sajti said:
Sajti,
Let me see if I get this. I understand the limited OL variation due to (low?) Vas output impedance, right? But how do you measure that? The Gm doubling will only appear in a limited region around the xover point. So, it would lead to distortion, but I doubt that you would see it as a chnage in large signal OL gain anyway. I guess the Gm doubling would occur in the region bounded by Iq, because that is where both devices conduct. For example, if you have Iq = 100mA, you would see the chgange in OL gain if you measure with an output signal limiting the output load current to +/- 200mA. Does that make some sense?
Jan Didden
janneman said:
Jan,
I never measured the Gm doubling. I just reflected the results of Mr. Self. The fixed OL gain will keep the nfb. constant with different loads, to avoid ringing, or oscillation. VAS resistors set the output impedance lower without high overall feedback.
But if the Gm doubling, or switching makes distortion it should be related to the output level. If the bias is about 50mA, the switch will be at 0.8V (8ohms). If the bias 500mA the switch will be at 8V (8ohms). Due the output level is 10 times higher, the distortion should be lower. Or no?
My experience that higher bias makes better sound in my amplifiers. But I can imagine opposite situations...
sajti
It is typical for a Bipolar output stage to have a
measured "sweet spot" for bias at a relatively
low bias, but it is also typical that listeners
prefer a higher bias setting.
measured "sweet spot" for bias at a relatively
low bias, but it is also typical that listeners
prefer a higher bias setting.
Hi Amplifier Guru,
Can you remember where you saw confirmation that Self's amps ran on regulated supplies?
Self says on p219 2nd edition "it seems clear that regulated supplies for power amplifiers are a Bad thing. Not everyone agrees with me;"
Can you remember where you saw confirmation that Self's amps ran on regulated supplies?
Self says on p219 2nd edition "it seems clear that regulated supplies for power amplifiers are a Bad thing. Not everyone agrees with me;"
Is it possible that HF harmonics are interpreted as highs that are "missing" when bias is optimized at a lower point? If so, this may be analogous to loudspeaker buyers interpreting overly bight speakers as "revealing", a trait clever sales guys sometimes exploit by turning up the treble knob.
sam9 said:
I don't think so. I don't recall that the "optimum" measured
performance had a lot of HF harmonics - it really did measure
better overall.
I don't think I wrote that right. What I meant was: is it possible that HF harmonics that are generated by high biasing (as opossed to optimal) are heard and interpreted as something that was missing when the bias was set at the optimal position. I.e, sort artificially generate HF content.
sam9 said:
I think it's been pointed out, perhaps in this thread, that higher
bias gives more 3rd harmonic, and I recall that being the case.
Hi Andrew T,
I haven't read any of Self's books. I did mull through the published EW&WW series though, looking for revelations.
My suggestion is that, while he might agree with most of the rest of the world that regulated supplies are not as desirarable for power amplifiers as unregulated ones, the tests were done for THD using regulated supplies, perhaps in the mistaken belief that this would eliminate the power supply as a contributor, to maintain focus on the amplifier proper.
Re: biassing of output stage for sympathetic distortions c.f. tuning a musical instrument.... wait a minute, aren't we meant to be designing amplifiers to accurately reproduce the performance , warts and all not doctor it.
I haven't read any of Self's books. I did mull through the published EW&WW series though, looking for revelations.
My suggestion is that, while he might agree with most of the rest of the world that regulated supplies are not as desirarable for power amplifiers as unregulated ones, the tests were done for THD using regulated supplies, perhaps in the mistaken belief that this would eliminate the power supply as a contributor, to maintain focus on the amplifier proper.
Re: biassing of output stage for sympathetic distortions c.f. tuning a musical instrument.... wait a minute, aren't we meant to be designing amplifiers to accurately reproduce the performance , warts and all not doctor it.
So, with all the self-proclaimed experts, expensive engineering degrees, and wonderful terminologies that can confuse Einstein 8 times over, we still don't know the thermal voltage of MOSFETs and jFETs?
Damn, what a waste.
