This is a review and detailed measurements of the Apt Holman vintage preamplifier. It is on kind loan from a member and has been refurbished by QuirkAudio.
The look is a cross between hifi and pro gear:
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Other than some scratches on top, the unit is a very good cosmetic shape. Rear connections are extensive:
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Yes, there was a time we had outlets in the back of stereos. The more there was, the higher end the gear was said to be! Wonder what led to their demise.
In case you are wondering as I did when I was first contacted about this unit, Holman is Tomlinson Holman or the T in THX (now works for Apple). Owner sent me the service manual which is not only extensive but has excellent tutorials on the design, instruments to test it with, and pages and pages of detail. It is incredible what used to be available compared to now.
Apt Holman Measurements
Let's start with our dashboard input. I selected Tape 1 as input but oddly front panel selector doesn't have Tape 1. I set it to Aux 1 and then pushed Tape 1 switch:
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Wow, this is excellent! I expected SINAD in 60s or 70s and here we have 90 dB. It is dominated by second harmonic at that level. Even more impressive is the signal to noise ratio with same unity gain:
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Frequency response was dead flat in audible band:
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Crosstalk is better than many devices I test today:
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There is essentially no frequency dependency in distortion+noise:
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Output level is optimized for about 0.4 volts or so:
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So you may want to pair it with a power amplifier that puts out most of its power at the above level.
Apt Holman Preamplifier Phono Stage Measurements
I adjusted the volume control to give a nominal 40 dB level (higher than preamp tests):
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While I like to see no visible distortion spikes in this test, its level at -100 dB is still very good. SINAD is set by the slight amount of mains noise which I could not get rid of with various grounding methods (typical).
RIAA equalization is very good but there seems to be a high frequency resonance that causes error above 10 kHz:
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I did not look to see if there is an adjustment/compensation for this in the service manual.
Be sure to use the balance control to restore equal level in both channels.
Level of headroom is good:
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And doesn't change a lot due to frequency:
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Conclusions
The owner who sent me this has a knack for finding these past jewels with excellent engineering. Their performance post refurbishing is extreme good even by today's standard which sadly has sled backward. Hopefully no one sheds a tear next time I complain about an audio product producing SINAD of 70 dB and such which this level of performance was achieved years ago.
I am happy to recommend the Apt Holman preamplifier. I see one on ebay for $550 although it will likely need thorough service like the sample I tested.
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