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Deciphering Integrated Specs - Step Up Matching

I have always struggled to make sense of my McIntosh MA352 hybrid tube/ss integrated amplifier’s published specs (see below) when trying to match, at least on paper, with a Moving Coil step-up device. In particular, the "Phono to Output 1 and 2" specs of 84dB and 55dB always throw me off as 40dB seems to be a more traditional voltage gain spec for a MM stage.

Of late, I have been using a Quadratic MC-1 SUT in conjunction with a Dynavector 20X2L cartridge (0.3mV output) with truly excellent results, really what matters in the end. The MC-1 has 22dB (12x) and 28dB (24x) taps. The latter seems to work best with the Dynavector and doesn’t present any volume knob/headroom problems.
 
I am considering switching to another moving coil cartridge with an 0.4mV output. But, as mentioned, I always struggle with how to interpret the integrated’s specs, and thus which gain setting to use on the SUT. I generally prefer the higher gain setting so would like to keep using that whenever possible.
 
Based on the attached specs, setting aside specific cartridge loading determinations, what is the best/simplest way (if there is one) to evaluate the MA352’s phono stage for matching cartridges with SUT gain options (e.g., 22dB or 28dB) so as not to cause any obvious matching or overload issues?
 
For example-
 
- Does the 2.5mV sensitivity imply a phono stage output gain of 40dB?
 
- If indeed the phono stage output gain is 40dB, does adding 28dB from the step-up device, for a total of say 68dB on its face present any particular problems when used with an MC cartridge with say 0.5 mV output or lower?
 
- Would a cartridge with 0.4mV output overload the unit if used with a 24x tap (would think not as 9.6mV seems to be well below the 80mV maximum input signal?
 
For what it’s worth, my understanding is that "Output 1" is the speaker output and “Output 2" is the output of the preamp section of the integrated amp - but I’m not completely sure.
 
Any thoughts/suggestions would be greatly appreciated.
 

jobeare
stereo5's avatar
stereo5
6,363 posts
 

I use output 2 on my McIntosh integrated amp to run to my powered subwoofer.  

jobeare OP
6 posts
 

I wasn't able to include a picture of the full specs, so here they are.

Power Output Stereo
Minimum sine wave continuous average power output per
channel, with both channels operating is:
200 watts into 8 ohm load
320 watts into 4 ohm load
Output Load Impedance
8 or 4 ohms
Rated Power Band
20Hz to 20,000Hz
Total Harmonic Distortion
0.03% maximum with both channels operating from 250
milliwatts to rated power, 20Hz to 20,000Hz
Intermodulation Distortion
0.03% maximum, if the instantaneous peak power output
does not exceed twice the rated power output for any com-
bination of frequencies from 20Hz to 20,000Hz
Dynamic Headroom
1.5dB
Wide Band Damping Factor
Greater than 200 - 8 ohm, Greater than 100 - 4 ohm
Power Guard
Less than 2% THD with up to 16dB overdrive at 1,000Hz
Frequency Response
+0, -0.5dB from 20Hz to 20,000Hz
+0, -3dB from 10Hz to 100,000Hz
Preamplifier Output Impedance
500 ohms
Sensitivity (for rated output)
High Level - 250mV unbalanced, 500mV balanced
Phono - 2.5mV
Signal To Noise Ratio (A-Weighted)
High Level - 93dB below rated output
Phono - 82dB below 5mV input
Input Impedance
High Level - 20K ohms
Phono - 47K ohms; 50pF-800pF
Preamplifier Output 2 (for rated input)
1.4V unbalanced (8V Maximun)
Maximum Input Signal
High Level - 8V unbalanced, 16V balanced
Phono - 80mV
Voltage Gain
High Level to Output 1: 44dB
High Level to Output 2: 15dB
Phono to Output 1: 84dB
Phono to Output 2: 55dB
Headphone Impedance
100 to 600 ohms

crustycoot
627 posts
 

You may be (are) over analyzing.  The 2.5mV input sensitivity MM phono spec is bog standard 40dB gain.  The Output 2 spec adds the maximum linestage gain.  The 80mV input overload spec is generous so a LOMC run through a 12x SUT should be perfect.  You say the 24x is fine…to me it seems like the volume range would be better at 12x, but your results speak for themselves.  Chill, enjoy!

lewm
12,876 posts
 

The only data that might help to answer your many questions are in the section headed by”voltage gain”, and there are a few different possible interpretations of those data. However, I’d start with your SUTset to 1:12, not 1:24. You can always choose the higher gain setting if 1:12 proves inadequate. Since your linestage seems capable of adding unusually high gain for a linestage, you might even get by with no SUT, depending upon the correct interpretation of the given info. Do you have an owners manual? If so, read it.

mijostyn's avatar
mijostyn
8,505 posts
 

It is really a matter of the signal to noise ratio and whether or not you can tolerate the noise with any given cartridge. As long as you have enough gain and the noise level is ok at the volumes you listen at you are in business. It looks to me that you will be fine. 

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