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Old 11th December 2019, 12:48 PM   #91
JeffYoung is offline JeffYoung  Ireland
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NAP250 amp boards & regulator boards
Hi Klaus,

My research also led to the FR103 for clamp diodes, although they're obsolete and I couldn't find a source for them. I did come across several pictures of toasted FR103s, so the 1N5621 seemed like a reasonable substitute.

I'm less clear on the Baxandall. Naim did appear to use the 1N4148. While my sims show it having to dissipate 200mW running full whack into a 3ohm load (cf: Linn Isobariks), I've never seen one toasted, so I don't think that would have been enough to cause me to deviate from the original spec. So why did I?

Oh to still have the memory of a younger man....

Cheers,
Jeff.
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Old 11th December 2019, 04:03 PM   #92
JeffYoung is offline JeffYoung  Ireland
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I did some more research on the Baxandall. While I didn't find much, I did find a recommendation from @Elvee that speed matters.

So originality favours the 1N4148.

But if you'd like the possibility of a bit more performance and a bit more survivability, the MUR120 looks to be a good candidate.

Cheers,
Jeff.
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Old 11th December 2019, 04:27 PM   #93
lohk is offline lohk  Europe
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One more funny detail about the NAP250 - it may have been discussed before, but probably a long time ago:
The input socket of the Classic 250 is a single normal three pin XLR socket, wired L, R, Ground. The cable is, or at least was when I opened one more than 30 years ago, a bog standard mains cable, 1.5mm2, blue, black and yellow/green, unscreened.

Conclusio: Consequently low impedances make expensive cables unnecessary.
I still believe that, although with many components it does not seem to be that easy.
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Old 11th December 2019, 04:37 PM   #94
lohk is offline lohk  Europe
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Last edited by lohk; 11th December 2019 at 05:00 PM. Reason: error
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Old 12th December 2019, 04:03 PM   #95
lohk is offline lohk  Europe
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The NAP200 - still quasi complimentary, also due to the clearly visible bax diode - uses a 12 Ohm resistor for the Zobel part (probably with the usual 100nF). Also the bias tracking transistor sits underneath the board (maybe touching the case).

Click the image to open in full size.
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Old 12th December 2019, 04:15 PM   #96
lohk is offline lohk  Europe
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And it is the same for the NAP300

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Old 12th December 2019, 10:48 PM   #97
John Luckins is offline John Luckins  Europe
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Boards arrived here. Look great. Thanks Jeff.
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Old Yesterday, 04:03 AM   #98
skunark is offline skunark  United States
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Boards arrived, thanks again!

Jim
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