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FS: one pair of Nelson Pass A40 PCBs
FS: one pair of Nelson Pass A40 PCBs
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Old 30th October 2019, 05:10 AM   #31
gary s is online now gary s  Australia
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Thanks again Alex, shouldn't you be asleep by now?
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Old 9th November 2019, 03:30 PM   #32
alexcp is offline alexcp  United States
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FS: one pair of Nelson Pass A40 PCBs
I have been asleep for longer than expected But I did test a bunch of LM334, DN2450 and J113 as current sources in place of Q11.

LM334 produces 2mA with the R9 value of 33ohm, as per the datasheet. Reducing R9 to 22 ohm increases the current to 3mA or so.

DN2540 gives 2mA with R9 around 680ohm, with small variation among a bunch of these MOSFETs from the same bag. Note there can be larger variation between different batches, which may require adjusting R9 value, but then the current is not that critical in this particular application.

J113 gives 2mA with R9 around 800ohm, with the standard value of 750ohm making the current somewhat higher. Again, there is some small variation between JFETs from the same bag, with more expected for transistors from different batches. Note that the J113 is rates at 35V of drain-gate voltage, which is just a small margin below A40's -32V power supply.
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Old 17th November 2019, 03:12 PM   #33
alexcp is offline alexcp  United States
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FS: one pair of Nelson Pass A40 PCBs
Default Example build

This is an example build of the A40 front end with 2N5551/2N5401 bipolar transistors, a DN2540 as Q11 (R9=680ohm, I(D1,D2)=2mA), RN55 resistors, Nichicon FW capacitors. Tested so far without the output stage ("NFB" connected to "-DRV" to close the feedback loop).
Attached Images
File Type: png A40 1.png (244.9 KB, 37 views)
File Type: png A40 2.png (268.3 KB, 35 views)
File Type: png A40 3.png (242.9 KB, 31 views)
File Type: png A40 4.png (250.2 KB, 32 views)
File Type: png A40 5.png (245.4 KB, 32 views)
File Type: png A40 6.png (243.5 KB, 12 views)
File Type: png A40 7.png (239.9 KB, 9 views)
File Type: png A40 8.png (246.2 KB, 12 views)

Last edited by alexcp; 17th November 2019 at 03:17 PM.
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