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

Showing 20 responses by jasonbourne52

A Jensen transformer is the best way to avoid the hot pin 3 problem - but at extra cost!
@kijanki : look at the specs for the 462 amp! Both 2.1 and 4.2 volts both produce output wattage of 450!  So if the input voltage is slightly increased to 2.4 ala the Marantz 8802 you say that the wattage will go down to 1/4 of 450!!!! 
@imhififan : OK! I can follow the math - but note that the specs for the 462 state "450 watts for either 2.1 or 4.2 volts"! That's way more than 147 watts according to your math!
Amazon has some adapters: GXR - 134 from zZounds for $8.65 each. However you may experience distortion when using an XLR/RCA adapter because they shunt pin 3 to ground at the unbalanced end. Pins 2 and 3 are out-of-phase signals. Some amps won't tolerate having an out-of-phase signal connected to their input ground!
I think you will really need an adapter using a transformer to avoid having pin 3 connected to the shield ground at the amp's RCA jacks.
You will get less than full power by using the Marantz's balanced outputs. About a bit more than 225 wpc into all impedances - the Mc462 uses autoformers on the output stages. Same if you used the Marantz's unbalanced RCA outputs. 
Here's the math: 2.4 ÷ 4.2 = .5714 × 450 = 257.14 watts into all impedances! 
@kijanki : so half of 4.2 is 2.1 volts. You say that the power in watts is 450 ÷ 4? That sounds way off!
I think that XLR/balanced outputs are over-rated! They are only useful if you need to run 10, 20, 30 ... feet cables! At one or two meters "No diffawrance" as the French chef said!
 @kijanki : an amp producing 25 watts is actually outputting 14 volts. At 50 watts  it is outputting 20 volts. I understand this type of non-linear proportion. I don't think it applies to voltage at the input stage! 
People here will say "this preamp or that preamp" will sound "better"! They will claim that their "golden ears" told them this! The 8802 is an excellent measuring - and sounding! - preamp! Plus it has a phono stage - something lacking in many current preamps. I expect that the 8802 will be "transparent" to the source! Replacing it would be a sideways move at best!
@kijanki : you get an F! My math is correct! It is just a simple linear proportion comparing 2.4 to 4.2! And then multiplying the result by 450. You are thinking of watts -to- volts of an amp's power output. So way off the mark!
@kijanki : go to the top and read the specs for the 462. Either RCA or XLR it outputs 450 watts for respectively 2.1 and 4.2 volts! Not 110.25 watts for 2.4 volts! 
The SE2B looks real good in the photos, with its wood side panels and neat interior wiring with two Jensen transformers! Front panel has a pair of RCA jacks and a pair of XLR jacks.
@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!
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. 
Back to the topic of XLR adapters! Member almarg had a post on 2-20-2017 where he addressed this issue. He thought it was potentially a problem because of shunting pin 3 to ground at the RCA input since pin 3 is active! Possibly damaging the amp! I agree and say don't do it! 
Success! EBay seller pinetreeaudio builds and sells a converter box using Jensen transformers for XLR -to-RCA : the Pine Tree Audio SE2B. $275 + $15 shipping. Build time 2 weeks. Located in Fitchburg, MA. Forget all the other cheap cr*p! This is the proper way to do the conversion!