[cwtim01]

   
Aren't V grade only used in high current applications of which GS-X does not need?
 
Btw, Nelson Pass is like a DIYer on steroids.  Love what he is doing with his First Watt company as he is still doing essentially DIY on the side even though he is the founder of Pass Labs.  Shows his love of the field.

I said "certain applications" and that does not include the GS-X, Justin already said that these JFETs run at Id of 1mA so even GR grade will do fine, there is not much point to go for a V grade, and then use a higher value source resistor to degenerate the Id down to 1mA.

 

[preproman]

 
I said "certain applications" and that does not include the GS-X, Justin already said that these JFETs run at Id of 1mA so even GR grade will do fine, there is not much point to go for a V grade, and then use a higher value source resistor to degenerate the Id down to 1mA.

 
What applications are you using them for - are you doing a DIY amp of some kind?

 

[cwtim01]

   
What applications are you using them for - are you doing a DIY amp of some kind?

Yes, I'm collecting the components to build a modified F5 using the BA-3 frontend with lateral HItachi MOSFETs as output device, just 25W into 8 ohm though. Can drive efficient speakers as well as the HE-6.

 

[preproman]

 
Yes, I'm collecting the components to build a modified F5 using the BA-3 frontend with lateral HItachi MOSFETs as output device, just 25W into 8 ohm though. Can drive efficient speakers as well as the HE-6.

 
Very nice...

 

[Crashem]

Yes, I'm collecting the components to build a modified F5 using the BA-3 frontend with lateral HItachi MOSFETs as output device, just 25W into 8 ohm though. Can drive efficient speakers as well as the HE-6.

 


Are you going to drive HE-6 off speaker posts or throw in headphone jack?

 

[cwtim01]

Are you going to drive HE-6 off speaker posts or throw in headphone jack?

 
Headphone jack. Lets get back to the GSX as I don't want to be OT.

 

[justin w.]

   
Justin already explained it, I recently purchased a matched quad of BL 2SK170/SJ74 and it cost me USD35. V grades are practically "unobtainium" in the market and only people who acquired them years ago will have them, V grade's higher Idss and transconductance will give an advantage in SQ for certain applications.
 
These JFETs are often found in the Nelson Pass (founder of Pass Labs and First Watt) designs and used as frontend input device, and are very popular in the DIY community.

 
i have 4 matched quads per GS-X = $140, i should just sell those
 
but i have enough parts to get 16 matches per unit, so i match better than quads
 
i think my stockpile was down to around 3,300 each before i started matching for this batch of GS-X. i am going through 800 of each for this batch. the next batch will take up to 1,200. there wont be many left

 

[tvolpe1600]

Can someone either explain or provide a link about why these parts are so rare now? I've seen various answers around on the forums and elsewhere, but would be interested in the history. As a soon to be owner, I would like to be well informed.

 

[justin w.]

The parts were discontinued because there was no longer a market to sell millions of them. Directly from page 1 of the datasheet, the parts are for "Low Noise Audio Amplifier Applications" and "Recommended for first stages of EQ and M.C. head amplifiers". Op-amps now fulfill those roles. By using discrete parts, you can tailor your own op-amp to your own needs, but this costs more and takes up more space. So it became a niche market, which is not enough to be worth Toshiba's time. Linear Systems has been making replacements, some of which are near a decade in the making, and cost at least 10x more than the original parts.
 
The same thing happened with high-voltage transistors which were used in electrostatic amplifiers. Most of those parts were used in the millions of CRT displays that were built, but then discontinued as everything shifted to LCD. However, some of them are coming back in different forms due to alternative energy technologies such as solar.

 

[justin w.]

round 1 of matching complete, now refining 10mV matches to 1mV
 

 

[bigfatpaulie]

  round 1 of matching complete, now refining 10mV matches to 1mV
 

 
Don't sneeze...  

 

[Hi Rez]

When Ayre found out that Toshiba was going to stop producing these, they executed a buy of 1,000,000 JFETs - somewhere between a 50 and 100 year supply for them.

 

[bigfatpaulie]

  When Ayre found out that Toshiba was going to stop producing these, they executed a buy of 1,000,000 JFETs - somewhere between a 50 and 100 year supply for them.

 
So what you're telling me is that one good sneeze could destroy Ayre...  

 

[kevin gilmore]

nelson pass needs the higher idss parts because he is driving relatively high capacitance
mosfets with them. jason does the same thing with 2sk373 in the mjolnir.
ayre uses 8 x 2sk389 and 8 x 2sj109 in each kx-r preamp, so the parts may not last
as long as they think

the jfets inside the gsx2 drive bipolar transistors with ultra low capacitance, so the high idss parts are not needed.

the cross coupled servo driven current sources that drive the fets will automatically adjust
the source voltages to make the currents 1ma.

the tight matching further reduces the THD. up to an extra 6db or so.

linear systems has been making excellent lsk389/lsk170 for years now and the BHSE uses them.

i just received a bunch of production lsj74 parts which i will be testing much further
on friday but initial testing indicates that these parts are now usable in the gsx2.

So about the time justin runs out of the original parts, there will be replacement parts.
The pricing issue however is several times that of the original parts.

 

[preproman]

So does that mean a future price increase on the GS-X mk??