Quick 'executive' summary of what we have acheived so far in this thread:-
1. Demonstrated 2 CFA designs (dadod and bonsai) that acheive low single digit ppm distortion performance at high power at 20 kHz, easily matching VFA in practice (sub 1ppm is a pipedream - lets not waste our time on this nonsense). We settled on ~3MHz as the upper ULGF to demonstrate this, and acknowledge that for a practical output triple amplifier, this figure would need to be 1.5 MHz or lower. This will increase distortion, but it will still be sub 10ppm
2. Shown that the amplifier complexity is about the same as competing VFA topologies; Separately, other CFA designs on the forum also demonstrate this - e.g. LC's VSSA, JLH 10 watter (from 1969)
3. Investigation in to the TIS lead us to conclude that a simple beta enhanced circuit is all that is needed to deliver very low distortion
4. The designs inherantly have high slew rates and bandwidths and this is set by the front end gm - the feedback resistor sets the SR and the loop bandwidth
5. For discrete audio power amplifier applications, we have shown in sims that we can apply Miller, TMC and TPC comp schemes, which helped us acheive the distortion performance mentioned above
6. We now plan to do more investigation on CFA PSRR
Nice summary/recap --
a PSRR result from my earlier entry in VSSA CFA vs same output Q, same bias, same added number of parts as Esperado' "fair" LTP comparison
but designed to take full advantage of LTP
minus rail PSRR of VSSA(yellow trace) vs TPC LTP (green)
any wanting to design for improved PSRR should look at the Sakinger paper I have been promoting for a decade now at diyAudio
Basically PSRR is a function of compensation reference topology and loop gain, NOT a inherent VFA/CFA difference
if you insist (low) "flat loop gain" is a design goal itself you're facing a handicap in the loop gain part of PSRR and really, really need to understand the rest of the Sakinger paper
but designed to take full advantage of LTP
minus rail PSRR of VSSA(yellow trace) vs TPC LTP (green)
any wanting to design for improved PSRR should look at the Sakinger paper I have been promoting for a decade now at diyAudio
Basically PSRR is a function of compensation reference topology and loop gain, NOT a inherent VFA/CFA difference
if you insist (low) "flat loop gain" is a design goal itself you're facing a handicap in the loop gain part of PSRR and really, really need to understand the rest of the Sakinger paper
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Quick 'executive' summary of what we have acheived so far in this thread:-
1. Demonstrated 2 CFA designs (dadod and bonsai) that acheive low single digit ppm distortion performance at high power at 20 kHz, easily matching VFA in practice (sub 1ppm is a pipedream - lets not waste our time on this nonsense). We settled on ~3MHz as the upper ULGF to demonstrate this, and acknowledge that for a practical output triple amplifier, this figure would need to be 1.5 MHz or lower. This will increase distortion, but it will still be sub 10ppm
....
6. We now plan to do more investigation on CFA PSRR
1. It doesn't need ppm distortions, I've tried many things, and if you have high damping amp without caring its sound quality, your amp won't better than krell100. Sub ppm at 20k is also not a dream if output transistor is very fast, and high hf loop gain applied, what a waste, 1ppm is not better than 0.01%.
6. PSRR is already good enough if feedback is as high as that 2 CFA (bonsai&dadod).
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I tried searching for the Sakinger paper - can you point me to it? The search function of this forum stinks.
We are not insisting on a flat top response - that's just a characteristic of CFA, and we have to deal with it, THD same way you have to in any engineering endeavor.
As already noted, the problem is solvable by augmenting the basic CFA with ripple eaters or AFEC, but it would be nice to dig into the fundamentals a bit more.
We are not insisting on a flat top response - that's just a characteristic of CFA, and we have to deal with it, THD same way you have to in any engineering endeavor.
As already noted, the problem is solvable by augmenting the basic CFA with ripple eaters or AFEC, but it would be nice to dig into the fundamentals a bit more.
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22 years old, I guess this would fall under "fair use". If not, somebody delete this post.
I try cap multiplier which designed by Rod Elliot to my variant of VSSA. Voltage ripple before cap. mult. is 120mVpp without input signal and I can not see a ripple on my scope after cap. mult.
But sound quality is worse, especially at high frequency. I do not have distortion meter, so I can not confirm the distortion of high frequency.
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minus rail is expected to be the worse for my LTP with the compensation connected there
http://www.diyaudio.com/forums/solid-state/240712-cfa-topology-audio-amplifiers-73.html#post3615032
http://www.diyaudio.com/forums/solid-state/240712-cfa-topology-audio-amplifiers-73.html#post3615032
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Can-you publish your cap multiplier schematic and the rail of your amp ? I cannot understand a reason why you can prefer it without if your cap multiplier is fast enough to not add any peak at square waves.
Is your VAS rail clean when high power modulation ?
L.C. preferred his VSSA without VAS DC filter, but he talked of basses. So i imagine it is the 2mF added to power rails when filters are shorted rather than the filter itself witch make the difference.
Who said an amp will never be better than its Power Supply
To jcx, my comparizon was not to demonstrate all CFA amps are better than VSA's ones. Listening is the only way to figure out this kind of thing.
My comparison was to lighten the main difference between CFA and VFA: Input stage, everything else equal.
Explore what are really the holly LTP's advantages.
Your companion was not demonstrating anything: not the same number of active devices (8 VS 6), not the same VAS gain, not the same VAS topologies (two stages asymmetrical VS one stage symmetrical). Apples VS Oranges.
Why don't you build and listen one day a CFA to make your mind about what we are talking of in all those thread's pages, instead of running in circles claiming "VFA is better, VFA is better "...? And stop making personal attacks against people witch does not think the way you ...think ?
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Emitter followers can oscillate so drive you amplifier with a signal and look at the output of the cap multiplier. Whst devices are you using?
I made cap. multiplier from this The Class-A Amplifier Site - The Capacitance Multiplier because almost all components I have on my box, except output transistor I use my ancients 2N3055 and MJ2955.
I am not sure, I only have a scope, may be I will check it...
For other people who can not design CFA amp better than VFA amp, it not because VFA better than CFA. But it caused by your ability
My VSSA is better sound quality (subjectively) than my complex VFA that I made about ten years ago. At that time I measured my amp have 300kHz power bandwidth, 150Watt/8Ohm, 93dB S/N (no weighted filter), and 0,006% THD at 1kHz and still live until now.
But now I only have a scope
Douglas Self has demonstrated that a VFA can deliver a tenth of that distortion. So-called "CFAs" are rubbish for audio.
Proved so many times all around the world (VSSA modules were sent to so many places in all continents). And that's what is bothering VFA fanatics, better sound quality gained from even the simplest CFA of them all.
And now imagine the appearance of a serious CFA amp gained from this thread. THE END.
