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Old 16th December 2012, 10:14 PM   #761
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Quote:
Originally Posted by zenelectro View Post
And the bigger the bjt the slower / more non linear it is.

There is an art to picking the right device for a particular place in this
circuit and running it at the right current.

Z
....and my silliness is once again lost on the populace at large... sigh.

but, to further the progress of technology and the conquest of nature in all her glory, here is a little something I cooked up in simland. I don't claim nuttin' good about it. Sim'd THD is 6x10^-5% for 6mA input. Just something for the bong.

mmmm, time to get out that steel polish and shine those babies up!
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Old 16th December 2012, 10:38 PM   #762
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by zenelectro View Post

There is an art to picking the right device for a particular place in this
circuit and running it at the right current.

Z
can we simple mortals, have a glance at your art, please enlighten us with your divine knowledge.
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Old 16th December 2012, 11:03 PM   #763
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Zenelectro, is it with lateral MosFets ?
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Old 17th December 2012, 01:29 AM   #764
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Well, sometimes slow is beautiful, like when you're lying naked with your wife... or sitting on the beach on a warm summer day, sipping your favorite alcoholic beverage, or both.
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Old 17th December 2012, 05:20 AM   #765
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Quote:
Originally Posted by smms73 View Post
can we simple mortals, have a glance at your art, please enlighten us with your divine knowledge.
Divine knowledge - too funny

Just use common sense.

Only use large geometry / high current bjts where they are absolutely
necessary - this will be in very few places if you think it through.

Sometimes you will be better off paralleling 2 x slightly smaller devices of
moderate current (337).

Where there is large voltage swing look for super low Cob / linear beta
devices. Sanyo have a very good range. Also 2SA1360/SC3423 are very
good for the 'helpers' that swing in voltage.

If you are going to do an IV for Sabre in mono mode where Z out = 98 ohms
at 16mA swing this will really require some fine tuning of current versus BJT
type etc. It will push an open loop design to the max - especially if you
do it without the CFP pairs.

I suppose I've played that tape before __

cheers
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Old 17th December 2012, 03:30 PM   #766
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Hmmm, with 16mA input, changing the IV resistor to 200 ohms yields THD of 3x10^-5%. Rock on...
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Old 7th January 2013, 01:19 AM   #767
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Looks like Wadia aren't sitting on their hands as far as I/V stages go.

Wadia Digital


"Wadia Swift Current Technology
The series 1 Upgrade, which will supercede the highly-regarded Wadia 860, is the first to use the company’s patented SwiftCurrent IC. This proprietary circuit, first introduced in the Wadia PowerDAC digital amplifier last year, performs the sonically critical current-to-voltage conversion with no negative feedback, resulting in demonstrably superior sound quality.

Conventional digital-to-analog converters perform current-to-voltage (I/V) conversion using feedback circuits based on operational amplifiers. Because the signal from the DAC chip consists of a series of step changes, the distortion introduced by this feedback circuit is a significant limitation on sonic performance.

In contrast, the SwiftCurrent circuit performs this I/V conversion with Wadia’s patented current-conveyor integrated circuit (IC) that eliminates feedback. This bipolar IC consists of an innovative connection of Wilson current mirrors, an emitter degeneration compensation scheme to optimize transient response and stability, and a novel current mirror arrangement to enhance output impedance."

BTW Sergio how is yours going? have not heard anything for a while?

Cheers George
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Old 7th January 2013, 05:24 AM   #768
Shinja is offline Shinja  Japan
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I found this post,george

Wadia Swift Current?
Quote:
Originally Posted by jan.didden View Post
Correct. The PA630 (and the '630A, which has connections for dditional FET drain followers at the output) was taken off the market a couple of years ago after the designer sold the rights and his remaining chips to Wadia. There have been at least two publications in EW/WW, plus several in the trade press. There is also a full chapter describing these chips in the book "Analog IC design, the current mode approach".
If you need info like internal schematics etc, drop me an email.

Jan Didden

Last edited by Shinja; 7th January 2013 at 05:26 AM.
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Old 7th January 2013, 05:49 AM   #769
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Would be nice if these were available to buy. I invited Jan Didden to this thread to comment, maybe he still has the internal schematics of the "Wadia" PA630/PA630A Opamp.

Cheers George
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Old 7th January 2013, 05:56 AM   #770
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Yes I still have the internals of those chips. They are from open sources so I can post them later today.
I also have the spice model but I believe that's proprietary but will check.

jan
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