"Stewart Pinkerton" wrote in message
...
: On Wed, 29 Mar 2006 15:32:14 +0200, "Ruud Broens"
: wrote:
: :
: : hm, about 12 W / 8 Ohm available, 7 % THD, 88 W idle with the 2SA1216
: : and CCS - you're saying there are no tubes that can beat that ?
: :
: : I read less than that into those curves, but even if true, that's
: : better than you'll get with the 300B.
: :
: : You are of course conveniently forgetting something else, the greatly
: : superior gain of the 2SA216. In the KISASS design, Tr2, the equivalent
: : of the 300B in KISS, has its emitter and collector loads set for a
: : stage gain of 6.25, to make it as similar as possible to the KISS amp.
: : This applies more than 20dB of local regeneration, equivalent to the
: : internal feedback of the 300B, cutting the distortion to about 0.5%.
: : Apples to apples, KISASS totally outperforms KISS.
: :
: : --
: :
: : Stewart Pinkerton | Music is Art - Audio is Engineering
:
: not forgetting anything here, just sticking with the topic - again -
: being inherent device linearity, not what you can do with fb - remember ?
:
: Yes, but PT already conceded that the 300B has internal feedback, so
: he had no problem with local degeneration in KISASS. After all,
: putting in a larger emitter resistor doesn't create any of the
: supposed horrors of loop feedback. Note also that you already conceded
: that it's as good or better than a 300B, without *any* feedback.
:
: ...40V supply, - 15 % efficiency and a large 1K/W heatsink for
: that 2SA1216 and say an LM350.
:
: See KISASS, if you can't remember the basic parameters of KISS.
: KISASS runs a 30 volt rail at the voltage amplifier, and is designed
: to run 100 mA idle current in the voltage amplifier stage.
:
err, wasn't remembering, just exemplifying what it takes.

: you are also conveniently forgetting that - as is -, you have an input
: impedance of about 5 Ohms ...
:
: See KISASS for the solution. Tubes use lotsa volts, BJTs use lotsa
: milliamps, same thing in the end for the 'black box' solution.

aha, now we're getting somewhere :-)
so if someone now comes up with an SE pentode output stage, so no fb,
that can do 12W out at 7 % THD, 88W dissipation,
you'll agree that even the 2SA1216 can be beaten ?
ok ;-)

(btw triodes don't have build-in feedback, more precisely,
they have a build-in feedback facilitating mechanism - as is
evident when you lock the anode voltage; no ~fb~ then)

Rudy

: more of a win some - loose some scenario, it seems,
: Stewart ;-)
:
: Not really, as KISS suffers similar problems. Naturally, one wouldn't
: expect a tubie to acknowledge this.
:
: -- -- --
: To reiterate the design process:
:
: KISASS came about as a suggestion by Iain Churches that I design a SS
: equivalent of Andre Jute's (so far mythical) KISS design, supposedly a
: single-ended tube amp with 300B output tube, a double-triode
: input/driver stage, zero loop feedback, and an output of less than ten
: watts. Ignoring a bunch of tube-centric 'rules' spouted by Patrick
: Turner, I had a think about how this should be done.
:
: In terms of parts count, we cannot beat the Nelson Pass ZEN design,
: which uses a single MOSFET, so we will use BJTs, the 'bete noir' of
: the tube fan. In terms of excellent performance from a minimal parts
: count, we have the classic 1969 Linsley Hood design, which ticks most
: of the boxes but does use global NFB.
:
: Where to go from here? OK, let's start from the simplest possible gain
: stage, a common-emitter BJT with emitter and collector loads (Tr2 in
: the schematic, the 2SC2922 device is recommended). This will set the
: transfer curve, and hence the sonic signature, of the amplifier. Such
: a stage does of course have a quite low input impedance, so we place a
: simple emitter follower buffer (Tr1, the MJE15028 will do, or any
: other decent medium power NPN BJT) ahead of it to allow a wider choice
: of source devices. The output impedance (as with the 300B) is much too
: high to drive a loudspeaker, so we need an impedance transformer. As
: one of the great advances of SS was that it allowed the removal of the
: OPT, we will not use iron. A simple pair of emitter followers (Tr3 and
: Tr4, for which the 2SC2922 and 2SA1216 will work well, but other
: modern complementary pairs may substitute) provide output impedance
: reduction without affecting voltage gain, and there we have the design
: in a nutshell.
:
: Further philosophical decisions were the avoidance of bootstrapping
: from the output to the gain stage (that could be construed as loop
: feedback), and the use of a heavily filtered power supply to keep the
: noise floor clean. The latter was in the cause of maintaining the
: 'first watt is the most important' philosophy, without which this
: design is utterly pointless. R15 and R16 reduce the rail voltage to
: give a maximum output power of less than ten watts into loads between
: 8 and 4 ohms, meeting one of the principal design parameters, while
: R12, R13 and R14 maintain the rail voltage of the gain stage at 5
: volts higher than the output rail, allowing better driving of the
: output while maintaining the natural transfer function of the gain
: stage.
:
: The bias current of the output stage is set to about 1 amp by R6,
: while the quiescent output voltage point is set primarily by R1/R2.
: This amplifier should be d.c. and thermally stable, but will reward
: careful layout, particularly in the utilisation of the 'star earth'
: philosophy, i.e. one central ground point to which all 'zero volt'
: connections are made. Given this, I'd expect less than 0.1% THD plus
: noise right across the audio band at an output of 1 watt into 4-8
: ohms, rising to several per cent just below clipping, in the usual
: 'SET' style. The output impedance will also be in the half-ohm region
: over most of the audio band.
:
: In terms of construction, it should be noted that R15 and R16
: dissipate 5 watts each, so should be at least ten-watt rated, while R5
: dissipates about 3 watts, and should be at least a 5-watt component.
: R12, R13 and R14 should be 2-watt rated, the others should be
: half-watt metal films. Note that for thermal stability, D1, D2, Tr3
: and Tr4 must share the same heatsink.
:
: Stewart Pinkerton | Music is Art - Audio is Engineering