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Results of Bi-Amped AR3a Experiment



 
 
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  #1  
Old September 10th 06, 11:20 PM posted to rec.audio.high-end
Peter Wieck
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Posts: 2,418
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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  #2  
Old September 16th 06, 03:23 PM posted to rec.audio.high-end
Jerry
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Posts: 115
Default Results of Bi-Amped AR3a Experiment

Peter wrote on 9/10/2006:

> 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.


Peter, you don't mention the bi-amping method. Was this a vertical or
horizontal test?

One thing I looked up, as I have the service manual, is the power rating of
the AR amps. According to my manual the rating is 60 wpc at 4 ohms and the
3a hovers around 4 ohms and lower for most of the frequency range.

The Scott LK-150 is a tube amp correct?? So where did you place it in the
bi-amp?

> 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


Again, Peter, was the LK-150 bi-amping or was it really a control and just
in a single amp arrangement.

> 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.


Hmmmm, I'm NOT liking this monaural very much. I believe I hear far better
stereo imaging with my bi-amp. Your test would be oblivious to stereo.

What is so important about the channels being matched? Actually I believe
that under ALL circumstances that I can hear and pick out individual
instruments much, much better under stereo than monaural.

> 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.


Again, I don't understand where the LK-150 fits in your test.

> 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.


OK, Peter, so why is bi-amping worthwhile on inefficient speakers? What did
you hear that made you conclude this?

Please remember that you matched the amps to each other, so that both were
producing the same output voltage. That would achieve little or nothing for
me. When I eliminated those blasted pots, the mid/tweeter became
considerable more sensitive. So I have to match based upon resulting
speaker volume.

Also don't forget that on the AR-90's our friends at Acoustic Research
admitted that they got very favorable results when they passively bi-amped.

> 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'd strongly recommend a horizontal bi-amp with either the AR amp or your
ST-80 driving the woofers. Then use the ST-70 to drive the mid/tweeter, but
throttle down the low frequencies. Just using the bass tone control gains
you tremendous headroom.

Next, I've read about a number of people who achieved terrific results by
using the tube amps on the mid and high frequencies, while letting the ss
amps handle the heavy power drain in the low frequencies.

Peter, please don't do this test in monaural. What we want to hear is the
full sound stage and especially look for difference between single and
bi-amp.

> 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, I'll bet your ST-80's would work just fine in a horizontal bi-amp
driving the woofers. As you saw from my impedance maps, the impedance for
the woofer alone is far better behaved and presents an easier load. Now one
aid to keeping clipping down would be to attenuate the high frequencies
while this amp is really focusing on the lows. The treble tone control
will help, but not nearly as much as the bass control gains headroom in the
mid/tweeter amp.

Regards,
Jerry

 




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