burnedfingers said:
Assuming for an instant that the leach 'sounded better' than the ATP, you couldn't conclusively attribute this to different front ends......
How, for instance, were you able ascertain that the neccesarily different PCB layouts, power supplies, etc did not have a bearing on the issue..?
"How, for instance, were you able ascertain that the neccesarily different PCB layouts, power supplies, etc did not have a bearing on the issue..? "
Probably due more to the differences in the voltage gain stages, and the TL072 in the APT vs the cross-coupled dual diff input, fully complementary from input to output circuit in the Leach.
The APT did sound better in bridge mode, but still not as good as the Leach. I'm sure a better opamp would have helped.
The Leach LSR&D 101 was the same price in kit form (a one hour project with a #2 philips screwdriver) as the APT, sounded better, and delivered 300W/4R X2 vs 100W/4R X2 for the APT.
The 1980 blurb comparing SOA of the Hitachi MOSFETs in the DH200 VS the MJ15024/25 in the APT was very good. The Hitachi cost $16 a channel for 400W SOA vs $10 for 1KW SOA of the Motorola. Why then did the APT have to sell for twice the price of the Hafler?
The loudness control on the preamp worked well. The phono section was dead quiet, being designed for a real source impedance, rather than to measure good with a shorted input. It also had good RIAA EQ with the new 30hz roll-off standard, and a switchable 20hz infrasonic filter. The phono channel balance was a nice touch, as was the image control. The weird volume control circuit required a large electrolytic cap and degraded the sound. Whole bunch of TL072s.
On the whole, a very sterile and un-involving piece to listen to, but I still liked it.
The 'distortion indicator' circuit in the amp was good. It did not come on at the on-set of clipping, but was delayed by about 40mS. This correlated well with audible distortion.
The Baker clamp allowed it to recover from clipping without the outputs 'sticking' to the rail, and could be driven quite hard without distress. Contrast this with many other better sounding amps that fell apart the instant they clipped.
I have no problem with stealing the good ideas, but there is a lot in the APT that I would leave on the shelf.
Probably due more to the differences in the voltage gain stages, and the TL072 in the APT vs the cross-coupled dual diff input, fully complementary from input to output circuit in the Leach.
The APT did sound better in bridge mode, but still not as good as the Leach. I'm sure a better opamp would have helped.
The Leach LSR&D 101 was the same price in kit form (a one hour project with a #2 philips screwdriver) as the APT, sounded better, and delivered 300W/4R X2 vs 100W/4R X2 for the APT.
The 1980 blurb comparing SOA of the Hitachi MOSFETs in the DH200 VS the MJ15024/25 in the APT was very good. The Hitachi cost $16 a channel for 400W SOA vs $10 for 1KW SOA of the Motorola. Why then did the APT have to sell for twice the price of the Hafler?
The loudness control on the preamp worked well. The phono section was dead quiet, being designed for a real source impedance, rather than to measure good with a shorted input. It also had good RIAA EQ with the new 30hz roll-off standard, and a switchable 20hz infrasonic filter. The phono channel balance was a nice touch, as was the image control. The weird volume control circuit required a large electrolytic cap and degraded the sound. Whole bunch of TL072s.
On the whole, a very sterile and un-involving piece to listen to, but I still liked it.
The 'distortion indicator' circuit in the amp was good. It did not come on at the on-set of clipping, but was delayed by about 40mS. This correlated well with audible distortion.
The Baker clamp allowed it to recover from clipping without the outputs 'sticking' to the rail, and could be driven quite hard without distress. Contrast this with many other better sounding amps that fell apart the instant they clipped.
I have no problem with stealing the good ideas, but there is a lot in the APT that I would leave on the shelf.
input stage is darlington differential type single ended, vas i think is push-pull so with the output stage.
it was featured in the audio magazine together with the schemtics, i will dig it up once i get home, but i am not sure if i still have the magazine copy of audio where it apeared.
as djk said it has two tiered power supply, i will try to post the schematics if i find it.
it was featured in the audio magazine together with the schemtics, i will dig it up once i get home, but i am not sure if i still have the magazine copy of audio where it apeared.
as djk said it has two tiered power supply, i will try to post the schematics if i find it.
Like many others, I'm interested by
Amplifier Schematics
and
"New Factors in Power Amplifier Design", Volume 29 Number 7/8 pp. 517-522; July/August 1981
Has any one an example to show me what a Barker diode is ?
The APT preamp had a bass tone control to address the problem of equal intensity loudnesses, still today refered to Fletcher and Munson, names which should be forgotten in favour of many more recent works on the same subject. Holman based the conception of the APT tone control on Stevens's works. Simulation shows that when its bass control button is turned fulyl clockwise, the boost is :
+1 dB at 400 Hz, 220 Hz + 3 dB, +14 dB at 32 Hz, +16 dB at 16 Hz, +17 dB (flat) at 3 Hz.
