Dear PMA,
What do you think, I don’t know? 😀 By the way Wilson mirrors can have rather good linearity…
What do you think, I don’t know? 😀 By the way Wilson mirrors can have rather good linearity…
Dear Steven, rather interesting,
I made at least dozen of Otala based amps in the late 80th…
>I still have the complete hand drawn copies of the PCB layout and the schematics derived from the layout.
would you share?
I made at least dozen of Otala based amps in the late 80th…
>I still have the complete hand drawn copies of the PCB layout and the schematics derived from the layout.
would you share?
I met Jan Lohstroh at Phillips Research Labs 30 years ago. Apparently both he and Matti Otala developed this amp design, but Matti got virtually all the credit for it.
I bought the very first prototype of this amp made by Per and his friends, after they demo'd it to me in Switzerland in 1975. I kept this amp for 15 years, until it was destroyed in the firestorm in 91. It is an especially good amplifier. A few years ago, I found one locally that cost me $200. I use it in my lab, today, and it still beats my cheaper designs. SY heard it when he was over here, once.
I bought the very first prototype of this amp made by Per and his friends, after they demo'd it to me in Switzerland in 1975. I kept this amp for 15 years, until it was destroyed in the firestorm in 91. It is an especially good amplifier. A few years ago, I found one locally that cost me $200. I use it in my lab, today, and it still beats my cheaper designs. SY heard it when he was over here, once.
Dimitri,
I am sorry. Firstly I have not loaded your image, so I was thinking that you were suggesting to add current sources to the three-stage circuit that I have shown 🙂
Sorry again.
I am sorry. Firstly I have not loaded your image, so I was thinking that you were suggesting to add current sources to the three-stage circuit that I have shown 🙂
Sorry again.
PMA said:
Very nice, maybe a little simple...
I know what has to be done but it is very difficult to do it.
dimitri said:Dear Steven, rather interesting,
I made at least dozen of Otala based amps in the late 80th…
>I still have the complete hand drawn copies of the PCB layout and the schematics derived from the layout.
I first have to scale them down on a photocopier before scanning. I only have an A4 scanner and the drawings I made are A3.
Steven
I will be watching this with rapturous anticipation.....
Will you take the easy way out and use Class A? Bah!! Mere pocket calculator stuff! (In the immortal words of Douglas Adams).
Once you have done this, perhaps, you might then design a conventional, global feedback amplifier which sounds as good.
The feedback amp will have a different sound, of course, but it might still be just as good. Leave the judgement to a panel of ten blindfolded non-audiophiles. Essential.
And low parts count. Also essential. With no jewellry. I'm going to make a fortune from this, and it had better be good. Oh, I will pay a small commission to the winner, of course. A few coffees. A nice box of chocolates, maybe. I'll even throw in a GM70, never been used.
Cheers,
Hugh
Will you take the easy way out and use Class A? Bah!! Mere pocket calculator stuff! (In the immortal words of Douglas Adams).
Once you have done this, perhaps, you might then design a conventional, global feedback amplifier which sounds as good.
The feedback amp will have a different sound, of course, but it might still be just as good. Leave the judgement to a panel of ten blindfolded non-audiophiles. Essential.
And low parts count. Also essential. With no jewellry. I'm going to make a fortune from this, and it had better be good. Oh, I will pay a small commission to the winner, of course. A few coffees. A nice box of chocolates, maybe. I'll even throw in a GM70, never been used.
Cheers,
Hugh
denial
This class A so-called "no feedback" stuff is all very well but you'll get a better sound if you entertain a wide menu of techniques.
Denying feedback is like telling a Formula 1 team that they'll win more races without the use of telemetry or active suspension or even a driver.
Feedback is your friend!
This class A so-called "no feedback" stuff is all very well but you'll get a better sound if you entertain a wide menu of techniques.
Denying feedback is like telling a Formula 1 team that they'll win more races without the use of telemetry or active suspension or even a driver.
Feedback is your friend!
traderbam,
that's what I have been thinking about. As a native speaker, you can tell it exactly.
