| hitsware |
| quote: | Originally posted by Bricolo
what scematic are you talking about? |
.... |
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| hitsware |
| quote: | Originally posted by PMA
I am sorry I meant 10kHz - 20kHz, as THD is usually worse at higher frequencies. |
I don't remember if I did 20k but did do 10k (don't have the analyzer any more). Also (and I think importantly) the distortion was ~same at all levels........mike |
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| PMA |
| Pretty confusion - I was speaking about image at Post No.81. |
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| hitsware |
| quote: | Originally posted by PMA
Pretty confusion - I was speaking about image at Post No.81. |
That one is in the conceptual stage. Should sound good though. :) |
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| Bricolo |
| quote: | Originally posted by hitsware
.... |
The 2SK170 has to be selected, but selected for what? I don't see the reason for it, there's no "matching" required (no dif pair, no multiple output transistors...) |
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| hitsware |
| quote: | Originally posted by Bricolo
The 2SK170 has to be selected, but selected for what? I don't see the reason for it, there's no "matching" required (no dif pair, no multiple output transistors...) |
To have it run in the center of it's operating range with the given resistor values.............jfets do vary somewhat |
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| PRR |
> I thought that dif pairs had a very high gain.
Voltage gain to one output is one-half of the same device working grounded-cathode (or whatever).
On another forum I just pointed out that if you have two triodes, cascading them gives 2*Mu more voltage gain than the same tubes as a diff-pair.
Diff-pairs are useful in high-gain DC amplifiers because the diff-pair has near-zero DC offset. They are often useful in audio with NFB because you get two "identical" inputs. They also avoid cathode bypass capacitors which are often problematic.
The diff-pair has half the gain of a single device, but using BJT, Pentodes, or cascoded FETs or Triodes the useful gain is really limited by stray leakage and capacitance, and may be further limited by overall NFB stability consideration.
If you take both outputs of a diff-pair (either two outputs or a current-mirror turn-around), the gain is identical to a single device. |
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| john curl |
Folks, please get your ducks in a row about this circuit.
Personally I don't like to use much series resistance in the base of Jfets, BECAUSE it increases the noise of the entire unit. SE is correct, if you want to make an input filter, then put 50-200pf mica or film cap to ground to have a LINEAR capacitance at the jfet input. Then you can reduce the input R to 1K or so. |
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| Bricolo |
| quote: | Originally posted by PRR
> I thought that dif pairs had a very high gain.
Voltage gain to one output is one-half of the same device working grounded-cathode (or whatever).
On another forum I just pointed out that if you have two triodes, cascading them gives 2*Mu more voltage gain than the same tubes as a diff-pair.
Diff-pairs are useful in high-gain DC amplifiers because the diff-pair has near-zero DC offset. They are often useful in audio with NFB because you get two "identical" inputs. They also avoid cathode bypass capacitors which are often problematic.
The diff-pair has half the gain of a single device, but using BJT, Pentodes, or cascoded FETs or Triodes the useful gain is really limited by stray leakage and capacitance, and may be further limited by overall NFB stability consideration.
If you take both outputs of a diff-pair (either two outputs or a current-mirror turn-around), the gain is identical to a single device. |
Understood.
Thanks for the explanations ;) |
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| hitsware |
To maintain the simplicity of the circuit (keeping the gain, Iq, etc. equal without the use of source resistor bypass caps) it seems a better approach to me to select jfets. IMO |
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| hitsware |
| quote: | Originally posted by john curl
Folks, please get your ducks in a row about this circuit.
Personally I don't like to use much series resistance in the base of Jfets, BECAUSE it increases the noise of the entire unit. SE is correct, if you want to make an input filter, then put 50-200pf mica or film cap to ground to have a LINEAR capacitance at the jfet input. Then you can reduce the input R to 1K or so. |
Input noted and appreciated :) |
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| hitsware |
You might want to revue that article yourself. (Thanks:) )
He suggests selecting devices.............mike |
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| Fred Dieckmann |
"Personally I don't like to use much series resistance in the base of Jfets"
Don't you mean gate?
I also like to use input filters with the series resistor the value of the characteristic impedance of the interconnect. this filters RF and helps to terminate the interconnect at high frequencies. This obviously calls for the use low impedance drivers but eases the requirements on build out resistors. I still think that a gate resistor of maybe the 100 ohm to 1K is not a bad idea to damp out RF resonances between device capacitance and trace and wiring inductance. Voicing the sound of tube circuits by the value of the grid resistor is a pretty well know design trick. I find that well damped circuits at RF frequencies often sound better and more consistent. I think these values shouldn't have too much effect on line level and power amps noise figures. I remember a recent thread extolling the virtues of JFETs for low noise for moderately high source impedances. The Noise Figure graph for the 2SK389 shows the device noise starting to dominate the resistor noise for impedances below around a few thousand ohms if I am not mistaken. |
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| Fred Dieckmann |
"He suggests selecting devices.............mike"
I select devices too, but you have know what you selecting for. To get a specific
value of quiesent current, you have to adjust the source resisitor. I think if you measure a handful of Jfets from the same bias group (GR BL or V) you will be suprised at the variations in Idss. |
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| hitsware |
| quote: | Originally posted by Fred Dieckmann
"He suggests selecting devices.............mike"
I select devices too, but you have know what you selecting for. To get a specific
value of quiesent current, you have to adjust the source resisitor. I think if you measure a handful of Jfets from the same bias group (GR BL or V) you will be suprised at the variations in Idss. |
With a given source resistor, load resistor, and PS, Iq can be matched simply by substituting devices until the (standard (of your choice)) quiessent drain voltage is attained. I think perhaps we're both saying the same thing from differant points in the design cycle.........mike |
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| PMA |
| Mike, tell me, what is the Vgs voltage of the Mosfets. Usually about 4V, isn't it? And they are biased by "large green LED diode" in your schematics, is it correct? |
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| hitsware |
| quote: | Originally posted by PMA
Mike, tell me, what is the Vgs voltage of the Mosfets. Usually about 4V, isn't it? And they are biased by "large green LED diode" in your schematics, is it correct? |
These (lateral) mosfets have a much lower threshold voltage than the IR types. The led has ~1.65 volts forward voltage, so each output sees ~0.8 V 'enhancement'. Not class A, but a nice warm AB. ~160ma. |
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| Fred Dieckmann |
"I think perhaps we're both saying the same thing from differant points in the design cycle.........mike"
No we are not. You are have to sort through a lot of jfets to find a specific Idss.
