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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old Today, 12:27 AM   #96291
TheGimp is offline TheGimp  United States
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We used to have a manual pick and place machine and oven in the lab, but got rid of them a couple of years ago.

Now all builds are done on the main manufacturing line, even a 10 board prototype.

The biggest difference between Prototype, Vorserie and Nulserie is the Prototype does not have ICT (in-circuit test), Vorserie has flying probe test, Nulserie (and subsequent production) has bed of nails final test.

There may not be any difference in the circuitry between the three builds. They are differentiated by their purpose. Prototype is for FW engineers to develop FW,and make minor changes to functionality, perform pre-Type Test evaluation for noise immunity etc. Vorserie is for Type Test and agency certification, Nulserie is per-production for manufacturing to prepare for sales, and they go into the warehouse for sale.
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Old Today, 01:08 AM   #96292
anatech is offline anatech  Canada
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John Curl's Blowtorch preamplifier part II
Hi TheGimp,
Quote:
If there are no dogs in Heaven, I don't want to go there.
Completely agree!
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Old Today, 03:19 AM   #96293
john curl is offline john curl  United States
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Some questions here take a little more than a comment to explain.
Here is some jfet history:
Complementary jfets first became generally available from Motorola back in about 1970. These parts were the low Gm type, with a Gm of perhaps 3-5K umho. They have remained useful, but not as useful as what came later from Siliconix. Siliconix in the early 70's started to make complementary jfets with higher Gm, so we started using them in newer designs, including the complementary differential jfet input stage that we first started to use commercially in 1973. Since then, and now about 45 years later, we still make preamps and power amps with this same input stage. By 1980, there was a revolution in complementary jfets that were released by a number of Japanese manufacturers initially, and later many dropped out of production, but Toshiba remained essentially a single source supplier of various configurations of the 2SK170 and the 2SJ74. The apparent superiority of this parts pair in some form, became a mainstay of Parasound's preamp and power amp designs for the last 25 years. Unfortunately, much like many other Japanese manufacturers, they pulled the plug, so to speak, and we were left with a deficit of these jfets, especially the 2SJ74, and the prices started to rise, perhaps 20 or more times, due to the scarcity of these parts, with no cost effective substitute. Parasound, itself, started to run out of these parts, so in some amps (the cheaper ones at first) they substituted the 2SJ103 that looks and acts similar, but has much lower Gm than the part it replaced. This effectively creates a gain difference in the differential stages, and this actually changes the second (driver) stage more by creating an unbalanced drive to the complementary pairs that are driving each other. This caused a lot of extra 2'nd (even order) harmonics that would normally be balanced out with the proper part.
The amp that I was testing was not a cheap amp, but a more expensive, mid-priced amp, this replacement was inappropriate for its position in the amp lineup.
Now here are some spec sheets of the two fets that were used, note the Gm of each.
Attached Images
File Type: jpg j75 Gm copy.jpg (643.9 KB, 79 views)
Attached Files
File Type: pdf 2SJ103a.pdf (247.6 KB, 10 views)
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Old Today, 04:30 AM   #96294
EUVL is offline EUVL  Europe
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2SJ103 is also obsolete these days, if I am nor wrong.

The transconductance you can make up by using multiples in parallel.
But what is a lot worse is its 10x higher noise than the 2SJ74.
There is no solution, other than perhaps the LSJ74.


Patrick
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Old Today, 04:42 AM   #96295
EUVL is offline EUVL  Europe
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Measurement was done with the P-JFET version of Scott's LNA :
My version of the G = 1000 low noise measurement amp (for Ikoflexer).

2SJ74BL was tested at 1.3nV/sqrtHz
2SJ103Y at 12nV/sqrtHz


Patrick

.
Attached Images
File Type: png 2SJ74BL.png (73.8 KB, 76 views)
File Type: png 2SJ103Y.png (73.1 KB, 75 views)
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Old Today, 11:32 AM   #96296
TheGimp is offline TheGimp  United States
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Quote:
Originally Posted by DPH View Post
Someone PM me when this thread finishes playing speculation on what they can and cannot hear, as my eyes only have so far to roll and I don't want to strain a muscle.
Do you consider Foobar with the A/B/X plugin a valid test for determining if one can or can not hear a difference in two files?

With the A/B/X plugin for Foobar, one can listen to file A, File B, and an unknown playback which can be A or B. One has to determine which it is.

I did not say I had a preference for either, only that I was able to hear a difference which was statistically significant (>80% probability).
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Old Today, 04:26 PM   #96297
scott wurcer is online now scott wurcer  United States
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John Curl's Blowtorch preamplifier part II
Quote:
Originally Posted by EUVL View Post
Measurement was done with the P-JFET version of Scott's LNA :
My version of the G = 1000 low noise measurement amp (for Ikoflexer).

2SJ74BL was tested at 1.3nV/sqrtHz
2SJ103Y at 12nV/sqrtHz


Patrick

.
That 103 looks to have bad GR noise, in fact I would check all late production lots for that. I found a few SK170's with it.
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