After a very drunken purchase I’ve now got an old Audio Note M7 preamp.
It’s the Audio Note ‘sound of the music’ M7 Tube ‘silver sound’ with phono stage one.
Problem is that with nothing playing there is a very noticeable noise, I’ve never heard one of these make any noise or hum when idle.
It sounds like a hum with a rushing noise in the background, the hum is constant but the rushing noise increases with volume. I’ve tried earthing/grounding the amp back to the DAC and phono stage but neither makes any difference.
I had exactly that model and remember that it was quite a noisy pre-amp, although mainly in terms of hiss. PQ gave me a box of 250 12AY7 and said find yourself some quiet valves. I tried loads but never got rid of the hiss/noise. I just concluded that it was a noisy design. I guess the rushing noise could be a duff valve.
Pretty sure they are 12AY7/6072. Be careful though, the pre really works best with the NOS GE version. Fitting the Electro Harmonix 12AY7/6072 for example, does not do the pre any favours.
AFAIK
The first valve M7 preamps (line-only version) had a solid state power supply and a single 5687 was used for signal amplification. In the next version the power supply employed 6X4 rectification again with a single 5687 for signal amplification (the version I have)
The first valve full-function preamps, also marketed as Audio Note, incorporated an MM phonostage and used 6072 in both the phono and line stages.
In 2000, the M7 became M7 IIk. Still retained the use of 6X4 as rectifier. But now the line-only version used 2 x 5687 and 2 x 12AT7 The full-function version used 2 x 5751 and 2 x 5687
That’s a wired one. If it’s a phono version, I’d expect 5x 6072A. But those tall ones (assume they’re the line stage tubes) don’t look like 6072A and the rectifier (by the mains transformer) doesn’t look like a 6X4.
Are you using it on phono or line? (presumably phono, as you say the noise varies with volume, and he phono stage is in front of the volume control)
The 6072A is a low-noise 12AY7 - if they’re 12AY7, then should be replaced with real 6072A (GE or Raytheon, not Chinesium crap), at least in the phono part.
The very first valve one he did had 2 x 6072 & 1 x 5687 in the phono stage & then 2 x 6072 & 1 x 5687 in the line stage. (in the typical configuration he’d use). But this looks to have a different line stage configuration.
