Thank you, Michael.
I would like to take this opportunity to ask for people's reactions to all the new material in APAD6 on push-pull VAS configurations. My conclusion was that far from being superior, as is often assumed, they positively bristle with extra problems.
I've written two articles on the push-pull TIS, one of which is to be published. Yes, you're right: they're really not worth the hassle, especially in medium power domestic applications.
Douglas you haven't responded to my post here:
http://www.diyaudio.com/forums/soli...self-wants-your-opinions-182.html#post3606113
An oversight perhaps?
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I've written two articles on the push-pull TIS, one of which is to be published. Yes, you're right: they're really not worth the hassle, especially in medium power domestic applications.
Douglas you haven't responded to my post here:
http://www.diyaudio.com/forums/soli...self-wants-your-opinions-182.html#post3606113
An oversight perhaps?
Lack of time to dig into the issue at the moment. No point in giving a half-thought-out answer.
Mr Self . I think you said in the past any error will show up in harmonic distortion test somewhere . Surely that is true ? I suspect people don't look hard enough or want something that says quicker ?
single tone THD, swept in frequency and level does do a lot more than the "THD is useless" crowd want to admit but it can miss some possible distortion mechanisms that require multiple tone excitation
rearanged with the added explaination post 1st
rearanged with the added explaination post 1st
Perception is good but the Czerwinski article gives more background and context on distortion properties and Volterra representation that suggests questioning the assumption by Geddes that a swept frequency single sine wave distortion measurement is sufficient to characterize a audio amplifier
I’ve updated my previous “Hidden Distortion” sim to show a simple circuit that has 1000x more distortion with a range of 2 tone excitations than can be seen with a swept frequency single sine wave distortion measurement
First build a distortion model circuit with hi and lo pass filtered frequency branches feeding into a multiplier
play with LtSpice Modulate source to get a 20 –20 KHz sweep and show the peak distortion output is –74dB – comfortably bellows mike’s 1000 ppm value
Then uncover the “hidden distortion” with a 2 tone 160 Hz + 16 KHz sine wave excitation with the same peak input amplitude (actually any 2 tones one <160 Hz, the other > 16 KHz will show this large distortion)
The behavioral source is simply multiplying the signal from the lo and hi pass filter branches, in a real amplifier most nonlinearities have only one input “port” but the usual diff pair input stage is virtually identical to a 2 port Gilbert cell multiplier, and thermal modulation (Lavardin in the audiophile world) can be modeled by adding a RC thermal model to a Temperature “port” of each transistor model (but not easily in spice transistor models)
This is an artificial example that gives rather more extreme results than could possibly be expected in practical amplifiers but it clearly illustrates the principle that single tone distortion measures are inadequate
The assertion that the GedLee metric and, by Geddes assumption, swept frequency single sine wave distortion measurement are sufficient for audio power amplifier charterization requires more empirical data – it is clearly not sufficient in principle and multitone techniques linked to perceptual modeling looks to be the way to move forward in amplifier testing as well as loudspeaker design
Does this differ from IM tests ? I accept that the tests might need looking at . I was reading ESP about single input Op-amps . He was delighted to say - 92 dB thrid harmonic and very little else ( 3 transistors and bootstrap VAS ) . Then says IM even better than other simple circuits at - 72 dB . Seems it is provable by existing tests if knowing bench mark fugues ? Great to be wrong as shortcuts to excellence are welcome . I have always suspected we don't talk enough about IMD let alone TID , TIS or whatever . Placebo is the difficult one . I have anti-placebo and hear my good stuff as only OK . I think that is called a perfectionist ? Shame because I know B---er all which is a slight fly in the ointment . Never stopped others ?
Do MOS FET's behave better in your tests ? No Vbe . Or was that all Vbe in all devices ? I do remember thermal modulation in the previous books .
Do MOS FET's behave better in your tests ? No Vbe . Or was that all Vbe in all devices ? I do remember thermal modulation in the previous books .
