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Sony VFET version 2 AL Boards Build Blog

Posted 8th August 2010 at 10:29 PM by Tea-Bag
Updated 25th January 2016 at 04:35 PM by Tea-Bag

In the rare case you happen upon matched pairs of these transistors, and you like drilling, and you think my boards may be Ok, then go ahead and read this blog.

As a starting point, we settled on this schematic for the working amplifier. Some modifications were done from the original, and Botte made some changes to get a slower turn on rate for the boards.

Click the image to open in full size.

Note, R37,R38 and C1 and C2 have been changed. However, feel free to use original values.
Also note, for greater viability of use of JFETs beyond 8ma IDSS, source resistors can be used here ( I used 10R with 9ma pairs) - Otherwise jumper this location.


Q13 and Q14 are BC550c and BC560c. Originally Toshiba bipolars were used on my boards, but they were not stable in voltage and gain suffered on the boards. The boards have since had the pads altered to remove them. The BC bipolars work like a charm.



We started building this amplifier (Botte, Flochhini and myself) with the Front end boards in mind. The intent of the boards was to allow for use as a pre-amplifier standalone, although I have not personally tested it's use for that.

Building this alone, it is possible to get the offset fairly good, assuming you have matched KJFETs.

Here is the front end (both sides, shorts by Gbethe). Board layout by CRT and myself
Board size is 36mm x 175mm
Click the image to open in full size.

Here is the Output Stage - board size is 54mm x 285mm
Click the image to open in full size.

So, here is a schematic to show what is really missing here, and what is added.

Click the image to open in full size.


Current measurements should be taken across a power supply with DMM on each rail assuming a resistance in PS .1R, then it will work like the Article description.

Here is the Output stage pre drilling. I used a small and large sharpie to outline the holes, and then generally made holes 140% the size they needed to be in the end, to allow for some room for errors in drilling, and to avoid shorts if the teflon covering of the FETs did not work.

Click the image to open in full size.

Botte version.
Click the image to open in full size.
Here is the built up version showing the connectors, the Aluminum Angle mounting piece.

Click the image to open in full size.

From Botte's fine work. Note how practical he is with his money, using the TO-247 IRFP's instead.

Click the image to open in full size.
Recommended
BOM Parts

Here is an important piece. The boards are ideally connected via the following 2x10x2.54 headers and pins.
PN are
4 - PPPC102LJBN-RC - Digikey - S5563-ND
4 - PBC10DBAN - Digikey PN- S2111E-10-ND

4- Front end Heatsinks - 637-10ABPE or similar
TL431ACLPR - Buy extra, if something will short, it will likely be these that die. The TL431B were found not to work well. Use "A" type.

For C1,C2, and C7,C8 winder spacing has been made for 50v Elna Silimic Caps. C1 and C2 are of larger value in this circuit. 50V as Botte deemed there might be more than 35v hitting them. I used 50v Panasonic FM throughout, and bypassed with small wima caps.


You should do your best to protect from shorts.
I put teflon around all the bolts, put them on pins to if you have the correct diameter teflon.

Click the image to open in full size.


Here is a few short videos of a working channel
https://youtu.be/kWSlbYg01pQ

https://youtu.be/4KhfLfaWXq0

GB Thread for board, if you've made it this far.
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