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Propeller Head Plaza

Here is a true story of mine.

69.156.196.162

In Reply to: RE: Objective vs. Subjective Dynamic Headroom for Amplifiers posted by morricab on February 25, 2008 at 02:06:30

Hi.

Talking about low power zip NFB tube amp beating high power SS amp, here is my testimonial. (I posted it before but here is more updated)

Two years ago, I built a 2x1W SET (single-ended triode) tube power amp as a little gift for my brother-in-law, an audiophile using SS amps only. His power amp is the famed Swiss Physics Model 6A 2x100W dual-mono class A power amp, with multi MOS-FET O/P devices. Built heavy duty like a battleship. Tagged USD5,000 in 1986. Driving his Westlake BBSM-6 reference monitor (91dB/m sensitivity).

I want to give a little tube delight for a change. Not expecting any miracles. I built this small mikey-mouse amp with the old old used parts idling in my part bins. Cheapie cheapie.

But so unexpectedly, this little tube David virtually killed the SS Golliah! It works out so well in his small living room with the loudspeakers 8 feet from the sweet spot. At the same moderate sound level for vocals & classicals, it put the SS power amp to shame, with the crucial music engagement & being-there feeling that the SS amp seemed to lack.

Because of this pleasant tube surprise, my brother-in-law decided to go for tube. So he commissioned a tube DIY guru locally to build a more powerful tube amp for him. The tube guru came up with a full blown 2x15W 6V6 push-pull stereo power amp, built big like a tank. It couldn't be cheap considering the no-compromise stuffs used.

On side-by-side comparison, with his costly hi-end CD player driving direct, no preamp, the 6V6 PP power amp sounded so grainy & so untasteful that he had to send it back for overhaul.

Don't ask me why, the 2x1W power amp sound so much headroom in the music
than the 6V6 PP, & so much more details at same average SPLs. We tried the sountrack of the famous "2001 - a Space Odyssey", the bass came up so much more details.

Hint: the 2x1W SET uses a very basic, simple 2-stage topology using only 3 tubes, half 12AX7 driving the power tube (a miniature beam tetrode, but triode strapped). Zip local & loop NFB !

Hereby I have proven it again: less hardware delivers more music.

c-J

Follow Ups:

RE: Here is a true story of mine. - Tony Lauck 11:33:40 02/26/08 (7)
When comparing the two amplifiers, did you control for polarity? It wasn't clear if they had the same number of gain stages, so their polarity might be opposite. If the amplifying set ups had opposite polarity then this might account for some of the differences heard.
- An oft-neglected consideration, agreed. nt - clarkjohnsen 14:10:07 02/27/08 (0)
  x
- I don't think so. - cheap-Jack 12:20:01 02/26/08 (5)
  Hi.
  
  The 6V6 PP power amp, after only simple triode-strapping, get a turn-around sonic improvement.
  
  Don't tell me triode-strapping on the O/P powerstage alone can change the polarity of the amp.
  
  Technically, a triode, having more linear signal transfer curves, inherently outperforms a pentode/tetrode. SET delivers more brain-friendly THD patterns that we perceive it better sounding than a PP topology.
  
  Please don't get "polarity" involved. Irrelevant in this case.
  
  c-J
  
  PS: this true story also reverses the claim that sight tests are influenced by sub-conscious pre-occupied preference.
  - RE: I don't think so. - Tony Lauck 12:51:41 02/26/08 (4)
    Agreed. Triode strapping won't change polarity. So the 6v6 tetrode and 6v6 triode have the same polarity.
    However, what about the SET, which after reading your two posts, is still considered the best sounding. It is a completely different design. Might it not have different polarity?
    
    Edits: 02/26/08
    - Can "polarity" really turn the dices around? - cheap-Jack 13:06:41 02/26/08 (3)
      Hi.
      
      My argument is the imaging & soundstaging of both SET & the triode-strapped 6V6 PP come pretty close. No signs of anything abnormal.
      
      The SET sounds a bit more quiet in the background, as contrary to conventional wisdom, claiming PP tends to cancel out AC hum noise 100% in the primary O/P winding, which won't happen with SET topology.
      
