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Old 11th June 2009, 08:29 PM   #451
jam is offline jam  United States
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Hi Mike,

I have built several amps. with CFP output stages and some of them worked quite well but were prone to instability driving certain loads especially electrostatics and so I opted for a more traditional approach.

Sometimes under heavy drive conditions ringing used to occur on the tops of waveforms and crossover artifacts become evident but by the same token the amps I design need to be unconditionally stable because of my speskers. In your case they might just fine. The added compensation I need to get them to work usually hurt the sound.

A viable option is the modified CFP that Mr.Nelson Pass used in the Stasis amplifiers, and this is the output stage I plan to use for my next amplifier (which will not use any loop feedback). Thie downside is that it requires a high bias.

Regards,

Jam

P.S. Please post your CFP stage. I would very much like to try it out,
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Old 11th June 2009, 08:39 PM   #452
iko is offline iko  Canada
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This time I have to agree with Lumba, it's a royal mess!!! But hey, if it works and it's stable as such an air sculpture, imagine what it should do with proper layout

Here it is, started with a clean board, and it evolved into this mess while trying out all sort of variations, and that is just in the last two days. Below, alive, feeding the salas phono while playing Dire Straits.
Click the image to open in full size.

Jam, I used two zeners because I needed a point in between to anchor the top transistor in the cascode. Ever since I can see microvolts on the scope I don't worry too much about the noise of the zener. There are plenty of other worries when you get to that level; that's not to say I'm careless when I choose the parts. For instance I could see with my eyes the noise of the zener when it was bypassed with a 10uF cap on the scope, and it was huge. Upped the cap to 1000uF and the noise was gone, just like that.

I don't doubt that using CFPs it's a valid concern. Sometimes though I need to try things out on my own, and see what happens, that's all.
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Old 11th June 2009, 09:39 PM   #453
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Keep going Ikoflexer, I think you could be on the verge of something special.
If it doesn't work first go it is just a matter of trial and error.

"Genius is 1% inspiration and 99% perspiration" Thomas Edison

or maybe this one is more appropriate

"Invention, my dear friends, is 93% perspiration, 6% electricity, 4% evaporation, and 2% butterscotch ripple" Willy Wonka
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Old 11th June 2009, 09:48 PM   #454
jam is offline jam  United States
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Thanks Iko..................looks like you went to the same prototyping school I went to.

Jam
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Old 12th June 2009, 12:15 AM   #455
Salas is online now Salas  Greece
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Iko, is it the circuit from post# 396?
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Old 12th June 2009, 12:51 AM   #456
iko is offline iko  Canada
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I had to make some compromises. It's not as good in simulation as the NMOS version that I had high hopes for, but it's stable and it works in practice. Here it is.

Very simple, but each addition brings something. The cascode and the buffer both lower and extend the bandwidth on the output impedance. It seems to be robust to different parts. I tried a number of NPN drivers, various gains from 200 to 500 and they worked, all just as well. Different than v1, which seems to get an improvement with a higher gain NPN (makes sense). I hope to get rid of the compensation caps by using RF transistors, which I'm waiting for. So it works, and it's stable, I'm listening to it now. Please feel free to comment, if you see anything odd, or if it can be improved somehow.
Click the image to open in full size.

Output impedance easier to see in db.
Click the image to open in full size.

Click the image to open in full size.

Noise analysis. I don't know how indicative this is, but relative to othe circuits this has lower noise.
Click the image to open in full size.
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Old 12th June 2009, 01:00 AM   #457
iko is offline iko  Canada
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And thank you guys for encouraging me and putting up with my aberrations, it's actually nice to see that someone is actually interested in this. I'm eager to move on for the moment to something else but those results I got earlier, I still hope to get them real one day.

Jam, I probably lost face big time with the photo of the prototype, but hey, what can one do. When you try a hundred things, it can't stay pretty. I've seen many photos of like prototypes from people working for big firms, it's just reality.
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Old 12th June 2009, 01:42 AM   #458
Salas is online now Salas  Greece
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If you have briefed me to lower the output impedance over an extended bandwidth, that is what I would try. A cascode and a buffer. Seems perfectly logical to me.

The way I develop things up to a point, is that I seek ''adequate'' subjective performance down to an arbitrary threshold that I consider the point of diminishing returns. I try to employ less components possible so to ''voice'' easier, and make easier.

But I also like your approach of seeking the technical edge on a proven basis. If you produce a PCB, I will make one so to examine if the added components skew the tone or just (most probably because they ain't many for the given tech boost) refine it.

Congratulations for your dedication and experiments.

No topological blocks are new, most ideas have been considered before in analogue electronics. Its the dedication and fine taste of the chef that wins the day.

Personally I never claim that a friendly to make, working assortment of components that serves a purpose well is some kind of an original fantastic idea. Mine or anybody's.

You can delete ''salas'' from your cct, its your refinement effort.

First there were electrons.
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Old 12th June 2009, 01:42 AM   #459
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The clarity of your thinking is what's important, not the rough collection of the components - the spaghetti does what you want and makes perfect sense to you, so how it looks doesn't matter a damn - and often, when you "neaten it up", it doesn't work as well!
It's marvellous that you not only can get the bloody computer SIMs to work so well, but can actually put all the bits together and it works at all!

I reckon you can take a big thank you from all of us for all your efforts.
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Old 12th June 2009, 02:04 AM   #460
Salas is online now Salas  Greece
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We also need to thank James for his PCB efforts.
Here is his latest refinement for V1. He has included every possible nut n' bolt. LEDs CCS, Vbe CCS, positive / negative shunt, Zener socket for changing Vout in a sec, clean, compact, star layout. I did not see anything wrong by looking at it, you may have your second look too. James is more suitable to comment on the options and how to implement them I guess. He has also made a few V1s (not in WWII) and maybe he can convey his experiences and applications if he likes to.

Thanks again for your contribution James.

Click the image to open in full size.

Click the image to open in full size.
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