On Mon, 28 Mar 2011 06:13:29 -0700, Arny Krueger wrote
(in article ):
"Audio Empire" wrote in message
You mean Like the Dynaco ST-120 running hard into class
'B' with it's VISIBLE crossover notch?
I have an all-orgional Dyna ST 120 and have tried all sort of schemes to
measure or hear any such thing.
AFAIK, this is an audiophile myth. It may have happened in equipment that
needed maintenance, but it was not a standard feature of properly-operating
equipment.
We've been down this road before. Dyna eventually fixed the problem and it
one point, they even offered a kit of parts for doing so. I even posted a
list of those parts for you. If you have a later ST-120, they don't exhibit
the problem, if you have one made before they finally fixed it, they did.
Or the early McIntosh SS deigns that used coupling transformers
A comprehensive archive of McIntosh schematics and service manuals can be
found he http://www.tubebooks.org/mcintosh_data.htm I find no McIntosh
SS amps with coupling transformers. Perhaps you can find some?
They were sold under the name "Mac" to differentiate between the tube
(McIntosh) and the transistor (Mac) gear. They abandoned the "Mac" name in
the early Seventies,
Driver transformers were widely used in the early days of the evolution of
SS power amps, with surprisingly good results. Manufacturers that used them
included Acoustic Research, Heath, Altec Lansing, etc., etc. These parts
were called on to handle relatively small amounts of power and therefore
were easily overdesigned and overbuilt. They overcame the expense and
relatively rarely of complementary driver and output devices. They were
eliminated as a cost-saving move when appropriate (complementary - similar
transistors that were available as both NPN and PNP parts) became widely
available at low cost.
Dynaco (ST-120, ST-80) and H-K (Citation 12) used complementary drivers to
drive their output transistors. It worked fine, but when one 2N3055 "went" it
usually took the two driver transistors with it (and often the other 2N3055,
as well).
McIntosh used autoformers as output devices in order to improve the
impedance matching between the limited output devices of the day and
real-world speakers. But these are neither for interastage coupling nor are
they transformers as they maintain a DC path between their inputs and
outputs.
beOr the
early Crown SS power amps that sounded terrible (but in
fairness, were essentially bulletproof.
The Crown SS power amps had conservatively rated SOA protection circuits
that contributed to their longetivity. As long as you stayed clear of highly
reactive speaker loads, they sounded fine.
Matter of opinion. I never thought that the Crown D150 or the D300 sounded
"fine".
Something you couldn't say of the early Dynacos or the Harman-Kardon
Citation 12, or any other 40-60 Watt/channel amps using
2N3055 output devices...).
The Citation 12 did not use 2N3055 output devices. Its output devices were
RCA 40636's which were similar, but then so were very many other silicon
power transistors of the day.
The kit I built certainly used 2N3055s,
The Dyna 120 was originally shipped with 2N3055 output devices but they were
quickly upgraded by Dyna to 2N3772 types which were an uprated device. My
Dyna 120 appears to have been factory built and shows no signs of parts
replacements or other maintenance. It came with 2N3772 output devices.
And was a later model that did NOT have the heavy class 'B' biasing, and thus
no crossover notch. Every one that I ever looked at had the crossover notch,
It's easy to see on the oscilloscope with a sine wave test tone. By the time
Dynaco "fixed" the ST-120, most of the audiophiles that I knew (including
myself) had moved-on.
IIRC, it was Bob Orban who showed me how to fix mine. He came up with a
re-biasing scheme which was similar to Dyna's later fix (he had a ST-120 as
well). The problem with the 2N3055s that Dyna used was that you couldn't just
replace them with off-the-shelf replacement parts. Dyna selected the 2N3055s
for V-sub-BE (I believe) and you had to buy your replacements from the
factory (they weren't even marked as 2N3055s). I got tired of the goddamn
thing blowing first one channel and then the other, so I moved on to a used
Citation two, (which was pretty bulletproof) and I liked the sound better
than that of the ST-120, as well.