Damn, what a waste.
I think you may cross swords with some in high-end circles who seem to be on an endless quest for a "musical" amplifier. I once had a conversation with someone who criticised an amp because it didn't sound "interesting". *We* may agree about accurate reproduction but there are those who think otherwise.
BTW, on some threads you would have been inviting flame-throwers when a few posts back you wrote something about just getting the bias reasonably close and letting NFB do it's job. I expected to read a "we-don't-want-no-stinking-feedback" post in response -- I guess those folks are not following this thread.
I think both approaches are valid, as long as you're clear which one is your goal. Personally I'm with you: I think that amplifiers should be purely for reproduction, and any nice-ifying should be either already part of the music or added by a dedicated circuit.amplifierguru said:
I thought Vt was a fundamental physical constant, nothing to do with transistor type?tlf9999 said:
HaHa Sam9,
"I expected to read a "we-don't-want-no-stinking-feedback" post in response -- I guess those folks are not following this thread."
I think I know the tune, it continues "We don't need no thought control.."
Greg
"I expected to read a "we-don't-want-no-stinking-feedback" post in response -- I guess those folks are not following this thread."
I think I know the tune, it continues "We don't need no thought control.."
Greg
well said Nelson Pass....🙂
Hi Guru,
I think Mosfets especially vertical ones needs at least required optimum biasing between 25mA to 55mA to eliminate the cross-over distortion to some extent... overbiasing them simply increases thermal noise floor when biased close to 200mA... and amps with gain at 56 times closed loop... thermal noise also seems to audible to some extent....
In our case we usually bais the mosfets at around 35mA to get good results...
what do you think!
Kanwar
Related the book, Graham Maynard could made dozen!
And inside his brain, there are informations to a lot of books.
Well, Dr. Self made his book, but this do not make it better researcher than another one that do not wrote a book.
Of course he is great, no doubts.
But Bible, we already have one to follow....more than one, there are many religions...and all them are rigth (as they say).
This show us that exist many trues....or... at least, will be interesting to accept things more flexible.
In my opinnion, low bias is not a good idea, as real world constructions shows that components are not easy to match...so..you go increasing bias and will perceive that, over emitter resistor measurements, the thing start with 9 milivolts to up half cicle, for instance, and 12 milivolts for lower half cicle .... when you go increasing... voltage (current of course) will be matched...so.... practical use, increase till them be matched.
Also low bias not a good idea because sometimes you can put too much lower!... representing some distortion in low volume...and we use more low volume than high volume.... real practical use, daily use is this way...also music is dinamic and goes to low volume from time to time.... avoid distortion in those moments are interesting...so...increase your bias a little please.
Over biasing an amplifier, as you all know, put output and drivers to work class A, this is very good as a musical result...also things goes automatic when you increase volume, this bias will not be enought to keep class A operation....so, you will have 2 conditions, A and AB...better to have both to evaluate when hearing ...and this is working inside the same amplifier...so you will be NOT comparing oranges and apples.
Graham Maynard is incredible, i had some days in close contact with him..... believe me, this is something that i think was a honor to me, as i am stupid compared to him...not only intelligence, but also know how difference is enormous.
He was sick and needing someone to construct some ideas to him, and he apreciate me because i am fast when i want, so, i was telling him that i like this and dislike that..... one day, 6 different designs he send...the man is an schematic factory, very creative and with deep know how.
If he said high bias is good.... i will not discuss this subject...of course this is personal, you may be so good, or even better than Graham.....but i am sure i am worst than he is in electronics matter.
Yes, i knew others and respect them all, but this one is a "machine" to produce ideas...he needs at least five "constructors" full time assembling to match his production speed.
Yes, he has a problem.... his language is sophisticated, hard to understand the guy (my problem), but asked him to instruct me as i had 5 years old.... and he do it as a teacher...but as i had 18 years old....he cannot reduce too much.
The high bias will produce early saturation...so... do as Graham...produce big power units...so, you will be using under the saturation level.
regards....hehe....you are all biased with that bias
Carlos
And inside his brain, there are informations to a lot of books.
