Pundit
Post by Gryffles on Aug 14, 2017 19:49:54 GMT 12
With using all valve phono stages directly into my 2A3 power amp I've found that record surface noise has increased.
The general noise has increased along with crackles and pops etc. Most annoying is with some LP's I hear a noise that sounds like I can hear the stylus dragging through the groove. Only in a certain place through a revolution though.
I have read that a lower input impedance lowers noise. Currently I'm using a 100k TKD pot would lowering it to say 50k help at all? The output impedance of the SPA II phono is 60 ohm's.
I'm not sire if I'm on the right track here but it was worth asking.
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Post by colinf on Aug 14, 2017 20:04:01 GMT 12
Sounds like the phono stage has very high resolution. There could be a number of things going on. Cartridge loading impedance; the Riaa eq accuracy; interconnects and power leads that sound synergistic with the system; the sound of your cartridge and TT in more detail. A high volume pot impedance would tend towards rolling off the top end depending on the cable capacitance and poweramp input capacitance. Lowering the impedance would allow the HF and ultrasonic frequency response to extend.
AMR-iFi R&D
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Pundit
Post by Gryffles on Aug 14, 2017 20:15:49 GMT 12
colinf thanks for your reply. So from what you have said there are a number of things that could cause these effects. My Benz Wood SL is loaded at 240ohms which is fine. Most load them between 200 and 350. Easy thing to do would be to play around with IC's and see what that does.
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Post by Owen Y on Aug 14, 2017 21:53:07 GMT 12
It's unusual (do you think colinf?) for the vol pot to be located un-buffered at the output? If so, then output imped would vary with volume level. Some further thoughts: I've found that the sound of 'noise' can be revealing of system tonal character - noise such a applause can be assessed like 'pink noise'. Cartridge stylus profiles change how record surface noise is picked up, some profiles can be rather annoying in their HF 'resolution'. The last time I tried implementing the 'Neumann Time Constant', I found that this emphasised EHF presence a great deal - I didn't care for it at all. Often these perceptions can be as a result of tonal balance - eg. less LF power can give rise to perceived brightness. Sometimes system peaks & resonances, can emphasise how upper freq noise & distortion is reproduced (or rather, the opposite way around), eg.... With that many tubes, & with the very high overall gain, I would expect some tube-related noise - eg some tubes exhibit microphonics & various noises can excite microphonic tubes, making such noises more prominent than they would otherwise be. Using tube coolers or dampers can help here to tame this - the trade-off is some loss of 'air' & low level detail. (I use Pearl Tube Coolers sometimes.)
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Pundit
Post by Gryffles on Aug 14, 2017 22:05:42 GMT 12
To clarify Owen Y the vol pot is installed at the input of my 2A3 amp. My room is tricky too. Bit small for the speakers but thats what I have. I have noticed the same thing with the Rhea and the SPA II. The SPA II is very quite for a valve phono stage though. Good idea re the tube dampers Owen, thanks. Bit of playing around to do I think.
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Post by Owen Y on Aug 15, 2017 10:30:11 GMT 12
Ah yes, my bad, the vol pot at input to the amp, so 100k is OK. (It forms a hi pass filter with the preamp output blocking cap, so changing the vol pot to 50k would raise the LF cutoff Hz.)
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