Simplistic NJFET RIAA

[Siberia]

Yours are Spendor S100 if I remember well? At 89dB/W/m as measured by Atkinson they should be much more comfortable than SHL5 with a circa 50W amp. Current delivery and damping factor from just a couple of drain out Mosfets in a low negative feedback amp won't be spectacular but your speaker does not dip impedance too violently. You will evaluate in time.

Yes, it's S100. That's why to VSSA or to TSSA is the question.

 

[Salas]

Piece of cake. VSSA class A/B in the bass TSSA 1.6 class A in the mids & highs. Both diminutive and SMD, both same power-same tone, you set their gain the same and you go biamp to push the 12 inchers better.

 

[Siberia]

Ha, ha. That's quite a heroic piece a' cake to me. And after its finished, I would need some Salas DCB2 pre! While staying in a dreamworld, I thought, I could build on of them and if it turns out a bad marriage with S100, I would ditch them for some potent DIY ones.

SMD keeps me at bay, but as LC says, there has to be a first time someday.

 

[The Space Egg Corp]

" He's convinced me !...
...gimme my Dollar back ! "

Cheers

Si.

 

[Tea-Bag]

Here is my stash of 60- 2SK369-BL measured at 9V for 20 seconds each.
These were purchased at AMPSLAB. The deviation seems similar to 2SK170BLs.

9
9.3
9.5
9.5
9.7
9.7
9.7
9.8
10
10.3
10.5
10.5
10.5
10.5
10.6
10.7
10.7
10.7
10.8
11.1
11.4
11.4
11.4
11.5
11.5
11.5
11.8
11.8
12.1
12.2
12.2
12.2
12.4
12.4
12.5
12.5
12.6
12.8
12.8
12.8
12.9
12.9
12.9
13.1
13.1
13.1
13.3
13.3
13.9
14
14
14
14.4
14.4
14.5
14.7
14.7
14.9
15.1

 

[Salas]

16 pcs from 10.5 to 11.5 already and pairs on every higher step. A very usable stash.

 

[Tea-Bag]

16 pcs from 10.5 to 11.5 already and pairs on every higher step. A very usable stash.

And the rest is not suitable for our purposes correct? or can the source resistor be raised to use higher IDSS pairs?

 

[Salas]

It can. But the smaller it stays the less it adds its own small noise. There is some good bunch around 12.5mA +/-1 also in yours. If others will report some stashes too we will have some statistic so to fix the IDSS spec to what will be expected as easier to chance on.

 

[Tea-Bag]

Another thought Salas is my measurement time. These are slightly higher numbers, because the higher the IDSS, the more they tended to drift up in IDSS. 20 seconds seemed to be the time where it settled, or just rose much more slowly.
Should we be measuring the first number we see, or standardize on a timeframe? I can remeasure if we all agree on a certain standard.
It looks like a 25 percent yield on a stash, so expect to order possibly 4x what you need. Of course based on my current results.

 

[Salas]

High transcondutance Fets tend to drift up noticeably because the warmer they get the easier it is to gain enough more current. We will say 20 secs time for all.

 

[Salas]

P.S. Another way is to measure their resistance from drain to source. If you will do a check you will notice that same IDSS pairs show the same RDS. The higher the IDSS the lower the RDS also.

 

[RCruz]

How do you measure rds ?

 

[Joachim Gerhard]

i found this :
JFET Matcher

 

[Salas]

How do you measure rds ?

Self explanatory. DMM in Ohm mode and you measure across drain to source.

 

[Salas]

i found this :
JFET Matcher

I bought a DCA Atlas Pro too. Just not in my hands yet. Has it been repeatable for Vgs(off)?

 

[massimo]

If others will report some stashes too we will have some statistic so to fix the IDSS spec to what will be expected as easier to chance on.

208 pcs 2SK369BL: see attached pdf

 

[Joachim Gerhard]

I did not measure so much Fets till now, more bipolar.
I can do some traces today with Fets.

 

[buzzforb]

208 pcs 2SK369BL: see attached pdf

Some of those would seem little high for BL grade.

 

[massimo]

Some of those would seem little high for BL grade.

Nope!
IDSS classification GR: 5.0~10.0 mA, BL: 8.0~16.0 mA, V: 14.0~30.0 mA

 

[Salas]

Many pairs and near pairs everywhere in the 208 lot.