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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 28th October 2019, 05:32 PM   #21
alexcp is offline alexcp  United States
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FS: one pair of Nelson Pass A40 PCBs
The power supply for the A40 is probably best built along the lines of the original article.

Since it is Class A, it draws a lot of current - about 1.5A per rail per channel - all the time. You will need a 250VA or better, 2x22V power transformer for each channel. One possible option in Europe is Amplimo type 78015 or 77015, rated for 300VA. A 25A+, 100V+ bridge rectifier and a pair of large - say 22,000uf @ 50V+ capacitors (if you feel like spending money, consider Mundorf HC type) - will complete the power supply for one channel. If you feel like spending even more, consider CLC filtering with another pair of capacitors and a pair of chokes in between for each channel.
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Old 29th October 2019, 06:19 AM   #22
gary s is offline gary s  Australia
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Alex, some questions for you.

1. You mention you have added a Zobel network as can be seen on the pcb artwork in post #13, C5 is 0.1uF but I cant read what value/rating the resistor is shown as R16 (Note, R16 on original schematic is an emitter resistor for output transistor Q7)

2. In post #17 you show a photo of the pcb, but the Zobel network components are not on that pcb - so I am assuming that is not the latest correct photo.

3. Also the Zobel network components are not on the Mouser project as far as I can see that you linked.
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Old 29th October 2019, 05:51 PM   #23
alexcp is offline alexcp  United States
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FS: one pair of Nelson Pass A40 PCBs
Gary,

Apologies for confusion here. The new boards have no Zobel network, as it was not implemented on the Nelson Pass’ board design as per the original article. The photos in post #17 are correct.

The confusion stems from the fact that my original boards, made years ago and shown in the photos attached to post #1, did have the zobel network implemented (R16/C5 on the silkscreen; should have been R20/C5). The motivation was that the board for the A75 has it, and there was some space available. For the new board, however, I reverted to the original design.

The shared project at Mouser has the resistor for the zobel network (R20, 10ohm 1W), but it seems the capacitor (C5, 0.1uF 100V) has vanished from the list. Sorry about this; I will update the project.
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Old 29th October 2019, 07:16 PM   #24
finwbu is offline finwbu  Finland
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Dear Alexcp

Please would you send me 4 pair of your PCB A40 to me?

Can i pay you with PayPal?

I will send you a private message.


Regards
Walter
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Old 29th October 2019, 10:00 PM   #25
gary s is offline gary s  Australia
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Hi Alex,

Thanks for clearing up the confusion on my questions. One can always add the Zobel network off the pcb.

Did you implement the Zobel network in your latest A40 build or leave it out?

Gary..
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Old 30th October 2019, 01:48 AM   #26
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FS: one pair of Nelson Pass A40 PCBs
Default Q11 pinout error in post #20 schematic

I spotted an error in my schematic in post #20 above - the LM334 current source is connected incorrectly. I am sorry I did not spot this one earlier.

In the schematic from post #20, the junction of D1, R8 and the base of Q3 is connected to the adjustment pin of LM334. It should be connected to the V- terminal - see the attached pictures. Because of that, when using LM334 as Q11 with the PCB, its adjustment pin and V- pin must be crossed. I apologize for this.

The markings "D G S" on the PCB are correct, and if you use a JFET or a depletion mode MOSFET as the current source, you can plug it in according to those markings.

On a positive note, you can use DN2540 depletion mode MOSFET in TO-92 package as Q11 on the PCB. Its pinout is "S G D", so it goes into the PCB with the flat side towards R8, not R9. I will post photos over the next couple of days.
Attached Images
File Type: png A40-Q11.png (5.1 KB, 63 views)
File Type: png LM334 datasheet.png (5.6 KB, 60 views)
File Type: png A40 pcb.png (31.8 KB, 61 views)
File Type: png LM334 pinout.png (5.0 KB, 62 views)
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Old 30th October 2019, 03:05 AM   #27
gary s is offline gary s  Australia
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Hi Alex,

Thanks for the correction here on Q11, you should correct the schematic with a revision # and repost that, referencing your post above and photo's so there in no ongoing confusion.

Cheers,

Gary..
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Old 30th October 2019, 04:02 AM   #28
alexcp is offline alexcp  United States
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FS: one pair of Nelson Pass A40 PCBs
Thank you Gary for the suggestion. Here it is:

This schematic corrects the error described in the post #26 above and replaces the schematic attached to post #20.

It also adds information on using LM334, DN2540N3, and J111/112/113 in place of Q11. Note that using a MOSFET or JFET as Q11, you need to determine the value of R9 experimentally, so that it sets the current thorough Q11 at 2..3mA.
Attached Images
File Type: png a40_sch.png (189.0 KB, 57 views)
Attached Files
File Type: pdf a40_sch.pdf (37.0 KB, 15 views)
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Old 30th October 2019, 04:23 AM   #29
gary s is offline gary s  Australia
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That was quick Alex, your revised schematic should be handy for all with those options.

Any clues as to what value to start with for R9 using the LM334 - I assume your testing will have you settled on a value - or are you still testing late at night there?
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Old 30th October 2019, 04:40 AM   #30
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FS: one pair of Nelson Pass A40 PCBs
Unlike FETs, LM334 is predictable, and for it R9 can be calculated using the formula from the datasheet. The formula gives about 22ohm for 3mA and 33ohm for 2mA. I will test it IRL and report.
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