Matching a couple Jfets for Idss greater than the desired bias current value and putting a trim pot to select to desired current is so much easier, that this is a no brainer. Sort a through few dozen Jfets to find a specific value and you will find out the hard way....... |
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| PMA |
| Non-feedback class AB? There must be a Gm doubling area (i.e. for smaller output voltages the gain is different than for higher output voltages, resulting in a kind of cross-over distortion). |
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| Elso Kwak |
| quote: | Originally posted by john curl
Folks, please get your ducks in a row about this circuit.
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Ducks???
:clown: |
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| hitsware |
| quote: | Originally posted by Fred Dieckmann
"I think perhaps we're both saying the same thing from differant points in the design cycle.........mike"
No we are not. You are have to sort through a lot of jfets to find a specific Idss.
Matching a couple Jfets for Idss greater than the desired bias current value and putting a trim pot to select to desired current is so much easier, that this is a no brainer. Sort a through few dozen Jfets to find a specific value and you will find out the hard way....... |
Perhaps my QC is a little laxer than yours. I look for fairly symetrical clipping and leave it at that. AND I'm not doing any quantities, so I'll continue this way. I do not like trimpots.
I can always take the rejects from 1 amp and adjust (fixed) resistors on the next and recycle that way. So far this method works for me, but thanks for the input...........mike |
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| hitsware |
| quote: | Originally posted by PMA
Non-feedback class AB? There must be a Gm doubling area (i.e. for smaller output voltages the gain is different than for higher output voltages, resulting in a kind of cross-over distortion). |
Yes, but it specs OK (for me) and sounds delightfull. The lack of feedback does something magical that swamps out any other shortcomings (IMO) ....... I'm surprised no one has mentioned the output capacitor ..... A bone of contention for many :) |
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| PRR |
> I still think that a gate resistor of maybe the 100 ohm to 1K is not a bad idea
The circuit which brought-out this side-discussion has a 390Ω impedance at the Gate.
If you can build it compact, with Gate very-close to that resistor, there's no need for an added resistor.
If you can't build it compact, you are liable to more troubles than a simple stopper can cure.
> Voicing the sound of tube circuits by the value of the grid resistor is a pretty well know design trick.
Yes, in part because R-C coupling tends to overload badly. Adding a few K of resistance in the Grid has little impact on the undistorted sound but a major effect on overload behavior for highly transient signals (speech/music). Adding grid resistance also lowers HF gain or feedback, which is a "voicing".
> I find that well damped circuits at RF frequencies often sound better and more consistent.
This may be true. I would wonder though why any RF is running around my circuit. Perhaps it has stability or shielding problems, and perhaps fixing that would be a better path. Yes, RF stability is a real dark hole for most audio designers, who must either schedule a second career in RF engineering or just apply band-aids.
> I think these values shouldn't have too much effect on line level and power amps noise figures.
Agreed. Some, since we know the ear is a pretty sensitive organ. But not a lot, and generally lost in the haze of other noise sources. (Preamp design is different.) And as you note, a typical JFET has more noise than a 1K resistor (which figures, considering its Gm).
In large power MOSFETs, Gate resistance is provably bad. See Pass's notes on Zen amps: the Gate capacitance is large and non-linear, and a few K of Gate resistance can make distortion rise several percent in the top of the audio band. Small JFETs have this effect, but much-much less, and a K or two is probably not going to be your biggest distortion source.
> has to be selected, but selected for what?
As noted, so bias current for V-LED/2 is appropriate and reasonable.
In Mass Production, that is intolerable. Who has time to sort and label production parts, much less stock sorted spare parts and deal with home-repairs using the "right" part but not properly selected? Even selecting or trimming source resistors is a pain. I remember bad old days like that, and I am glad they are gone.
For home-brew, or high-price boutique gear, selection can give "better" results than robust use-any-part design. It does mean more hassle in building and repairing, so you better be sure the results are worth it. For many people here, it probably is (unless you have to buy 20 parts to get 2 that work as hoped). |
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| PMA |
I have nothing against non-global feedback amps (you will find one of them, class A, on my web pages). But I do prefer lower distortion and higher damping factor, and higher output power as well ;)
Pavel |
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| hitsware |
| got the outputs drawn wrong .... sources should go to rails |
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| hitsware |
| and devices switched |
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| Bricolo |
| would adding a 9.5k between the 2nd input and ground be a good idea? (matching the input impedances) |
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| hitsware |
| quote: | Originally posted by Bricolo
would adding a 9.5k between the 2nd input and ground be a good idea? (matching the input impedances) |
A little maybe but with mosfets (no bias current) don't make much differance.. |
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| Bricolo |
| is it only usefull for bipolars? |
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| hitsware |
| quote: | Originally posted by Bricolo
is it only usefull for bipolars? |
With bipolars it balances the pair offsetwise. With fets that's not a problem, but there may be some dynamic considerations. Perhaps someone with better understanding will chime in here. |
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| Bricolo |
I would use it.
After all, it's only one more resistor. And when designing the PCB, it could even make things simplier in some situations. You don't have to make the ground trace go to the 2nd gate, take a resistor to connect the gate to ground :) |
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| john curl |
| Fred, originally proposed a sophisicated and 'improved' biasing stage. I felt that it was not a 'universal' schematic, because it lacked placement of a source degeneration resistor in the N channel rail. However, Fred is correct in this one specific case with using J109's and K389's. Thanks Fred, I didn't notice the difference between Gm's before, in these two devices. However, if you were using K170's and J75's, the difference would be less, and almost unmeasurable. Personally, in a simple circuit like this, I prefer to use high Idss types and run them as hard as possible. This includes even slightly overbiasing the input devices in the forward direction, under transient peaks. Please think it through, before attacking my comment. |
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| lumanauw |
As pointed before, I looked at http://www.ne.jp/asahi/evo/amp/J200K1529/report.htm and find many "not-ordinary" designs there. Are they practical design, or just design idea? Has someone have a chat with those Japanese designer, I think they have different spirit about audio amplifier from person like Mr.Pass or Mr.JC.
