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Tea-Bag's IXYS Depletion Mosfet Group and SemiSouth R100 JFET group buy.

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Nelson Pass

Nelson Pass

The one and only
Joined 2001
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Tea-Bag said:
Next week, I am ordering some Depletion SemiSouth SJDP120R085 JFET's.

I plan on getting a few for personal use and a few for others on the list who have shown interest.

If you would like a pair, let me know fairly soon. These will be $70.00 a pair. I won't have enough to match them.
Click to expand...

Did you get that together? I have a gentleman in Russia
looking for some.

:cool:
 
generg

generg

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Joined 2009
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hi tea-bag,:p

just to inform you.... iI replaced all 6 IRF240 with your SemiSR100, not only the upper part.
Sound changed again, a very dark soundscape,
first impression where are the highs?
second impression is there someone in the room (I was sleeping a little bit) voices very naturally .......

my last goal with this amplifier more power, I need new heatsinks, so I can drive a higher bias current.

I hope I have only this disadvantage:

" The most important topological difference is that the output stage current source is no longer an “Aleph” current source, but a version of the classic “Mu Follower”..... This approach was chosen because the JFETs can take better advantage of distortion cancellation than Mosfets, but won't do so if the current source is tightly regulated. This has a little less precision, but lower distortion." (Nelson in J2 pdf)

I drive the outputstage directly by modified Pumpkin.


have a nice day:)
 
Last edited:
Tea-Bag

Tea-Bag

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Joined 2006
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f2j uses 47R, so it looks like lower is better.
Generg, I am confused, did you rewire it to be a mu-follower? Otherwise it's just a current source still, running on lower vgs critter, which probably isn't ideal.
I would worry less about sink temperature with these devices myself.
 
generg

generg

Member
Joined 2009
Paid Member
Tea-Bag said:
f2j uses 47R, so it looks like lower is better.
Generg, I am confused, did you rewire it to be a mu-follower? Otherwise it's just a current source still, running on lower vgs critter, which probably isn't ideal.
I would worry less about sink temperature with these devices myself.
Click to expand...

:DNo teabag, i cannot do that up to now. But before sleeping I look at the BA-1 outputstage and parallel at the tries of people of the J2 thread and I try to see the difference.
I also bought "Audio power amplifier design handbook" from Douglas Self, some things got clearer, but the Mu-follower is not described in the book.

But Nelson I suppose himself started with Aleph configuration and the disadvantages do not seem very important. I know Vgs and so on, no headroom etc. but its worth a try (only a bit expensive:)).

I quote once again: ".....The most important topological difference is that the output stage current source is no longer an “Aleph” current source, but a version of the classic “Mu Follower”. This approach was chosen because the JFETs can take better advantage of distortion cancellation than Mosfets, but won't do so if the current source is tightly regulated. This has a little less precision, but lower distortion .... "

may be this solution only has higher distortion but seems to work pretty nice!:)

This is a good description: http://www.freewebs.com/valvewizard1/mufollower.html

You can understand why Mu! In Germany it is the sound of a cow!
 
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qusp

qusp

Member
Joined 2009
yeah, need more than a single pair. so will wait for the next round for RO85. will look up the IXYS part datasheet and get back to you later today. if you dont hear from me by the end of the day just pack up the PCBs. i'll check in tomorrow night my time a few hours earlier than this
 
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