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Old 15th September 2011, 11:41 PM   #271
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Quote:
Originally Posted by padamiecki View Post
Hi Elvee, Kenpeter!
back to xquad idea, you can use 4 IRF610 and input voltage 2V will not saturate irfs...
You realize what happens to drain capacitance at 2V?
Transition toward symmetry with source capacitance.

Deceptively low Miller in spec sheet is rated at 10VGS
and 0.8xBVDSS. Thats 160Volts, my friend, Not two...

Going by Figure 11 of Fairchild spec sheet: I see about
90pF Gate to Drain at 2V... Climbing to 120pF at 1V...
I would assume at 0V that maxes to 135pF, same as
gate to source? Anyways, its much bigger than 16pF
suggested value...

Crazy varactors do seem the ideal way to aggrivate
an already unstable xquad into complete madness...
Tentacles, flutes, the whole nine yards...

Last edited by kenpeter; 15th September 2011 at 11:56 PM.
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Old 15th September 2011, 11:51 PM   #272
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I am reminded of Blumlein's garter bias, which has a half loop gain of 1/2 and can't latch.
Maybe something of that sort, but push the half loop gain to 0.9 or therabouts. Yet if
the xquad was not a barely tamed superregenerative monster, it might not prove any
more interesting than a Darlington LTP...

Last edited by kenpeter; 15th September 2011 at 11:54 PM.
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Old 16th September 2011, 12:15 AM   #273
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Hi,

Regarding to wakibaki's Rev.3 pcb at post#53,

It seems there is a misprint between C3's 1-1 pins. 1-1 are same pins, aren't they?

Regards.
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Old 16th September 2011, 07:07 AM   #274
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by terranigma View Post
Hi,

Regarding to wakibaki's Rev.3 pcb at post#53,

It seems there is a misprint between C3's 1-1 pins. 1-1 are same pins, aren't they?

Regards.
You are right.

That's very strange, in principle the netlist should be common to the schematic and PCB.

Anyway, you just have to put a big enough blob of solder to unite the two pins 1 of C3

Quote:
Originally Posted by padamiecki
Hi Elvee, Kenpeter!
back to xquad idea, you can use 4 IRF610 and input voltage 2V will not saturate irfs...
As Ken said, using MOSFETs there could be troublesome.
It could be made to work by tying a cap large enough between the inputs, to combat the effect of capacitances.
The Tringlotron is a sort of asymetric Xquad, and it is made to work with MOS transistors.

But as I said above, if the Xquad is part of an amplifier, saturation is not a problem (except for latch-up).

It is only when you want to use it as a stand alone amplifying stage that you could be confronted with the problem.

And there is a very simple workaround with bjt's: you just have to increase the Vbe of the transistors by using a zener, or stacking more junctions in series with the base. (shunted by a big cap, of course)
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Last edited by Elvee; 16th September 2011 at 07:17 AM.
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Old 19th September 2011, 01:32 PM   #275
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A note - for best real world performance imo do not use 1/4 watt resistors... use resistors rated at minimum at 2x the power that seems to required. In is case 1/2 watt minimum.

_-_-bear
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Old 19th September 2011, 03:17 PM   #276
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Quote:
Originally Posted by bear View Post
A note - for best real world performance imo do not use 1/4 watt resistors... use resistors rated at minimum at 2x the power that seems to required. In is case 1/2 watt minimum.

_-_-bear
Now, which resistor(s) would you be talking about? I've been using my Circlophone with +-39V and 1/4W 1% MF for a while now, no problems.
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Old 19th September 2011, 05:03 PM   #277
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by odysseybmx414 View Post
Now, which resistor(s) would you be talking about? I've been using my Circlophone with +-39V and 1/4W 1% MF for a while now, no problems.
The only resistor that could benefit from an upgrade is R17, the main feedback resistor.
http://www.diyaudio.com/forums/attac...irclophone.gif
With relatively high supply rails, it could dissipate up to ~50mW, and to eliminate any possibility of thermal distortion, a 10x factor could be applied, leading to 0.5W.
But this amplifier doesn't target the ppm, and a normal 0.25W metal film should not degrade significantly the performances under normal circumstances.
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Old 19th September 2011, 05:33 PM   #278
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Quote:
Originally Posted by Elvee View Post
The only resistor that could benefit from an upgrade is R17, the main feedback resistor.
http://www.diyaudio.com/forums/attac...irclophone.gif
With relatively high supply rails, it could dissipate up to ~50mW, and to eliminate any possibility of thermal distortion, a 10x factor could be applied, leading to 0.5W.
But this amplifier doesn't target the ppm, and a normal 0.25W metal film should not degrade significantly the performances under normal circumstances.
Thanks. I don't think I will be changing it.
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Old 19th September 2011, 10:50 PM   #279
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I wouldn't... amah jes' sayin'... it has nothing to do with the ppm, it has to do with spectra of distortion... that's my take on it. Ymmv.

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Old 20th September 2011, 12:16 PM   #280
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I wouldn't... amah jes' sayin'... it has nothing to do with the ppm, it has to do with spectra of distortion... that's my take on it. Ymmv.

_-_-bear
I know about thermal distortion, but I am so satisfied with the sound that I am not going to change anything. Maybe I'll put it in a solid block of epoxy
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