I learned that Mr.JC is former designer of MarkLevinson. Could anyone give me a brief schematic of what is inside MarkLevinson Ref.No.33 (The 200kg mono power amp)? Does it uses basic schematic like Ref.no.2 or JC-3? |
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| jam |
I believe that Mr.Curl did not design the Ref.33.
The Ref.33 is not a complementary design and nowhere as elegant as Mr.Curl's work. It looks more like a parts farm, to quote another member of this forum.
Regards,
Jam |
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| johnferrier |
The outside certainly *looks* impressive. The "what's inside" pics seem to be dead currently.
JF |
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| Peter Daniel |
I noticed that occasionally they are inactive, but check later, they'll work fine. Those are high res pics, showing even the print on ICs.
I know that some guys don't like ML, but I was always impressed with their engineering. So recently, I bought myself ML38 preamp board. At $140 it seemed hard to refuse. Finally, I have a piece of a cake too.;) |
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| johnferrier |
| quote: | Originally posted by Peter Daniel
I noticed that occasionally they are inactive, but check later, they'll work fine. |
Maybe like Vishay's websites. They seem to be operational about 40% of the time. I think they turn their servers off at night (US time). Haven't ran into many sites like theirs.
JF |
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| hitsware |
The 2SJ200/2SK1529 power amplifier which challenges to the limit of 2 stage constitution
[ 1 ] First experimental circuit Generally, the power amplifier, e.g., the first level, the drive step and the output step, furthermore the source follower enters foreward the output step with, is formed with the stage of 3 steps or more, but it can estimate the deterioration of the extent sound where this stage numbers are few that it decreases.
With the experiment which is developed here, the amplifying stage of the past design absolutely necessity?, you try probably to take a second look whether the efficiency which that brings essentially is important.
Fundamental reformation is necessary in restructuring of amplifier constitution, but well is, when like this is, rather than expressing theoretical empty theory, as I of practice principle, as for here even if it is not possible with the meaning be no other choice but to it tries making the amplifier where with you can obtain sufficient efficiency the less stage number and, it just is found, the て something topic you think that perhaps, the new road opens with the calling and the theme which derives from there.
[ 2 ] Revised circuit
[ 3 ]Crss symmetrization circuit
[ 4 ]Emitter follower drive addition
[ 5 ] The first level FET multiple connection
[ 6 ] Output step source follower/overall NFB
[ 7 ]The output step source follower/there is no overall return
[ 8 ] The first level circuit
[ 9 ] カプリオ クアッド circuit
[ 10 ]The PP circuit which utilizes the opposite quality of MOS-FET
[ 11 ] Experiment of intersection type output circuit
[ 12 ] Revised edition voltage amplification circuit
[ 13 ]2SJ200/2SK1529 power amplifier 1st number
[ 14 ]2SJ200/2SK1529 power amplifier 1 reforming
[ 15 ]About 2SJ200/2SK1529
[ 16 ]2SJ200/2SK1529 voltage mirror
[ 17 ]2SK2313 Kanada system
[ 18 ] Invertedtype
[ 19 ] The first level reforming inverted type
[ 20 ] Decrease return source follower inverted type
[ 21 ] ZD level shift system NFB type
[ 22 ] ZD level shift system non return type |
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| johnferrier |
| quote: | Originally posted by hitsware
The 2SJ200/2SK1529 power amplifier which challenges to the limit of 2 stage constitution
... |
Watch out, thought I saw some NFB stuff there. Might be contagious.
Borbely's super buffer and all FET line amp (figs. 7-9) also seem instructive (at least to me):
http://www.borbelyaudio.com/borb502.pdf
JF |
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| hitsware |
>Watch out, thought I saw some NFB stuff there. Might be contagious.
For a common drain (output stage(sorta attractive for swinging up (and down)to the rails)) I don't have a way to do 0 feedback (short using xfmrs) .......... any ideas ? |
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| Steve Eddy |
| quote: | Originally posted by hitsware
The 2SJ200/2SK1529 power amplifier which challenges to the limit of 2 stage constitution
[ 1 ] First experimental circuit Generally, the power amplifier, e.g., the first level, the drive step and the output step, furthermore the source follower enters foreward the output step with, is formed with the stage of 3 steps or more, but it can estimate the deterioration of the extent sound where this stage numbers are few that it decreases.
With the experiment which is developed here, the amplifying stage of the past design absolutely necessity?, you try probably to take a second look whether the efficiency which that brings essentially is important.
Fundamental reformation is necessary in restructuring of amplifier constitution, but well is, when like this is, rather than expressing theoretical empty theory, as I of practice principle, as for here even if it is not possible with the meaning be no other choice but to it tries making the amplifier where with you can obtain sufficient efficiency the less stage number and, it just is found, the て something topic you think that perhaps, the new road opens with the calling and the theme which derives from there. |
So you're the guy who writes all the owners manuals for Japanese electronics? :D
se |
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| Steve Eddy |
| quote: | Originally posted by hitsware
>Watch out, thought I saw some NFB stuff there. Might be contagious.
For a common drain (output stage(sorta attractive for swinging up (and down)to the rails)) I don't have a way to do 0 feedback (short using xfmrs) .......... any ideas ? |
Why stop short of using transformers?
How 'bout something like this: |
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| hitsware |
| quote: | Originally posted by Steve Eddy
Why stop short of using transformers?
How 'bout something like this: |
OK ....... Do you have a description of exactly how your circuit operates .... The bottom half is particularily non evedent to me.
