@mulveling, great post.
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.
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Sure was @mulveling, thank you. And thank you all for the helpful responses. |
As a post script, the 0.4mV cartridge that I’m considering using is the Hana Umami Blue. Its coil impedance is 8Ω and its suggested load impedance is >80Ω. The input impedance of the Quadratic MC-1 is reported to be 70Ω in high mode (24x/ +28dB) mode and 200Ω in low mode (12x/+22dB), although by my calculations the impedance would really seem to be 81.6 (high) and 326 (low). Given @mulveling ’s comments and the Hana’s suggested load impedance of >80Ω, would the Quadratic’s input impedance in high mode of 70Ω (or 81.6 if that’s really the case) suggest any compatibility issue with the Hana or otherwise affect the considerations? |
8 ohms into 70 ohms is fine - it’s far from an egregious mismatch, and the main value in these paper calculations is to avoid something egregious. For reference, 70 / 8 is a 9x ratio and I’ve used as low as a 5x ratio before. You’ll lose some effective output (like 1dB or so) in such a configuration, maybe alter the FR a bit, but it’s not a huge deal. As @theflattire mentioned, use your ears to decide the winner at this point. For a 2-tap SUT, 12x and 24x is a really nice choice of ratios, IMO. That covers a lot of MC ground! |
- 12 posts total