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Peter Wieck Peter Wieck is offline
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Default Results of Bi-Amped AR3a Experiment

From my e-mail to Jerry:

Jerry:

Results are interesting.

Handel's "Let the Bright Seraphim" was the test piece, a combination of
solo voice, light brass, and then full orchestra, choir, brass and
kettle-drums, a valid test for any speakers as volume must be
substantial to get the full effect. My SWAG is a peak-to-average of
about 20dB +/- 3dB.

http://www.amazon.com/Kiri-Te-Kanawa...e=UTF8&s=music

Is a link to the precise recording. You may click on that track for a
bit of it on your computer speakers.

Electronics used were two (2) AR integrated amplifiers, rated at
50wpc/rms into the 3a load, one Scott LK-150 rated at 75wpc/rms, a pair
of 6550 outputs in PP per channel, then back to the Citation 16 at
225wpc/rms into that 4-ohm load, also stable below 1 ohm of dynamic
load.

No units were driven to continuous clipping. I believe that the LK-150
was shaving at the top during the loudest passages, but the other two
choices

Feed came from a Revox B225 CD player, I chose not to set up the FM-3
as I could not be sure of matched outputs and did not want to diddle
with variables. I also did not try the ST-80s as I felt that only 40wpc
was not a fair test... and although the PAT-5 has matched outputs,
again too many variables for a really close test. I used the "null"
setting on the amplifier from a monaural signal to be sure that either
channel was electrically matched.

OK... the AR amplifiers were just great. The LK-150 did shave off the
top, I expect. It sure sounded a bit tubby at the loudest passages
where the ARs did not. And the Citation 16 was the most transparent at
the loudest passages, but otherwise quite close to the ARs. I played a
bit with the volume controls and tone controls (the AR electronics
allow separate tone settings for each channel, and also have a "Null"
setting (see note above)... send through a monaural signal, and the
channels may be balanced electronically very precisely... which I did.

My conclusion is that bi-amping power-pig speakers is definitely a
worthwhile endeavor if the components are closely matched. **But when I
started diddling with the controls, the sound went
all-over-the-place.** Sometimes that was temporarily pleasing, mostly
not. I also came to the conclusion that unmatched components would be a
very difficult proposal. I also conclude that a brute-force amplifier
such as the 16, or the Dynaco 416 is the best and simplest solution.

I am wondering if a pair of ST-70s would be better as single-amp
strapped, or bi-amped separately... so, my goal at Kutztown this fall
will be to snag another inexpensive ST-70 for that experiment. Point
being to test the tube sound in a true bi-amp configuration. As LK-150s
are running between $1200 and $2000 these days, I doubt I will be able
to afford one of those for a bi-amp experiment.

I also concluded that the ST-80s are nice, and would be worthwhile for
slightly less hungry speakers (maybe the AR2ax), but simply did not
measure up in this case. And the clipping would have been dangerous had
I driven them to the levels I did with the other units. I did not worry
so much with the LK-150 as tube clipping is not of the same nature as
SS clipping.

Peter Wieck
Wyncote, PA
 
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