........mike :) |
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| Steve Eddy |
| quote: | Originally posted by hitsware
OK ....... Do you have a description of exactly how your circuit operates .... The bottom half is particularily non evedent to me.
........mike :) |
Sure. The transformer provides the circuit's voltage gain. R1 and C1 are a damping network for that particular transformer, giving it a smooth Bessel rolloff. R2 doubles as the transformer's secondary load as well as volume control. The output is a JFET/bipolar Sziklai pair (a complimentary version of the Darlington pair) used as a voltage follower. The bottom half is the same pair used as a current source.
se |
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| hitsware |
how do you get a 'current source' off of the emitter of a xsistor?
i have a tendancy to think of emitters as 'voltage sources' |
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| Steve Eddy |
| quote: | Originally posted by hitsware
how do you get a 'current source' off of the emitter of a xsistor?
i have a tendancy to think of emitters as 'voltage sources' |
Because that PNP bipolar ultimately behaves as an NPN. Or perhaps more accurately, the pair behaves like a single N-type device. Look up "Sziklai pair" or "complimentary feedback pair" or "complimentary Darlington."
se |
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| hitsware |
>So you're the guy who writes all the owners manuals for Japanese electronics?
Ya Mon .... Me new gig ! ..... Ain't computers wonderfull ? :) |
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| Steve Eddy |
| quote: | Originally posted by hitsware
>So you're the guy who writes all the owners manuals for Japanese electronics?
Ya Mon .... Me new gig ! ..... Ain't computers wonderfull ? :) |
Yeah, when they're not busy being evil incarnate. :)
se |
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| hitsware |
| quote: | Originally posted by Steve Eddy
Because that PNP bipolar ultimately behaves as an NPN. Or perhaps more accurately, the pair behaves like a single N-type device. Look up "Sziklai pair" or "complimentary feedback pair" or "complimentary Darlington."
se |
Yea...OK..sorta got it. Would there be a way to bootstrap the CS 'dynamic class A' ? |
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| Steve Eddy |
| quote: | Originally posted by hitsware
Yea...OK..sorta got it. Would there be a way to bootstrap the CS 'dynamic class A' ? |
I suppose. But why make it more complicated? Not too many posts ago you were advocating using the parasitic input capacitance of a FET in order to keep things simple and avoid having to use a literal capacitor. What happened to that guy? :)
By the way, came across a quote by Antoine de Saint-Exup駻y a while back you might enjoy:
"Perfection is attained not when nothing more can be added, but when nothing more can be taken away."
se |
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| john curl |
| Looks like SE has hijacked another thread. :) |
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| PMA |
Sirs,
I am sorry but I do not understand. So many posts talking about inherently very poor circuit designs (horrible THD and IMD, high output impedance, low linearity, low power). Simple does not necessarily mean very poor, but most of the circuits shown here do. What's the reason? Just for fun? ;) |
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| Steve Eddy |
| quote: | Originally posted by PMA
I am sorry but I do not understand. So many posts talking about inherently very poor circuit designs (horrible THD and IMD, high output impedance, low linearity, low power). Simple does not necessarily mean very poor, but most of the circuits shown here do. What's the reason? Just for fun? ;) |
You mean like this one? :D
se |
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| PMA |
Oh no :D :D (Was awaiting who comes first ;) )
But even that one is much better :D |
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| PMA |
| But mean like this one, e.g. : |
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| Bricolo |
PMA, are you telling that amps without glogal feedback aren't good?
From what I've read, Mr Curl has another opinion about that |
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| PMA |
| quote: | Originally posted by Bricolo
PMA, are you telling that amps without glogal feedback aren't good?
From what I've read, Mr Curl has another opinion about that |
Bricolo, can you see any global feedback in the circuit of post no. 159 and have you seen the specs (www button below). And not only specs, but listening tests with well-known amps? (Quite difficult to perform here, I know).
This is not only a question of feedback or non-feedback, but the circuit. |
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| Steve Eddy |
| quote: | Originally posted by PMA
Oh no :D :D (Was awaiting who comes first ;) ) |
Hehehe. Sorry. I woke up at 4:00AM and couldn't get back to sleep so... :))
| quote: | | But even that one is much better :D |
Well, I guess it depends on how one defines "better." Better in pure technical terms doesn't necessarily mean better in subjective sound terms. If that were the case, we'd never have to bother to listen to anything. We'd all just pick whatever measures best.
se |
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| PMA |
| Subjective terms, Steve. But I do not speak about the case when you need to mask imperfection of the audio chain by coloured amp's sound ;) |
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| Steve Eddy |
| quote: | Originally posted by PMA
Subjective terms, Steve. |
But subjective terms are ultimately individual terms. And no one individual's terms are inherently superior to another's.
| quote: | | But I do not speak about the case when you need to mask imperfection of the audio chain by coloured amp's sound ;) |
But if one ultimately prefers that case, who is anyone else to judge?
se |
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| Bricolo |
| quote: | Originally posted by PMA
Bricolo, can you see any global feedback in the circuit of post no. 159 |
No.
But in fact, it was more a "general" question, after having read your other posts here, I thought that you dislike amps without global feedback. And I wanted to know why |
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| PMA |
It would be a never ending story, Steve.
In case you need distortion to get more "pleasant" sound, then something wrong is in your chain, and unfortunatelly this happens in 98% of cases. This is not about preferences. Take a group of people and give them a choice (listening test). In 99% they will prefer better solution - that's my experience.
I give up further argueing;) |
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| hitsware |
| quote: | Originally posted by Steve Eddy
Why stop short of using transformers?
How 'bout something like this: |
Because (we've done a mini full circle here)
In order to have a 'reasonable' input Z
(say 10K), and a 'reasonable' Av (say 10)
there are no xfmr/output device combos
that will work. (unless we add more devices
(than the simple 2 xsistor follower (in which
case the xfmr becomes unneeded)))
IMHO ......... mike |
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| john curl |
I had hoped that we would stick to input stages, primarily those that could be normally driven from external sources like preamps, cd's etc. I recently saw some interesting input, but it is now effectively lost in subsequent posts.
