In article , ~misfit~
wrote:
Somewhere on teh intarwebs Arny Krueger wrote: [snip]
As time marched on, fairly inexpensive and modest-sized output devices
with excellent SOA and reasonble high frequency resposnse made it
relatively inexpensive to build very high powered audio power
amplifiers.

Arny, would you care to give a rough time-frame on this? I have a few
old SS amps (and might grab a few more if I see them at bargain prices)
but would love to know roughly when, in your opinion, SS amps became
stable and fairly clean across the frequency scale. Thanks.

Arny will no doubt have his own views in that, but I'll add mine FWIW.

I don't think the progression was as clear as it might be. Devices evolved
as the demands and expectations increased. So back in the 1960s people
would have been quite happy with a 20W power amp, but by the 1980s expected
rather more, and for it to deliver more current into awkward loads as
speakers got less efficient and speaker designers threw their problems over
the fence for amp designers to pick up. :-)

Also some designers and designs dealt with issues like stabilty or
delivering high currents better than others.

So circa 1970 you might expect to see amps that could deliver 40 watts per
channel in the UK. But the details would have varied.

Buy a Quad 303 and you got decent heatsinks and fairly well limited design
that would survive most loads - but at the cost of current limiting at a
few amps.

Buy an Armstrong 621 and you'd have got much the same 'headline' power of
around 40 Watts. But the heatsinks were small, so not suited to large
continued currents. OTOH no specific current limiters (other than fuses) so
would give you higher peak currents into demanding loads than a 303.

Since real music tends to be occasional peaks, say, over a factor of 10
higher than the average, you can argue that for many it was a better
tradeoff. But you could certainly find others who be better off with the
303.

Both designs were stable OK.

By c1980 powers in the Uk might now have drifted up to more like, say, 70W
and the devices around were much better. FWIW using paired output devices
in parallel I managed over 200W per channel continuous (and 30A rms
continuous) by then in a design that was pretty robust. Doing that would
have been a nightmare a decade or more earlier as the transistors weren't
available. Also unconditionally stable.

Yet you could also buy an early Naim amp. The heatsinking was 'adequate'
but it wasn't unconditionally stable and was known (by the trade) to
oscillate into some loadings. And some blew up in use, almost surely for
that reason. However many people liked it provided they used it with the
speakers and cables that Naim 'approved' - i.e. sounded OK and avoided
instability.

So some designers had fixed matters like stability many years before
others. And - like things like heatsinks and current demand/limiting - some
judged the issues differently to others.

Yer pays yer money... :-)


Most of the money ended up in the heat sinks, power supply
transformers and filter capacitors. The former are continuing to
shrink as improved output devices improve their reliabiity at higher
operating temperatures and power supplies are making greater use of
switchmode technology.

I've always wondered why amplifiers never (at least AFAIK) embraced the
use of heat-pipe technology to move the heat to side or back of case
passive radiators.

TBH I never saw the point of these in a power amp. I simply went for big
heatsinks. With high powers in the past you tended to need paralleled
output devices anyway, which spread out the dissipation. And you needed a
lot of sinks to get rid of what pipes could have conveyed to them, anyway!


I've actually used a heatpipe cooler from a laptop for just this purpose
(although it needs a fan on the radiator, as that's how it was designed,
the fin area isn't big enough to passive) when I re-housed a basic
subwoofer amp from a nasty plastic housing (previously mounted on the
front of the driver's box, with connections on the back) into a re-used
bookshelf speaker box.

The Shuttles I use also employ heat pipes to get the CPU waste from the CPU
to a big sink and large fan. They let you get a lot of heat out of a small
volume. But a CPU is somewhat different to a power transistor.

BTW I disconnected the fan on the Shuttle I use in the audio system, and
use a SSD to get a setup that makes no mechanical noises. This is fine
provided I only have doing basic tasks like playing audio files.

Slainte,

Jim

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