• Re: Brady, Toccata & queries - Dave Davenport 08:23:51 11/18/03 (5)
  In Reply to: Re: Brady, Toccata & queries posted by James D on November 15, 2003 at 07:51:04:

  Hi James,

  Yes this is very interesting, thanks for the informative post. I have studied it and have been thinking about it and have a couple of questions for you.

  First, and probably most important, how does it sound? How does adjusting the operating point effect the sonics, and what differences do you hear between the different methods?

  I think that a capacitor between the cathode and cold end of the input is technically correct. However I have tried it and not heard any difference. Do you hear a difference?

  I think, if I understand your post correctly, methods 1,2,3,and 5 change the operating point of the tube and are what I call "DC balance. Method 4 is what I call AC balance; the pot doesn't change the DC bias but the relative levels of the two signals. Is this correct? What are the sonic differences?

  You use a mix of fixed and cathode bias. I have tried both fixed and cathode bias but not a mix. What is your experience with a mix?

  Dave
  
  
  

  ---

  • ...Long and winding reply... - JamesD 11:56:35 11/21/03 (4)
    In Reply to: Re: Brady, Toccata & queries posted by Dave Davenport on November 18, 2003 at 08:23:51:

    Hi Dave,

    Sorry for the delay in replying, I'm 'on the road' and have only occasional 'net coverage'. Anyway to your questions...

    1) How do the various changes affect the sound?

    Hmmm... Very good question! As always in a high-resolution system every change makes a difference but lets have a general stab at it. I have found the character of the sound changes with changing distortion profile (no surprise there..) The distortion profile comprises several components such as harmonic and intermodulation etc etc. Fortunately tube amps with zero interstage feedback have the least number of distortion mechanisms and so I'm can generalise certain conclusions.

    For harmonic distortion the profile should show a decrease with between order 6dB and 18dB per octave with 12dB being optimum. It should also have orders higher than 6th in the noise floor. This provides the least THD generated sonic profile - moving away from this profile makes an amp sound tuby or ss in character - depending on which way one moves. So I try to voice my amps to achieve this. I also try to achieve the lowest overall THD figure as lower is better and increases the level of fine detail or overall transparency in the amp.

    For Intermod. then I try to minimise the ability of any stage to affect any other stage - this is also affected by the op point chosen - and I find that very well dynamically balanced op points in pp can be quite sensitive to intermod mechanisms as they are very, very transparent.

    I have found that I can use any of the mechanisms for adjusting the amp and get the same level of sound quality. Not always the same sound as each sounds slightly different and it is personal taste as to which is best. This was what caused me to try combining methods to try and get the best combination of 'voice' to the amplifier - or rather the most neutral to my ears... I have also found that at this level of finesse there is no absolute right way to configure any given stage – different valves and overall topologies change which method works best. Different components – particularly different transformers have a big influence on which method is best too...

    What I am tweaking for each time is the least sonic signature from the amplifier – to my ears and the most resolution. I find this also equates to the most relaxing sound from an amplifier i.e. a low distortion and high-resolution system is also the most relaxing and emotionally involving… it lets you listen deeply into the music or just ride it’s surface depending on your mood.

    This is not terribly descriptive of each method and how it changes things but I have not found – yet – that there are hard and fast rules except that the dc balance point is not the point of best sound… play with things and see what works best. Of course this introduces all sorts of other variables into the testing – such as what sort of day one has had so far, etc. etc. So when I have found a point I like I leave the amp for a few days and then change things back to how they were before and after a few days see if I miss the previous change – if I do then the change goes back in and stays.

    2. I think that a capacitor between the cathode and cold end of the input is technically correct. However I have tried it and not heard any difference. Do you hear a difference?

    Yes – most of the time but certainly not always, probably about 60:40. Generally I only hear it once the amp is close to being optimised unless the IT has some issues (in-circuit resonances) that this dampens. I try all sorts of things out including neutralising caps – they work in some circumstances and not in others. The neutralising caps are very system dependent as I always over size the current delivery of my driver stages in my designs but they can help and can be heard – sometimes…

    3) I think, if I understand your post correctly, methods 1,2,3,and 5 change the operating point of the tube and are what I call "DC balance. Method 4 is what I call AC balance; the pot doesn't change the DC bias but the relative levels of the two signals. Is this correct? What are the sonic differences?

    Conventionally this is correct for Class A1, I had a Class A2 pp amp that was in A2 for no signal and then Method 4 did move the dc op point.