That said, I would like to clarify a few random assertions.
I have NOT worked with Mark Levinson since 1976. Therefore I did not design the 6,7,etc products produced later. However, most design concepts are based on 3 or 4 design topologies. The JC-2 used 2 of these topologies. Some of these later ML designs use either these 2 topologies or something similar in many products.
I am neither for or against negative feedback. I just don't like to use an output stage feedback pair inside of a global feedback loop. There is justification for this that was debated extensively on a previous thread, somewhere. |
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| Steve Eddy |
| quote: | Originally posted by hitsware
Because (we've done a mini full circle here)
In order to have a 'reasonable' input Z
(say 10K), and a 'reasonable' Av (say 10)
there are no xfmr/output device combos
that will work. (unless we add more devices
(than the simple 2 xsistor follower (in which
case the xfmr becomes unneeded)))
IMHO ......... mike |
Well, I don't see an input impedance of 1.5k unreasonable, except perhaps for some sources with tube output stages but they're the exception, not the rule. You offered up an amplifier that'd do about 6 watts into 8 ohms, and with a nominal 2 volt source such as a CD player, you wouldn't need a gain of 10 to achieve that.
se |
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| Steve Eddy |
| quote: | Originally posted by john curl
I had hoped that we would stick to input stages, primarily those that could be normally driven from external sources like preamps, cd's etc. |
Well, the circuit I put up can be normally driven from external sources like preamps, CDs, etc. And since this thread veered away from single versus dual differential long ago (with your complicity I might add), I fail to see how anything I posted was any more threadjacking than what you have been posting.
se |
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| hitsware |
>Well, I don't see an input impedance of 1.5k unreasonable,
You may be right but most circuits (I've seen) have some sort of resistance ~600 or 1k ohm in series with the output.
My tuner has the outs off of a collector which I'm sure would go bunk with a 1.5K load. (though I've not tried it)
>You offered up an amplifier that'd do about 6 watts into 8 ohms, and with a nominal 2 volt source such as a CD player, you wouldn't need a gain of 10 to achieve that.
Any lower gain and (if'n I was to try to sell some) people would say "this ain't got no power". Though a misinformed stance, this is prevalent. People equate (to a great extent) power and fidelity with not turning the nob much for alot of gain. The x22 usually used is maybe alittle hotter than needed but not much......mike |
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| Fred Dieckmann |
Back to the original topic before the usual troublemaker derailed the entire thread again just to get attention.
"Fred, originally proposed a sophisicated and 'improved' biasing stage. I felt that it was not a 'universal' schematic, because it lacked placement of a source degeneration resistor in the N channel rail. However, Fred is correct in this one specific case with using J109's and K389's. Thanks Fred, I didn't notice the difference between Gm's before, in these two devices. However, if you were using K170's and J75's, the difference would be less, and almost unmeasurable. Personally, in a simple circuit like this, I prefer to use high Idss types and run them as hard as possible. This includes even slightly overbiasing the input devices in the forward direction, under transient peaks. Please think it through, before attacking my comment.'"
I would not dream of attacking your comment as I think it is good design advice and you have about a 20 year head start over me on amplifier design. The idea for splitting the bias resistor between the jfet pairs was for a pretty specific application. Many mosfets have differing transconductances between the P and N channel devices with the N channel having significantly higher Gm the P channel. I was looking for a simple way to compensate by reducing the gain of the P jfet pair to equalize the gain of each jfet/mosfet half of the circuit. I know that decreasing the bias for the jfets knocks down the transconductance of the jfet and requires a larger load resistor for a given voltage gain and the effects on bandwidth and source impedance must be considered. Thanks again for your excellent advice on running jfets near to there Idss values. I always appreciate your feedback positive or negative. One actually learns much more for being told what one is doing wrong and I enjoy the learning experience. Now that I think about it something similar to this was done for the front end of the Hafler XL-280, a Borbely design I believe.
http://www.hafler.com/techsupport/p...280_amp_man.pdf |
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| Steve Eddy |
| quote: | Originally posted by hitsware
>Well, I don't see an input impedance of 1.5k unreasonable,
You may be right but most circuits (I've seen) have some sort of resistance ~600 or 1k ohm in series with the output. |
Yes, though most tend to be around 150 ohms or so.
| quote: | | My tuner has the outs off of a collector which I'm sure would go bunk with a 1.5K load. (though I've not tried it) |
Not necessarily. The Apex power opamps I use have collector outputs but still have a low output impedance.
>You offered up an amplifier that'd do about 6 watts into 8 ohms, and with a nominal 2 volt source such as a CD player, you wouldn't need a gain of 10 to achieve that.
Any lower gain and (if'n I was to try to sell some) people would say "this ain't got no power". Though a misinformed stance, this is prevalent.[/B][/QUOTE]
So why perpetuate it?
Certainly so few watts won't statisfy most out there, but so what? There are still a lot of folks out there with high efficiency speakers (and that number seems to be growing with more recent renewed interest in horn loaded loudspeakers--c'mon, Mike, you hang out over at Melhuish's). Since when has high-end been about appeasing the lowest common demoninator? :)
| quote: | | People equate (to a great extent) power and fidelity with not turning the nob much for alot of gain. The x22 usually used is maybe alittle hotter than needed but not much...... |
Then why offer up circuits that'll only do 6 watts? :D
se |
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| Steve Eddy |
| quote: | Originally posted by Fred Dieckmann
Back to the original topic before the usual troublemaker derailed the entire thread again just to get attention. |
If I'm just trying to get attention, then you and Curl with your remarks such as these are just playing into my hands and drawing even more attention to me.
Who's looking for attention here? These comments, instead of simply going on about what it is you wish to discuss, seem to be saying "Hey, don't look at Steve, look at me!"
se |
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| hitsware |
>Then why offer up circuits that'll only do 6 watts?
