Re: Supersizing SET


"Ruud Broens" <broensr@xxxxxxxxxx> wrote in message
news:44d5fa8f$0$6999$dbd4d001@xxxxxxxxxxxxxxxxxx

"Trevor Wilson" <trevor@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote
<>some snippents<>
And here is some snippents of what the RDH4 says:
:
: Chapter 13.1
: "With push-pull Class A1 triodes the even harmonics are cancelled and
only
: small third and higher odd harmonics remain. Push-pull class A1 triode
: operation is regarded as providing the best fidelity obtainable without
the
: use of feedback."
:
: Chapter 13.5
: "Push-pull operation tends always to reduce the effects of hum in either
the
: grid bias or plate supply Voltage."
:
: Chapter 13.5 (8)
: "Owing to the good linearity of the composite characteristics for Class
A1
: operation, and the freedom from limitations in the vertical direstion,
: elliptical loadlines may be accomodated with less distortion than with
any
: other method. Negative Voltage feedback makes such an amplifier
practically
: distotionless for any type of load, resistive or reactive, of any value
of
: impedance; the only limitation is regarding grid current."
:
: Of course, there's other stuff, but that is the crux of it. RDH4 is
clear
: and unequivocal in it's statements about the superiority of PP over SE
: operation. I concur with their assessment. I find it quite surprising
that
: you dispute what is writtne in that august journal.
:
.................................................................................
..................
you have fallen into the steady state thinking trap. sure, one can measure
thd, imd, phase & frequency response, at certain voltage levels, and to
some
extent, that characterizes the amplifier.

**Indeed. In fact, if an amplifier delivers inaudible levels of faults, then
it can be considered as possibly faultless. If an amplifier exhibits an
audible flaw (as characterised by any one measurement) then that amplifier
can be assumed to be insinuating it's own distortions into the signal chain.
IOW: Listeners are listnening to AMPLIFIERS and not the music.


speakers, however, are mean loads, not just complex impedances, but
time delayed voltage sources as well (the mechanical system stores energy,
then gives it back). the proof of the pudding would be measuring the
speaker
output, in an anechoic room, driven by the amplifier - that's what comes
out, eh
?

**No argument from me. It is a classic mistake to assume that speakers
represent a simple resistive load. As you say, not only speakers exhibit
resistive, capacitive and inductive characteristics to the amplifier, but
they act as an an energy generator as well. That enegery MUST be damped
effectively by the amplifier.


i once suggested something along those lines to Stewart Pinkerton, where
quasi musical digital files could be compared with measured output in
digitised form, then listening panels with those amp-speaker combinations
in a listening room stating preferences - could lead to interesting
correlations.

**Possibly.


for most listeners, it is hard to detect less than 0.1% distortion in a
400 Hz
sinewave under ideal conditions played on headphones. taking into account
that in musical signals, various masking effects in perception operate,
those
0.1% are thorougly unproblematic. So, depending on speaker sensitivity,
listener preference, and for most - acoustical isolation to neighbours
:-),
0.5 to 10 W at or below 0.1% distortion for average listening level is
fine.

**Agreed. Except for the power level. You cannot say what power level is
appropriate for all listeners. Some may require considerably more than 10
Watts. One of my own amplifiers is equipped with a peak power meter and many
people who listen to my 89dB/2.83V/M speakers listen at levels where the
music peak at 100+ Watts. The room is around 5 Metres X 4 Metres. In larger
rooms, considerbaly more power will be required for realistic listening.


peaks in the musical signal will for a few ms run up the power required
and make the amp create more distortion (not to mention what the
speaker does), but of course, we don't perceive it as 'now it's 1%, now
5, now 10', our perceptive analyses is just too slow for that, we get a
compounded impression of the distortion profile

a trumpet, when blown very soft, creates nearly a sinewave output.
as it is blown with increasing force, the amplitude increases, but an
ever increasing number of upper partials, overtones, are created also
at full force, up to some 50 kHz components

with many natural sounds, louder is often also 'having increased
noise content',
heh

so that for loudness perception, that is somewhat exchangeable:
you can simulate loudness by increasing overtones level
i'd suggest that an amplifier with a steadily increasing level of
distortion, but with higher order harmonics staying below
lower order distortion can suggest with good approximation
a far larger power amp, that _then_ will create far larger speaker
distortion levels,
so, why the better absoluteS ?