This should be a good start to reintroduce one of the most lacking feature of so-called hi-end equipment : tone controls.
~~~~~~~~ Forr
§§§
Amplifier Schematics
and
"New Factors in Power Amplifier Design", Volume 29 Number 7/8 pp. 517-522; July/August 1981
Has any one an example to show me what a Barker diode is ?
The APT preamp had a bass tone control to address the problem of equal intensity loudnesses, still today refered to Fletcher and Munson, names which should be forgotten in favour of many more recent works on the same subject. Holman based the conception of the APT tone control on Stevens's works. Simulation shows that when its bass control button is turned fulyl clockwise, the boost is :
+1 dB at 400 Hz, 220 Hz + 3 dB, +14 dB at 32 Hz, +16 dB at 16 Hz, +17 dB (flat) at 3 Hz.
This should be a good start to reintroduce one of the most lacking feature of so-called hi-end equipment : tone controls.
~~~~~~~~ Forr
§§§
Quote:
This should be a good start to reintroduce one of the most lacking feature of so-called hi-end equipment : tone controls.
High end equipment doesn't need tone controls. A true audiophile
doesn't purchase equipment that has or needs to have its output colored by cheap degrading tone controls.
This should be a good start to reintroduce one of the most lacking feature of so-called hi-end equipment : tone controls.
High end equipment doesn't need tone controls. A true audiophile
doesn't purchase equipment that has or needs to have its output colored by cheap degrading tone controls.
Burnedfingers
"High end equipment doesn't need tone controls. A true audiophile
doesn't purchase equipment that has or needs to have its output colored by cheap degrading tone controls."
1. Your ears need tone controls at low volumes.
2. The amount of bass because of the room gain may need to be corrected.
3.etc.. etc..
Tone controls are definitely a good thing whatever the equipement.
~~~~~ Forr
§§§
"High end equipment doesn't need tone controls. A true audiophile
doesn't purchase equipment that has or needs to have its output colored by cheap degrading tone controls."
1. Your ears need tone controls at low volumes.
2. The amount of bass because of the room gain may need to be corrected.
3.etc.. etc..
Tone controls are definitely a good thing whatever the equipement.
~~~~~ Forr
§§§
Burnedfingers,
To be pleasant on this Christmas day:
1. Tone controls are not there to compensate for poor amplifiers, they are there to compensate (at least to a degree) for room acoustics, loudspeaker inefficiencies, ears, and taste. Also read "compensate", i.e. to correct that has already gone deficient somewhere else.
2. The statement is often heard that tone controls degrade. Kindly define in technical terms! I agree that some over-simple lousy circuits exist, but a good design set for flat, has NO detectable phase or amplitude difference compared to a straight wire. A loudspeaker has much more.
3. I am afraid blind tests have consistently indicated that "hearing the degradation" by (well-designed) tone controls is a fallacy. I myself have on occasion been naughty here. I believe I have a well designed amplifier (others say so), and I have often heard folks mention that they can hear the difference when actuating the tone control cancel switch during a demonstration. Fact is, that switch was not wired in....
As said on another thread, may all have a very memorable festive season and 2006. It has been a great advantage for me to have joined this site.
To be pleasant on this Christmas day:
1. Tone controls are not there to compensate for poor amplifiers, they are there to compensate (at least to a degree) for room acoustics, loudspeaker inefficiencies, ears, and taste. Also read "compensate", i.e. to correct that has already gone deficient somewhere else.
2. The statement is often heard that tone controls degrade. Kindly define in technical terms! I agree that some over-simple lousy circuits exist, but a good design set for flat, has NO detectable phase or amplitude difference compared to a straight wire. A loudspeaker has much more.
3. I am afraid blind tests have consistently indicated that "hearing the degradation" by (well-designed) tone controls is a fallacy. I myself have on occasion been naughty here. I believe I have a well designed amplifier (others say so), and I have often heard folks mention that they can hear the difference when actuating the tone control cancel switch during a demonstration. Fact is, that switch was not wired in....
As said on another thread, may all have a very memorable festive season and 2006. It has been a great advantage for me to have joined this site.
Yep - Remember the Apt product line very well. For us it was position between our entry level Hafler and high end Theshold.
For us it worked quite well. Good build quality, above average sonic signature.
Superior to the Hafler line up, but fell far short of Threshold.
With that being said, I doubt if it warrants the cost of service or rebuild and that applies to both the amp and preamp. Outstanding for their day. Same can be said of Hafler as well.
Threshold on the other hand,in my opinion warrant service or rebuild. True mil-spec products, built to last 50 years or more,and they continue to deliver superb sonic presentation.
This is not meant to disparage Hafler or Apt. But what they cost new and whats out there today, plus the vintage Threshold that warrants the service,if needed, seems that resources could be placed elsewhere,where the return is greater.
For us it worked quite well. Good build quality, above average sonic signature.