My point is that whether you have 1Watt or 1kWatt (well maybe alittle exageration :) ) you need the same gain for a 'comfortable' response from the nob. The other 999 Watts is overhead. As enlightened as I consider myself, I don't want to turn up something 3/4 of the way for normal listening. Just has a bad "feel" ........ But that's just me. (and customers in the past)
..........mike |
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| AKSA |
I would unreservedly support the concept of global feedback. I believe that done right it cures far more problems than it makes. I also believe that all this wooden cross BS about global feedback is tantamount to ignorant sloganeering; the product of a fevered marketing department..... I see a future where recent work on distortion spectrum and harmonic distribution will yet be optimized, and the solution will probably be a GNFB amplifier.
Pavel, have you tried the prosaic double emitter follower output stage, particularly Self's Type II, in side by side listening comparisons, against your CFP? I have done tests with others some years back and concluded strongly in favor of the double emitter follower.
You make some challenging comments about RF injection into the amp too, which I'm looking into. Great work, Pavel!
Cheers,
Hugh |
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| fdegrove |
Hi,
| quote: | | As enlightened as I consider myself, I don't want to turn up something 3/4 of the way for normal listening. Just has a bad "feel" ........ But that's just me. (and customers in the past) |
Ah...another 11 o'clock listener like myself....
I tend to agree with you in that it's good practice to have some gain/power left for better dynamic range.
| quote: | | I also believe that all this wooden cross BS about global feedback is tantamount to ignorant sloganeering; the product of a fevered marketing department..... I see a future where recent work on distortion spectrum and harmonic distribution will yet be optimized, and the solution will probably be a GNFB amplifier. |
Certainly. I reckon the fever originated from the obsession with figures some 30 years back which resulted in amps sounding as flat as a pancake amongst other oddities.
As with anything else, the truth sits somewhere in the middle; GNFB has been abused by incompetent designers and the ommission of it has been advocated by even less competent designers it seems.
No offense to any camp in particular but I feel that it's wise to design with reasonably linear blocks right from the start, GNFB would then only be the icing on the cake when implemented correctly.
Just my 2 cents, ;) |
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| hitsware |
>No offense to any camp in particular but I feel that it's wise to design with reasonably linear blocks right from the start, GNFB would then only be the icing on the cake when implemented correctly.
Yes ! :)
Until recently I have always tinkered with amps with the feedback loop closed. On a trip of trying to emulate 'tube' characteristics (with SS) I remembered that most (I think) tubes amps are stable and operable without the feedback. (in fact at a place I worked years ago we did the entire QC (tube amp) procedure open loop and as a final step tacked in the feedback resistor). I then decided I didn't need no stinkin' feedback afterall, but your point is right on. Icing on the cake..................mike |
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| AKSA |
Hitsware,
Tube amps are highly unstable with feedback, depending primarily on the transformer! IIRC the Williamson had around 16dB of global NFB and was acknowledged by the designer to be on the verge of instability; this at a time when global negative feedback was regarded as the cortisone cure-all of audio, just as NONE is now!
The problem with the transformer is phase shift, which turns negative feedback positive, seriously affecting the amp's ability to handle reactive loads and making a mighty fine oscillator. So, since almost all tube amps use transformers, that one is out. Believe me, if tube designers could use 60dB of NFB like many SS amps, they would!
Cheers,
Hugh |
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| Steve Eddy |
| quote: | Originally posted by hitsware
My point is that whether you have 1Watt or 1kWatt (well maybe alittle exageration :) ) you need the same gain for a 'comfortable' response from the nob. The other 999 Watts is overhead. As enlightened as I consider myself, I don't want to turn up something 3/4 of the way for normal listening. Just has a bad "feel" ........ But that's just me. (and customers in the past) |
Well if it feels good, do it. :)
Personally, knob position has never been an issue for me. With the possible exception of instances where there's so much gain that knob positioning is excessively limited and I find it hard to dial in a "just right" setting.
se |
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| Bricolo |
What are exactly the problems that GNFB intoduces?
Unstability due to phase shift (neg fb becoming pos fb) is obvious
Mr Curl told about TIM and IMD poroblems, could you developp?
Is there anything else? |
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| fdegrove |
Hi,
| quote: | | Tube amps are highly unstable with feedback, depending primarily on the transformer! IIRC the Williamson had around 16dB of global NFB and was acknowledged by the designer to be on the verge of instability; this at a time when global negative feedback was regarded as the cortisone cure-all of audio, just as NONE is now! |
This is all true and specifically true for the Williamson circuit which is, by design, on the brink of stability.
Hugh's analysis is quite correct although, IMO, it leaves out some important factors.
A triode has build in feedback by nature. How else would one be able to create a device with reasonable gain and still maintain some linearity?
This, however is local feedback, not global, and as such can react much quickly timewise.
The point of feedback encompassing the OPT is very real indeed and as a matter of fact OTL amps can tolerate much higher levels of GNFB which are much needed to reduce the Zout of the amp in order to be able to interface correctly with a common speaker's impedance.
IOWs, it wouldn't work without it and the same is true for most common sand amps.
By ommitting the OPT you can use more NFB but it doesn't have to include the input stages.
For tube amps using OPTs it would be advisable to use local NFB and distortion cancellation techniques, something that's certainly not all that easy to implement but it can be done.
One way is the use of cathode feedback winding(s) on the OPT but there are other ways.
| quote: | | What are exactly the problems that GNFB intoduces? |
GFNB is always running behind on what it's trying to correct; it's a kind of "Back to the Future" artefact.
It may seem to work statically but dynamically it sucks big time.
Same goes for most measurements made that are not dynamic, they don't reveal what's going on in "real time".
Cheers, ;) |
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| hitsware |
>GFNB is always running behind on what it's trying to correct; it's a kind of "Back to the Future" artefact.
Yea that is a BASIC flaw (though in practice seems not to show much). Same thing as 'bootstrapping' (in reverse). The transit time of the signal through the amp makes either sorta nebulous.
Only really shows up (on my humble equipment) in recovery or settling time, but has audible implications beyond that.....mike |
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| fdegrove |
Hi,
| quote: | | Yea that is a BASIC flaw (though in practice seems not to show much). |
The faster the response time of the loudspeaker the more it becomes obvious...
