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Tube preamp sweet spot/amp compatibility?

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Posted on May 19, 2015 at 09:25:24
Highdecibel
Audiophile

Posts: 10
Location: Scottsdale, AZ
Joined: May 19, 2015
 I have a Bel Canto SEP-1 hybrid preamp hooked to Quicksilver Silver Mono amps. At low volume levels, quiet listening, the resolution, detail, realism of vocals is amazing. Problem is, I like to listen to music a little bit louder. As I turn up the volume, the lush midrange goes away and it sounds kinda washed out. I'm wondering if it's "normal", or if it's an impedance issue, or I need better tubes. Preamp uses two 6922 tubes (I use RCA branded 1970 d/c, Siemens I think). Amp input impedance is 100k ohm. Preamp output impedance is 150 ohm. thanks, Jeff

 

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RE: Tube preamp sweet spot/amp compatibility?, posted on May 19, 2015 at 12:24:14
fantja
Audiophile

Posts: 15524
Location: Alabama
Joined: September 11, 2010
 Welcome! Jeff-

I am certain that one of tubed inmates will be able to help you.

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 19, 2015 at 14:21:43
BCR
Audiophile

Posts: 2446
Location: connecticut
Joined: April 7, 2009
 I have Quicksilver Silver Seventy amps. What tubes are you using? What speakers are you driving with the amps? I use GE tubes with my Quicksilver Phono and Linestage preamps. BTW,there is no problem with the impedance match between the Amp and Preamp.

 

Important piece missing, posted on May 19, 2015 at 15:54:00
Awe-d-o-file
Dealer

Posts: 21037
Location: 50 miles west of DC
Joined: January 10, 2004
 What speakers and maybe how big is the room


E
T

ET

"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 19, 2015 at 16:04:05
Highdecibel
Audiophile

Posts: 10
Location: Scottsdale, AZ
Joined: May 19, 2015
 The preamp has 6922's I bought off EBAY 12 yrs ago, not matched or tested which could be the issue. They are RCA branded, E88CC/6922 labeled. I think the date code was 7004. Just put brand new tubes in the amps except for the 12bh7 (GE). Shuguang KT-88-98 (Ruby), Mullard GZ34, RCA 12AX7A (from VTS).
Speakers are Reference 3A MM de Capo (92db).
I recently pulled this all out of storage and am trying to get it dialed in. At low volumes there's tons of midrange lushness/detail/liquidity and when I turn up the volume to "fill the room" level (not blasting it) the sound kinda dries out a little. It still sounds good, but not nearly as lush as at a really quiet volume level. Just wondering if maybe the gain isn't matching the amps or I'm overloading the tube and it's distorting or something that's causing the sound quality to degrade at the higher volumes.

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 19, 2015 at 16:17:56
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 My preamp uses 6922's so you may want to try this trick. Reverse the speaker leads.

In my case the preamp used inverted phase amplification. That MAY be your problem. My stereo had the same exact sound. Fine at low volumes. Turn it up and it sounded "hollow". the lead reversal did fix that.

post your results.

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 19, 2015 at 16:41:23
BCR
Audiophile

Posts: 2446
Location: connecticut
Joined: April 7, 2009
 I presume you have the tubes biased between 90 and 110 ma. You might as well replace that 12bh7 in the amp and also the old RCA 6922 tubes in the preamp. I doubt that the output voltage of the preamp is not enough to drive those amps.

 

RE: Important piece missing, posted on May 19, 2015 at 17:11:00
Highdecibel
Audiophile

Posts: 10
Location: Scottsdale, AZ
Joined: May 19, 2015
 13 X 16 one side opens to the dining room and the other side opens partially to the entry way. I have GIK Bass traps behind the listening wall (short wall) and Gik tri traps in the front corner opposite of the fully open side into the dining room if that makes sense.
Listening position is a couple feet from the back wall.