Superior to the Hafler line up, but fell far short of Threshold.
With that being said, I doubt if it warrants the cost of service or rebuild and that applies to both the amp and preamp. Outstanding for their day. Same can be said of Hafler as well.
Threshold on the other hand,in my opinion warrant service or rebuild. True mil-spec products, built to last 50 years or more,and they continue to deliver superb sonic presentation.
This is not meant to disparage Hafler or Apt. But what they cost new and whats out there today, plus the vintage Threshold that warrants the service,if needed, seems that resources could be placed elsewhere,where the return is greater.
Attachments
Don't be afraid of tone controls. I saw the most expensive preamp I've ever seen (USD125.000) has a 5 band tone control integrated in the unit.
Hi, Dimitri,
Could you look at http://www.diyaudio.com/forums/showthread.php?postid=798064#post798064
Hi, Dimitri,
Could you look at http://www.diyaudio.com/forums/showthread.php?postid=798064#post798064
Quote:
1. Tone controls are not there to compensate for poor amplifiers, they are there to compensate (at least to a degree) for room acoustics, loudspeaker inefficiencies, ears, and taste. Also read "compensate", i.e. to correct that has already gone deficient somewhere else.
I will take care of room problems first. In other words proper acoustic treatment of the room instead of trying to cover up the room problems by cranking up the bass and treble controls.
Proper EQing of the system using pink noise and analyzer. The usage of a 31 band EQ in my case. I favor a Shure DFR 22 for a sand amp application.
Personally I will leave the tone controls to the same morons that put happy faces on Eq's.
1. Tone controls are not there to compensate for poor amplifiers, they are there to compensate (at least to a degree) for room acoustics, loudspeaker inefficiencies, ears, and taste. Also read "compensate", i.e. to correct that has already gone deficient somewhere else.
I will take care of room problems first. In other words proper acoustic treatment of the room instead of trying to cover up the room problems by cranking up the bass and treble controls.
Proper EQing of the system using pink noise and analyzer. The usage of a 31 band EQ in my case. I favor a Shure DFR 22 for a sand amp application.
Personally I will leave the tone controls to the same morons that put happy faces on Eq's.
burnedfingers said:For all you APT lovers out there. There is a ebay 7 day listing with 4 days remaining on this APT power amplifier for $199.99 on a buy it now EBAY NUMBER 5845141180
Here is a chance for your undeservedly forgotten classic APT amplifier.
A good price. Sold , of course. Too bad.
HI Johan Potgieter
"The statement is often heard that tone controls degrade. Kindly define in technical terms! I agree that some over-simple lousy circuits exist, but a good design set for flat, has NO detectable phase or amplitude difference compared to a straight wire."
Tone controls based on Baxandall circuit use virtual earth at standard line levels so they introduce almost no distorsion. However I think their bad press is coming from the pots which genarally are of very poor quality. This is a place where real audiophile exigence should be, using first class grade for these electro-mechanical parts. twelve positions switchs commutating resistors can reliably replace pots at low cost in tone controls.
~~~~~ Forr
§§§
"The statement is often heard that tone controls degrade. Kindly define in technical terms! I agree that some over-simple lousy circuits exist, but a good design set for flat, has NO detectable phase or amplitude difference compared to a straight wire."
Tone controls based on Baxandall circuit use virtual earth at standard line levels so they introduce almost no distorsion. However I think their bad press is coming from the pots which genarally are of very poor quality. This is a place where real audiophile exigence should be, using first class grade for these electro-mechanical parts. twelve positions switchs commutating resistors can reliably replace pots at low cost in tone controls.
~~~~~ Forr
§§§
burnedfingers said:
Excellent! Good for you Burnedfingers! We have made progress on at least 2 matters. Firstly you have acknowledged that the judgment on tone controls expressed in your post #29 as dogma, is just your personal opinion - your right to that cannot be taken away.
Secondly I now know what at least one fellow member thinks of me. So.
You have still not quantified your disdain for tone controls (and thus other kinds of filters) in technical terms, but I will let that ride, seeing that it is still Christmas. But not everybody wants to or have the freedom to convert their living rooms into studios utilising all manner of acoustic treatment and/or exotic digital equalisers. Or needs to.
It remains a matter of compromise, usually limited to one small position in a room. Anybody who has done research into room acoustics knows that displacement of a microphone by only one person's size can change 10 dB peaks to 10 dB dips. I won't even go into getting rid of low frequency standing waves, influence of group delay and all that. We are getting off-thread.
Forr,
Yes, I am afraid bad press has been responsible for more 'urban legends' than I can count. Ken Kessler once said: "Repeat anything often enough and everybody will believe it." You would know full well what it did regarding 'feedback is ba-a-a-d', not to mention the exotic cable frenzy.
I use the Swiss Elma 24 position switches for more professional work with a very light index locator, or without that for 47 step work if required.
Now for an effort to get back to thread.
Regards