Take FR speakers with low moving mass, ELSs or ribbons and you'll quite likely hear the effect.
Most other, more conventional speakers, are way too slow.
Hope this helps,;) |
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| hitsware |
>Believe me, if tube designers could use 60dB of NFB like many SS amps, they would!
Good one ! Thanks :)
You use single differential right?
Your amps are well regarded on
the FR driver forum..........mike |
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| Steve Eddy |
I've some serious reservations about that article.
By Ohm's law, the current in a speaker voice coil is the amplifier output voltage divided by the speaker impedance. Therefore, the current can only be linearly related to the voltage if the speaker presents a purely resistive load to the amplifier.
Excuse me? Reactive circuits violate Ohm's Law? Last I looked, current is linearly related to voltage in reactive circuits with only a relative phase change between current and voltage.
When, as is usually the case, the speaker impedance varies with frequency, amplitude, voice coil temperature etc., these dynamic impedance fluctuations translate directly into distortion of the driving current, as I = V / Z.
I = V/Z looks like a linear relationship to me. So where does he get this notion that current can only be linearly related to voltage if the load is purely resistive?
The negative feedback often used in power amps is totally blind to all of these problems, and with the reliance upon "damping factor" (electromagnetic-mechanic damping at resonance), huge back-EMF currents (at high voice coil velocities near resonance) are dumped back into the output of the power amp...
Huge back-EMF currents? Back EMF is greatest at and near resonance, which is where impedance is highest and by Ohms Law, current is lowest. So where are these "huge back-EMF currents" coming from? Hell, many loudspeakers' impedances exceed 100 ohms near resonance. There will be FAR more current in the circuit at the impedance minimums above and below resonance.
What's this guy talking about, Mike?
se |
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| Fred Dieckmann |
"If I'm just trying to get attention, then you and Curl with your remarks such as these are just playing into my hands and drawing even more attention to me.
Who's looking for attention here? These comments, instead of simply going on about what it is you wish to discuss, seem to be saying "Hey, don't look at Steve, look at me!"
Go start your own thread then. I can't that any of your post have anything to do with differential input stages, or can't you get any response to your post accept by crashing threads where you have no knowledge of the topic? Be a man and stand on your own two feet instead of clinging to people's coattails till they get tired of you dragging things to a halt. I guess I could respond to people via Email instead of dealing with the constant threadjacking......... most of us are sick and tired your thread wrecking. I (and many others) are extremely sick of you ****ing Mr. Curl off in the middle of his giving extremely useful input on a topic. When you run somebody of his caliber off you are going to be even more unpopular than you are now.
Wake up and smell the coffee! |
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| hitsware |
I=V/Z is a linear relationship BUT
the Z of a driver (or any reactance)
is (by definition) not. Something to
do with 'rate of change' ........mike |
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| fdegrove |
Hi,
Seems to me some people have difficulty in differentiating DC from AC behaviour...
Back to the kindergarten and Thevenin for some of us I reckon??
Please, people, do grow up and leave your inflated egos behind...
Cheers,;) |
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| AKSA |
Fred,
Not long back, when Steve so exasperated me with his behavior, at his suggestion I hit the 'ignore' button. Now I only look at his comments when I'm feeling benign, composed and amused. Works for me! :D
Hitsware, the problem with feedback is exactly as Frank explains it; thanks Frank, you covered the gaps.
Here's another view, based on the order of events: input signal enters the amp, is magnified to the output (with errors), fed back to the feedback node and found to differ from the input. The error thus identified (by a diff pair with SS, with a tube it's usually cathode injection), creates an error signal which is despatched to the amp to CORRECT the output.
Notice the sequence of events. The signal takes time to pass through the amplifier, called group delay, and the correction is made AFTER the event since it's taken from the output and fed back to the input.
Now, in practice this is quick, particularly if fast devices (with high Ft) are used. So, a tiny error will soon be picked up, and corrected BEFORE it gets big. However, this creates overshoot, rather like a governor on a stationary diesel engine, which also reacts after the event, or temperature control of the human body, or respiration rate, triggered by carbon dioxide levels in the blood.
All feedback systems, absolutely by definition, will involve this delay, sometimes called hysteresis, which leads to tiny overshoot.
As it happens, by Fourier analysis, it can be shown that sharp blips in audio waveforms are made up of higher harmonics. And the problem is that even the initial overshoot will cause the feedback loop to react further, trying to correct the overshoot which results of the mechanism. In turn, this creates a cascading series of tiny overshoots, which spawn other overshoots, and so on. It is this unhappy chain of events which leads to the condemnation of global negative feedback, and like most folklore, there is some truth in it.
It would seem intuitive that if we knew the error the amp would introduce in advance of processing the signal, we could make alterations to our amplifying devices so that it came out just right!! In truth, we do this to a minor degree by ensuring that each gain block is as linear as possible to begin with. This minimizes the correction necessary using global feedback, but a moments thought tells us that to achieve this we will need to modify the transfer function of our active devices to make them more linear. And guess what! To do this we reduce the gain of our devices on the spot (locally), but this actually reduces the feedback factor we can apply globally!! SNOOKERED!! :bawling:
You really are damned if you do, and damned if you don't. IOW, amplifier design is just life - these sorts of dilemmas are a part of life itself. The classic expression of this, in macabre but entirely logical terms, is 'The operation was a success, but the patient died'.
One valid, real-world approach, in my opinion, is to have extremely fast devices and very short, non-inductive feedback and signal paths which minimize group delay and thus bring down overshoot and distortion to vanishingly low levels. We should also use very fast topologies, where possible, and make the slowest part of the amplifier the gain block, so as to control phase shift to avoid oscillation. Since the ear is preternaturally sensitive to high order harmonics, particularly odds, we have to design amplifiers which bring the H5 and beyond harmonics below the noise floor, so that any sonic impact of this unfortunate but necessary topology is subliminal rather than directly audible. Even so, no amplifier is perfect, and the discussion of sonic color added by the SET brigade brings up a whole new can of worms. I'd recommend reading Fred Nachbaur's website here: http://dogstar.dantimax.dk/tubestuf/miniblok.htm for a full and intelligent discussion of the SET, which incidentally I like very much.
