I recall reading an article which described a test that allowed 2 amps to be
connected to a single speaker. If and only if there were differences
between the 2 would the speaker make any sound at all.

Anyone know of this test?

wrote:
I recall reading an article which described a test that allowed 2 amps to be
connected to a single speaker. If and only if there were differences
between the 2 would the speaker make any sound at all.

Anyone know of this test?

I think this was the metho used by Bob carver in his Stereophile
challenge where he claimed he could make his amplifier sound just like
a much more expensie tube amp.


Scott

" wrote in message
...
I recall reading an article which described a test that allowed 2 amps to
be
connected to a single speaker. If and only if there were differences
between the 2 would the speaker make any sound at all.

Anyone know of this test?

That would be the differential test. If a) the polarity of both amps is the
same, and b) the gain setting is the same, you can test amps that way by
connecting the 2 low sides together and the speaker between the 2 high
sides. The gain can best be set by simply adjusting it until the output of
the speaker is at a minimum.

Norm Strong

wrote:

I recall reading an article which described a test that allowed 2 amps to be
connected to a single speaker. If and only if there were differences
between the 2 would the speaker make any sound at all.

Anyone know of this test?

Yes, of course.

I don't know what it's "called" in various circles, but it's a
"differential test". The test shows up the difference between not only
the signals but the difference between the errors. You can try it
between two ams in a stereo unit, or between two different amps. The
main problem is you have to PRECISELY match the gain of the two amps.

In article ,
wrote:

I think this was the metho used by Bob carver in his Stereophile
challenge where he claimed he could make his amplifier sound just like
a much more expensie tube amp.

Which he did, judging by Stereophile's golden ears of the time,
IIRC.

Billy Shears wrote:
In article ,
wrote:

I think this was the metho used by Bob carver in his Stereophile
challenge where he claimed he could make his amplifier sound just like
a much more expensie tube amp.

Which he did, judging by Stereophile's golden ears of the time,
IIRC.

Yes they did concede that. Unfortnately he could not maintain the same
levels of likeness in his production model based on the challenge. that
was not only the conclusion of the Stereophile review of that
production amp but a concession made by Bob Carver himself. Bt in a
world where all amps sound the same what could any of this mean? Oh
yeah, the test was done blind. hmmmmmm.


Scott

Billy Shears wrote:
In article ,
wrote:
I think this was the metho used by Bob carver in his Stereophile
challenge where he claimed he could make his amplifier sound just
like a much more expensie tube amp.

Which he did, judging by Stereophile's golden ears of the time,
IIRC.

Yes, in 1985, but only using the Carver to drive the midrange and
treble drivers of an Infinity panel speaker. Later tests in 1987
showed that the Carver could be distinguished from the tube
amplifier by ear when it drove a Celestion speaker fullrange,
something admitted by Bob Carver.

Both the 1985 and 1987 tests were fully described in Stereophile.
Using a differential method between the two amplifiers, I could
not achieve a null greater than 36dB, and then only in the midrange.

John Atkinson
Editor, Stereophile

Billy Shears wrote:
In article ,
wrote:

I think this was the metho used by Bob carver in his Stereophile
challenge where he claimed he could make his amplifier sound just like
a much more expensie tube amp.

Which he did, judging by Stereophile's golden ears of the time,
IIRC.

It wasn't a Stereophile challenge, but Audio Critic challenge. Bob
Carver and his "transfer function" said he was able to make his amp
sound identical to any amp. The amp that was chosen was a Mark Levinson
ML25, a class "A" amp. Pete Azel oversaw this event. Afterwards, Carver
took his amp "home' for final clean up, and began making the 1.5t (which
I bought. I brought my then, just spec'ed and repaired Phase 400 to a
stereo salon I frequented and knew the employees well. The 1.5t had just
come in. I told them that my Phase would certainly hold it's own against
this new "wonder amp", so they told me to bring it in. I did. I hooked
it up and they left me alone for a couple of hours. I listened to
everything I brought and lp's they had there. I left holding my head
down, with my Phase under my arm sadden by the fact that the Carver 1.5t
sounded much better. So, I bought one. Mind you, I went there with the
confidence of having my just spec'ed out Phase to be more than equal to
the 1.5t. It wasn't).
Carver later said that all of his amps would sound like the ML25. He
bought a couple for null testing against random amps from his
manufacture. Hence the "t" after all his later amps.

