I see cascode Q10 base is actually driven by Q8. Is there an improvement on the cascode performance as compared to the traditional method of using diodes/zeners/resistors?
Hi Elvee,
I'm afraid you missed an important aspect. I'm sorry if I'm not clear enough. Perhaps it helps if you also read my website on this subject ('where TMC really shines').
Cheers,
E.
Hi Michael,
Absolutely! Please see the Hawksford cascode: Malcom Hawksford, "Reduction of Transistor Slope Impedane Depedent Distortion in Large-Signal Amplifiers.", J. Audio Eng. Soc., Vol. 36, No. 4, 1988 April. His paper can be downloaded here: http://www.google.nl/url?sa=t&rct=j...sg=AFQjCNHcTo1xdijLr1lxMJljwpiezktaKw&cad=rja
My implementation differs slightly as it is based on: Dimitri Danyuk's, "On the Optimization of Enhanced Cascode", AES paper, October 2008.
It differs in that the base current of the cascode transistor is almost completely 'recycled' (i.e. by a factor alpha), while in the Hawksford cascode this base current flows back partly into the preceding trannie and partly into the emitter degen. resistor. So some of it gets lost.
Cheers,
E.
One of the important things in this circuit is the high impedance at Q8's collector and it's complement. This makes the Baxandall pair work exceedingly well. However it may work too well and oscillate.
Also, the 100k resistors connected to the current mirrors will eliminate PSRR issues, which is one problem with the Baxandall cascode, it needs a good source.
It does not correct the basic nonlinearity of the input pair Vbe's, but they could easily be modified with someone's solution to this. Degenerated cross-comp (Doug Self's book) comes to mind, although without degeneration it may just be more nonlinear.
The Baxandall cascodes may cause serious problems with stability, do you know what to do if this happens?
I like it a lot!
Also, the 100k resistors connected to the current mirrors will eliminate PSRR issues, which is one problem with the Baxandall cascode, it needs a good source.
It does not correct the basic nonlinearity of the input pair Vbe's, but they could easily be modified with someone's solution to this. Degenerated cross-comp (Doug Self's book) comes to mind, although without degeneration it may just be more nonlinear.
The Baxandall cascodes may cause serious problems with stability, do you know what to do if this happens?
I like it a lot!
Super TIS
Hi keantoken,
You're right and I'm aware of this caveat.
Nice (and simple) trick, isn't it?
Well, yes and no. Nothing has been done to lower the distortion of the input stage itself, that is, when operated in isolation. BUT... the crux is that everything has been done to lower the (differential) signal level. At full power and at 20kHz in the order of only 1uA at the collectors or 10uV between inverting- and non-inverting input. With such low signal levels, 'tanh' can't do any harm.
Yes. Please have a look at my (updated) website , Fig.2, C10 & C11.
Thank you. I would be very flattered if you would build this front-end.
Cheers,
E.
BTW, what's your real name?
Hi keantoken,
You're right and I'm aware of this caveat.
Nice (and simple) trick, isn't it?
Well, yes and no. Nothing has been done to lower the distortion of the input stage itself, that is, when operated in isolation. BUT... the crux is that everything has been done to lower the (differential) signal level. At full power and at 20kHz in the order of only 1uA at the collectors or 10uV between inverting- and non-inverting input. With such low signal levels, 'tanh' can't do any harm.
Yes. Please have a look at my (updated) website , Fig.2, C10 & C11.
Thank you. I would be very flattered if you would build this front-end.
Cheers,
E.
BTW, what's your real name?
Hi Homemodder,
Thank you!
So it might be new.
Regrettably, I've lost that article. Maybe somebody else would be so kind to send us a copy.
Cheers,
E.
BTW, what's your real name?
Dizzy. The music goes round and round...
Speaking of which, while I have all of you here looking at that schematic, might I request that you all take a look here, and lend a hand? There may be some similarities, but I am not sure:
Les Sage Amps
Regardless of similarity, the question is how does this one work?? It is alleged to have both sliding bias and also SOA protection of some sort. (post 44 and beyond have real schematics)
_-_-bear
Speaking of which, while I have all of you here looking at that schematic, might I request that you all take a look here, and lend a hand? There may be some similarities, but I am not sure:
Les Sage Amps
Regardless of similarity, the question is how does this one work?? It is alleged to have both sliding bias and also SOA protection of some sort. (post 44 and beyond have real schematics)
_-_-bear
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constant current sources
Please have a look at my (updated) website , Fig.2, Q7 & Q8.
Cheers,
E.
Hi Andrew,
Please have a look at my (updated) website , Fig.2, Q7 & Q8.
Cheers,
E.
Hi Bear,
I'm sorry to say so, but 'Les Sage Amps' is a totally different kettle of fish.
Cheers,
E.
Its Alex, you should have my full name from the emails we exchanged some months back.
I based a design around the crossquad idea, problem is I get 20Khz openloop bandwith, unity close to 100 Mhz and 85 db loop gain. Linearity wise not great but 10ppm levels independant of amplitude and frequency till 50 khz is appealing. Feedforward can better this but trying for least complexity. I am on the same as this design of yours but ppb from the crossquad no way.
I based a design around the crossquad idea, problem is I get 20Khz openloop bandwith, unity close to 100 Mhz and 85 db loop gain. Linearity wise not great but 10ppm levels independant of amplitude and frequency till 50 khz is appealing. Feedforward can better this but trying for least complexity. I am on the same as this design of yours but ppb from the crossquad no way.
Sure, but if any of you would care to analyze and comment on them it would be appreciated.
_-_-bear
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