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Old 13th December 2011, 03:41 AM   #511
EUVL is offline EUVL  Europe
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Toys arrived.
Will start matching soon .....




Patrick
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File Type: jpg 2SK369-250pcs.jpg (658.6 KB, 964 views)
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Old 13th December 2011, 06:47 AM   #512
qusp is offline qusp  Australia
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cool, i'll probably grab some spares. so i got tracking info from my friend, sent fedex international priority at great expense, partially due to the delay caused here and partially because i need things in it too. jesus they know how to charge, cost nearly 400 dollars. it will all be here monday, hopefully the 2sk369-v will be here before then as well.
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Old 19th December 2011, 07:49 PM   #513
EUVL is offline EUVL  Europe
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So for those who intend to use the Vref version for the likes of ES9018, we recommend using a quad set of 2SK369V for each single channel of SEN, or 4 sets of quads for 2 channel balanced.

We bought 250 pieces of 2SK369V (as shown in post #511), then curve traced 12 of them at random, then tested a pair of them in circuit to make sure there is no question at all with them. We have now measured and sorted them all. Out of 250 pieces, we can only make up 8 sets of 4 quads (i.e. each set has 16 FETs for 2 channel balanced SEN) to the level of match that we would use ourselves. The matching loss rate is then almost 50%.

Here is a typical set (see attached). Within each quad, Idss under 9V Vds (= SEN operating conditions) is within 0.2mA. This is only important for equal heat dissipation, and is equivalent to <+/-1% dissipation difference. But when paired as recommended, the different in bias between top & bottom pairs are below 0.02mA. This is important to input DC offset. And 0.02mA is equivalent to ~0.4mV input offset.

The 8 sets will only be offered to Vref kit subscribers. Please indicate interest at the GB thread :

SEN / CEN All JFET IV Converter Evaluation Pack

As we are only interested in enabling you to build the circuit, they will be offered at well below commercial rates :

matched 2SK369-V for sale

... just like we did with the 2SJ74BL's in the original GB. Price to be announced later.
If the demand far exceeds supply, we will consider ordering another 250 for further matching.


Patrick
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File Type: jpg 2SK369V Sets for SEN.jpg (28.0 KB, 823 views)
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Last edited by EUVL; 19th December 2011 at 07:54 PM.
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Old 19th December 2011, 08:47 PM   #514
bcarso is offline bcarso  United States
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Patrick, although the concern with dissipation is a good one, have you had a chance to see how close to the zero temperature coefficient point these parts are, typically? I've found 170BL to be often quite close to a zero drain current tempco at 0 Vgs. In fact some of them require a slight forward bias for the zero point! The canonical approximate operating point for JFETs is about 600mV away from the pinchoff voltage, based on the simple models.

When I was measuring some BF862 parts for various parameters recently, I found that they too are very stable with temperature at 0 Vgs. A nice attribute.

Last edited by bcarso; 19th December 2011 at 08:47 PM. Reason: mistake
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Old 19th December 2011, 08:54 PM   #515
EUVL is offline EUVL  Europe
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While it is an interesting point, it is of no issue here as long as the upper and lower JFETs track each other thermally, as is the case.

This thermal concept allows you a wider choice of devices at varying operating points.
It alleviates the need to operate at zero tempco.
If the FET is close to zero tempco by coincidence, so much better.


Patrick
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Old 20th December 2011, 08:56 AM   #516
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I had a question in mind about the CEN, since I read the article: I remember, that in your analysis of the F5, you point out that the 2SK170 and 2SJ074 are not true complementary, and suggested an asymmetric circuit to compensate for that.

Why in this topology it doesn't apply ? (Or is negligible)

Thanks,

Davide
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Old 20th December 2011, 11:09 AM   #517
EUVL is offline EUVL  Europe
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It applies also here, but as explained already in the article, Kirchoff's law guarantees i_in = i_out.
Whether there is equal current sharing between N & P JFET does not matter at all.

You have to bear this in mind -- it is not an amplifier. It is a current conveyor.
It just suffles current from input to output, while keeping Zin loa and allowing a high R_load.


Patrick
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Old 21st December 2011, 03:03 PM   #518
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I'm sorry if I've missed it, but has anyone tried SEN with PCM58 and what values should be used with this DAC.

Btw, great project, can't wait to test it
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Old 21st December 2011, 04:43 PM   #519
EUVL is offline EUVL  Europe
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PCM58 has a current output of +/-1mA.
Normal CD Player has 2Vrms outout ~ +/-2.8V.

Riv = 2.8V/1mA = 2.8k.
So choose 2.7k standard value.

JFETs with Idss > 6mA (BL grade) would be fine.


Patrick
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Old 21st December 2011, 09:42 PM   #520
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Thanks for the reply.

And you said earlier that "You can also use a pair of matched 2SK369 to replace 4x 2SK170s", and I have 2 x 2SK146 (which are supposedly 2 matched 2SK369 in one package), and if I understand correctly, I can build a mono SEN with one 2SK146.
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