APT 1 power amp – undeservedly forgotten

I'm really wondered when somebody will start discussion (cloning) of this quarter century old but excellent amplifier here – but couldn't wait more and start this by myself.

The designer of APT power amplifier and preamplifier is Tomlinson Holman, formerly with Advent, later with Lukas film, THX and TMH Labs. The principles that he used to design APT power amplifier and preamplifier can be found in JAES:
New Factors in Phonograph Preamplifier Design, Volume 24 Number 4 pp. 263-270; May 1976
Phonograph Preamplifier Design Criteria: An Update, Volume 28 Number 5 pp. 325-330; May 1980
Loudness Compensation: Use and Abuse, Volume 26 Number 7/8 pp. 526-536; July/August 1978
New Factors in Power Amplifier Design, Volume 29 Number 7/8 pp. 517-522; July/August 1981

Clear explanation and important content made these papers essential for amp designer.
 
Thd+n

Here is THD+N and output power for both channels driven. Don’t pay attention to the slope (low frequency noise), have a look on THD prior clipping point.

all these mesasurements were done with my good old APT...
 

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Hi Dimitri,

Ah... I used to have both the first and last of his papers you've listed, and value his material. My early phono preamps were built fully cognisant of his definitive preamp paper.

both have walked.

Looking at the APT -20db FFT, looks like a few PS artefacts there, but then the floor is quite low.

A schematic would be good?

Hi djk,

Same output stage as Leach, hey - must've been in vogue around 1980?

Cheers,
Greg
 
"Sometimes it's better keep silence than talk nonsense."

If by that you mean you disagree, then I must infer you have not done a comparison.

"must've been in vogue around 1980?"

Complementary output pairs had become widely available. The EF stages were easier to stabilize than the CFP types, so the EF became the standard. There was only one quasi-comp design I ever found that came close in sound.
 
dimitri:

i had one a long while back. i really enjoyed it. i lived i an apartment at the time and got a BAD lighting strike one night that took out all the electronics on my floor of the building (started a fire, too, but that missed my unit, fortunately). the only survivor was my vtech 900MHz cordless phone. i was repairing **** for months ...

the lightning hit killed all the amplifier circuit semiconductors and burned the circuit board beyond usability. i would have liked to rebuild it, but i never got around to that.

it WAS a good amp. tomlinson said he would have used a JFET front end if he could have found good JFETs in the US to use. i wondered what the designer did afterwards i audio. I think his name was mark dinsmore???

the design paper from Electronic Design i 1980 (I think that was the year) was excellent. same issue had a paper on the hitachi power mosfets and the hafler dh200 design, so they called it a showdown of mosfet versus bipolar. heh, heh, heh

good ole days ...

anybody making APT1 boards, i'll go for a set.

mlloyd1

edit: i didn't know c-r-a-p was a bad word
 
mlloyd1 said:
the design paper from Electronic Design i 1980 (I think that was the year) was excellent. same issue had a paper on the hitachi power mosfets and the hafler dh200 design, so they called it a showdown of mosfet versus bipolar.

You have a good memory, Mr Lloyd, thanks for the refresher.
Good thing about lagging behind in the Ol' world is getting to read something years later. :clown:

Translations to English from Russian are sometimes an improvement, i see.
 
dimitri

I can't help but think that you have never auditioned any other amplifier except for the APT. Open your eyes! You will find that there are far more deserving amplifiers out there than your prized APT.

The preamp wasn't much better. Neither deserving of any praise by anyone calling themselves an audiophile.

Compare a Leach to the APT sometime and you will go home feeling like you have just been voilated.

Quote: From Mr. DJK

The APT output stage is the same as a Leach, and uses two pair of MJ15024/25 for outputs.

It has a high voltage tier and a Baker clamp for the front end.

The Leach front end sounds better than the ATP.

I'm sure that DJK can go further into detail or maybe I should say lack of detail as far as this amplifier is concerned as well as thousands of other designs.

As one that has auditioned this amplifier as well as testing it when it came out I will still maintain my unimpressed status.