, even when incredibly difficult loads are present

Now, when doing this, you will indeed create more heat and depending on how hard you push the amplifier, you could cause the thermal protection circuits to engage from overheating it. Fan cooling is never a bad idea. Both also apply to competitive designs that lack autoformers . . .

A good indication of how capable a given amplifier is at driving difficult loads is its output current rating. Most McIntosh amplifier provide this in the OM. This current rating is derived by connecting a load equivalent of 20% of the tap rating to the 8 Ohm tap - 8 x .2 = 1.6 Ohms. Some loudspeakers are more difficult to drive than others, like the Infinity Kappa 9s for example, so there is never any worry of driving those from the 8 Ohm tap of a McIntosh power amplifier. And, if you prefer, you can also experiment with driving such a speaker from the 4 Ohm tap and see which suits you.

So there you have it.
 
Well I like what the 7106 I have does when you double up and bridge at 8 ohms. No autoformers but a hell of an amp for performance to price on used market. You still have powerguard with Kabuki style meters. It is one quiet amp. It easily doubles down in price compared to a MC7270 used. Selling less than half and offering better performance numbers if bridged and leaving two 100 watt or two 160 watt channels . As for running hot not an issue.
 

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If you want to see performance of Mac amps without autoformers, down load the owners manual for the 7100 or 7200. The 7200 performance at 2 ohms and 1.33 ohms will blow your mind. 625 watts continuous for 2 ohms and 726 watts at 1.33 ohms. What surprising is the peak capability at 1 ohm, 882 watts.

My 207 is driving woofers with an average load of 3 ohms with a dip at 1.88 ohms with ease, not over heating, clipping or distortion with 2 channels, 2 more channels driving the mid and tweeters average about 10 ohms, and the two clusters of super tweeters average about 6 ohms driven by two more channels. The 207 has been performing that way for over 8 years with out any signs of stress or over heating. The 7 th channel of the first 207 and the seventh channel of the Second 207 drive the center front- bi amped system with about a 7 ohm average. for the woofers and the mid/high freq averaging 9 ohms with a 6 ohm supper tweeter with out an issue The second 207 bi amps the rear channels and powers the side speakers all with out issues. The 206 powers 2 pairs of remote 4 ohms speakers on 4 channels and drives one set of the electrostatic headphones. The 2505 drives the other. All the Mac SS amps I've owned (11) have been very trouble free. My Mac tube (7) and Crown amps (6) should have been so good and trouble free.

And though people would lead you to believe Crown amps can double .. They Don't. Maybe Accuphase amps can. Krell and Threshold don't either.
 
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The original McIntosh transistor amps from the 1960s, would not 'double down' as impedance is halved due to the characteristics of the output transistors and their limited SOA, safe operating area.
As time moved on transistors improved dramatically as the transistor's SOA increased so did the size of the McIntosh power supplies. The result is that modern McIntosh amplifiers will double down. So say an MC1.2K amp is connected to 8 ohms. It will make more than 1200 watts broadband. If a two ohm load is connected to the 8 ohm taps it will make over 3000 watts. This connection will of course cause the amp to run hot so it is not recommended but in the case of a speaker with wild impedance swings this is a good thing.
Thanks,
Ron-C
 
I thought this was true and it made sense.My Paradigm and Klipsch speakers sound better and play louder on the 8ohm taps.Heat is no longer a worry due to fans.My MC-252 can run all day/night with some power guard flashing without getting hot.I think both of my speakers are closer to 4ohms.Only one pair at a time of course.One day I will mis my hearing but that happens eventualy to everone.Cheers
 
If you want to see performance of Mac amps without autoformers, down load the owners manual for the 7100 or 7200. The 7200 performance at 2 ohms and 1.33 ohms will blow your mind. 625 watts continuous for 2 ohms and 726 watts at 1.33 ohms. What surprising is the peak capability at 1 ohm, 882 watts.

My 207 is driving woofers with an average load of 3 ohms with a dip at 1.88 ohms with ease, not over heating, clipping or distortion with 2 channels, 2 more channels driving the mid and tweeters average about 10 ohms, and the two clusters of super tweeters average about 6 ohms driven by two more channels. The 207 has been performing that way for over 8 years with out any signs of stress or over heating. The 7 th channel of the first 207 and the seventh channel of the Second 207 drive the center front- bi amped system with about a 7 ohm average. for the woofers and the mid/high freq averaging 9 ohms with a 6 ohm supper tweeter with out an issue The second 207 bi amps the rear channels and powers the side speakers all with out issues. The 206 powers 2 pairs of remote 4 ohms speakers on 4 channels and drives one set of the electrostatic headphones. The 2505 drives the other. All the Mac SS amps I've owned (11) have been very trouble free. My Mac tube (7) and Crown amps (6) should have been so good and trouble free.

And though people would lead you to believe Crown amps can double .. They Don't. Maybe Accuphase amps can. Krell and Threshold don't either.
Twiiii - I will buy an MC7200 at some point based on your glowing reviews of it.
 
I thought this was true and it made sense.My Paradigm and Klipsch speakers sound better and play louder on the 8ohm taps.Heat is no longer a worry due to fans.My MC-252 can run all day/night with some power guard flashing without getting hot.I think both of my speakers are closer to 4ohms.Only one pair at a time of course.One day I will mis my hearing but that happens eventualy to everone.Cheers
There's our resident MC252 owner! I recall you discussing the addition of the cooling fans - solving this amp's Achilles heel of too little heat sink mass given its power capability.
 
