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.
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.