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Is there such a thing??-- Tube Preamp Question

Hello All,

I have recently acquired my first tube preamp. Its a Blue Circle 21.1 with the stepped attenuator. From the start its been a journey. When I received it there was a distinct buzz/hum. I sent it out for repair and they found it was the power transformer. They made me a spiffy new external power supply which solved the problem. I truly love what it does for tonality, richness of voices and my sound stage appears deeper to me with good placement of instruments within it. However, and maybe my expectations are just to high, the hiss and tube replacements (needed to replace tubes after 6 months) along with a generally fussy nature in terms of the need to pop the top and clean to get the fuzzy sounds out occasionally just seems a bit much. Are all tube pres susceptible to this level of need an "fussy" temperament? Another issue, is when I am watching TV and/or using TV as a source, between songs there are strange sounds(bleeps and squeaks) and moments of scratchy sounds noted in quiet passages and seem triggered by moving from one song to the next. It seems very sensitive to picking up TV noise which I have never noted using solid state gear.  While it isn't evident at medium to high volume it just bothers me and I know that its there. 

Can I have all that this does for me in terms of tonality and sound stage along with a less fussy nature? Does such a thing exist for a reasonable price($1000-$2000). I would like a more silent background with less need for constant attention. 

Does such a thing exist?
128x128birdfan
birdfan's avatar
birdfan OP
175 posts
 
Thanks Newbee and All. 

The preamp has a handy dandy gain switch which can be accessed from inside the cover. I have played with this and swapped in a range of speakers. My OB Spatial holograms certainly do magnify the problem as they are higher efficiency. when those are in the mix I set the gain switch to its lower settings. When using my Anthony Gallo 3.1's I use the lower setting. The associated equipment as follows:

Amps: Red Dragon M1000 (mkI) Mono Blocks-- I'm not sure the input sensitivity
Cabling: All interconnects are Anti Cable entry Level. Cullen pwoer cables, 
Tubes: Currently Running Electro harmonix 6922
Speakers: Green Mountain Audio Continuum 1's, GMA Chroma HD, Gallo 3.1, Magnepan 1.7i, Magnepan MMG, Spatial Hologram M3 Turbo S
Power conditioning:  Furman Power Conditioner (PST-8)
Sources: TV, JA Michel Gyrodec, Thorens TD166, Bluesound Node 2, 
Phono Stage: Lounge Audio LCR mkIII

 
lowrider57's avatar
lowrider57
5,417 posts
 
I couldn’t find the output gain spec of your preamp, but a reviewer wrote the gain is "quite high."

I think you should stop using the gain switch. Since your pre has high gain, use the low setting for both sets of speakers. Your monoblocks don’t need the increased gain to drive your speakers.

Very nice system, btw.


newbee
4,775 posts
 
Wow, you have a lot of speakers! From the spec’s on the speakers and the Amp I would guess that the greatest noise issue would develope when you are using the Spatials. Very high sensitivity amp (2.9v) coupled with high speaker efficiency (95db) would probably operate best with minimal to no pre-amp gain. (Contingent on a lot of other issues of course). The other speakers should be less problematic, but never the less still need less fixed gain. All depends on your pre-amps minimum fixed gain as well as the input from your sources and how much attenuation you apply to this signal via you use of the VC on the pre-amp. At a minimum I would set the pre-amp to its minimum setting as suggested by Lowrider.

BTW, while I doubt that you would be guilty of this, do not judge your pre-amps ’quietness’ by just rotating the VC to max and putting your ear in front of the tweeter. That will always result in a worst case scenario and create unnecessary angst. Just select an input and set your VC to produce the maximum volume you would use. Then mute your source and the residual noise you hear is really all that matters. I think an ear about 3ft from the speaker would be a good distance to judge noise, although some even go so far as judging from the listening position.

BTW, tube life - if you are using low noise tubes appropriate for the pre-amp (Some pre-s are very hard on less than ’rugged’ tubes but other than that you should expect at least 3000 hours or much much more).

FWIW finding a good used tubed pre-amp for $2000 should not be at all difficult, but from what I’ve read about your’s I’m not sure how much you would improve your situation. I would look for other cures first.
lowrider57's avatar
lowrider57
5,417 posts
 
Once again I'm in total agreement with newbee. That's a well regarded preamp, I would not be looking to ditch it. You've had it serviced and there is no hum present. 
This won't solve your problem, but order some NOS tubes; matched and tested for noise and microphonics. You'll have a lower noise floor and improved sonics over the EH tubes.
It's possible one of your tubes is microphonic. In this state, the preamp can pick up and present all kinds of crazy sounds. It's like having a microphone in your system.

Your TV uses a SMPS, a switched mode power supply, which often adds noise to your AC line and into the audio signal. I suggest unplugging the TV while you do some troubleshooting.  

Are all your components plugged into the Furman? Are you using a shared AC line that also has lights or dimmers on it?


bluorion
479 posts
 
This is an interesting question. I'm a newbie too so please forgive me for this stupid question: but do these issues occur in solid state preamps? The reason I'm asking is because I'm about to get a new preamp (my first tube preamp) and I hope I don't have these issues. I prefer low maintenance equipment so this better not happen. If so, I'm going back to SS! 
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