Wrong assumption based on the postulate that linearity,
or rather lack of , is frequency independant , wich is not the case at all.
Hi Damir,
I had the same issue (sensitivity to the load) with the super-TIS. A pre-driver with bootstrapped collectors remedies this. Also the load from a HEC OPS might introduce extra distortion. Also in this case you could insert a pre-driver. See fig.17 on this webpage for an example (Q19 & Q20).
Cheers, E.
Hi Edmond,
I used boostraped predriver in one of my simulation, distortion was quite OK but slew rate was very bad, look this simulation and tell me what is wrong. http://www.diyaudio.com/forums/solid-state/240712-cfa-topology-audio-amplifiers-102.html#post3626368
If I connect predrivers collectors to the rails I get better slew rate but distortion is going up.
BR Damir
Hi Damir,
>what is wrong?
Just a guess: Q23 and Q24 get saturated. Vce is simply too low.
What if you bootstrapped the collectors the 'old fashion' way, i.e. connect the collectors via resistors to the supply rails and via capacitors to the output. (as in fig.12 on my website)?
Cheers, E.
Agree, its one of the reasons miller compensation is suboptimal for use with CFA. With shunt compensation the open-loop bandwith is increased and ULGF can be made much higher although the limiting factor will be the outputstage. From sims I find TMC not to be of much benefit as loop gain is small although TPC is useful. From the sims I showed of my CFA design these differences are very small, sims shows it has 7 Mhz ULGF, although I doubt it has in practice. Reducing the ULGF in sims to 3Mhz by increasing the compensation, only results in increase from 6.4ppm THD20 to 7.1ppm. TPC does sim better figures but I only endorse a scheme after I see actual performance on practical design.
Kgrlee, Ill see to your request soon, just need a day or 2 to remove the cobwebs after a couple of days of beach bum life on european south coast.
(a) No, only if incompetently applied (like between low impedance points).
(b) No, at least without compromising the stability margins.
(c) Impossible, in a single dominant pole configuration (Miller or shunt). GBW is constant, hence halving the ULGF will also halve the loop gain, hence double the distortions.
Yeah right
If I had patients for unexperienced book nerds such as yourself, I would prove with sims but really youre not worth the effort.
Yeah right
If I had patients for unexperienced book nerds such as yourself, I would prove with sims but really youre not worth the effort.
Very right, and without any personal insults. Please provide the simulations for others to be able to reproduce your amazing results and conclusions. Or are they under a confidentiality agreements, as all other proofs you were requested to provide?
I agree. Indeed, it is also not a good idea to chase extremely low noise at the expense of all else. This is true of most performance aspects.
It is also important to understand what that "all else" is, as well.
Cheers,
Bob
Particularly when no source component we know of, let alone any recording played back via that, comes anywhere close to the power amplifier achievable noise.
This ease of low noise does lead to puzzlement when some acclaimed amplifiers are astonishingly noisy.
Being a book nerd is not an insult, my brother is one. He comes up with all these brilliant ideas and designs and can even explain the existance of the universe through maths, the problem is its not practical. Spending your time just repeating whats written in books gets you nowhere and dont think it makes you look superior or important, quite the opposite.
I will not provide simulations, you forget I did, and the member Wahab did in fact simulate the design and showed and verified every claim I made from THD specs to ULGF. What more proof do you want ?? Theory only gets you half way, what you learn through experience is the other half, area where you sadly lack.
Dont underestimate people you have no clue who they are, I just prefer not to be a book nerd. The more you think you are impressing me or thinking you are showing superiority or what ever youre thinking just makes me think youre bigger a fool than I at first suspected.
Originally Posted by Bonsai
Stop chasing THD to the expense of all else.
Originally Posted by Bob Cordell
I agree. Indeed, it is also not a good idea to chase extremely low noise at the expense of all else. This is true of most performance aspects.
It is also important to understand what that "all else" is, as well.
So, gentlemen... why searching extremely high maximal slew-rates, very extended bandwidths and many other features claimed to be the privilege of CFAs ?
Originally Posted by Bcarso
some acclaimed amplifiers are astonishingly noisy.
In some circumstances, a bit of additional noise can unveil details not perceived otherwise. The effect is well known in photography, it also occurs with sound :
"Can noise improve your hearing ?"
Electronics World + Wireless World, December 1993, p976.
The article quotes :
- Franck Moss and colleagues from the University of Missouri
- Nature vol 365, No 6444
Stop chasing THD to the expense of all else.
Originally Posted by Bob Cordell
I agree. Indeed, it is also not a good idea to chase extremely low noise at the expense of all else. This is true of most performance aspects.
It is also important to understand what that "all else" is, as well.
So, gentlemen... why searching extremely high maximal slew-rates, very extended bandwidths and many other features claimed to be the privilege of CFAs ?
Originally Posted by Bcarso
some acclaimed amplifiers are astonishingly noisy.
In some circumstances, a bit of additional noise can unveil details not perceived otherwise. The effect is well known in photography, it also occurs with sound :
"Can noise improve your hearing ?"
Electronics World + Wireless World, December 1993, p976.
The article quotes :
- Franck Moss and colleagues from the University of Missouri
- Nature vol 365, No 6444
Please provide evidence for your a,b,c statements above. You did not provide anything consistent so far.
"... why searching extremely high maximal slew-rates, very extended bandwidths and many other features claimed to be the privilege of CFAs ?"
Probably for the same reason you chase sub ppm distortion VFA's at the expense of all the other specifications.
I'd like to think my outlook on amplifier design is a lot more balanced than yours.
😎
Probably for the same reason you chase sub ppm distortion VFA's at the expense of all the other specifications.
I'd like to think my outlook on amplifier design is a lot more balanced than yours.
😎
It is not that difficult to get sub-ppm distortion together with other high specifications for slew-rate or noise. Let's not forget PSRR...
Yes, we know that trick.
Just pile on the loop gain. When you can do it with 60dB of loop gain, you have made progress.
Just pile on the loop gain. When you can do it with 60dB of loop gain, you have made progress.