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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
newbee
4,775 posts
 
Tvad sez, "First of all a MC cartridge is not intended to be used in a MM phono circuit"

To pick a nit....there is no difference between an MM and an MC circuit except for its ability to respond to the loading and gain demands of the cartridge. There are MC cartridges that are high gain and load at 47K (or up to). A flexible phono stage with adequate gain can handle both types of cartridges (my SP10 does it quite well). But as with Ggavetti, using my .9v output Benz produces tube hiss when you run up the volume to LOUD. It is basically noise free with high output cartridges, MC or MM. Low output cartridges need not apply.

BTW, while tube selection is critical, noise free tubes will not overcome tube rush caused by inadequate gain.

At least I think so this morning. :-)
Post removed 
newbee
4,775 posts
 
"I still believe a gain mismatch is contributing to the OP)'s noise issue"

As you should, you are correct! In fact it is central to the issue. IMHO of course.
ggavetti OP
143 posts
 
Well, in terms of load, I checked the specs of the Sumiko, and there is no problem. So, that is not an issue.

I agree that the load mismatch can exacerbate the problem, but I do not think it is the root cause or the central issue -- the problem is that no matter whether the turntable is connected or not to the preamplifiers, when I turn up the volume I hear a lot of background noise. The underlying problem must be somewhere else...at this point I am convinced it's a tube issue. Thanks.
newbee
4,775 posts
 
Sorry, I didn't pay much attention to your original post........

If you are getting tube rush/hiss without a TT connected, then you have either a phono stage with a high(ish) noise floor, noisy tubes, or very efficient speakers which will reveal noise floors not readily apparent with less efficient speakers (like 102db v 86db speakers). Ask some owners of horn speakers. Some time ago I had 82db speakers and every thing was quiet. Then I got some 92db speakers and discovered all kinds of hums and buzzes. :-)

The only way to figure this out is get some phono stage quality tubes tested for low noise. If you still get the hiss you've just got a spare tube or two, or four, etc, and a different decision to make.
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