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Old 12th September 2003, 01:08 AM   #11
jam is offline jam  United States
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I will remember that if I see you at the next CES.
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Old 12th September 2003, 01:33 AM   #12
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Default posting such an irresponsible schematic

The Hitachi K1058 and J162 mosfets have internal gate clamping zeners. The usual quality advice we have come to expect ......

BTW real schematics have device part numbers and resistor and power supply values, unless you are just trying to throw something together on paper with no concern about it being anything that might actually work.......
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Old 12th September 2003, 02:15 AM   #13
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Default Re: posting such an irresponsible schematic

Quote:
Originally posted by Fred Dieckmann
The Hitachi K1058 and J162 mosfets have internal gate clamping zeners. The usual quality advice we have come to expect ......
It wasn't actually advice. It was just poking some fun at the hysteria over protection diodes.

Quote:
BTW real schematics have device part numbers and resistor and power supply values, unless you are just trying to throw something together on paper with no concern about it being anything that might actually work.......
Was just offered as a basic concept. Just like DrG's schematic, which although it contains component values and part specifications hasn't even been simulated let alone built and tested.

You're mighty selective in your criticisms, Fred.

se
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Old 12th September 2003, 12:31 PM   #14
DrG is online now DrG  South Africa
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Thank you Steve. I suspect there are a few other odd parts missing here and there. Your circuit suggestion is an SE CFP with xf coupling. Simple and effective, especially in a class A design, although I'm personally not a huge fan of CFP/Sziklai o/p stages in class AB, despite their lower distortion spectra. But that's just me...

I was thinking more along the debate (other threads) regarding o/p stages with gain being allegedly superior to simple followers and saw a way of doing both at the same time, with complementary BJT pairs. I've never seen an approach such as this. Do you think that it will "work"... missing protection diodes etc notwithstanding?

Quote:
BTW real schematics have device part numbers and resistor and power supply values, unless you are just trying to throw something together on paper with no concern about it being anything that might actually work.......
I hadn't calculated the bias chain values yet, but that should be easy. The rest of the values seem servicable to an initial approximation. Supply voltages aren't critical but make them say +/- 35v.

And yes, I would like to know if it would work. Do you think it will, Fred?

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Old 12th September 2003, 04:10 PM   #15
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Default Will it work

Very poorly if at all in my estimation.

Obsolete 2 MHz BJT and I see potential stability issues well. Jocko has more experience with compound BJT pair

Bias pots will inject power supply noise into summing junction for a poor PSRR. The power supply noise looks like an input signal with this bias scheme.

No real ground reference for the negative feedback.

The power mosfets are designed for output stage and will have a very low transconductance at 10ma.


Why not start with some thing a little more
conventional.
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Old 12th September 2003, 05:49 PM   #16
DrG is online now DrG  South Africa
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Quote:
Why not start with some thing a little more conventional?
I've built quite a bit, Fred. Mostly tube and hybrid. Only a couple of pure ss. I pretty much think most "conventional" avenues have been followed, so I like exploring the unconventional. To boldly go where no man has gone before and all that...

Quote:
Bias pots will inject power supply noise into summing junction for a poor PSRR. The power supply noise looks like an input signal with this bias scheme.
Perhaps, but I plagiarized this circuit segment straight from the Pass Zen v.5. It may be imperfect, but it does work. But I take your point and will bias instead via large series R (47-220K) from the pot/divider network and add some bypass caps to the latter.

Quote:
No real ground reference for the negative feedback.
Inherent in inverting stages. Not a trainsmash.

Quote:
The power mosfets are designed for output stage and will have a very low transconductance at 10ma.
Again, point taken. Will up mosfet Iq or use alternate devices.

Quote:
Obsolete 2 MHz BJT and I see potential stability issues well. Jocko has more experience with compound BJT pair
Yeah I know they're old... but I have a dozen pairs. So say I use 2SA1216/2SC2922 instead. Take another look though, this is not a conventional compound pair at all... But I would still welcome Jocko's input.
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Old 12th September 2003, 06:18 PM   #17
PMA is offline PMA  Europe
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Dr. G,

do you think that it makes any sense to mix CE and CC output stage? First with high Zout and second with the low one? Like steam and electric loco?
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Old 12th September 2003, 06:54 PM   #18
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Quote:
Originally posted by DrG
Thank you Steve. I suspect there are a few other odd parts missing here and there. Your circuit suggestion is an SE CFP with xf coupling. Simple and effective, especially in a class A design, although I'm personally not a huge fan of CFP/Sziklai o/p stages in class AB, despite their lower distortion spectra. But that's just me...
That's fine. I'm not a huge fan of class AB, Sziklai or otherwise.

Quote:
I was thinking more along the debate (other threads) regarding o/p stages with gain being allegedly superior to simple followers and saw a way of doing both at the same time, with complementary BJT pairs. I've never seen an approach such as this. Do you think that it will "work"... missing protection diodes etc notwithstanding?
Don't see any reason it couldn't ultimately be made to work.

And since you've achieved your basic design goal, I'd chalk it up as a "success." Unless of course you want to take the next step and actually build it and nail it down fully. But that'll be your headache, not mine. I'm dealing with my own at the moment.

se
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Old 12th September 2003, 07:01 PM   #19
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Quote:
Originally posted by PMA
do you think that it makes any sense to mix CE and CC output stage? First with high Zout and second with the low one? Like steam and electric loco?
But his goal was "to do something substantially "different" and combine CC and CE output devices..."

He seems to achieved it. Doesn't necessarily have to make any particular sense.

Didn't make much sense when I hitched an N-channel silicon JFET to a PNP germanium bipolar. But it sounded fantastic.

se
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Old 12th September 2003, 07:07 PM   #20
PMA is offline PMA  Europe
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Steve,

have you seen http://www.pha.inecnet.cz/macura/bifollower_en.htm
(from my page )
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