Question for Amp Designers

I just ran across this old article. Apparently Bob Carver had it figured out long ago and used distortion pots to mimic sonic signatures. 

"Carver caused a stir in the industry in the mid-1980s when he challenged two high-end audio magazines to give him any audio amplifier at any price, and he’d duplicate its sound in one of his lower cost (and usually much more powerful) designs. Two magazines accepted the challenge.

First, The Audio Critic chose a Mark Levinson ML-2 which Bob acoustically copied (transfer function duplication) and sold as his M1.5t amplifier (the “t” stood for transfer function modified).

In 1985, Stereophile magazine challenged Bob to copy a Conrad-Johnson Premier Five (the make and model was not named then, but revealed later) amplifier at their offices in New Mexico within 48 hours. The Conrad Johnson amplifiers were one of the most highly regarded amplifiers of the day, costing in excess of $6,000 a pair.

Of note that in both cases, the challenging amplifier could only be treated as a “black box” and could not even have its lid removed. Nevertheless, Carver, using null difference testing, (null difference testing consists of driving two different amplifiers with identical signal sources and exact levels, but out of phase by exactly 180 degrees. If the amplifiers were 100% identical, no sound would be heard. If sound was heard, the audio amps had different properties). Bob Carver used "distortion pots" to introduce amplifier characteristics, fine-tuned to null-out any sound differences. His "motel-room" modified amplifier sound was so similar, Stereophile Magazine editors could not tell the difference between his amplifier and one costing more than $6,000. This amplifier was marketed as the M1.0t for about $400.00. Bob Carver may have single-handedly debunked any number of theories about sound quality by using physics, blind and double-blind testing and unbiased measurements, such as "Gold-plated" speaker wires sound better than copper wires, etc.) Carver successfully copied the sound of the target amplifier and won the challenge. The Stereophile employees failed to pass a single blind test with their own equipment in their own listening room. He marketed “t” versions of his amplifiers incorporating the sound of the Mark Levinson and Conrad Johnson designs which caused him some criticism by those who failed to understand the true nature of the challenge — that it was possible to duplicate an audio amplifier's sound in two completely dissimilar designs. In light of this criticism, Carver went on to design the Silver Seven, the most expensive and esoteric conventional amplifier up to that time and duplicated its sound in his M 4.0t and later models which sold for some 1/40th the price (around $600–$1500).

This also started Carver's departure from the M-series amplifier to the more robust and current-pushing TFM series amplifiers. The TFM amplifiers were designed specifically to drive the demanding load of the Amazing ribbon loudspeakers. The apex of Carver's amplifier line was the Lightstar, which is now a collectors' item. Only approximately 100 of the amplifiers were made. The original Lightstar amplifier, called the Lightstar Reference, featured a dual-monoblock design, with separate power cords for each channel. A later version, called the Lightstar 2.0, featured one power cord & other cost-saving measures to shave approximately $1800 off the retail price. The two are reported to be sonically identical."

 

" But the OP has said both in this thread. In his initial post that posed the question and then with his own observations....

I’ve heard it with my own amps. I have 3 systems in my house and for some strange reason I Iike to swap out pieces to hear the changes."

That's not entirely true. In his OP, he words things in such a way that I couldn't tell if he actually heard the differences himself or was reading about them. That's why I asked the question in the first place. 

" Maybe. But if the OP was going by other people’s comments and not by his own observation, then we don’t know if the amps really sound like that. There may be no problem at all. "

Given that I wasn't sure if the OP actually heard the amps, its a legit comment. If he didn't make the observation himself, you can't be sure a problem exists. 

" I think its fair to say that we hear it all the time in the world of audio.  "

Your statement there us ultimately correct because you assumed he heard the differences where, I didn't. My question was just to obtain all the facts. I wasn't able to come to the same conclusion that you did until I had the whole picture. 

