Apt Holman/Hafler vs Vintage Integrated and Receivers

[GKTAUDIO]

If you have the Apt preamp, it was severely bandwidth limited in an attempt to filter RF noise coming in on the inputs.

Can you specify your metrics? Are you referring to audio range (20-20k) frequency response?

I haven't found any properly working/restored Apt Holman preamps to measure poorly in that regard.

At the moment I only have this Audio Precision 20-20k reading on my laptop, but can post up some more AP and QA FR test results when I'm on my main computer, many of which were runs up to 80kHz.

 

[mcgjohn]

Can you specify your metrics? Are you referring to audio range (20-20k) frequency response?

I haven't found any properly working/restored Apt Holman preamps to measure poorly in that regard.

At the moment I only have this Audio Precision 20-20k reading on my laptop, but can post up some more AP and QA FR test results when I'm on my main computer, many of which were runs up to 80kHz.

View attachment 3774047

NP. perhaps I was not clear. The Apt does very well at 20 to 20K. Above 20K its filters roll off higher frequencies. When these freq are rolled off a greater phase shift in the signal is the result. When the phase shift is increased, imaging and soundstaging deteriorate.

If you look at many high end preamps today, they are striving to achieve flat response 10 to 100k or more.

The other area the apt pre benefits greatly from is a much lower impedance power supply. The stock transformer is a 10 or 11 watt type. If this is increased to 250 to 350 watts at the same output voltages, the apt becomes much more dynamic sounding and takes on an ease in the sound that very organic sounding.

If you want to experiment first, pretty easy thing to do is mount an outboard transformer on a square of plywood, run the two secondaries into the chassis and connect it up.
will be really tough to return to the stock transformer.

 

[GKTAUDIO]

With respect to frequency response - you would have to make the same comparison of almost all preamps designed 45-50 years ago to contemporary high end preamps that strive for flat FR to 100kHz. I've measured a lot of preamps and the only one that has come close to that is my Spectral. The design criteria for that company included designing for frequencies well outside the audio band, and that required special cable to avoid potential RFI and amplifier oscillation. Perhaps you can point to other preamps of that era, or contemporary consumer-grade preamps that don't roll off after 20kHz? There are reasons that rolloff is designed into preamps.

WRT the gargantuan power supply you keep promoting - I've lost count of how many times you've made these claims in other threads, without ever answering any of the counter arguments that have been made to you.

It sounds like you base your claims on the lower impedance of a huge transformer, without addressing any of the other bottlenecks in a power supply - bridge rectifier, filter cap ratings, capacitor types, voltage regulators, PS characteristics of the op amps themselves, and all of the other electrolytic caps in the circuit.

I'll share your claims with Tom Holman and the assembled attendees at the Apticon conference in a couple of days. I doubt anyone will waste their time replying on this forum, but it could be entertaining.

 

[PabloTincho]

With respect to frequency response - you would have to make the same comparison of almost all preamps designed 45-50 years ago to contemporary high end preamps that strive for flat FR to 100kHz. I've measured a lot of preamps and the only one that has come close to that is my Spectral. The design criteria for that company included designing for frequencies well outside the audio band, and that required special cable to avoid potential RFI and amplifier oscillation. Perhaps you can point to other preamps of that era, or contemporary consumer-grade preamps that don't roll off after 20kHz? There are reasons that rolloff is designed into preamps.

WRT the gargantuan power supply you keep promoting - I've lost count of how many times you've made these claims in other threads, without ever answering any of the counter arguments that have been made to you.

It sounds like you base your claims on the lower impedance of a huge transformer, without addressing any of the other bottlenecks in a power supply - bridge rectifier, filter cap ratings, capacitor types, voltage regulators, PS characteristics of the op amps themselves, and all of the other electrolytic caps in the circuit.

I'll share your claims with Tom Holman and the assembled attendees at the Apticon conference in a couple of days. I doubt anyone will waste their time replying on this forum, but it could be entertaining.

Maybe you can ask Tom about the unreleased amp and the schematics, we can cloned, also the tuner

more info about the model 2 amp