 

RE: Important piece missing, posted on May 19, 2015 at 17:24:47
Awe-d-o-file
Dealer

Posts: 21037
Location: 50 miles west of DC
Joined: January 10, 2004
 I wanted to know what speakers you are driving w/ your 90 X 2. That's the most important missing piece. We know from your moniker you like loud which is fine. Seems an average or little bigger than average room. Another thing we don't know is was it better than now some time in the past with this gear or has it always been like this with this gear? Test the output tubes and always make sure to bias it for longer tube life and proper operation.


E
T

ET

"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 19, 2015 at 17:31:40
Highdecibel
Audiophile

Posts: 10
Location: Scottsdale, AZ
Joined: May 19, 2015
 tubes at 100ma. I can drive the speakers stupid loud. so voltage is fine.

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 19, 2015 at 17:39:42
BCR
Audiophile

Posts: 2446
Location: connecticut
Joined: April 7, 2009
 You can hookup the speakers to different taps on the amp and see if that improves things. Just a shot in the dark!

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 19, 2015 at 17:46:20
Highdecibel
Audiophile

Posts: 10
Location: Scottsdale, AZ
Joined: May 19, 2015
 Let me try this and get back to you all tomorrow. Thanks for your help. Fingers crossed...read about phase reversal but never tried switching the speaker leads...

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 19, 2015 at 20:02:33
Sondek
Audiophile

Posts: 9632
Location: Fort Worth
Joined: May 17, 2000
Contributor
  Since: April 5, 2002
 Siemens 6922's are not known for their mid-range magic. They are good tubes with good extension on both ends of the audio spectrum and s'loads of detail, but their mids are scooped-out sounding compared to the likes of Amperex for example. Amperex 6922 cannot match the extension and detail of the Siemens, but they do get the mids right. For my part, if the mids ain't right it just ain't right. The Tele 6922 is my all around favorite 6922. They're more extended and detailed than Amperex, but not quite as much as Siemens, and they get the mids right - although Amperex better them ever so slightly in this area. A very, very good current manufacture 6922 I can recco is the JJ gold pin version 6922. They come really close to the sound of my vintage Teles. You can get them selected/matched/low-noise from Tube Depot for like $30 a piece. No association with Tube Depot, just a customer.

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 19, 2015 at 20:21:33
Tidycat1
 I am curious as to your results of the phase reversal.
Another 6922/6dj8 option to try is the Mullard.The standard Mullard is very midrange oriented with great musicality.The military versions add a little sparkle to the mix.
For tube characteristics,you can check out Tube World.Just pick the model you are interested in and TW will give you a run down on the most-to-least desirable.Also their sonics.
Good luck problem solving
Is it possible that you are pushing the speakers too hard to fill the space?Maybe a slightly larger speaker system with 8-10" woofer.
Bass loading can have a perceived difference on volume/power.

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 20, 2015 at 08:19:05
Highdecibel
Audiophile

Posts: 10
Location: Scottsdale, AZ
Joined: May 19, 2015
 phase refersal worked! It was subtle to NOT SO subtle differences. I listened to several tracks and there was a definite improvement across the board. Thanks, I had read about it but never tried it. Thanks!

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 20, 2015 at 08:23:44
Highdecibel
Audiophile

Posts: 10
Location: Scottsdale, AZ
Joined: May 19, 2015
 I'll try that on my day off tomorrow. the phase reversal did the trick!

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 20, 2015 at 08:52:07
Highdecibel
Audiophile

Posts: 10
Location: Scottsdale, AZ
Joined: May 19, 2015
 the phase reversal was a success. On Madonna's "Vogue" track (I know, I know...don't start flaming), instrument and vocal placement was more precise, better separation, leading edges to notes more distinct. A major improvement.
Chris Isaak's Blue Spanish Sky, his vocal inflection was more realistic instead of the flatness that I had before the phase switch.
Despite my moniker, I wasn't listening that loud during testing, nor do I listen at extreme volumes that often. My MM de Capo speakers have a 8" woofer, just a capacitor rolling of frequencies to the tweeter, and I run two sets of identical wire to them (bi-wired). Bass is very deep, you'd think I have a subwoofer, even in my 13x16 room that is fully open to one side and partially open to the other. Don't even start me going on bi-wiring! My speakers benefitted from bi-wiring dramatically, despite all of what I have read that say it makes no difference. When I get the time I'll post my experience with that. Thanks for everything! -Jeff

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 20, 2015 at 09:31:11
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 You've gotten some unusual responses here...