You guys that take pot shots at Julian Hirsch, my god, give the poor guy a break. For obvious reasons he can no longer defend his position on such matters. And no, more often than not, I didn't always agree with his assessments. But try writing a review on a piece of audio gear and send it to the Editor of one of the big audio rags out there. I'm sure he would tell you that you shouldn't quit your day job......

Maybe. But if the OP was going by other people’s comments and not by his own observation, then we don’t know if the amps really sound like that. There may be no problem at all.

But the OP has said both in this thread. In his initial post that posed the question and then with his own observations....

I’ve heard it with my own amps. I have 3 systems in my house and for some strange reason I Iike to swap out pieces to hear the changes.

Now I am not in the camp that says all amps sounds the same. IMO, they don’t. Nor am I an electrical engineer. But I have also wondered how some can be described as warm, laid back, etc. while others are forward, lively, etc? Especially when comparing two different brands of amps with a near identical power output rating, bandwidth and THD. I have been told this in the past when selecting my own gear. For example, I have been advised many times, on this board and others, that my Marantz PM15S2 is warm and laid back and shouldn’t be paired with warm speakers like Vienna Acoustics or Sonus Fabers.  Why?  It has the proper output to meet a 4 ohm speakers needs in an average sized room.

So again, what exactly do the designers do to give an amp a signature sound that would earn these attributes by both audiophiles and those who sell them? And yet maintain the same low THD at all frequencies for its rated output?

" Yeah, too bad we can't get Julian Hirsch in here to answer this one!"

I'll answer for him.

"We put this amp through our most rigorous tests, and here's what we found out. 

For the first test, we pushed the power button. It passed with flying colors. The amp lit up like a Christmas tree.

The nest test was for sound quality. It passed with flying colors again. We know that all amps sound exactly the same, and this amp was no exception.

In conclusion, we give this amp our highest recommendation. It performed flawlessly during all of our tests. If you're looking for a state of the art amp, this is the one for you.

 

"Have you heard this for yourself or are you going by what someone else said?"

"I think its fair to say that we hear it all the time in the world of audio. "

Maybe. But if the OP was going by other people's comments and not by his own observation, then we don't know if the amps really sound like that. There may be no problem at all.

Yeah, too bad we can't get Julian Hirsch in here to answer this one!

haha. I think that the Behringer A500 is the beauty that they used to test. 

Hold on a sec- didn't I read an article a while back about all amplifiers with the same rated power and THD sound EXACTLY the same as PROVEN by double blind listening tests?  (My tongue is firmly in cheek) .  Have a Happy Holiday!

Have you heard this for yourself or are you going by what someone else said?

I think its fair to say that we hear it all the time in the world of audio. 

Someone seems to always be describing one amp as warm while another says this model is clinical.  Or its a bad fit with this speaker or that speaker because of some character that has nothing to do with the amps specs.  I remember one member on this forum constantly dissing certain brands because they were not 3 dimensional.  That seemed to be his favorite metaphor for describing an amp.  Despite specs that were better or as good as the brands he was claiming were 3 dimensional.

I think the OP raised a very intriguing question and I would like to know how these metaphoric attributes can be designed into an amp too?

I've heard it with my own amps. I have 3 systems in my house and for some strange reason I Iike to swap out pieces to hear the changes. 

" What in the design gives these two amps the above sound signatures?"

Have you heard this for yourself or are you going by what someone else said?    

Good luck with that!!!!!

Great question. I would like to know too.

Also lets not forget both amps are rated across the entire frequency spectrum, 20Hz-20kHz with the same THD at every frequency. So surely if the amp was tuned to sound better at certain frequencies, wouldn’t this affect the THD at these altered or accentuated frequencies to give the amp a signature sound? 

I’m not an amp designer, but have built many tube and s/s for myself and friends.
There are too many parameters/factors to list that can do the above.
Just a couple for the
"laid back, mellow, & slower" can be.

limited bandwith
high impedance output (low damping factor)
little or no feedback, (creating the low damping factor)
Induced 2nd harmonic distortion
poor current ability
high impedance power supply (eg: tube reg)

and many more
Cheers George