John Curl's Blowtorch preamplifier part II - Page 1305 - diyAudio
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Old 22nd June 2011, 07:40 AM   #13041
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by ostripper View Post
Nope , toshiba custom SIP . Same as the JVC super A , custom manufactured for luxman.
Toshiba for sure. But I suspect if you look closer you find one is a 2SK389 used in the DC Restorer (aka DC Servo) and the other 2SJ109 used in the "Distortion Extraction Amp".

It is a few years ago I saw the more detailed schematics in MJ, so things are a wee but hazy (my memory ain'f what it used to be, then again, it never was anyway)...

The main forward part are AC coupled Bipolars in parallel with Cascode, the bit on top is actually a current mirror (possibly with gain), this directly drives tripple Darlington outputs. The "other side" of the current mirror is a simple resistor, so local degeneration and loads set the gain overall. No global feedback, output stage runs as very overbiased Class AB. Such an Amp easily can do < 0.1% THD at 1W and < 0.5% THD at full power, 20KHz.

The DC restorer is linked into the forward path, with quite low gain and has a long timeconstant.

The Error Amp is a simple P-Channel Differential, cascoded and current mirror loaded if memory serves. One input gets the input signal, the other the scaled output (this probably needs adjustment of very precise resistors setting gain everywhere and massive amounts of degeneration in the forward path). The output of this "distortion extractor" is an Emitter follower that drives the load resistor for the open loop VAS.

Looking at the distortion gain in the distortion feedback circuit, there is maybe 30dB gain, so distortion is lowered by that amount, the degree of correction this circuit is capable off is quite small, however, even if it saturates, the open loop forward path will scarecly care and keep working at increased THD, but no clipping, sticking, TIM etc....

I would have probably used J-Fets for the Input stage and lateral mosfets for the output (especially with 60W/8R Class A operation, but that's just me...

Ciao T
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Old 22nd June 2011, 09:07 PM   #13042
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Nobody's interested? It's a pretty elegant little circuit element that includes a differential input (and output, if needed), good power supply rejection, low noise, yada yada. Not practical for monolythic IC's because requires device matching and many volts headroom.

I've come to see it as a natural offshoot of the John Curl input stage, and its complement in many ways. But if nobody's interested.....
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Old 22nd June 2011, 09:32 PM   #13043
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Schematics? Even a block diagram would be interesting.
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Old 22nd June 2011, 10:33 PM   #13044
mlloyd1 is offline mlloyd1  United States
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stop teasing; of course we are interested!
:-)

mlloyd1

Quote:
Originally Posted by Chris Hornbeck View Post
Nobody's interested? It's a pretty elegant little circuit element that includes a differential input (and output, if needed), good power supply rejection, low noise, yada yada. Not practical for monolythic IC's because requires device matching and many volts headroom.

I've come to see it as a natural offshoot of the John Curl input stage, and its complement in many ways. But if nobody's interested.....
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Old 23rd June 2011, 02:25 AM   #13045
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Been recording a soprano this afternoon, so I'm a little punchy, but here goes. Hope it works!
The resistor with ?? marks just came to me, in desperate attempt to supplant a Schubert lieder in headspace.
circuit_1.jpg

circuit_2.jpg
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Old 23rd June 2011, 05:51 AM   #13046
EUVL is offline EUVL  Europe
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A question about JFETs in general, and those from Toshiba / Linear Systems in particular.

Many JFETs (including those from NXP and Sanyo) are symmetrical, i.e. the drain and the source can be swapped.
I have tried this on BF862, e.g., and it works perfectly.

Does this also apply to the likes of 2SK170s or LSK170s ?
Or any JFETs for that matter ?


Patrick
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Old 23rd June 2011, 06:08 AM   #13047
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Yes for 2SK170/2SJ74.
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Old 23rd June 2011, 07:05 AM   #13048
EUVL is offline EUVL  Europe
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You are right.

I was curious, and remembered that I had a few samples lying around.
So I measured one of each.

LSK170 is not quite identical when reversed.

Left (11mA Idss) is 2SK170.
Red line is as per datasheet. Blue crosses are D-S reversed.


Patrick

.
Attached Images
File Type: png 2SK170 Reverse.PNG (5.7 KB, 393 views)
File Type: png LSK170 Reverse.PNG (5.7 KB, 371 views)

Last edited by EUVL; 23rd June 2011 at 07:07 AM.
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Old 23rd June 2011, 07:09 AM   #13049
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Good job, Patrick.
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Old 23rd June 2011, 08:07 AM   #13050
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d'oitashimashite.
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