2. amps-preamps
  3. 149712-84789

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

Showing 3 responses by lowrider57

lowrider57's avatar
lowrider57
5,397 posts
 
Agree with everything @newbee stated. I couldn’t find the output gain spec of your preamp, but a reviewer wrote the gain is "quite high." This would support newbee’s comments.

This preamp requires low-noise tubes. This would at least reduce any tube hiss and provide a lower noise floor for your sources. You can use
6922, 6DJ8, or possibly 7308 (slightly higher voltage) tubes.

You need to tell us about your setup; type of amp, sources, your power situation, eg, is your TV on the same circuit as your audio.
It’s possible the noises you hear may be from the TV and other devices contaminating the AC line.


lowrider57's avatar
lowrider57
5,397 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?


lowrider57's avatar
lowrider57
5,397 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.


More to discover