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-   -   SS 120R085 Depletion Mode Jfet (http://www.diyaudio.com/forums/pass-labs/190438-ss-120r085-depletion-mode-jfet.html)

buzzforb 7th June 2011 09:23 PM

SS 120R085 Depletion Mode Jfet
 
Is there any wat to buy the SS depletion mode Jfets without buying large quantities?

Blues 7th June 2011 09:25 PM

Tea-Bag...

buzzforb 7th June 2011 09:28 PM

I was looking for the R085 depletion mode. I thought he was selling the R100 enhancement mode.

wrenchone 7th June 2011 09:38 PM

He also sells the 085 - check his group buy thread.

buzzforb 7th June 2011 09:41 PM

Thanks for the help.

Tea-Bag 11th June 2011 11:28 PM

I did get some more in, but I dont want this, and the moderators dont want this to be a sales thread.

On this totally rained out day in NE, I put one in an F3 clone with NO mods, and it plays, although the gain is super-low. That's no good for a already low gain amp.

I measured the in circuit vgs as -.850v approx.

I am looking at New Pass DIY layout website and the ArchNemesis document is there. Thinking of how to do that circuit without a transformer. So looking at that, and the ZV8 schematic to look at the basics. The F3 is regulated slow start with CCS, so it has the backbone for this kinda amp with a cap output.
I think I need to jumper the cascode FET and raise the source resistor up to 3-5R or so.
I know I am doing this off the cuff, but any comments?

Nelson Pass 12th June 2011 12:17 AM

Go for it.

:cool:

buzzforb 12th June 2011 01:01 AM

I was wanting to try the R085 and the LU Jfet in a Kimmel Mu Follower type amp. I don't see why it would be any different than the F3, but i thought it might be worth a try. With the LU, i would try to keep the cascode setup and slave the CF/SF to it. Just a learning experience more than anything. Don't see anything beating the Aleph CS. Looking for more tubey sound for my FR drivers. To be specific, i am hoping for a little more soundstage depth. I figure this will tell me if its the amps or the speaker setup. I currently have DIY AJ monoblocks and they are great, but i don't know if they are ideal for these drivers. I will also try the DCB1 in collusion with my new F3 to see if the full SE route suits them better. I couls think of worse things to do with my spare time:D

What do you mean by jumper the cascode fet? If that means getting rid of it, it should work considering the main reason for it in the F3 was protection. I still wonder in what situation cascoding is not a good idea, considering the fact that it allows you to extract the exact operating points out of your main transistor.

Increasing the source resistor would throw away more gain, correct?

Tea-Bag 12th June 2011 01:54 AM

Buzz,
With the R085 in the De-light, It didn't like the low source resistor. I believe I was using 3-5R in there, depending on V+. It was more finicky than the R100 in enhanced mode in the same circuit. I have not played with that platform in some time (Or built much of anything honestly)

I think removing the feedback out of the loop would give some additional gain as well.

buzzforb 12th June 2011 11:09 AM

Do you see the R100 as being a better transistor or just easier to work with?


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