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NAP250 amp boards & regulator boards
NAP250 amp boards & regulator boards
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Old 5th November 2019, 12:14 PM   #1
JeffYoung is offline JeffYoung  Ireland
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Location: Ireland
NAP250 amp boards & regulator boards
Default NAP250 amp boards & regulator boards

I'm putting together a small group buy of NAP250 boards.


This is a true nostalgia project with considerable research done into the original circuit and device selection. I'm even deleting the silkscreen and solder-mask on the boards. (It will be a two layer board with plated-through holes and a lead-free HASL finish, so not entirely old-school).

Click the image to open in full size.

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Click the image to open in full size.


I have designs for both the original regulators (again, without SOA), and an inverted one which references the VAS to ground, greatly increasing its PSRR at high frequency.

See more here:

NAP250 clone

Please copy the last-posted list and add your own name, along with which regulators you're interested in.

Cheers,
Jeff.
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Old 5th November 2019, 12:16 PM   #2
JeffYoung is offline JeffYoung  Ireland
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Join Date: Jul 2017
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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 legione 2 amp (original_reg, inverted_reg, or both?)
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Old 7th November 2019, 01:05 AM   #3
gary s is offline gary s  Australia
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Hi Jeff,

Any clues as to where to source the BC239C input transistors and either of the output TO3 metal can types you have on the schematic. Not stocked at Mouser. All the other transistors are in stock in qty at Mouser , so no problems with those.

Or, have you further alternatives, should not be too hard for the inputs TR1 and TR2. Maybe the output stage TR11 and TR12 need to be as close to original design semi's as possible.

Look forward to your thought on these devices.

Gary..
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Old 7th November 2019, 01:06 PM   #4
JeffYoung is offline JeffYoung  Ireland
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NAP250 amp boards & regulator boards
Hi Gary,

The NAP is like a treasure hunt.

I got my BC239Cs (and ZTX108s) from Langrex. (They're mostly a vintage tube supplier, but also stock some semis.)

I got NOS Siemens BDY58s from NJSemi. Ask for Ron. (FWIW, they also have Harris IRFP9240s.)

I got NOS BUV20s from 2 different sellers on eBay. Much care is required here -- the BUV20s are actively counterfeited. (And FWIW, the BDY58s were factory spec in early units, whereas the BUV20s never were.)

The most important transistors to this design are probably TR4 and TR6 (for their unusually high Cob), followed by the drivers and output devices.

A lot of folks swear by the MJ15003 for output devices, but they fly in the face of the speed JV was aiming for. You can colour me somewhat skeptical regarding them.

Cheers,
Jeff.


One of my BUV20s opened up to ensure it was what it was supposed to be inside:

NAP250 amp boards & regulator boards-buv20s-jpg
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File Type: jpg BUV20s.jpg (236.4 KB, 1355 views)
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Old 7th November 2019, 02:16 PM   #5
aster1x is offline aster1x  Greece
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How do you connect the two grounds GND_A and GND_B with respect to the input signal ground and the chassis ground?
Do you connect the GND_A at the mid tap of the transformer?
Do you connect the GND_B at the input signal ground or at the speaker output ground?
Do you float the input signal ground from the output speaker ground to isolate the high currents from the low level signal currents?
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Old 7th November 2019, 04:40 PM   #6
JeffYoung is offline JeffYoung  Ireland
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NAP250 amp boards & regulator boards
Both GND_A and GND_B go back to the star ground (as do the two GNDs on the amp board -- one of which is connected to the input signal ground).

The star *should* be a short 'T' from the wire between the two smoothing caps, but Naim originally used the negative speaker output, and then the wire between the caps without a 'T'. The latter is probably sufficient (and is what I plan on using), but I wouldn't recommend the former.
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Old 7th November 2019, 05:28 PM   #7
JeffYoung is offline JeffYoung  Ireland
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Join Date: Jul 2017
Location: Ireland
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 legione 2 amp (original_reg, inverted_reg, or both?)
jean michael 4 amp, 4 inverted_reg
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Old 7th November 2019, 08:43 PM   #8
gary s is offline gary s  Australia
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Hi Jeff, appreciate the info on the Semi's.

Will look into it.

regards,

Gary..
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Old 7th November 2019, 08:47 PM   #9
gary s is offline gary s  Australia
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Join Date: Nov 2002
Location: Australia
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
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Old 8th November 2019, 06:55 PM   #10
Quantensprung is offline Quantensprung  Germany
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Location: old roman city on the Rhine CCAA
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
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