I just saw this write up on social media by Ken Zelin and thought it was a really good read explaining the working of the MC1000.
McIntosh’s MC1000 Monoblock Power Amplifier- What made it so special?
The MC1000 was a 1000 Watt single-channel power amplifier with almost unmeasurably-low noise and distortion.
While it’s true that most music has limited dynamic range, and you seldom need more than 10 Watts for that, bass drums need a HUGE amount of power to sound “live”. In fact, with “ordinary” sensitivity speakers (around 88dB), reproducing a bass drum at realistic volume levels requires about 4000 watts!
Trying to play a recording like The Drum Record recorded by Sheffield Lab with only, say, 200 Watts per channel is hopeless if you want to hear it at live volume levels.
That’s why McIntosh decided to build a 1000-Watt power amplifier. And it needed to be a monoblock, since a stereo amp with 100 Watts per channel would pull too much from a regular 15-amp wall outlet.
Designing a 1000-Watt power amplifier is a real challenge.
Using “normal” circuit layouts, that high a power level would require very high voltages to be applied to the output transistors, and transistors that can handle that voltage level may not have very good characteristics for audio (they were usually designed for video applications).
The solution was to use lower-voltage transistors, and let the Output Transformer (a McIntosh exclusive feature) boost the voltage. That DID increase the CURRENT through the output stage, but that’s simple to account for by simply paralleling many more transistors.
The other big problem is noise.
Higher power means more transistors (or tubes) in any amplifier, and each one adds noise to the signal. So a 1000 Watt amplifier will have more available power (good) but more noise, also (bad). And you can’t reduce the noise past a certain point unless you super-cool the amp, which makes your listening room a bit uncomfortable, to say the least.
That’s why most power amps don’t sound quite as detailed as lower-power amps; the tiny details in the quiet parts of the music are buried in the background noise of the amp. It’s the MASKING effect.
Although you can’t REDUCE the noise past a certain point, you can do something else...you can CANCEL it, the way BALANCED cables work.
That means building a 1000 Watts amp with two 500-Watt sections. One amplifies the music signal, and the other amplifies the same music but the signal is INVERTED, or OUT OF PHASE. Both amp sections produce noise.
But AFTER the signal is amplified, and we have a 500-Watt signal with noise, and an INVERTED 500-Watt signal with noise, we again INVERT the already INVERTED signal. The signal that got INVERTED TWICE is back to it’s original form, but the NOISE in the INVERTED channel is now INVERTED NOISE.
Combine the two channels, and the power doubles, and the noise cancels.
Other companies have tries to produce a noise-canceling amp, but it’s a ticking time bomb. If you try to put two amplifier channels in PARALLEL, necessary for true noise canceling, some day some noise will come through ONE of the signals but not the other and the amp blows up.
So McIntosh developed a double-wound, mirror image output transformer that does the inversions, adds the power into 1000 Watts, yet isolates the amps electrically from each other. The combining and canceling is done MAGNETICALLY in the output transformer.
How well did this work? The noise level of the MC1000 was 120dB below rated output!
Distortion? .005% at full power at any frequency from 20-20,000Hz.
Bandwidth? 10-100,000Hz.
Damping Factor of 200.
And because the noise cancelling also cancels any minute amount of CROSSOVER distortion from the amp, MC1000s do not need to have high-biasing, so they run amazingly cool. They actually pull less from the wall at normal listening volume than many 200-Watt power amps.
The MC1000 was a nearly perfect amplifier with lower noise than a typical 1-Watt amplifier, but, at the same time, the highest power ever offered in a home-use power amplifier.
Although called DOUBLE-BALANCED at the time, it’s the same circuit as in the MC1201, MC1.2kW, and the current MC1.25kW, but the name was changed to Quad Balanced in those later models.
If you are looking at a used MC1000...
-MC1000s are very reliable, though the meter lamps can go bad. They do require soldering skills to replace, but it’s not too hard a job. Lamps were replaced with long-life LEDs in later amps like the MC1.25kW.
-Later MC1000s have Power Control jacks so they can be triggered on and off with preamp triggers. Earlier production units lack the Power Control jacks, and must be turned on and off manually.