Thanks,
Pavel
that's what I have been thinking about. As a native speaker, you can tell it exactly.
Thanks,
Pavel
TBam,
I agree entirely, unequivocally, and resoundingly. Even my damping factor accords very nicely with your comments!
Now this is seminal, we have rarely agreed.... Break out the champers!
Pavel,
I have never noticed any difficulty in your clear, accurate expression.
You know, one thing which interests me is the unequal current mirror. Last night I was thinking how it might be possible to use a small triode, resistively loaded, to drive a SET ouput transformer.
Anyone have any ideas on this?
Cheers,
Hugh
I agree entirely, unequivocally, and resoundingly. Even my damping factor accords very nicely with your comments!
Now this is seminal, we have rarely agreed.... Break out the champers!
Pavel,
I have never noticed any difficulty in your clear, accurate expression.
You know, one thing which interests me is the unequal current mirror. Last night I was thinking how it might be possible to use a small triode, resistively loaded, to drive a SET ouput transformer.
Anyone have any ideas on this?
Cheers,
Hugh
My idea:
Bridged amp. No feedback loop around output stage.
Left input: Amp input
Right input: left input X ( left output - left input ) / left output
Bridged amp. No feedback loop around output stage.
Left input: Amp input
Right input: left input X ( left output - left input ) / left output
My intuition says that it's best to get an amp as good as possible and accept whatever inherent non linearities remain rather than getting into distortion cancelling and all that stuff.
but there again, I admit that I'm a simplicity freak...😉
but there again, I admit that I'm a simplicity freak...😉
AKSA said:
Greetings Hugh,
Seems things are getting very lateral and civil at
the same time 🙂 good to see.
WRT resistive loaded triode, there is a guy up here
in Sydney, David Astley, brilliant designer, who has
some hybrid MOS cascoded into DHT into resistive load
with SE OPT amplifier. Single stage amp, very simple.
This might come close to qualifying as true zero FB
but lets not get into a bun fight about it.
They do sound very very good and quite different from
the usual SET type of sound. Very clean with awesome
resolution. One of the best amps I've heard, but 10W is
all you get!
Terry
Fanatics for fanatics
I am here approximately one year and I see, that here is one basicaly problem. All disscuses about good or the best sound are based on experiences and knowledges all guys, but experiences of all are not the same and every have therefore little different opinions. When some man show some schematic, often another can't or may not verify, that is right or not. All is only about confidence to the another men, but it's unfortunately insufficient. It goes to the neverending discusses without concrete result. In our country we have with this problem the same experience, so we once by year ( or twice ) make some meeting, where who can, take his own product and try to defend it in forum. Is interesting, that " forum " have in this case practicaly ( in 95 - 98 % ) quite identical opinions for quality of sound. 'cos world is much more larger, we can't to do similar meeting, but I mean that it should do only in " local region " - Europe, America etc. . What are you thinking about this ? 🙂
I am here approximately one year and I see, that here is one basicaly problem. All disscuses about good or the best sound are based on experiences and knowledges all guys, but experiences of all are not the same and every have therefore little different opinions. When some man show some schematic, often another can't or may not verify, that is right or not. All is only about confidence to the another men, but it's unfortunately insufficient. It goes to the neverending discusses without concrete result. In our country we have with this problem the same experience, so we once by year ( or twice ) make some meeting, where who can, take his own product and try to defend it in forum. Is interesting, that " forum " have in this case practicaly ( in 95 - 98 % ) quite identical opinions for quality of sound. 'cos world is much more larger, we can't to do similar meeting, but I mean that it should do only in " local region " - Europe, America etc. . What are you thinking about this ? 🙂
Terry,
Thanks for your post. I believe I've met Astley; he has a repair business, I believe? If it's the same man I sold him a couple of GM70s about five years ago; he drove them in grounded grid. I spoke with him, and he seemed extraordinarily aloof about his designs (perhaps he is me in a parallel universe??).
In any event, I'm fascinated to hear you mention him.