    Having said that, I don’t really distinguish between the dc and ac op point when thinking about how to design and balance the amp. I think of static i.e. no signal conditions and dynamic conditions i.e. with signal. We listen to the dynamic condition so the static condition is only the starting point for setting the amp up. As L.O. has remarked, triodes are three terminal devices with differential inputs and outputs. The valve doesn’t care about topology or components etc. it just responds to the instantaneous voltage and current differences present on its terminals – there may be some ‘lag’ or ‘memory effect’ but the instantaneous ‘output’ is directly related to the instantaneous ‘inputs’ so I’m after the best sound under dynamic conditions and that can only be obtained by trial and error and listening… test signals are all quasi-static or highly repetitious or single event to enable us to capture and measure various parameters. This can be a good guide to getting into the right ballpark but the final set up is always by ear. Design and build by using your head but listen with your heart!

    So when I am adjusting the 'balance' of the amp it is only the 'ac' balance that really concerns me and I set this by ear using trial and error. Of course I measure everything I can think of because I hope that one day I will find a corresponding set of parameters that I set by measurement and get it right first time... some hope :-) As I stated earlier, I try to get the most neutral sound from the amp that is also the most relaxing and has the most resolution. My standards of neutrality are BBC based and so are centred on accurate reproduction of the human voice, piano, violin and chello followed by trumpet. I'm lucky in that my family members all play various of these instruments so I am always hearing them.

    By resolution I am refering to musical resolution i.e. the mix of timbre and timing that communicates the true emotional value of a piece of music. I find I am in agreement with a lot of what James Boyk writes about music and sound reproduction. I listen for the subtle beauty of music.

    Dave, I haven’t directly answered your questions – mainly because I don’t know how to yet. I’m still learning about zero feedback valve amps and I find that good ones are so transparent that anything and everything changes how they sound and there is very little overall consistency between amps but each individual amp is consistent with itself so some set of interactions that I don’t yet understand will one day explain all this…

    Hope this is interesting…

    Ciao
    James

    
    
    

    ---

    • Re: ...Long and winding reply... - Dave Davenport 20:45:02 11/24/03 (3)
      In Reply to: ...Long and winding reply... posted by James D on November 21, 2003 at 11:56:35:

      Hi James,

      You wrote: Hope this is interesting…
      
      That was a wonderful post, one of the most thought provoking that I have read in a long time. I will certainly try some of those things that you mentioned in my next design. It has taken a while to respond because I wanted to digest it all.
      
      You wrote: For Intermod. then I try to minimise the ability of any stage to affect any other stage - this is also affected by the op point chosen - and I find that very well dynamically balanced op points in pp can be quite sensitive to intermod mechanisms as they are very, very transparent..

      You lost me a little bit here. What do you do to minimize the ability of any stage to affect any other stage?

      You wrote: What I am tweaking for each time is the least sonic signature from the amplifier – to my ears and the most resolution. I find this also equates to the most relaxing sound from an amplifier i.e. a low distortion and high-resolution system is also the most relaxing and emotionally involving… it lets you listen deeply into the music or just ride it’s surface depending on your mood.

      Yes, yes, exactly.

      You wrote: My standards of neutrality are BBC based and so are centred on accurate reproduction of the human voice, piano, violin and chello followed by trumpet.

      Again, right in line with my philosophy. I have several good female voice recordings that I use for a reference, but no good male voice. Do you have a recommendation there? The best piano recording that I have found for hearing differences when I make changes or tweaks is Keith Jarrett’s “The Kõln Concert.” I have used it as a reference for over 20 years. I haven’t focused on strings but do like brass instruments and also the saxophone for listening evaluations. Maybe the sax, because I used to play sax so I am very sensitive to the sounds of that instrument.
      
      You wrote: Design and build by using your head but listen with your heart!

      I’ll pin that one up on my wall :-))

      Now a question: Are all of your balanced differential circuits traditional push-pull topology or have you tried any of the differential parafeed designs?

      And if you would, please drop me a private note off-list so that I will have your your e-mail address. I expect that I will have a question or two for you when I try some of the things you covered.

      Ciao,

      Dave
      
      
      

      ---

      • Re: ...Long and winding reply... - JamesD 05:57:18 11/29/03 (0)
        In Reply to: Re: ...Long and winding reply... posted by Dave Davenport on November 24, 2003 at 20:45:02:

        Hi Dave,

        Thank you for your reply. I'll attempt some answers below and then I'll send you an email.

        Regarding Intermod. Dave asked:

        > What do you do to minimize the ability of any stage to affect any other stage?

        Ohh...where to start. A bit of background. For twenty years, on and off, I designed, with various friends and colleagues, lots of solid-state audio circuits for hobby and professional use. During this time I came to realise that spurious signal injection into each stage (my broad definition of intermod) caused most of the residual problems once topology and components had been optimised. Of course the obvious feedback derived intermods are well documented but there are many other mechanisms and these apply to valves every bit as much as to ss. Here is a list of most of the mechanisms that I try to control...

        1) PSU related intermods. Voltage and current related. Regulation issues and pulse issues.
        2) Earthing related issues.
        3) RFI issues.
        4) Signal current return loop issues.
        5) Capacitive coupling - both ground plane and wire-to-wire.
        6) Inductive coupling - both ground plane and wire to wire
        7) Feedback issues - Local or interstage or global.

