The David N.J.White 100W MOSFET amplifier - diyAudio
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Old 13th April 2014, 02:32 PM   #1
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Default The David N.J.White 100W MOSFET amplifier

This is an old project that I never got around to finishing, the PCB's have been lying around for donkeys years. I do remember testing them individually and setting the bias but they never saw action as a stereo pair.

Now, they have been built into a Dual Mono pair. As the transformers were bought at different times their characteristics are slightly different. Although both nominally 35-0-35 at 250VA, the DC voltage to the two amps is slightly different. One has 50-0-50 and the other 53-0-53.

AFAIK this will not affect them in any way other than the fact that one will clip slightly earlier than the other.
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Old 13th April 2014, 02:42 PM   #2
The Dastardly Dad of Three
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Interesting ... Looks like a classic cottage industry britamp from the 80's - any selling points from the designer on this one ?
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Old 13th April 2014, 02:46 PM   #3
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It's only going to be doing bass duties which it is pretty good at.
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Old 14th April 2014, 01:44 PM   #4
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This wasn't intended as an amplifier comparison thread. I'm simply asking will the difference in rail voltages affect the amps.
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Old 14th April 2014, 02:03 PM   #5
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Quote:
Originally Posted by kasey197 View Post
Interesting ... Looks like a classic cottage industry britamp from the 80's - any selling points from the designer on this one ?
It is based on the original Hitachi Lateral FET data sheet. JLH implemented it in his 80W MOS-FET amplifier as did Maplin with their 150W MOSFET amplifier.

I beleive this comes from about the early 90s.

It's still a very competent amplifier that will beat most commercial offerings hands down.
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Old 14th April 2014, 02:26 PM   #6
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It's nothing like the Hitachi data book circuit, it uses an op-amp as input stage and providing most of the voltage gain then the output stage provides a low amount of gain to boost the limited swing from the op-amp.

In practice, no, you won't see any difference in performance with the rail difference betwen channels and your assumption is correct.

As a building standards comment, it looks good but green/yellow coloured wire is reserved for safety earth connections only. Also you should insulate your switch terminals.

It looks like the amplifier ground is not connected to safety earth, I think you had some ground loop problems on another thread, but it's worth trying to get right for safety reasons.
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Old 14th April 2014, 02:28 PM   #7
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Ok so I don't think the power rail differences are going to matter much.
There's something quite interesting about the amplifier schematic tho that's not so run of the mill..... For starters the op stage is not operated as a follower (output is taken from the drains) which is a stark contrast to the datasheet amps but there is localized feedback and loop feedback. The way the op stage is biased is also interesting ....

If you have the article would be worth a post IMO.....
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Old 14th April 2014, 03:11 PM   #8
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The op-amp is set up as a follower. TR1 and TR3 are current source/sink and form part of the bias network as well as feed the drivers. Output stage is CFP with gain.
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Old 14th April 2014, 03:28 PM   #9
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The PDF article found after a casual search on the forum:
Anyone recognise these ?
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Old 15th April 2014, 12:21 AM   #10
bluevas is offline bluevas  Indonesia
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This is the other schematic WNA Class AB 125W Mosfet Amp Schematic Discussion

how to increase the power into 250 watt?

best regards,


josh
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