[sdiy] Tube amplifier question

[Czech Martin]

I have an elektor circuit magazine whcih contains a direct
output tube headphone amplifier. No iron needed.

If you are interested, I can dig it out.

m.c.

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of
> jhaible at debitel.net
> Sent: Mittwoch, 4. August 2004 11:27
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Tube amplifier question
> 
> 
> I've aquired a taste for building tubes stuff right now. (;->)
> 
> I want to build a small amp that will replace the Studio monitor amp
> and the HiFi amp in the basement. Right now I run both thru a cheap
> Sony HiFi amp.
> 
> I think of something like this:
> 
> Small power amps with 2x EL84 push pull for the speakers (I never hear
> music very loud over speakers, so that should be plenty)
> 
> Separate Headphone amp with EF86 (connected as triode) and 12BH7 as
> cathode follower with no overall negative feedback loop.
> 
> Phono preamp (yes, for my old records) with 12AX7 and passive 
> equalisation
> 
> This all should fit into a 19" enclosure, 2 or 3U high. No 
> need to display the 
> tubes outside (;->)
> 
> 
> Now I have the following questions:
> 
> (1) Is the 2x EL84 pp a good choice for a "transparent" HiFi 
> amplifier?
>     Is there an alternative that is only slightly more 
> expensive (no vintage
>     tubes in the 100 dollar price range), but which would give much
>     improovement?
> 
> (2) Is an ultralinear transformer the way to go? I have seen 
> some "famous"
>     amps like the Quad II use cathode feedback instead of the 
> ultralinear
>     configuration (other tubes, too, of course ...). What's 
> the general
>     pro and con of ultralinear vs. cathode feedback, or 
> should I even use
>     both ? (I see that the winding is easier in ultralinear, and these
>     transformers are very common, so I'd need a good reason to do it
>     otherwise.)
> 
> (3) Is the headphones amp with EF86 and 12BH7 a good idea? 
> Should I use
>     an output transformer, or bring the output impedance down 
> with a WCF
>     and don't use a transformer? (My Sennheiser HD450 phones 
> are 300 Ohm
>     types, and I can get down to ca. 100 ... 150 Ohm with the 12BH7 in
>     WCF configuration. Not much damping then, and I worry 
> about the transients
>     thru th ephones during power-on.
> 
> Any ideas, hints, recommendations?
> 
> Thanks in advance,
> 
> JH.  
> 
> 
> 
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