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In the Forum: Analog Playback
In the Thread: AMR PH-77: just another phonostage or more?
Post Subject: Phonostages and noise.Posted by Romy the Cat on: 7/5/2009

Yes, I have paid attention to the ridicules noise specification.  - 147dB is ever higher then 24bit dynamic range – good luck with those numbers in tube phonostage! They use 'A' weighted measurement that is not kosher from my perspective and juts a way to manufactures to publish better marketing numbers. 'A' weighted scale is emphasizing human most sensitive zone, while rolling off high and low frequencies. It reportedly measures subjectively perceived loudness but in my view it is very not objective characteristic to talk about S/N. It is like you say that that it is 27420053 degrees of temperature outside but “forgot” to mention that in your scale the water freezes at 2711053 degrees…

Anyhow, they do report the ultra low noise accomplishment and I do feel that the noise in this phonostage might be very low. Ironically ANY manufactures I know when they make phonostages report the “ultra low noise” but the phonostage noise never bothered me. Any more or less properly build phonostage has 80dB S/N and it is absolutely enough not to worry. I believe the record in phono S/N ration was achieved by John Curl in his Vendetta phonostage where he had 96dB or something like this. I think anything after 80dB-85dB is irrelevant. The key is not the amount of noise but the harmonics of noise and how the noise talks with the normal LP noise (surface noise etc…)

I think at any given playback, within a context any specific amplification gain and speakers sensitively if you max out all you attenuators and have at max gain no noise from loudspeakers then any further worry about noise is irrelevant.  Not to mention that most playbacks the majority of analog playbacks nosier does not come from phonostages but from externals cables and cartridges. In case of AMR when they use 3 arms it might be tricky… I always prefer to have grounding flexibility and be able with given cartridge to stick grounds in different locations. I am sure the AMR guys took care about all possible grounding configuration, particularly combining the MM and MC cartridges and mono and stereo cartridges …

The  12AT7’s own noise?  Well, pay $8K and it will be an opportunity for you to learn how it might be. My only concern with the ultra low reported noise number is that they might defeat the noise intentionally. In their power amp they run feed-forward injection and they might come up with some kind intelligent back-face noise injection. It would certainly lower the noise numbers but I am not a big fun of those wide-bandwidth injections. I do not claim that they did anything like this but to operate 12AT7 at 147dB S/N (even ‘A’ weighted) … I do not know, it would be interesting to hear further comments about it ether from  AMR or from anyone who will write about it.

The Cat

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