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Background noise

Hello folks. I have a Shindo Monbrison, a wonderful preamplifier, with a wonderful phono section. That said, I noticed a fairly high level of background noise when I turn up the volume without playing music (and this doesn't change by unplugging the interconnects). When the volume control is at its maximum level, you even listen to a little whistle.

Is it normal for a tube preamp or do you think there is a tube problem or another issue? I never experienced this problem in the past, but I've always used SS phono sections.

thanks.
ggavetti
rcprince
3,075 posts
 
Sounds like it could be tube rush from the tube(s) in the phono stage. If you have enough gain from your cartridge/phono stage combination, it may not be noticeable in ordinary listening. Could also be a noisy tube, though, in which case you'll probably need to get your replacement from Shindo, I think they use some unusual tube types in their gear, at least the amps.
ggavetti OP
143 posts
 
I think the hypothesis that this is tube rush is sensible. The gain is ok but not great: I use a MC Sumiko Blackbird through the MM phono section. The Blackbird is 2.5 mV, and the Shindo dealer says the minimum MM should be 3 mV. Despite this slight mismatch, I find the combination to be wonderful...except that I can hear some noise when I turn up the volume level during music reproduction.

I'll find out what tubes are used for the phono stage and see if I can find a replacement. Thanks
swampwalker's avatar
swampwalker
5,138 posts
 
I use a MC Sumiko Blackbird through the MM phono section. The Blackbird is 2.5 mV, and the Shindo dealer says the minimum MM should be 3 mV.
OK, now we are getting somewhere. You probably have a noisy tube or tubes that is exacerbated by being below the minimum recommended input voltage, therefore needing to crank up the gain. Its also possible that you may have a loading mismatch by going into an MM phono stage (typically 47k ohms), but I'm not sure what that would sound like. See if you can get some phono grade/v, low noise tubes from a reputable dealer and report back.
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isanchez
276 posts
 
I noticed a fairly high level of background noise when I turn up the volume without playing music (and this doesn't change by unplugging the interconnects). When the volume control is at its maximum level, you even listen to a little whistle. Is it normal for a tube preamp or do you think there is a tube problem or another issue?

My tube preamp is absolutely silent with the volume all the way up and putting my ear against the speakers. Of course, everything is turned on. Considering that my preamp has six tubes, I was very surprise by this total silence.

I'm not sure what the problem would be, but it is not normal to have such level of noise. Since yours is a second-hand unit, I would probably start by replacing the tubes.

Best,

iSanchez

ggavetti OP
143 posts
 
Swampwalker, actually there is no loading mismatch, but I think your diagnosis is correct -- noisy tube, exacerbated by being below the minimum input voltage.

I'll look into it and let you know. Thanks.
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