Pavel Dudek,
I agree with you, a standard is required. Standards always hold back engineering, because commercial and engineering interests so often collide. But how to do it? Impossible, I would say, because subjective opinion of sound is not something people ever agree on. One man like sound stage; another likes deep bass, a third hates intermodulation, a fourth loathes sibilance. We should not have too high an expectation in this forum; this is not, after all, an academic discussion group, it is a hobbyist corner. People don't even have to respond if they don't wish to.
Cheers,
Hugh
Thanks for your post. I believe I've met Astley; he has a repair business, I believe? If it's the same man I sold him a couple of GM70s about five years ago; he drove them in grounded grid. I spoke with him, and he seemed extraordinarily aloof about his designs (perhaps he is me in a parallel universe??).
In any event, I'm fascinated to hear you mention him.
Pavel Dudek,
I agree with you, a standard is required. Standards always hold back engineering, because commercial and engineering interests so often collide. But how to do it? Impossible, I would say, because subjective opinion of sound is not something people ever agree on. One man like sound stage; another likes deep bass, a third hates intermodulation, a fourth loathes sibilance. We should not have too high an expectation in this forum; this is not, after all, an academic discussion group, it is a hobbyist corner. People don't even have to respond if they don't wish to.
Cheers,
Hugh
AKSA said:
Hugh,
I do not think so. Pavel Dudek tries to say that during listenning tests 98% of the people present usually prefer the same audio chain, regardless their "paper" preferences were different. This is our experience.
Regards,
Pavel (Macura) 😉
Different wishes
Hugh, what you say, is generaly used ( declared ) nonthrue. People don't know, what they can, but when they are in some comparison, absolute majority give the same order to the same tested machines. And for many of this is surprise, that this results objective follow technical parameters of machines, but often not prices. But you must have some objective realy good component - if you will compare several s..t, immediately rise " taste " and situation is there what you write. I say again , realy good component is necessary, belive or not, and doubt will falling.
Hugh, what you say, is generaly used ( declared ) nonthrue. People don't know, what they can, but when they are in some comparison, absolute majority give the same order to the same tested machines. And for many of this is surprise, that this results objective follow technical parameters of machines, but often not prices. But you must have some objective realy good component - if you will compare several s..t, immediately rise " taste " and situation is there what you write. I say again , realy good component is necessary, belive or not, and doubt will falling.
Maybe do you mean:
Is feed-forward able to substitute feedback?
Is it free from the harmonic spread?
Note: harmonic spread is not associated only to feedback circuits
……...rather with recursive circuit. Feedback cir are a sub set of
……...recursive cir. But due to the Ohm low near every circuit
……...is recursive. Irrespective of the fact that it contains or not
………active devices or 3 legs devices. Also a non linear resistance
………originates harmonic spread if it is connected with a non ideal
………source ( ri>0).
Federico
Federico,
let me explain:
if you divide input through output on the left side, you have the ratio of the voltages.
If input is 3V and output is 6V you have the ratio 0,5.
Output minus input is 3V.
Multiplicate the two and you get 1,5V.
This is fed into the other side.
The other side got the same error ratio as the left side.
Output is two times the input.
So output is 3V.
left side 6V, right side 3V makes differential voltage across load 3V.
Perfect. 😀
As this is done real time, the error is always compensated.
The problem is the analog division and analog multiplication of the signals and both sides have to be very equal and division through zero occurs with use of + and - rails.
let me explain:
if you divide input through output on the left side, you have the ratio of the voltages.
If input is 3V and output is 6V you have the ratio 0,5.
Output minus input is 3V.
Multiplicate the two and you get 1,5V.
This is fed into the other side.
The other side got the same error ratio as the left side.
Output is two times the input.
So output is 3V.
left side 6V, right side 3V makes differential voltage across load 3V.
Perfect. 😀
As this is done real time, the error is always compensated.
The problem is the analog division and analog multiplication of the signals and both sides have to be very equal and division through zero occurs with use of + and - rails.
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