      Subjectively, we found the SET seems to deliver more music textures than the PP amp, & we feel more enjoyable in listening to it.
      
      c-J
      - RE: Can "polarity" really turn the dices around? - Tony Lauck 13:56:19 02/26/08 (2)
        
        In Reply to: RE: Can "polarity" really turn the dices around? posted by cheap-Jack on February 26, 2008 at 13:06:41
        
        Well if the imaging and soundstaging are similar, then it is likely that the polarity of the amps is the same, especially if the imaging and soundstaging are good.
        [There is a simple test anyone can perform to see if two channels of audio are in relative polarity. It requires no test equipment, just muscles, ears and brains: Make sure the two channels have equal volume and then place two box speakers facing close to each other. If they are out of phase you will hear severe bass cancellation. It is possible to extend this test to compare two amplifiers by sending one channel through each amplifier. The test works best with mono recordings as some stereo recordings have bass phase shift between channels depending on microphone position. Not recommended with heavy speakers or mono blocks with short speaker wires! Never tried this with dipoles -- don't think it will work with them.]
        
        Edits: 02/26/08
        
        Are we talking about "polarity" or "phase"? - cheap-Jack 08:19:12 02/27/08 (1)
        
        In Reply to: RE: Can "polarity" really turn the dices around? posted by Tony Lauck on February 26, 2008 at 13:56:19
        
        Hi.
        
        How come phase come in the polarity picture?
        
        Yes, I always use vocal/dialogue & mono music to test the phase/spatial coherence of equipment. My rig reprduces dialogue/mono vocals at dead centre between the pair of loudspeakers even I wave my head.
        
        A good system plays excellent imaging & soundstaging of both stereo & monaural music, although stereo music sounds much wider & more dimensional.
        
        c-J
        
        PS: Just received updated impression my brother-in-law emailed me on the 2W SET I built for him vs his 6V6 triode-strapped 6V6 PP amp:-
        "It (SET) is better in detail with warmth, sweet high & vocal. Would say both are euphonic & musical. But the 6V6 is better in jazz, but more punchy & more body."
        
        RE: Are we talking about "polarity" or "phase"? - Tony Lauck 08:38:59 02/27/08 (0)
        
        In Reply to: RE: Are we talking about "polarity" or "phase"? posted by cheap-Jack on February 27, 2008 at 08:19:12
        
        We are talking about polarity.
        
        I mentioned "phase" because the bass cancellation test procedure that I suggested works best if there is little or no phase shift in the bass frequencies between two channels. This will be the case with all monaural recordings, many stereo recordings, but not all stereo recordings all of the time.
        
        If there is a significant phase shift the test procedure might not work well. For example, if the program material consisted of a 100 Hz sine wave, if the two channels were were out of phase by 90 degrees on the recording then the test would be inoperative. (If the two channels were 180 degrees out of phase, then the test would give consistent incorrect results.)
RE: Here is a true story of mine. - Chris O 15:13:25 02/25/08 (1)
Sounds like his "DIY guru" skills are lacking. I have a 6V6 PP amp that is probably my best sounding amp. Don't shoot the topology but you can shoot the designer.
_______________________________
Long Live Dr.Gizmo
- Yours can sound even better.. - cheap-Jack 11:10:54 02/26/08 (0)
  Hi.
  
  Let me carry on to finish up my story.
  
  I recommended to have the 6V6 PP amp "upgraded" by simply triode-strapping the 6V6s. So it was done & the Golliah amp now sounds so much finer than its original beam tetrode PP topology before, getting pretty close to my 2x1w SET (which is, incidentally, a beam pentode triode-strapped).
  
  Now my brother-in-law gets back smiles on his face as he knows he can still keep the 6V6 PP amp for high power music though he prefers the little David SET amp for vocals.
  
  Part of the problem could be, IMO, is the complex long-tail phase splitter stages, using 2x6SN7, driving the powerstage. More active devices mean more difficult to get the music right.
  
  Another problem is there are not many DIYers who can go listening as good as soldering.
  
  I told him I can improve even more the now refined triode-strapped 6V6 PP power amp by replacing the triode-strapping resistor with a passive voltage level shifter network, which I already installed in my PP power amp for a couple years, & works flying colours.
  
  Refined topology makes good sound even better.
  
  c-J

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