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Digital1955

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Darlington Labs MM-6 then upgraded to MP-7. This was an expensive experiment. ASR on the MM-6 didn't recommend it due to noise issues and the MP-7 didn't really improve on it. While the MP-7 did some things really well, like instrument separation in the sound stage, I just could't get past the high noise floor. Sold it.

"ASR on the MM-6 didn't recommend it due to noise issues" - where did you read this and what do you mean by noise issues?
 

deniall83

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"ASR on the MM-6 didn't recommend it due to noise issues" - where did you read this and what do you mean by noise issues?
Possibly meant the MM-5.

 

krichard2496

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Possibly meant the MM-5.

Most clients have significantly praised the nearly-silent background noise floor of our units, even with the typical highly-inductive Moving Magnet style cartridge -- where most BJT designs fall down significantly -- and this aspect is not tested in ASR's methodology.

Most other units -- whether discrete and therefore utilizing a single stand-alone BJT transistor or a pair -- or op-amp-based with an internal BJT differential pair -- result in a 'hissy' character to their noise floor (concentrated towards the upper octaves) with the majority of cartridges in use. Ours, rather, using a carefully-selected High-Voltage J-FET with nearly unmeasurable current noise, remains both very low in overall level, and quite flat in the residual noise spectra, more akin to the sound of high-speed open-reel tape with Dolby-A or SR noise reduction.

For further discussion, see (for example) “Noise of Sources”, National Semiconductor Application Note, John Maxwell, February 1977, or the even-more-math-intensive analysis of a Shure V15-III in National Semi’s application note AN-104 from May 1974.

Regarding low frequency noise, it has been our experience that careful dressing of the AC inlet cable, relative to the audio input cable, and proper positioning of the unit, reduces any residual hum that is induced by the physical installation to below audibility. Our noise specifications are intentionally very conservative, partially to account for variabilities in an individual installation. Of course, tastes in sound can differ, and overall system matching remains important in generating a satisfactory auditory result.
 
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Digital1955

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Most clients have significantly praised the nearly-silent background noise floor of our units, even with the typical highly-inductive Moving Magnet style cartridge -- where most BJT designs fall down significantly -- and this aspect is not tested in ASR's methodology. Most other units, when they are discrete, utilize a discrete BJT transistor on the input stage and this results in a 'hissy' character to the noise floor, biased towards the upper octaves. Ours, using a carefully selected High-Voltage J-FET with nearly unmeasurable current noise, remains both very low in level, and relatively flat in the residual noise spectra.

For further discussion, see (for example) “Noise of Sources”, National Semiconductor Application Note, John Maxwell, February 1977, or the even-more-math-intensive analysis of a Shure V15-III in National Semi’s application note AN-104 from May 1974.

Regarding low frequency noise, it has been our experience that careful dressing of the AC inlet cable, relative to the audio input cable, and proper positioning of the unit, reduces any residual hum that is induced by the physical installation to below audibility. Our noise specifications are intentionally very conservative, partially to account for variabilities in an individual installation. Of course, tastes in sound can differ, and overall system matching remains important in generating a satisfactory auditory result.

The original poster didn't come back and answer my question. But I think he was simply repeating that (the MM-5) SINAD was limited by "noise" (Amir's word).
Surely high frequency "hiss" would show up clearly in the FFT plot of the 1Khz test signal if it were there. In the MM-5 case, I think SINAD was limited solely by the the 2nd harmonic. I guess that is the "noise"?
 

krichard2496

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The original poster didn't come back and answer my question. But I think he was simply repeating that (the MM-5) SINAD was limited by "noise" (Amir's word).
Surely high frequency "hiss" would show up clearly in the FFT plot of the 1Khz test signal if it were there. In the MM-5 case, I think SINAD was limited solely by the the 2nd harmonic. I guess that is the "noise"?
Yes. Inaudible though the 2nd harmonic is believed to be, in the small proportion that it exists in our products due to the response of the human ear, it dominated his SINAD measurement which is "flat" and unweighted. We have requested that ASR provide a test output conforming to the D. L. Shorter / BBC Research Department proposed methodology of October 1949, with N^4 harmonic weighting, or any other similarly-supported acoustically-weighted real-world tailoring, seemingly with no response or interest.

We are reminded of that ASR thread regularly when listening to music on local FM broadcast, from what are very clearly needle-drops of original 1970s and 1980s LP pressings, and our earlier comments about how broadcasters can "see" tune-outs and audience interest on a cut-by-cut basis.

If you are using your phono preamp solely to amplify the output from a medical transducer or in a similar laboratory application, and looking at the result on a spectrum analyzer -- rather than listening to music on an audio system -- then perhaps a simple low-cost, high-feedback or differential design might be preferable to our units. Our understanding is that most EKG units generate primarily low-frequency output and so any TIM or slew-rate limiting on musical peaks and surface noise that would affect your music enjoyment won't even come into play.

Amir's test setup also appears to have induced a slight amount of LF mains noise into his input cabling which can be seen in the LF spectrum residual in the review. We addressed this in the sections above.
 
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Cwopete5

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Possibly meant the MM-5.

Yes, thank you for the correction.
 
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