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NAP250 amp boards & regulator boards
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Old 9th November 2019, 03:00 AM   #11
skunark is offline skunark  United States
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Join Date: Sep 2011
Location: Pacific Northwest
NAP250 amp boards & regulator boards
JeffYoung: 6 amp, 2 original_reg, 4 inverted_reg
lohk: 2 amp, 2 inverted_reg
john.luckins: 2 amp, 2 inverted_reg
avtech23: 2 amp, 2 inverted_reg
ultima legion: 2 amp (original_reg, inverted_reg, or both?)
jean michael: 4 amp, 4 inverted_reg
gary s: 2 amp, 2 inverted_reg
Quantensprung: 4 amp, 2 original_reg, 2 inverted_reg
Skunark: 4 amp, 2 original_reg, 2 inverted_reg
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Old 9th November 2019, 08:42 AM   #12
gary s is offline gary s  Australia
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Hi Jeff,

Looking at chassis options, can you give me the dimensions of the amp and reg pcb's?

Also I assume on the mains side of the transformer Naim just had an IEC input socket, mains fuse, mains switch into the transformer primary.

What VA rating was the transformer, and what were the voltages on the sec windings?

What did they use for a bridge rectifier and what did they have for the main PSU caps?

Sorry for the questions if you have covered this elsewhere, but could not find it.

The other question is did they have a separate regulator pcb for each channel - hence the need for 2 off for a stereo amp.

Regards,

Gary..
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Old 9th November 2019, 12:42 PM   #13
JeffYoung is offline JeffYoung  Ireland
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NAP250 amp boards & regulator boards
Amp PCBs are 127mm x 89mm
Regulator PCBs are 121mm x 89mm

Note that the Naim temp compensation relies on a constant temp inside the case. So a heavy case without any ventilation will work best. That being said, a lot of folks have built clones ignoring this.

Here's a good picture of the insides/layout of a factory example:

Click the image to open in full size.

(Note that this is using Naim's earlier star ground on the speaker terminals, which I don't recommend. Better practice would be to put it between the two capacitors.)

The transistors/boards are mounted using aluminium C-section which is then bolted to the bottom of the case (with some thermal paste). You can make your own, or you can get nice pre-drilled, tapped and anodised ones from Les at Avondale Audio.

I think the transformers were 450VA; some argue they were 500VA. 2 x 41V secondaries. (A 41-0-41 centre-tapped will also work.)

Standard full-wave bridge rectification using block rectifiers bolted to the case. One smoothing cap per rail. Factory spec was Sic Safco FELSIC CO39 63V 15,000uF; most people are using 22,000uF Kendeils these days.

IEC, fuse and power switch. No soft-start or inrush-limitation. Not even an RFI suppression cap. (Julian Vereker even campaigned against the EU EMC directives as he thought they killed the music.)

Cheers,
Jeff.
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Old 9th November 2019, 12:47 PM   #14
JeffYoung is offline JeffYoung  Ireland
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NAP250 amp boards & regulator boards
We've got it down to a reasonable EUR 13.55/board, so I'm going to plan on ordering boards Monday.

(Folks can still sign up as EuroCircuits sometimes sends me extras, but only folks on the list as of Monday will be guaranteed boards.)

Cheers,
Jeff.
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Old 9th November 2019, 08:38 PM   #15
gary s is offline gary s  Australia
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Thanks for the info above Jeff, amp insides is neatly wired as well.
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Old 12th November 2019, 08:32 PM   #16
JeffYoung is offline JeffYoung  Ireland
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NAP250 amp boards & regulator boards
I've attached the BOM I'll be using for the amp boards. Here's the stuffing guide:

NAP250 amp boards & regulator boards-youngnap_stuffing-jpg
Attached Images
File Type: jpg YoungNAP_stuffing.jpg (344.1 KB, 304 views)
Attached Files
File Type: zip YoungNAP_BOM.csv.zip (1.4 KB, 17 views)
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Old 12th November 2019, 08:50 PM   #17
JeffYoung is offline JeffYoung  Ireland
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NAP250 amp boards & regulator boards
The original Naim's used automotive style connectors for the various board connections. I'm an old-car guy so I've had a lot of experience with them -- not all of it good.

The boards therefore have holes sized for soldering in the pins from MIL-DTL-26482 II connectors. These are the ones you want (male for the board and female for the wires):

https://www.mouser.ie/ProductDetail/...52BzLVXA%3D%3D

https://www.mouser.ie/ProductDetail/...58AdxsdQ%3D%3D
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Old 12th November 2019, 09:13 PM   #18
gary s is offline gary s  Australia
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Thanks for that Jeff.

I assume you will repeat for the reg boards.

Just a small comment, can you show the stuffing guide without the black background - easier to look at when printed out and saves on black ink as well.
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Old 12th November 2019, 09:45 PM   #19
JeffYoung is offline JeffYoung  Ireland
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NAP250 amp boards & regulator boards
Yep, regulators to follow.

I've attached a PDF for printing.
Attached Files
File Type: pdf YoungNAP_stuffing.pdf (85.5 KB, 41 views)
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Old 12th November 2019, 10:01 PM   #20
gary s is offline gary s  Australia
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Thanks again Jeff, you are a champ.

For the MIL style connectors you link, how many do we need to do all 4 pcb's for a stereo chassis, will add them to a Mouser order I will be finalising today hopefully.
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