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K&K Audio / Lundahl Transformers Welcome! Need support, you got it. Or share youe ideas and experiences. |
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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 Wordâ€
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
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Follow Ups
- Re: ...Long and winding reply... - JamesD 05:57:18 11/29/03 (0)
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