        Of course a lot of these are different views on the same fundamental problem - and so a solution to one might help solve another or make it worse...

        Fortunately by working only with valve Class A(1&2) circuits a lot of problems are minimised compared to ss - but to get the best results all aspects must be covered ( and probably more - I'm discovering other sensitivities all the time...).

        I have used a lot of interstage transformers in my ss design over the past ten years as I found they helped control a lot of the above problems. Needless to say most of my valve designs use interstages too. In particular the ability to break the grounding scheme for each stage from each other stage is a godsend!

        I tend to use star psu distribution too with local smoothing and or regulation as I think fit. The power feed is also taken through a forward biased diode to help isolation from the star point.

        I don’t like metal chassis! I know shielding can be useful but any metal chassis introduces too many capacitive and inductive coupling issues for my liking. I use wood, acrylic and open chassis design a lot.
        I could write lots more on intermod… maybe one day I will and put it on a website. And don’t get me started on guitar amps and intermod!!!

        Dave asked:

        > …but no good male voice. Do you have a recommendation there?

        Just a few:

        1) Anything by Roch Voisine (Canadian singer with a quite pure male voice – sort of a male equivalent to Eva Cassidy in style).
        2) Anything by Chris Isaak except for his live work where he is often a little flat…
        3) Peter Green’s Fleetwood Mac ‘Live at the BBC’ especially “Man of the Word”
        4) Led Zeppelin ‘Live at the BBC’
        5) The Very Best of Louis Armstrong
        6) Richard Burton ‘Under Milkwood’ and ‘Burton at the BBC’ – both spoken.
        7) Richard Harris ‘MacArther Park’

        Then for Choirs:

        1) Treorchy Male Choir ‘A Garland of Welsh Songs‘
        2) Handel ‘Messiah’ – several versions.
        3) Mahler Symphony No. 8 ‘The Resurrection’ – several versions.

        There are others but these are my consistent references and I have heard all except Chris Issak live more than once.

        Playing an instrument really opens up ones ability to judge how well it is being reproduced. I play guitar and bass badly but it still helps. The rest of my family play several instruments quite well so that helps keep me honest! Playing Sax would be a real help. All those woody tones right in the middle of the frequency range!

        I haven’t heard the Keith Jarrett – now I will search it out – thanks!

        Dave asked

        > Are all of your balanced differential circuits traditional push-pull topology or have you tried any of the differential parafeed designs?

        I have tried parafeed differential and I found I could hear the cap signature quite clearly when compared to non-parafeed interstage. It had it’s own strengths – particularly the ability to tune the extreme l.f. performance to work optimally with the rest of the system. In general I prefer to remove the cap signature from the midrange and treble whilst allowing the lf to go it’s own way… I have been toying with a valve sub-woofer amplifier and making that parafeed to take advantage of the lf tweaking it allows…

        As Gary Dahl says ‘…so many valves…so little time…’

        Ciao

        James

        
        
        

        ---
      • Keith Jarrett’s “The Kõln Concert.” - Bas Horneman 14:54:15 11/25/03 (1)
        In Reply to: Re: ...Long and winding reply... posted by Dave Davenport on November 24, 2003 at 20:45:02:

        Hi Dave,

        Very nice album...am listening to it now as I type. Read your post this morning...and went looking for it in my collection ..I also have and love "Works" from Keith. The best recording of a piano I own is Nojima plays List by Reference Recordings..especially the 2nd Track.."La Campanella" it is really beatiful. I first heard it at an audio show...and knew I had to have it. Just like I knew I had to have your PP line stage...;-)

        Cheers,
        Bas

        
        
        

        ---

        • Re: Keith Jarrett’s “The Kõln Concert.” - Dave Davenport 19:04:33 11/25/03 (0)
          In Reply to: Keith Jarrett’s “The Kõln Concert.” posted by Bas Horneman on November 25, 2003 at 14:54:15:

          Hi Bas,

          I have quite a few of Keith Jarrett's recordings, but haven't heard "Works." I'll have to get it. I have also head good things about Nojima Plays List, I guess I'll have to get that too.

          I had used the Kõln Concert on vinyl for years as one of my reference recordings and ran out to get it when it was released on CD. Well I was disappointed - it sounded terrible. Hard, ringing, aggressive sound. Then as I improved my system the CD sounded better and better with each improvement. Now it is excellent. That CD is merciless for showing up the slightest defect. There are some changes that I have made that that is the only CD I can hear the difference on. I suggest that you keep it handy as you go through the changes to your power supply and see if it is as good tool for you as for me.

          Dave
          
          
          

          ---

This post is made possible by the generous support of people like you and our sponsors:

Kimber Kable

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---