McIntosh’s MC1000 Monoblock Power Amplifier- What made it so special?
The MC1000 was a 1000 Watt single-channel power amplifier with almost unmeasurably-low noise and distortion.
While it’s true that most music has limited dynamic range, and you seldom need more than 10 Watts for that, bass drums need a HUGE amount of power to sound “live”. In fact, with “ordinary” sensitivity speakers (around 88dB), reproducing a bass drum at realistic volume levels requires about 4000 watts!
Trying to play a recording like The Drum Record recorded by Sheffield Lab with only, say, 200 Watts per channel is hopeless if you want to hear it at live volume levels.
That’s why McIntosh decided to build a 1000-Watt power amplifier. And it needed to be a monoblock, since a stereo amp with 100 Watts per channel would pull too much from a regular 15-amp wall outlet.
Designing a 1000-Watt power amplifier is a real challenge.
Using “normal” circuit layouts, that high a power level would require very high voltages to be applied to the output transistors, and transistors that can handle that voltage level may not have very good characteristics for audio (they were usually designed for video applications).
The solution was to use lower-voltage transistors, and let the Output Transformer (a McIntosh exclusive feature) boost the voltage. That DID increase the CURRENT through the output stage, but that’s simple to account for by simply paralleling many more transistors.
The other big problem is noise.
Higher power means more transistors (or tubes) in any amplifier, and each one adds noise to the signal. So a 1000 Watt amplifier will have more available power (good) but more noise, also (bad). And you can’t reduce the noise past a certain point unless you super-cool the amp, which makes your listening room a bit uncomfortable, to say the least.
That’s why most power amps don’t sound quite as detailed as lower-power amps; the tiny details in the quiet parts of the music are buried in the background noise of the amp. It’s the MASKING effect.
Although you can’t REDUCE the noise past a certain point, you can do something else...you can CANCEL it, the way BALANCED cables work.
That means building a 1000 Watts amp with two 500-Watt sections. One amplifies the music signal, and the other amplifies the same music but the signal is INVERTED, or OUT OF PHASE. Both amp sections produce noise.
But AFTER the signal is amplified, and we have a 500-Watt signal with noise, and an INVERTED 500-Watt signal with noise, we again INVERT the already INVERTED signal. The signal that got INVERTED TWICE is back to it’s original form, but the NOISE in the INVERTED channel is now INVERTED NOISE.
Combine the two channels, and the power doubles, and the noise cancels.
Other companies have tries to produce a noise-canceling amp, but it’s a ticking time bomb. If you try to put two amplifier channels in PARALLEL, necessary for true noise canceling, some day some noise will come through ONE of the signals but not the other and the amp blows up.
So McIntosh developed a double-wound, mirror image output transformer that does the inversions, adds the power into 1000 Watts, yet isolates the amps electrically from each other. The combining and canceling is done MAGNETICALLY in the output transformer.
How well did this work? The noise level of the MC1000 was 120dB below rated output!
Distortion? .005% at full power at any frequency from 20-20,000Hz.
Bandwidth? 10-100,000Hz.
Damping Factor of 200.
And because the noise cancelling also cancels any minute amount of CROSSOVER distortion from the amp, MC1000s do not need to have high-biasing, so they run amazingly cool. They actually pull less from the wall at normal listening volume than many 200-Watt power amps.
The MC1000 was a nearly perfect amplifier with lower noise than a typical 1-Watt amplifier, but, at the same time, the highest power ever offered in a home-use power amplifier.
Although called DOUBLE-BALANCED at the time, it’s the same circuit as in the MC1201, MC1.2kW, and the current MC1.25kW, but the name was changed to Quad Balanced in those later models.
If you are looking at a used MC1000...
-MC1000s are very reliable, though the meter lamps can go bad. They do require soldering skills to replace, but it’s not too hard a job. Lamps were replaced with long-life LEDs in later amps like the MC1.25kW.
-Later MC1000s have Power Control jacks so they can be triggered on and off with preamp triggers. Earlier production units lack the Power Control jacks, and must be turned on and off manually.