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I just point it out as a theoretical possibility, there are possible distortions that are only seen with multi-tone excitations - in practice I don't think the conditions can be anywhere near those of my example
IMD also results from simpler distortion causing terms that do show fully with single tone measurements
so there is always IMD when multitones excite any distortion mechanism - its just that there could be "extra" IMD in some situations
and not surprisingly (except to the willfully ignorant, those pushing the "conventional engineer" characteurs) multitone tone tests, the widely separated 2-tone IMD test, swept frequency IMD, the reasons for using them has been known to conventional engineers for a good fraction of a century now
Cordell and others have speculated on other combinations particularly for the suspect “thermal modulation” effects with lower low frequency or 3 tone with a 2 having fractional Hz separation for varying thermal conditions of the amp
IMD also results from simpler distortion causing terms that do show fully with single tone measurements
so there is always IMD when multitones excite any distortion mechanism - its just that there could be "extra" IMD in some situations
and not surprisingly (except to the willfully ignorant, those pushing the "conventional engineer" characteurs) multitone tone tests, the widely separated 2-tone IMD test, swept frequency IMD, the reasons for using them has been known to conventional engineers for a good fraction of a century now
Cordell and others have speculated on other combinations particularly for the suspect “thermal modulation” effects with lower low frequency or 3 tone with a 2 having fractional Hz separation for varying thermal conditions of the amp
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While my OPINION is that ESP is nice for newbies, mentioning his ideas here is a bit like comparing kindergarten to post doctoral work!
ES
As far as power amplifiers are concerned, ESP isn't even nice for "newbies"; it isn't even nice for anything or anybody.
JCX, thanks for these simulations and results.
But with respect, they simulate faults which have been known to the better (??) speaker makers for a long time ... rather than for a single (at most 2 identical ones for da 'symmetrical' amps) path minimum phase wideband device like a power amp.
For such a device, there is an exact relation between each harmonic and a multi tone intermodulation product. IMHO, this holds even for the usual Gilbert cell IPS power amp.
In Jurassic days, wen i kud kunt en reed en rite, I worked these out up to the 7th and scribbled it on my copy of the B&K 1902 instruction manual with scaling factors to match how it measured harmonics & various types of intermod.
Any mathematicians here care to repeat this exercise today? My single senile brain cell is no longer capable of such activity and I no longer have my copy.
I ask this cos though I've been happily using my newbie adventures with LTspice to pursue 1ppm THD @ 20kHz, this actual metric in itself is of little importance cos all sources available to us are severely bandlimited. The real relevance is the intermod that this should somehow reflect but it would be nice to have some numbers relating the two (or three or four ...).
May I thank you for your input into Dvoskin's THD analyzer
While some of Rod's circuits may not be state of art, they all work and have reasonable performance. Some of his stuff, eg on Balanced ins & outs and on Intermodulation stand out for their quality.
ALL his stuff is useful .. unlike the output of semantic pedants .. of use to neither man nor beast and circuits with very poor performance.
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@Kgrlee
Agreed on Rod.
I wish I had his texts back in 1975, and Bob's, and Douglas', and Ben's - agree or not, all these are most instructive works. Put together, for a novice, they are jet works with afterburners.
Then again, at 60, I am definitely of the book generation, whereas most kids today are not.
Agreed on Rod.
I wish I had his texts back in 1975, and Bob's, and Douglas', and Ben's - agree or not, all these are most instructive works. Put together, for a novice, they are jet works with afterburners.
Then again, at 60, I am definitely of the book generation, whereas most kids today are not.
Why don't we use null tests ? Quad said if you did on the 405 ( ? ) you would hear no musical content and few clicks . Now I wonder .
If it had musical content why would that be bad ? In mechanical engineering one can put a screw driver to the ear to listen . It becomes a cheap and valuable tool . A null test if used often must yield real understanding . How to use it needs defining .
No musical content and clicks . That seems something I wouldn't feel comfortable to boast . We know what the clicks are .
The beauty of null is it uses music , many and every music or test waves . A poor substitute for an Audio Precision research tool and remember we aren't interested in music anyway ( it's hi fi dummy that we are interested in ) . I must contact Mr ESP and ask him to ship his AP across . He obviously didn't use it right . I will give him $199 for his trouble and pay the shipping , I have a nice Ferrograph he can use . Did you every See star Trek when Q ...........
If it had musical content why would that be bad ? In mechanical engineering one can put a screw driver to the ear to listen . It becomes a cheap and valuable tool . A null test if used often must yield real understanding . How to use it needs defining .
No musical content and clicks . That seems something I wouldn't feel comfortable to boast . We know what the clicks are .
The beauty of null is it uses music , many and every music or test waves . A poor substitute for an Audio Precision research tool and remember we aren't interested in music anyway ( it's hi fi dummy that we are interested in ) . I must contact Mr ESP and ask him to ship his AP across . He obviously didn't use it right . I will give him $199 for his trouble and pay the shipping , I have a nice Ferrograph he can use . Did you every See star Trek when Q ...........
