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Question on Preamp Outputs.

I was hoping that you guys can answer a question.

My preamp, a Marantz 8802a has a max output of 2.4 volts balanced output. I am looking into a McIntosh Amp that is rated for a higher input potential. I am generally pleased with my Marantz. Below are the specs pf the McIntosh and the Marantz.

McIntosh MC462
Power Output Minimum sine wave continuous average power output per channel, with both channels operating is: 450 watts into 2 ohm load 450 watts into 4 ohm load 450 watts into 8 ohm load Output Load Impedance 2, 4 or 8 ohms Rated Power Band 20Hz to 20,000Hz Total Harmonic Distortion 0.005% maximum harmonic distortion at any power level from 250 milliwatts to rated power, 20Hz to 20,000Hz Dynamic Headroom 3.0dB Frequency Response +0, -0.25dB from 20Hz to 20,000Hz +0, -3.0dB from 10Hz to 100,000Hz Input Sensitivity (for rated output) 4.2 Volts Balanced 2.1 Volts Unbalanced

Marantz 8802a
Analog Input sensitivity/Input impedance: Unbalanced RCA input:200 mV/47 kΩ/kohms Balanced XLR input:400 mV/94 kΩ/kohms Frequency response: 10 Hz – 100 kHz — +1, –3 dB (Direct mode) S/N: 105 dB (IHF–A weighted, Direct mode) Distortion: 0.005 % (20 Hz – 20 kHz) (Direct mode) Rated output: Unbalanced RCA pre-output : 1.2 V Balanced XLR pre-output: 2.4 V 0 Digital D/A output: Rated output — 2 V (at 0 dB playback) Total harmonic distortion — 0.008 % (1 kHz, at 0 dB) S/N ratio — 102 dB Dynamic range — 100 dB Digital input: Format — Digital audio interface 0 Phono equalizer Input sensitivity: 2.5 mV RIAA deviation: ±1 dB (20 Hz to 20 kHz) S/N: 74 dB （IHF-A、with 5 mV input) Rated output: 150 mV Distortion factor: 0.03 % (1 kHz, 3 V)


Since my Pre has 2.4 volts , what does that mean in the grand scheme? Aside from getting a better dedicate two channel preamp .. I know I should, but that will come later. 

Thank you In advance.
Rick
knowitall
kijanki's avatar
kijanki
4,428 posts
 
His pre outputs 2.4V for balanced output. His amp outputs 450W for 4.2V balanced input.

Amplifier’s output voltage will be a linear function of the input voltage. It has to be or amplifier will have huge distortions. Output power P = V^2 / R If you drive this balanced input with 2.4V instead of 4.2V output will become 24V instead of 42V and power will be (24^2) / 4 = 144W instead of (42^2) /4 = 441W
jasonbourne52's avatar
jasonbourne52
2,863 posts
 
@kijanki : read the 462 specs again! 2.1 volts in produces 450 watts through the RCA's. 4.2 volts in through XLR's produces the same 450 watts because of the autoformer-coupled output stage. Even though gain is different from RCA vs. XLR!
jasonbourne52's avatar
jasonbourne52
2,863 posts
 
Using autoformers in a present-day transistor amp is really backward engineering! Anyway the hot -or should I say cool- stuff is the interest and further development of class D amps. 
kijanki's avatar
kijanki
4,428 posts
 
So what?  This amp has double gain at unbalanced input (26dB vs 20dB), for the output power to be 450W at nominal voltage at given input, but output voltage will be a linear function of input voltage at given input.  If you lower voltage at given input by 50% output voltage will become 50%.   1/2 of the output voltage produces 1/4 of the output power.
kijanki's avatar
kijanki
4,428 posts
 
As for the output being always 450W. It is always 450W because for different speaker load transformer has different output voltage (amp has different gain). 8ohm speaker would normally produce half of the 4ohm speaker, but amp’s gain for 8ohm output is higher. We are not talking about this. We are talking about amp with speaker fixed to one output and pre fixed to one input.
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