Well, Dr. Self made his book, but this do not make it better researcher than another one that do not wrote a book.
Of course he is great, no doubts.
But Bible, we already have one to follow....more than one, there are many religions...and all them are rigth (as they say).
This show us that exist many trues....or... at least, will be interesting to accept things more flexible.
In my opinnion, low bias is not a good idea, as real world constructions shows that components are not easy to match...so..you go increasing bias and will perceive that, over emitter resistor measurements, the thing start with 9 milivolts to up half cicle, for instance, and 12 milivolts for lower half cicle .... when you go increasing... voltage (current of course) will be matched...so.... practical use, increase till them be matched.
Also low bias not a good idea because sometimes you can put too much lower!... representing some distortion in low volume...and we use more low volume than high volume.... real practical use, daily use is this way...also music is dinamic and goes to low volume from time to time.... avoid distortion in those moments are interesting...so...increase your bias a little please.
Over biasing an amplifier, as you all know, put output and drivers to work class A, this is very good as a musical result...also things goes automatic when you increase volume, this bias will not be enought to keep class A operation....so, you will have 2 conditions, A and AB...better to have both to evaluate when hearing ...and this is working inside the same amplifier...so you will be NOT comparing oranges and apples.
Graham Maynard is incredible, i had some days in close contact with him..... believe me, this is something that i think was a honor to me, as i am stupid compared to him...not only intelligence, but also know how difference is enormous.
He was sick and needing someone to construct some ideas to him, and he apreciate me because i am fast when i want, so, i was telling him that i like this and dislike that..... one day, 6 different designs he send...the man is an schematic factory, very creative and with deep know how.
If he said high bias is good.... i will not discuss this subject...of course this is personal, you may be so good, or even better than Graham.....but i am sure i am worst than he is in electronics matter.
Yes, i knew others and respect them all, but this one is a "machine" to produce ideas...he needs at least five "constructors" full time assembling to match his production speed.
Yes, he has a problem.... his language is sophisticated, hard to understand the guy (my problem), but asked him to instruct me as i had 5 years old.... and he do it as a teacher...but as i had 18 years old....he cannot reduce too much.
The high bias will produce early saturation...so... do as Graham...produce big power units...so, you will be using under the saturation level.
regards....hehe....you are all biased with that bias
Carlos
Welcome to party Carlos,
I simply love your way of writing the comments!
Please tell me one thing?
Since you are in Brazil Then you must know Selenium Speakers and their reputition...would do please tell me about something about Selenium speakers of Brazil...
regards to Carlos,
Kanwar
I simply love your way of writing the comments!
Please tell me one thing?
Since you are in Brazil Then you must know Selenium Speakers and their reputition...would do please tell me about something about Selenium speakers of Brazil...
regards to Carlos,
Kanwar
bocka said:
And it is the same math that gives us gm of transistors so all transistors should have the same gm?
Seriously, what is the intuitive meaning of Vt and why should the bias be set so that Vt is dropped off emitter resistors?
Any of those engineering types can shed some light on this?
hi Greg
my friend is a studio music producer and he adds intentionally some distortion to a recorded song. And nearly all producers do add compression. So let's leave it for them and focus on reproduction. But my question is how come are you sure that one amplifier reproducts music better than the other? Steady state sine THD on resistor load? Or even sqare wave response on capacitive load? Do you think you can answer my question basing on measurements?
I think no one did ever make a real reproduction test, like play a song from a CD, record music from the speaker and compare it with original signal.
Regards
my friend is a studio music producer and he adds intentionally some distortion to a recorded song. And nearly all producers do add compression. So let's leave it for them and focus on reproduction. But my question is how come are you sure that one amplifier reproducts music better than the other? Steady state sine THD on resistor load? Or even sqare wave response on capacitive load? Do you think you can answer my question basing on measurements?
I think no one did ever make a real reproduction test, like play a song from a CD, record music from the speaker and compare it with original signal.
Regards
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