I enjoyed the sound of the 1.5t for over 10 years driving my wonderfully
power hungry Acoustat 1+1's Medallion mod in a 24x14x8' listening room
to loud levels (love full scale classical dynamic stuff). Then, it bit
the big one, so replaced it with a Counterpoint SA220 (and yes, they did
sound different).

techdeveloper wrote:
I recall reading an article which described a test that allowed 2
amps to be connected to a single speaker. If and only if there were
differences between the 2 would the speaker make any sound at all.

Anyone know of this test?

Yes, of course.

I don't know what it's "called" in various circles, but it's a
"differential test". The test shows up the difference between not only
the signals but the difference between the errors. You can try it
between two ams in a stereo unit, or between two different amps. The
main problem is you have to PRECISELY match the gain of the two amps.

It is the same connection as driving the amps in x-bridged mode but the
second signal is not inverted. Of course the gain-matching has to be done at
a particular frequency i.e. 1kHz. Then we can not only compare the frequency
response but also the phase response. If there are different treble cut.off
frequencies, phase differences will show up in the audio range making a
trebelish output, the same is true for the low frequencies with a rumblish
sound. Only if both amps perform identical and are not overdriven, we will
get silence. We can do this test also with one amp only and comparing the
left and right channels in the same way.
--
ciao Ban
Bordighera, Italy

In article ,
wrote:

Billy Shears wrote:
In article ,
wrote:

I think this was the metho used by Bob carver in his Stereophile
challenge where he claimed he could make his amplifier sound just like
a much more expensie tube amp.

Which he did, judging by Stereophile's golden ears of the time,
IIRC.

Yes they did concede that. Unfortnately he could not maintain the same
levels of likeness in his production model based on the challenge. that
was not only the conclusion of the Stereophile review of that
production amp but a concession made by Bob Carver himself.

No, that's not right. Carver conceded Holt could tell the
difference (although IIRC Holt thought Carver's amp was the tubed
amp during the test), but Carver claimed that the original tube
amp had changed in the intervening time. Not an implausible
assertion given the nature of tubes. And I think the original
Carver-tweaked solid state amp - the one Holt and his
golden-eared pals couldn't distinguish from the tube amp - had
been lost or left behind or something ... bad science there.

Bt in a
world where all amps sound the same what could any of this mean?

I don't think anyone has claimed all tube amps sound like all
solid state amps. Do you have a reference for such a claim?

yeah, the test was done blind. hmmmmmm.

Well I think both tests were blind, so what is your point?

In article ,
TonyP wrote:

Billy Shears wrote:
In article ,
wrote:

I think this was the metho used by Bob carver in his Stereophile
challenge where he claimed he could make his amplifier sound just like
a much more expensie tube amp.

Which he did, judging by Stereophile's golden ears of the time,
IIRC.

It wasn't a Stereophile challenge, but Audio Critic challenge.

It was a Carver Challenge, wasn't it? And Stereophile took him up
on it. And then later there was a Carver/Audio Critic event along
the same lines. I think ...

"Billy Shears" wrote in message
...

Snip...

I don't think anyone has claimed all tube amps sound like all
solid state amps. Do you have a reference for such a claim?

I thought ALL amps which met minimum performance levels (specs?) sounded the
same as long as they were not pushed beyond their design limits.

Billy Shears wrote:
In article ,
wrote:

Billy Shears wrote:
In article ,
wrote:

I think this was the metho used by Bob carver in his Stereophile
challenge where he claimed he could make his amplifier sound just like
a much more expensie tube amp.

Which he did, judging by Stereophile's golden ears of the time,
IIRC.

