Roender's FC-100 Rev.1 Group-Buy

[jprco]

Rudi, received the transformer today - very nice. Thank you. Also, like many others have noticed, the shipping was much more than you estimated and charged us. I will send you a Paypal transfer to cover the difference. You do more than enough to be out of pocket on these GB's. Jean

[pinnocchio]

Received the transfo today as well

Extremely well designed transfo. Good quality!

I will add an extra 5 euros to you for the extra shipping

Thanks for everything
Do

[Rudi_Ratlos]

Gentlemen, please do not refund me any money!

My kitchen scales has shown me a weight of 480 gr incl. packaging, but the offical post-scales has shown 540gr !

I ordered a new kitchen-scales and will remember this expense and my mishap concerning the transformer's weight, when I do the next round
of group-buy for the beautiful FC-100 amplifier.

Best regards - Rudi_Ratlos

[jprco]

Rudi, completed the shunt PCBs and tested the transfo. Maybe should post this in build thread rather than GB anyway - results:
Transfo: 120 VAC in, Left:Out 1/2 39.4 VAC, 3/4 39.4 VAC
Right: Out 1/2 39.6 VAC, 3/4 39.6 VAC
PCB (No load or 2K Load doesn't seem to matter that much):
Left: Out + 37.2 VDC, - 37.3 VDC
Right: Out + 37.0 VDC, - 37.2 VDC

Note: Canadian Hydro is 120 VAC instead of 115 VAC

[jprco]

Forgot to add that the Shunt heat sinks under 2K load are at about 50-55 degrees C.

[Rudi_Ratlos]

Jean: this is exactly, how it should be!
Go ahead, please!

Best regards - I will keep my fingers crossed for your build - Rudi

P.S. I love your pictures!

[Rudi_Ratlos]

I have been asked to match 2SK170 - transistors for Mihail's FC-100.
The 1st image shows the LTSpice - model of my test-rig, the second image shows the result, when I measure the Vgs of a 2SK170 DUT.

LTSpice tells me to expect a value of about 80mV, but my DMM shows a value of 630mV.
The deviation should not be so big, and I think that the 2SK170-LTSpice model that I am using is "too rough".
Does anyone have a current LTSpice modell of a 2SK170BL?

Best regards - Rudi_Ratlos

[mj777]

Hello Sir Rudi can you share the pcb lay out of the test rig, i need to much some 2sk170 for the fc-100.

regards,
marjohn

[AndrewT]

the input jFETs operate over a range of current.
That range is determined by the level of input signal.
The two halves of the LTP should "amplify" the two halves of the signal they each see by the same amount.
That requires the jFETS to be matched over a range of currents.

Set up an LTP jig with the Sources connected together and the gates connected together.
Each drain connects to supply with 0.1%, or better, resistors.
Apply a fixed source current using the gate voltage as a trim. Measure the Vdiff at the drains. Sweep the source current and see how Vdiff varies. That is matching for use in an LTP.

This is quite different from selecting Idss for use in a B1.

I selected Idss in a matter of a dozen hours (600 devices).
Then, I matched the devices for use as LTP pairs. That took me hundreds of hours.

[roender]

Originally Posted by AndrewT

the input jFETs operate over a range of current.
That range is determined by the level of input signal.
The two halves of the LTP should "amplify" the two halves of the signal they each see by the same amount.
That requires the jFETS to be matched over a range of currents.

Set up an LTP jig with the Sources connected together and the gates connected together.
Each drain connects to supply with 0.1%, or better, resistors.
Apply a fixed source current using the gate voltage as a trim. Measure the Vdiff at the drains. Sweep the source current and see how Vdiff varies. That is matching for use in an LTP.

This is quite different from selecting Idss for use in a B1.

I selected Idss in a matter of a dozen hours (600 devices).
Then, I matched the devices for use as LTP pairs. That took me hundreds of hours.

I second that. It's not an easy job and took many hours to closely match jfets.