What you're hearing is likely the power amplifier performance deteriorating as you demand more from it. You would have to have a horribly designed preamp, or be asking for a ton of voltage from it to have a drastic sonic change like the one you describe, and those Quicksilver monoblocks probably don't need more than 0.5V or so of signal to get to full power.

My guess is that you're hearing crossover distortion in the monoblocks.

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 20, 2015 at 13:51:50
Awe-d-o-file
Dealer

Posts: 21037
Location: 50 miles west of DC
Joined: January 10, 2004
 Or something amp related as I see it. Old weak tubes in an amp and/or where bias was not looked after may make the amp put out 1/4 of its full capability or less. I too don't understand why people aren't focusing on the amp. Also he has not mentioned his speakers even though I asked that of him as inefficient speakers or ones that drop in impedance with loading may run better on the four ohm tap even though they are an 8 ohm class speaker.

E
T

ET

"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936

 

Great!!!! , posted on May 21, 2015 at 06:09:50
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 I'm no engineer but there seems to be something about those 6922's that begs to be reversed.

Enjoy your new sound.

charles

 

RE: Great!!!! , posted on May 24, 2015 at 07:00:26
Mr Peabody
Audiophile

Posts: 1109
Location: St. Louis, MO, USA
Joined: August 14, 2010
 Yeah, a lot of tube gear is phase inverting, I had to do the math when I had Conrad Johnson and then a Audio Note tube DAC. From what I've heard if both pieces the amp and preamp are both inverting then normal hook up should be fine but if an odd number of inverting,llike when I added a tube DAC then the speaker lead inverting came to play. Some debate the importance as many recordings aren't in phase but it does seem to make a difference in focus vs. more diffuse sound. Fortunately, I didn't have the same issue as you and the poster describe. However, as one poster mentioned I used a 4 ohm tap off my power amp though my Dyn's were 6 ohm, when I had the amps converted to mono I discussed this with the tech and they suggested often 4 ohm output is better though speakers may be more impedance.

 

RE: Great!!!! , posted on May 25, 2015 at 13:56:05
Nick77
Audiophile

Posts: 10
Location: Austin Tx
Joined: February 13, 2012
 Just switched to a tube preamp as well with 6922 circuit.

 

RE: Tube preamp sweet spot/amp compatibility?, posted on May 25, 2015 at 14:58:04
Highdecibel
Audiophile

Posts: 10
Location: Scottsdale, AZ
Joined: May 19, 2015
 I apologize for not giving enough information or a better definition of what I was experiencing. I will make sure to give better, clearer information in the future.
The Reference 3A mm de capo speakers I have are rated 8 ohms, but apparently they drop to 5.1 ohms at one point according the the graphs I found. I was running the 8 ohm taps, and I did switch to the 4 ohm taps, after suggestions to try it. Sound became fuller, less bright, and better mid to high frequency clarity, less shrilly. Definitely sounds better on the 4 ohm tap.

 

RE: Great!!!! , posted on May 25, 2015 at 15:24:00
Highdecibel
Audiophile

Posts: 10
Location: Scottsdale, AZ
Joined: May 19, 2015
 The phase inversion and the 4 ohm tap change that were recommended by inmates made a substantial difference. I did find an older recording (Manhattans: Kiss and say goodbye) where bells were out of phase...strange as I was so accustomed to hearing them sound "correct" when I had the phase the incorrect way. This is the only recording so far that I have noticed something sounding wrong. Despite my poor description of what I was hearing, You all collectively were able to help me. Fantastic. Thanks.

 

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