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- Phil Allison
August 3, 2005, 11:25 am
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** World comes to an end this month .....
The guys at SC magazine have broken one of their longest held vows - never
to publish the design of a valve amplifier.
Worst of all, it is not a hi-fi amp but an SET ( single ended triode)
design, beloved by the miniscule 1930s retro-brigade among "tube heads".
As if to spit in the eye of such Luddite wankers, it sports back to back
wired toroidal transformers in the PSU, 100 volt, PA line transformers for
output, common guitar amp valves wired to work as power triodes and a
*transistor* buffer stage driving the two ( paralleled ) output valves
????
Good grief !!!
No seriously exotic, obsolete or hand made components to add mystery value
at all !!!
.......... Phil
Re: Silicon Chip publishes SET amp
"Trevor Wilson"
** What utter rubbish.
Distortion generated by that 9H iron cored inductor goes directly into the
output signal - at 30Hz it has an impedance of only 1700 ohms while the
output transformer primary is nominally 2000 ohms - so it winds up becoming
the dominant source of non linearity and low end response roll off.
The OT is a 100 volt type intended for PA use - so poor to no low
frequency preformance.
.......... Phil
Re: Silicon Chip publishes SET amp
**Good point.
**I am not attempting to defend what is, essentially, a complete waste of
valuable paper and ink. The output topology is, however, considerably better
than regular SET output stages. BTW: I agree that the use of a crappy output
transformer is a big mistake. Leo claims that the thing has a decent
frequency response, despite the use of a crappy transformer. I can't
confirm, because I have not measured it.
Personally, I don't see the point.
--
Trevor Wilson
www.rageaudio.com.au
Trevor Wilson
www.rageaudio.com.au
Re: Silicon Chip publishes SET amp
"Trevor Wilson"
** Saying the same dumb thing it over and over does not make it any better.
Using a choke plus cap plus OT ( called para-feed) is inferior to using a
well designed OT alone.
For the damn choke to NOT spoil the results, its inductance value has to be
huge - so it must be huge - and it must be made with the best grade of
transformer iron to avoid generating THD.
Easier and cheaper to design a OT with the desired performance.
.......... Phil
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