You ask about the AKSA. Yes, it is a single differential input pair, using highly matched transistors, very carefully chosen, and VERY carefully laid out.
Cheers,
Hugh |
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| hitsware |
Hugh,
Thanks for the link. :)
Could we say (getting back to single vs dual differential)
that perhaps the single differential has a little of the euphoric
qualities of the SET while the dual doesn't ? Or does the
' differentialness ' destroy that as compared to say a single jfet or bipolar xsistor as a front end. ( I know there is some differance between the 2 (fet vs bipolar) ......... Thanks again ...... mike |
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| fdegrove |
Hi,
| quote: | | One valid, real-world approach, in my opinion, is to have extremely fast devices and very short, non-inductive feedback and signal paths which minimize group delay and thus bring down overshoot and distortion to vanishingly low levels. |
Magnificent post, Hugh.
This reminds me of the only possible flaw I made when designing my OTL amps...I should have made the feedback path shorter by building along the width of the chassis not the length.
Thank you for reminding me,;) |
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| johnferrier |
From the peanut gallery, I certainly value John Curl's presence at a public forum; at the same time, I also value Steve Eddy's opinions. My wish is that they would give each at least another chance. Seems like they are both close to, if not on the mark. Of course, everyone has his or her quarks. Just don't let the other bother you. Seems like the same goal is in mind.
So, metaphorically, I'm for dual differential (more local feedback, less global feedback).
JF |
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| hitsware |
>So yeah, I'm for dual differential.
Why ? |
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| lumanauw |
Maybe the that Japanese design is trying to search the limit of minimum power amp stages. But I think the best 2 stage power amp is Aleph. The 2 stage power amp with only 1 differential. I've tried to figure 2 stage power amp, and never got better idea than Aleph. Good sound, good stability (although very hot).
Reading the previous post, I think I began to understand what Mr.Pass said about "Anchoring" the whole amp with CCS. Dual differential cannot do that, the standing current will vary as the transistor getting hotter or more cold (bias in VBE to temp). If stability of standing current is important to output signal for an audio amp, then single differential with CCS is the best. Although it is the "OLD DESIGN" like some refer to Doug Self design.
But IF single differetial with CCS is better from dual differential, why is there so many famous brand (like Crest) is using dual differential up until now? |
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| johnferrier |
Don't want to go off topic, but one: I was writing metaphorically and two (and my ducks aren't in a row yet): I'm interested in a cross-couple differential out design that uses only N-channel JFETs and NPN follower or only N-channel JFETs (for a headphone amplifier). Again, why? "Sounds" good to me. I planned to sketch this out for another thread. I wonder if the N-channel and NPN components tend to be better, why they aren't just used in a bridged mode (and it may be easier for a headphone amp). In a way, mirror the circuitry East and West (versus North and South). I'll take this to another thread.
JF |
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| AKSA |
To keep it simple:
Dual differential permits use of a dual voltage amplifier; completely symmetrical all around. This looks great and works well.
However, and accounting for the minor transfer function differences between NPN and PNP, their distortions largely cancel, and certainly this is true also in the voltage amplification sections. The result of this is that only symmetrically disposed distortions remain - the asymmetrical ones cancel pretty well - and you are left with very low levels of odd order.
The single differential input drives the designer towards use of a single-ended voltage amplifier. This creates considerable asymmetrical distortion, or even order harmonics, which is largely diminished by the global negative feedback loop (as are all distortions, regardless of order).
This generally means that dual diff will have lower levels of even order, and low levels of odd order. But single diff will have low levels of even and odd; all are produced, however, not just odds, and with reasonably fast GNFB the incidence of these harmonics will progressively lessen with order.
The SET sound has progressively lessening harmonics; petering out at around the 5th harmonic. With a well designed GNFB SS amplifier, it is possible to emulate this profile to a certain extent, though the levels of distortion will be typically two orders of magnitude superior to the SET, but with a few more distortion artefacts.
My own belief is that it is the recording process which strips away the higher harmonics of recorded music. The SET goes part the way to reconstituting this denuding of the harmonic profile, richening up the sound, literally 'filling' it out.
Cheers,
Hugh |
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| Steve Eddy |
| quote: | Originally posted by Fred Dieckmann
Go start your own thread then. |
Why? Nothing I'd said was any more out of context with the original post in this thread than what a number of others were talking about.
I'm not the one who started talking about power amps, output stages and negative feedback. I just went with the flow of the discussion.
| quote: | | I can't that any of your post have anything to do with differential input stages... |
You mean you missed the differential input stage in that circuit I posted? How'd you miss that? It was the only other stage beside the output stage.
| quote: | | or can't you get any response to your post accept by crashing threads where you have no knowledge of the topic? |
Well, John said:
SE is correct, if you want to make an input filter, then put 50-200pf mica or film cap to ground to have a LINEAR capacitance at the jfet input.
So I guess I know a little something.
| quote: | | I guess I could respond to people via Email instead of dealing with the constant threadjacking......... most of us are sick and tired your thread wrecking. |
What are you talking about? You don't have to deal with anything. You're not a moderator here. Either report my posts to those who are moderators, or put me on ignore.
| quote: | | I (and many others) are extremely sick of you ****ing Mr. Curl off in the middle of his giving extremely useful input on a topic. |
What are you talking about? I didn't say a word to John and nothing I had posted prevented John from going about what he was doing.
| quote: | | When you run somebody of his caliber off you are going to be even more unpopular than you are now. |
Don't have to worry about that happening. He followed me over here. He tried to say it was so he could get away from me over at that other place but in fact he knew I was posting here so he came over here so he could **** and moan about me.
He's something of an obsession with me. He even goes onto other message boards that I don't participate on and ****es and moans about me.
So don't worry. John would be more likely to stop posting here if I left than if I stayed.
se |
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