**No. It doesn't work that way. The distortion needs to remain below audible
limits, to be, well, inaudible. Once distortion levels become audible, the
amplifier is then insinuating it's own character on the music. I will
readily acknowledge, however, that when _I_ look at amplifier specs, _I_
tend to prefer one which exhibits a gradually rising level of distortion,
with increasing power output. At all intended listening levels, that
distortion needs to remain below the human threshold, however.



: **Really? Let's discuss facts then.
:
: An SE amp which delivers 10 Watts @ 8 Ohms, can only deliver 5 Watts @ 4
: Ohms. OTOH, a PP amp of 10 Watts MAY be able to deliver as much as 20
watts
: @ 4 Ohms. Given the fact that speakers are designed to be driven from
: Voltage sources, a PP amp is a much better choice.
:
hmm, you're doing ss thinking, Trevor, with an SE transformer using a
different tap you can still do those 10W in 4 Ohms. if you mean dynamic
load indifference, that's a function of the flatness of the loadline and
the
tubes' dynamic output resistance, subject to further nfb if present.

**No, that is not what I am saying. The maximum output of a SE amplifier is
dictated by the bias current. The maximum output of a PP amp is not so
constrained. Halving the load impedance connected to a SE amp results in
less power output, whilst halving the load impedance connected to a PP amp
results in more power output. IOW: A PP more closely approaches that of an
ideal pure Voltage source, whilst the SE amp is reverse.


with a theoretical perfect voltage source, a 0 ohm dynamic output
impedance
triode, the 'transfer curves' would be vertical lines,

**Nope. Those curves will be straight lines, but not vertical. Otherwise
amplification cannot occur.

so the same voltage
swing would be possible with about _any_ load, as tilting the loadline
would
give the same intersection voltages (for the graphically minded:)
- speakers are not pure resistor loads, the resulting real world
elliptical
loadlines would pose no problem, though.

**For an ideal source that is correct.


back in the real world, it is a matter of making choices, compromises, to
come close to the perfect voltage source output

**Certainly.


<>some snippents<>
: > Only marginally if class AB1, and not any more efficient if pure class
A.
:
: **I suggest you hit the books again. A SE amp can only be a maximum of
25%
: efficient (under ideal conditions), whilst a PP (Class A) amp can be 50%
: efficient. Therefore, PP can be more efficient than SE.

nope, that would be the case for an ss output stage with a current sink to
bias it halfway. a tube amp using a transformer would under ideal
conditions
reach 50 percent.

**Nope. According to RDH4 13.2 (iii) it is 25%. PP Class A amps can, of
course reach (theoretically) 50% efficiency. SE cannot.


take that 0 ohm dynamic output impedance triode as an example,
biased at V volts, I amps for V*I idle power
0 grid voltage would be along the y axis, at 0 Vak, so a swing of 2V
and 2I, give 4V*I/8 or 50 % of idle power as output power, so 50%
efficient. the closest approximation in the real world is high power
transmitter tubes running at high voltage, with a high reflected load
impedance

*didn't i give the 4cx350 as a >40% efficiency possible example?*
(that wasn't an april 1st joke, you know :-)
(of course, this is neglecting fil power and assuming constant load)

Rudy
balancin' facts & perception

**I further cite RDH4 13.2 (v) where the figure of 25% efficiency is quoted
again. If you have a cite from RDH4 where the 50% figure (for SE output) is
quoted, I will look it up.


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

.

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