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NAP250 amp boards & regulator boards
NAP250 amp boards & regulator boards
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Old 12th November 2019, 10:19 PM   #21
JeffYoung is offline JeffYoung  Ireland
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NAP250 amp boards & regulator boards
Depends. The amp board has 9, but only 7 need populating if you're using the regulators. In fact you can get away with 6 if you don't carry both grounds back to the star ground -- but I wouldn't recommend that for the amp boards.

The regulator boards have 6. Again you can use only 5 if you don't carry both ground back to the star-ground, and it would be less of an issue for the regulator boards.

One stereo set with regulators and "proper" grounding therefore requires 26. 24 with "less pristine" grounding and 22 with "dodgy" grounding.

Cheers,
Jeff.
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Old 12th November 2019, 10:32 PM   #22
JeffYoung is offline JeffYoung  Ireland
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NAP250 amp boards & regulator boards
A few words on one of Naim's quirks: there's no Zobel network on the output, instead relying on the inductance of the speaker cables.

There was some suggestion that Naim did this to sell their own speaker cables. Whether true or not you certainly don't need to use Naim speaker cables... but you DO NEED a minimum inductance in your speaker cables.

The specs of Naim's cables:
Quote:
Capacitance: 16pF per metre
Resistance: 9 milliohms per metre
Inductance: 1uH per metre

Minimum length: 3.5 metres per channel
Maximum length: 20 metres per channel (note that longer lengths can be used up to around 25 m but then some small signal loss must be expected)
The things to note are the inductance and the minimum length. (The minimum length also means don't power up the amp with no speaker cables.)

Nearly any "normal" speaker cable will meet those specs, but some "avant garde" woven cables (such as Kimber Kable) will not. If in doubt, check the inductance specs of the cable.

Cheers,
Jeff.
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Old 13th November 2019, 04:54 AM   #23
gary s is offline gary s  Australia
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Thanks again Jeff for details in both your above posts.
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Old 13th November 2019, 04:05 PM   #24
JeffYoung is offline JeffYoung  Ireland
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NAP250 amp boards & regulator boards
Next instalment: original regulator BOM and stuffing guide.
Attached Files
File Type: pdf YoungREGORIG_stuffing.pdf (73.9 KB, 9 views)
File Type: zip YoungREGORIG_BOM.csv.zip (770 Bytes, 5 views)
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Old 13th November 2019, 05:47 PM   #25
TungstenAudio is online now TungstenAudio  United States
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It has been fun to watch a GB take place for one of my favorite amplifiers. I have an old Olive era NAP 250 that has undergone some careful modification. It still sounds wonderful, although my First Watt clones are getting a lot more playing time these days.
I also use a Naim XCD2 and NAC 82 in my system. I built a pair of custom power supplies using two of these: NAIM style Full Aluminum preamp Chassis / Power Amplifier Enclosure 430*90*358mm | eBay
This case has plenty of room to hold a pair of 300VA toroidal transformers, which would be my recommendation. The NAP 250 uses its entire case as the heatsink for the regulator and amp boards. The output transistors may be bolted onto thick wall square aluminum tubing to transfer heat to the case.
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Old 14th November 2019, 05:04 AM   #26
gary s is offline gary s  Australia
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Thanks for the tips TungstenAudio - appreciated.
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Old 14th November 2019, 05:15 PM   #27
JeffYoung is offline JeffYoung  Ireland
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NAP250 amp boards & regulator boards
I've built all my Pass & FirstWatt clones with Toroidy transformers, and they're great.

But I remember in all my Naim trawlings someone recommending a transformer builder in the UK, and that they used the nice matte-black wrappings as the original Naim.

Only now I can't remember who it was, and Google isn't helping me much.

Anyone know of any clues?

Thanks,
Jeff.
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Old 14th November 2019, 08:40 PM   #28
John Luckins is offline John Luckins  Europe
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Terry at Canterbury Windings did matte black wrappings on my 1200VA Toroids. They are also electrostatically screened and have a GOSS band. Worth googling and dropping him an email.

John
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Old 14th November 2019, 10:00 PM   #29
JeffYoung is offline JeffYoung  Ireland
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Thanks, John. I've dropped him a line....
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