640p preamp problems!

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Aug 10, 2019
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Hi all, just bought a new Cambridge Audio 640p phono preamp today to sit between my Nad C352 amp and Aiwa PX-E800 turntable. When all assembled correctly, I get a horrendous noise coming out of the speakers, extremely loud and distorted. There is some noise there even when the turntable is not operating. I've been using the turntable up to now just plugged into one of the spare channels on the amp and though not as loud as the other channels, has been fine sound-wise. I've read something about the need to ground the turntable, but there's no grounding lead apparent and if this was the problem, why had it not surfaced before? Any suggestions gratefully received! Cheers, Tom
 

John Duncan

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Jan 8, 2008
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I'm confused. If the Aiwa was working properly before in any of the spare channels in the NAD, then it sounds like you don't need a phono stage - ie that there's one built in?

I've also checked, the 352 doesn't appear to have a phono stage, so that rules out your plugging a phono amp into a phono amp.

Tell us exactly what's plugged into what.
 

fatboyslimfast

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Jan 10, 2008
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[quote user="bakes"] I get a horrendous noise coming out of the speakers, extremely loud and distorted. There is some noise there even when the turntable is not operating.[/quote]

I assume you are using a Magnetic cartridge - you haven't plugged it into the MC inputs have you? the gain is much higher and may cause the distortion.

Apologies if I'm stating the obvious...
 
A

Anonymous

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The turntable is plugged in to the MM connectors on the Cambridge and the output is set to MM, so everything seems to be fine in that regard.
The turntable was working fine but not at the volume of the other channels which is why I bought the preamp. Perhaps there is a built in one which simply does not amplify to as high a volume as line-level inputs?
 

John Duncan

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Jan 8, 2008
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[quote user="bakes"]The turntable was working fine[/quote]

Strange. Any phono stage boosts volume but also applies a steep tone curve to it, so if it sounds fine (but quieter) then maybe there is a phono stage in there, just with less gain. Am googling.
 

John Duncan

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Jan 8, 2008
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Aha. I have found a manual for the 850 (which I presume is similar) - it has a built in phono stage. See if there is a switch behind the platter that says 'Equalizer Amp On/Off'. If so, turn it off.
 
A

Anonymous

Guest
John,
thank you so much for your help. Switch located and turned off!
Cheers again,

Tom
 

John Duncan

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Jan 8, 2008
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Cool (that'll be twenty guineas)
emotion-1.gif
 

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