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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 20th April 2018, 03:19 AM   #11
alexcp is offline alexcp  United States
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FS: one pair of Nelson Pass A40 PCBs
Just sent you a PM.

Quote:
Originally Posted by Freecrowder View Post
If there are boards still available I would like a pair.
let me know how to proceed.

Thank you
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Old 19th June 2018, 01:21 PM   #12
Freecrowder is offline Freecrowder  United States
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FS: one pair of Nelson Pass A40 PCBs
If I'm correct there are some differences in this board vs. the original boards in the first article? The extra ground connection and possible artwork around the FET.
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Old 19th June 2018, 03:34 PM   #13
alexcp is offline alexcp  United States
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FS: one pair of Nelson Pass A40 PCBs
Yes, you're right - thank you for spotting it.

There are two minor differences.

First, the original board uses the Source-Drain-Gate (SDG) pinout for the JFET, while my board uses the GSD pinout, which matches the LM334 current source that I used. As Nelson Pass wrote in "Part Substitution", his second article on A40: "note that the source pin of the Jfet is attached to R9, and there has been some confusion about that, with some different pinouts on the 2N5248".

Second, I added a Zobel network to the board, which has that extra GND terminal. Its other end is connected to the FB terminal (the right side of R5). The whole thing can be left out.

I attach the artwork copied from the original "The A40 Power Amplifier" article by Nelson Pass and the artwork of my board for comparison.
Attached Images
File Type: png A40 orig.png (237.3 KB, 369 views)
File Type: png A40.png (78.1 KB, 360 views)
File Type: png A40 orig 2.png (296.3 KB, 353 views)
File Type: png A40 2.png (162.3 KB, 355 views)

Last edited by alexcp; 19th June 2018 at 03:54 PM.
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Old 20th June 2018, 06:00 PM   #14
Eric is offline Eric  United States
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FS: one pair of Nelson Pass A40 PCBs
Here is the document from Audio Amateur about the PCBs and the schematic.
Attached Files
File Type: pdf a40PCBError.pdf (34.7 KB, 51 views)
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Old 20th June 2018, 07:01 PM   #15
alexcp is offline alexcp  United States
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FS: one pair of Nelson Pass A40 PCBs
Quote:
Originally Posted by Eric View Post
Here is the document from Audio Amateur about the PCBs and the schematic.
Thank you Eric! Yours is a curious document.

It concerns the PCB that (I understand) was being sold in 1997. The amplifier input network includes the usual (although some say harmful to stereo imaging) low pass filter. The original article says:
Quote:
... we start with C1 forming an input rolloff filter in conjunction with the typical 600 Ohm to 1k Ohm source impedance. Lower frequency rolloffs can be achieved using higher capacitance values and higher source resistance values.
However, the board mentioned in the document you provided was made inconsistent with the schematic and the above description: the rolloff filter was formed by C1, the source impedance, and R1. Not a big deal, but still an inconsistency.

My boards (which I still have a few left, BTW) are consistent with the schematic, including the input rolloff filter and the Zobel network, which is on the schematic but not on the original board.
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Old 20th June 2018, 09:38 PM   #16
Eric is offline Eric  United States
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FS: one pair of Nelson Pass A40 PCBs
Ah - I did more of a side-by-side comparison between the two circuits that you posted and spotted the differences. They appear to be fairly minimal. In the boards that I have, there was a trace error for which a correction was issued. At some point, Nelson indicated that the difference in the PCB from Audio Amateur was mostly irrelevant. Since I was unable to open the Gerber file you posted, I wasn't sure of the source for your board.

Either way, this is still a nice amp!
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Old 21st October 2019, 05:47 PM   #17
alexcp is offline alexcp  United States
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FS: one pair of Nelson Pass A40 PCBs
Default New batch of A40 boards arrived

UPDATE: a new batch of A40 PCBs arrived. Unlike my first boards, these are double sided (eliminating the need for one wire jumper) with plated-through holes and solder mask and silkscreen on both sides.

These boards also follow the original article more closely; the only difference is the pinout of Q11, providing for the use of LM334 as the current source.

The price is the same: US$10 per pair of boards plus shipping.

PM me if interested.
Attached Images
File Type: png A40 - 1.png (562.9 KB, 184 views)
File Type: png A40 - 2.png (603.1 KB, 94 views)
File Type: png A40 - 3.png (445.4 KB, 73 views)
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Old 27th October 2019, 02:29 PM   #18
mauric is offline mauric
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Default please you send me 1 pair to Switzerland?

Dear Alexcp

Please would you send me one pair of your PCB A40 to me?
i will pay you with PayPal?

mauric@gmx.ch

Regards
Mauri
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Old 27th October 2019, 03:51 PM   #19
alexcp is offline alexcp  United States
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FS: one pair of Nelson Pass A40 PCBs
Sent you a PM.
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Old 27th October 2019, 04:40 PM   #20
alexcp is offline alexcp  United States
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FS: one pair of Nelson Pass A40 PCBs
Attached is the schematic for the board only. The only difference from the original article's is that Q11 is replaced with an LM334 current source and R9 is adjusted accordingly.

Also, here is shared project at Mouser. It has all parts for one channel, including the output power Darlingtons, but not the power supply. All parts are currently available at Mouser. The project is just to give some guidance - if you wanted to build A40 for some time, you probably have some parts already.
Attached Images
File Type: png a40.png (124.7 KB, 80 views)

Last edited by alexcp; 27th October 2019 at 04:52 PM.
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