APT 1 power amp – undeservedly forgotten

dimitri · 22nd December 2005, 08:32 PM

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.

dimitri · 22nd December 2005, 08:34 PM

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...

dimitri · 22nd December 2005, 08:35 PM

1kHz fft just prior clipping point

dimitri · 22nd December 2005, 08:36 PM

1kHz fft 20dB below clipping point

dimitri · 22nd December 2005, 08:38 PM

1kHz fft 40dB below clipping point

dimitri · 22nd December 2005, 08:45 PM

small peak on 19.5kHz - AP2 artefact
again, 20db rise in noise floor afer 3kHz is also AP2 artefact
red and yellow - different channels

dimitri · 22nd December 2005, 08:50 PM

20 db below clipping point

dimitri · 22nd December 2005, 08:52 PM

40dB below clipping point

lineup · 22nd December 2005, 08:59 PM

It is most likely a very, very good amplifier.

How much does it cost?

You have any schematic, so I can build it?

djk · 22nd December 2005, 09:34 PM

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.

22nd December 2005, 08:32 PM	#1
dimitri diyAudio Member Join Date: Oct 2002 Location: retired	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.

22nd December 2005, 08:59 PM	#9
lineup diyAudio Member Join Date: Dec 2005 Location: the north	It is most likely a very, very good amplifier. How much does it cost? You have any schematic, so I can build it? __________________ lineup

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22nd December 2005, 09:34 PM	#10
djk diyAudio Member Join Date: Feb 2001 Location: USA	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.

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