Background noise

yes...i'll look into the tubes. Actually, i just opened it, and noticed that the housing of one of the tubes is a bit loose. so, that might be the culprit...or one of the tubes. i'll keep you posted. thanks.

I'll add that the Shindo units I have heard are astonishingly quiet, so that would also make me lean towards a noisy tube as the culprit.

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.

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.

"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.

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. :-)

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.

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

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.

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

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.

there is no noise I can hear from the other inputs, even at maximum volume levels. Just to give you a better sense of the loudness of the noise, I just set it at the maximum level, stepped out of my listening room, moved to another room that is approximately 8 meters away from the listening room, and could still hear it.

BTW, I bought the Monbrison 3 months ago from someone who bought it in October. Called Shindo and they told me that the warranty is not transferable...weird policy for a luxury product, if you care about keeping your customers. That said, the Monbrison is just wonderful

Sounds normal but I agree with Tvad, hard to tell based solely on info given. Do you notice any difference between other inputs and Phono or is it all the same result?