On Mon, 14 Mar 2005 17:21:32 +1100, Patrick Turner
wrote:
Stewart Pinkerton wrote:
Patrick wrote:
This is a perfectly lousy result, and well below what the 300B is capable of.
Bull****, since your assumptions are incorrect. Check your facts.
Without being told what transistors you are using, I was left to assume whatever
I cared to.
Had you troubled to check the thread, you'd have seen my recommended
devices separately listed, no need to ass u me.
When posting schematics, be prepared to be made to look a fool
if you are sloppy with your presentation.
Likewise, with false assumptions.
But from what you have now suggested about the chosen transistors,
you are indeed correct, I have no argument.
Add about 0.11 ohms to the Rout you got.
So Rout would still be just less than 1 ohm, and is acceptable
imho, but does not the 70 dB of series voltage FB
render itself rather ineffective because of the "current reflection"
to the input stages?
Yes, it does, but the circuit is simple to understand, should be
nicely stable, and its transfer function is totally dominated by the
voltage gain stage Tr2.
Had I been attempting an *optimum* simple 10-watt 'sorta kinda
single-ended' class A SS amp, I'd simply have pointed you to the
classic 1969 Linsley Hood design, as I've mentioned several times.
Get your head out of RDH4 and look at what modern multiple-emitter
poer BJTs can do.
Get you head into RDH4, and see what tubes can do.
I did - forty years ago, when tubes were relevant technology, and RDH4
was still in print. Indeed, I still have my copy of Landee, Davis and
Albrecht's 'Electronic Designers Handbook', a 1957 tome which I
consider to be a somewhat superior reference.
I've mentioned elsewhere that my very first 'hi-fi' amp was a
single-ended 5-watt valve design - but audio has moved on a *long* way
since then.
The rule for simple *low power* power amps is that
the average levels should be 1/10 the maximum levels for clipping,
so if an amp clips at 5 watts, then only expect a nice average 0.5 watts and no
more.
Except of course properly conceived amps like the 1969 Linsley Hood
10-watter, which is just fine all the way from half-power downwards.
A williamson also is fine on the same basis.
And that basis is for a sine wave to R load.
And evan at full 16 watts, the W makes only 0.1% thd.
I was being overly cautious, checking the 1969 article reminds me that
the original JLH amp remained well below 0.1% THD right up over 10
watts, almost to clipping at 12 watts.
Average power for music is quite different.
1/10 full power means the output voltage is about
1/3 the full clipping voltage.
Much pop music from radio stations has an average voltage level
only 6 db below the maximum voltage level transmitted.
If you monitor a radio stations's signal just have a dummy load and take the music up to
where it
begins to clip as shown on a CRO with a signal which is rap, bebop, rock or whatever,
and you will measure an RMS voltage about 1/2 the sine wave voltage for full power and
clipping.
OTOH, when listening to pop music from a radio broadcast, is
*amplifier* quality of much relevance? :-)
But one has to allow for much more headroom for classical or un compressed music,
and a 10 dB voltage headroom is a minimum; more headroom is better.
Yes, I'd always seen 20-26dB peak to average SPL quoted as typical for
classical music, which does require significant power to avoid
clipping peaks, especially on solo piano.
0.5 watts into a speaker with 95 db efficiency with 1 watt means you
get 92 dB, and that's way too loud for me, so
0.05 watts for 82 db is about all I need.
5 watts allows a 102 db ceiling, quite enough in the kitchen.
Shame that there are *very* few decent 95dB/w/m speakers, and they
tend to cost many thoiusands of dollars.
Its easier to use 4 tubes instead of 1 and use 89 db speakers than be
compelled to use 95 dB speakers with one tube imho,
unless the tube is a biggun.
You won't get any argument from me on that score!
AFAIK, there are not many cheap easily available gigantic transistors or mosfets
rated
for safe continuous dissipation of 200 watts.
As you point out, not a problem if you just parallel them up.
Alternatively, grow a brain and build a 100 watt Class AB BJT design
with negligible distortion at *any* level up to 3/4 of full power.
Yes but I have customers who have such amps, and they still prefer the tubes.
They sometimes go back to the SS just for an hour every few months.
Last month one told me that when he tried this for a couple of hours,
he thought the musicians were all playing separately.
Then when he goes back to the tubes he says they all sounded like they were together.
I don't argue with them.
Arguing with one's customers is not generally advised, if business
longevity is desired!
I'd still wanna build an SE mosfet amp rather than yours.
I'm not arguing on performance grounds, but others have already
created such designs. I havent seen a BJT one recently, hence KISASS.
You snipped out the juicy bits from my post, so
it wasn't worth your while to comment.
I do try to cut to the chase and to avoid rambling on - which general
opinion seems to suggest is a weakness of yours. :-)
--
Stewart Pinkerton | Music is Art - Audio is Engineering
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