APT 1 power amp – undeservedly forgotten - diyAudio
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Old 22nd December 2005, 09:32 PM   #1
dimitri is offline dimitri  United States
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Default 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.
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Old 22nd December 2005, 09:34 PM   #2
dimitri is offline dimitri  United States
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Default 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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Old 22nd December 2005, 09:35 PM   #3
dimitri is offline dimitri  United States
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Default 1kHz fft just prior clipping point

1kHz fft just prior clipping point
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Old 22nd December 2005, 09:36 PM   #4
dimitri is offline dimitri  United States
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Default 1kHz fft 20dB below clipping point

1kHz fft 20dB below clipping point
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Old 22nd December 2005, 09:38 PM   #5
dimitri is offline dimitri  United States
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Default 1kHz fft 40dB below clipping point

1kHz fft 40dB below clipping point
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File Type: jpg apt-1khzfft-40db.jpg (49.6 KB, 3973 views)
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Old 22nd December 2005, 09:45 PM   #6
dimitri is offline dimitri  United States
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Default CCIF (19kHz and 20kHz) just below clipping

small peak on 19.5kHz - AP2 artefact
again, 20db rise in noise floor afer 3kHz is also AP2 artefact
red and yellow - different channels
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Old 22nd December 2005, 09:50 PM   #7
dimitri is offline dimitri  United States
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Default CCIF 19 and 20kHz

20 db below clipping point
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Old 22nd December 2005, 09:52 PM   #8
dimitri is offline dimitri  United States
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Default CCIF 19 and 20kHz

40dB below clipping point
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Old 22nd December 2005, 09:59 PM   #9
lineup is offline lineup  Sweden
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It is most likely a very, very good amplifier.

How much does it cost?

You have any schematic, so I can build it?

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Old 22nd December 2005, 10:34 PM   #10
djk is offline djk
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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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