Yes they did concede that. Unfortnately he could not maintain the same
levels of likeness in his production model based on the challenge. that
was not only the conclusion of the Stereophile review of that
production amp but a concession made by Bob Carver himself.

No, that's not right. Carver conceded Holt could tell the
difference (although IIRC Holt thought Carver's amp was the tubed
amp during the test), but Carver claimed that the original tube
amp had changed in the intervening time. Not an implausible
assertion given the nature of tubes. And I think the original
Carver-tweaked solid state amp - the one Holt and his
golden-eared pals couldn't distinguish from the tube amp - had
been lost or left behind or something ... bad science there.


No, that's not right. Carver conceded that the production version of
his amp did not perform the same null as the hand tweeked version. he
simply claimed it was close enough.



Bt in a
world where all amps sound the same what could any of this mean?

I don't think anyone has claimed all tube amps sound like all
solid state amps. Do you have a reference for such a claim?


Actually it has been often claimed that all "competent" amps sound the
same and some have claimed that the Conrad Johnson amps are quite
competent. no one i know of has claimed that their amps are
incompetently designed or built. So the logical conclusion should be
quite obvious.




yeah, the test was done blind. hmmmmmm.

Well I think both tests were blind, so what is your point?


That the claims of no competent amps having a sonic signature under
blind conditions run contrary to those blind tests.


Scott

"John Richards" wrote in message
...
"Billy Shears" wrote in message
...

Snip...

I don't think anyone has claimed all tube amps sound like all
solid state amps. Do you have a reference for such a claim?

I thought ALL amps which met minimum performance levels (specs?) sounded
the
same as long as they were not pushed beyond their design limits.

When I bought my first solid state amp, I noticed immediately that it seemed
to have a leaner sound with less bass. Being an engineer, I of course
refused to accept this situation without some explanation. I started by
putting a 1 ohm resistor in series with each speaker. Amazing! The sound
of my tube amp was reproduced almost exactly.

I was in "experimental mode" so I went back to the tube amp and connected my
speakers to the 4 ohm tap on the output transformer. Lo and behold, the
lean sound returned, although the output was much lower.

Going back to the transistor amp, I replaced the 1 ohm resistors with 3 ohm
wirewound rheostats. I found out quickly that you could get as much bass
hangover as you wished by dialing in more or less resistance. I should
mention that my speakers were the acoustic suspension type; bass reflex
speakers would have behaved differently. I ended up leaving about 10% (0.3
ohms) in series with the amplifier.

As far as I can tell, the difference between tube and transistor amp sound
is almost entirely a function of the amplifier output impedance.

Norm Strong

In article ,
wrote:

Billy Shears wrote:
In article ,
wrote:

Billy Shears wrote:
In article ,
wrote:

I think this was the metho used by Bob carver in his Stereophile
challenge where he claimed he could make his amplifier sound just like
a much more expensie tube amp.

Which he did, judging by Stereophile's golden ears of the time,
IIRC.

Yes they did concede that. Unfortnately he could not maintain the same
levels of likeness in his production model based on the challenge. that
was not only the conclusion of the Stereophile review of that
production amp but a concession made by Bob Carver himself.

No, that's not right. Carver conceded Holt could tell the
difference (although IIRC Holt thought Carver's amp was the tubed
amp during the test), but Carver claimed that the original tube
amp had changed in the intervening time. Not an implausible
assertion given the nature of tubes. And I think the original
Carver-tweaked solid state amp - the one Holt and his
golden-eared pals couldn't distinguish from the tube amp - had
been lost or left behind or something ... bad science there.


No, that's not right. Carver conceded that the production version of
his amp did not perform the same null as the hand tweeked version.

My recollection is Carver conceded the production version sounded
different from the tube amp used in the first round of tests. But
Carver's hand-tweaked solid state amp was not in Santa Fe for the
second round of tests, so how could he have conceded what you
say? I also remember that Carver claimed, perhaps in a letter,
that the original tube amp had changed in the interim.