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Question on phono input noise levels

Earlier this year, I had my Parasound P5 Preamp connected to my 35+ year old Bang and Olufsen turntable, with a moving magnet cartridge. I noticed that with the turntable connected (including the ground wire) I noticed quite a bit of hiss when not playing a record and the turntable was idle. In other words, the noise level was much higher when the input selector on the P5 was set to phono vs. other inputs.  Later, I upgraded to the Parasound P6 preamp. I noticed the same hiss, when the volume was turned up. I just assumed it was the turntable, since the problem (albeit minor) happened with both preamps.

As some of you may recall from a recent posting, I just purchased a new turntable. Yesterday, I received it - my new Rega P8 turntable with factory installed Alpheta2 moving coil cartridge. The hiss is worse!! So now I have experienced this background hiss with two different preamps and turntables. is this normal?  I'm wondering if the higher gain needed for the moving coil cartridge is adding to the noise level.  Could I be expecting too much out of the phono preamp section of the P6?

Note that both the turntable and amps have power run through an Audioquest Niagara 1200 line filter, so I do not think it is AC noise.  But the noise level is much higher on "phono" compared with other inputs.  Do any of you all notice this with your equipment?

btanchors
millercarbon's avatar
millercarbon
12,531 posts
 
Its a turntable. Some noise is normal. 
mulveling's avatar
mulveling
1,913 posts
 
That hiss is normal noise from a phono stage. Be thankful you don't also have a hum or buzz from a grounding issue to track down. For a low or medium output MC cartridge you can try the combination a step-up transformer with a phono stage in MM mode. The higher the step-up ratio, the more that hiss noise will be pushed down - however it is also increasingly difficult to retain sound quality with higher step-up ratios, and you have to be careful not to cut too far into the phono stage's overload margins, and also to not load the cartridge too heavily (which loses signal, and makes your signal-to-noise ratio poor again). Basically you'd typically want a SUT ratio of 10x to 30x for cartridges in the range of 0.5 mV to 0.3 mV.

The other approach is just to buy a higher quality separate phono stage, and/or a cartridge with  a higher output level. But some amount of hiss is normal - you'll have to judge what you consider acceptable or not. 
uberwaltz's avatar
uberwaltz
13,381 posts
 
It is quite conceivable with the extra gain required to boost the much lower MC signal that the " hiss" is more noticeable to you now.
Is it audible from your normal listening position?
At a normal volume setting on the amp?
Or do you need to crank the volume to hear it or be right up against the speakers.


btanchors OP
13 posts
 
Definitely no hum or buzzing.  Just a combination of “hiss” and a “rushing” noise.  I can hear it at my listening position, at a volume setting I would consider to be medium.  The sound comes out of both the tweeter and midrange drivers.  The output of the cartridge is 0.3 millivolts - is that considered a low or medium output for a moving coil cartridge?
uberwaltz's avatar
uberwaltz
13,381 posts
 
0.3mv is right about average for a lomc and should not truly produce excessive hiss with a quality Phonostage.
60 to 65db of gain should be more than adequate, the higher the gain, sure it will require less volume control to play louder but the background hash or hiss will be conversely increased as well.
I used to always go with the least gain possible for a decent listening level and no more.

But of late I have also gone the SUT route and run into a MM only Phonostage right now.
One table has some slight hiss ( yes Miller my Garrard 401!) But my DD tables are both inky black silent.

I am not familiar with the p6, does it have adjustable gain or is it simply mm or mc options only?
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