Salas hotrodded blue DCB1 build - Page 152 - diyAudio
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Old 29th November 2011, 10:47 AM   #1511
AndrewT is offline AndrewT  Scotland
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you have me re-thinking.
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Old 30th November 2011, 12:19 PM   #1512
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Is there any advantage in replacing the 2sk170-BL with the 2SK369-V ? Do I have to change the psu?

D.
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Old 30th November 2011, 02:55 PM   #1513
Salas is offline Salas  Greece
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You will gain in linearity due to large Yfs, you will lose bandwidth due to large Ciss, you will need TO-92 sinking due to large IDSS. You will want even less source impedance (small volume pot) to stay ''fast''. PSU can take much more, no need changing.

P.S. Your stash is now targeted by the unobtainium FET Pink Panther team.
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Old 1st December 2011, 07:00 AM   #1514
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:-) You can find nice stuff here in Japan, sometimes.

Andrew, another think that I noticed is that inverting the order of two JFET, with similar Idss on the measurement setup you recommended, in one case you have higher Vgs then in the other case, but the value is always positive. I guess the right order is the one with the lower value.

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Davide
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Old 1st December 2011, 08:30 AM   #1515
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Let me see if I got it right:

1) The lower jfet is the CCS, in the mesmerize board these are the external JFET.
2) The CSS sets the current for the upper JFET.
3) The upper JFET should run at a current that is not larger than his Idss.
4) So that's why we want the lower Idss device to be the CSS (Lower in the schematic, external in the board)
5) What we see as offset is the Vgs of the upper device at the current forced by the CSS.
6) Hence if they are perfectly matched the offset will be zero.

Learning is more difficult than building things :-)

D.
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Old 1st December 2011, 08:31 AM   #1516
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I forgot:

7) Thermally coupling the devices, should help them to track each other Idss vs ambient temperature.

D.
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Old 1st December 2011, 10:18 AM   #1517
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Nikon1975 View Post
1) The lower jfet is the CCS, in the Mezmerize board these are the middle pair of JFET.
2) The CSS sets the current for the upper (Follower) JFET.
3) The upper JFET should run at a current that is not larger than it's Idss.
4) So that's why we want the lower Idss device to be the CSS (Lower in the schematic, )
5) What we see as offset is the Vgs of the upper device at the current forced by the CSS.
6) Hence if they are perfectly matched the offset will be zero.
7) Thermally coupling the Follower to it's CCS device, should help them to track each other Idss vs ambient temperature
I have corrected your 7point statement and the correct version is shown above.
You were almost right.
The DCB1 and Hyp and Mez all have the 4 jFETs in exactly the same layout.
The inner pair are the two CCSs, the outer pair are the Followers.
If you turn the PCB over you will see all 4 middle pads connected together and the connecting trace goes off to the -ve rail.
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Last edited by AndrewT; 1st December 2011 at 10:21 AM.
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Old 1st December 2011, 03:16 PM   #1518
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Thanks!

Question: why in this project higher currents do not give better results? Or parallel devices?
D.


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Old 1st December 2011, 03:39 PM   #1519
Salas is offline Salas  Greece
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I wrote higher linearity, more input capacitance, dissipation. A step forward and two nuisances. You pick.
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Old 1st December 2011, 08:32 PM   #1520
Nick77 is offline Nick77  United States
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I finally got things installed into a Hammond case and the front panel is Lacewood.

I have had this DCB1 board in my desk drawer for at least six months, I was so content with my Pass diy B1 with TX2575 and Sonicaps w/teflon bypass that i just didnt have any incentive.

I am SO glad I took the plundge, this thing rocks and eaisly dethrones my current B1. As been said before the soundstage is scary big, low level detail is off the charts. I am listening at much lower levels with all the detail and resolution.

Build list includes:
Mundorf AG caps
TX2575 220r
Caddock 132 1m
Caddock TF020 220k
Antek 100va

Another big thanks to Salas,Teabag,Blues and Ed.

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