About Null test . Bob Carver said years ago that he could clone any amp using a Null test . He won the bet and embarrassed a lot of people . Bob concluded many did in fact make better sounding amps than him ( I was told ) . If he cloned them , they were identical . He said they had better ears ( I was told ) . If that is true it is bandwidth alone ( and harmonics ) ! Would you bet your house to prove Bob wrong ? The cloning was to null until minimal difference , that's all . As climate change an inconvenient truth .
The Carver Challenge Page 3 | Stereophile.com
I don't mind anyone designing a nice machine . If it sounds OK then that is excellent . If you then go on to say anyone now or ever could say it sounded better than accepted hi fi standards I have doubts you truly know your subject . Not doing what you would do is no proof of unsuitability . Like a gun it's function is not so exacting as to risk a duel ?
I would suggest any of ESP's better offerings ( FET ) could be clone matched to any of the Q designs .
The Carver Challenge Page 3 | Stereophile.com
I don't mind anyone designing a nice machine . If it sounds OK then that is excellent . If you then go on to say anyone now or ever could say it sounded better than accepted hi fi standards I have doubts you truly know your subject . Not doing what you would do is no proof of unsuitability . Like a gun it's function is not so exacting as to risk a duel ?
I would suggest any of ESP's better offerings ( FET ) could be clone matched to any of the Q designs .
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Just in case anyone cares I measured and published a test to measure the distortion of a carbon comp resistor (1982 real Allen Bradley old school). Didn't find much <-130dB at 10V p-p.
http://www.diyaudio.com/forums/anal...ch-preamplifier-part-ii-4269.html#post3606797
Nothing new this was in 1982 the resistors were probably much older. Resistors have a TC and when you use them at high levels the get hot then cold, all predictable. When used far below their rating there is no problem only folklore.
http://www.diyaudio.com/forums/anal...ch-preamplifier-part-ii-4269.html#post3606797
Nothing new this was in 1982 the resistors were probably much older. Resistors have a TC and when you use them at high levels the get hot then cold, all predictable. When used far below their rating there is no problem only folklore.
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Hi Guys
From everything that Rod has written, he does not have an AP THD test system. He has also stated several times that "distortion below (a certain number) is inaudible", so some here may discount what he says - but as usual, they should not discount everything simply because of disagreement with some of it.
Rod has helped a lot of hobbyists and builders learn about audio, electronics and even life. Yes, he has opinions but he allows for others to have theirs too.
Have fun
Kevin O'Connor
From everything that Rod has written, he does not have an AP THD test system. He has also stated several times that "distortion below (a certain number) is inaudible", so some here may discount what he says - but as usual, they should not discount everything simply because of disagreement with some of it.
Rod has helped a lot of hobbyists and builders learn about audio, electronics and even life. Yes, he has opinions but he allows for others to have theirs too.
Have fun
Kevin O'Connor
I don't think rode is yet an AP devotee. His distortion analyser is not up to that automated level but probably ranks a little better than a Ferrograph RTS. Here's the humble workbench, for the curious.
I think I upgraded him . He and I need the poor mans AP as in #1775 . We have AP at work . Alas work is an EasyJet flight now .
Lets send Rod a Radford HD 250 to clone . I bought one and was very disappointed . It was the most blameless amp in the world when I did ( Radford said so ) . Circuit looks great so no idea what went wrong .
My Ferrograph came out of Chipping Norton Studios . It has listened to this being made .
Fairground Attraction"A Smile in a Whisper" - YouTube
Lets send Rod a Radford HD 250 to clone . I bought one and was very disappointed . It was the most blameless amp in the world when I did ( Radford said so ) . Circuit looks great so no idea what went wrong .
My Ferrograph came out of Chipping Norton Studios . It has listened to this being made .
Fairground Attraction"A Smile in a Whisper" - YouTube
Scott, not to read literally thousands of messages, what is "John Curl's Blowtorchpreamp"?
I mean, obviously a preamp, but is it a commercial project, or a DIY project?
Oh yeah, I care, but then, you people at AD already own me body and soul, I swear by AD. My current favorite is AD 829.
I mean, obviously a preamp, but is it a commercial project, or a DIY project?
Oh yeah, I care, but then, you people at AD already own me body and soul, I swear by AD. My current favorite is AD 829.