Damacman, like always good posts and explanations from you. Thanks for these posts.
Only two little comments from my side (in general I aggree with your post):
1. There are some amps like for example the Accuphase A200 or M6200 which almost "double down" also in reviewed measurements (factor 1.96 from 8 to 4 Ohm, factor 1.94 from 4 to 2 Ohm)
2. There are very comprhensive reviews in the italian Audio Magazine Audio Review. The measure every tape from 8 to 2 Ohm. Here you can see an example for the MC 601:
http://www.mpielectronic.com/NewsFiles/McIntosh C2300 e MC601.pdf

You can see that from the 8 Ohm tap the amp feels "comfortable" to ca. 2.7 Ohm. From the 4 Ohm and 2 Ohm tap you get almost the "double down" effect.

Best regards

Martin
 
Damacman, like always good posts and explanations from you. Thanks for these posts.
Only two little comments from my side (in general I aggree with your post):
1. There are some amps like for example the Accuphase A200 or M6200 which almost "double down" also in reviewed measurements (factor 1.96 from 8 to 4 Ohm, factor 1.94 from 4 to 2 Ohm)
2. There are very comprhensive reviews in the italian Audio Magazine Audio Review. The measure every tape from 8 to 2 Ohm. Here you can see an example for the MC 601:
http://www.mpielectronic.com/NewsFiles/McIntosh C2300 e MC601.pdf

You can see that from the 8 Ohm tap the amp feels "comfortable" to ca. 2.7 Ohm. From the 4 Ohm and 2 Ohm tap you get almost the "double down" effect.

Best regards

Martin
Martin - very nice to see a magazine measure amplifier power this way - resistive, inductive, and capacitive loads. This more accurately demonstrates the amplifier's ability to drive loudspeakers. The MC601s appear to have done quite well in regard - a testament to a robust power supply - at least from what I can infer from the graphs.

When I worked for Rockford, we had a few AudioGraph Power Cubes in engineering. Hafler and Rockford Fosgate amplifiers were analyzed extensively with it to aid in power supply development.

I too greatly enjoy your posts about amplifier listening evaluations.
 
Wow - look at the MC275! That's really something.

I read JA's analyses on each of the components he tests in Stereophile and I feel like he's speaking to engineers ... This Italian mag has it figured out!
Yeah the MC275 and MC2301 the only tube amps in the list. Wish the article could be easily translated but Text is not easily selectable.
 
I wonder how much of this doubling down really relates to producing music or is just a added marketing scheme to justify the expense of lots of extra heatsink area, transistors and close to, or class A biasing.

For the dozen or so huge proponents of doubling down you could find a equal dozen of highly acclaimed tube amp designers that couldn't double their output in their dreams.

Yes there were and are speaker designers who build speakers with out regard to the amps that need to run them......but they usually don't last long in the cutthroat actual outside world not that of the magazine reviewers.

Who here has actually listened to set of Scintillas.......I think I would rather chew a piece of aluminum foil than listen to them again.
 
I wonder how much of this doubling down really relates to producing music or is just a added marketing scheme to justify the expense of lots of extra heatsink area, transistors and close to, or class A biasing.

For the dozen or so huge proponents of doubling down you could find a equal dozen of highly acclaimed tube amp designers that couldn't double their output in their dreams.

Yes there were and are speaker designers who build speakers with out regard to the amps that need to run them......but they usually don't last long in the cutthroat actual outside world not that of the magazine reviewers.

Who here has actually listened to set of Scintillas.......I think I would rather chew a piece of aluminum foil than listen to them again.
Chris - I believe the money spent on a power supply that can allow the amplifier to maintain its output voltage into difficult reactive loads is money well spent. Doubling down can be a byproduct ...
 
"Doubling down" is a characteristic of solid state amps with ample current capability output stages and a power supply capable of supporting it at low impedance loading, useful for powering speakers at high levels that have an uneven current draw. Tube amps can't/ don't double down in the same way, but don't blow up when presented with very low impedance loading as do typical solid state amps pushed way beyond their current capability without overload protection.
 
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If you want to see performance of Mac amps without autoformers, down load the owners manual for the 7100 or 7200.

I had a 7100 (that I recently traded for an MC2120) that made 130w into 8 ohms before clipping/power guard activating, I never tested it at 4 ohms but I strongly suspect it would have been over 200. The 7100 makes a fantastic mono amp at 8 ohms, manual states 300 but it's always more. During testing, the lights in the room would dim when driving both channels to max power. That's what makes a Mac so strong, the output stages have a lot more current sinking ability than most other amplifiers.

Haven't tested the MC2120 on the bench yet, but it seems like about the same power level to me driving the same speakers.
 
Chris - I believe the money spent on a power supply that can allow the amplifier to maintain its output voltage into difficult reactive loads is money well spent. Doubling down can be a byproduct ...

Says a guy who wants a thousand horsepower on the street, but does it help you cut the apex of a turn?

The theory of doubling down is fine but does it make for more accurate real world sound?

I believe it is more of a marketing statement for certain companies existence and reason to be than a true measurement of long term sound reproduction.

A salesperson or reviewer's "talking point" for sure, ration d'être, sure, sound quality, big maybe.
 
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