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JLH 10 Watt class A amplifier
JLH 10 Watt class A amplifier
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Old Yesterday, 02:13 PM   #5151
Bigun is offline Bigun  Canada
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JLH 10 Watt class A amplifier
I've also been thinking about putting some drivers in my JLH, turning the outputs into discrete Darlington pairs in order to reduce the impact of beta droop on the 'phase splitter' device sitting at the heart of the amplifier.
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Old Yesterday, 04:32 PM   #5152
fredbloggstwo is offline fredbloggstwo  United Kingdom
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Hi Bigun,

this might give you some food for thought.

JLH-D16

Cheers

Mike
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Old Yesterday, 10:47 PM   #5153
Bigun is offline Bigun  Canada
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JLH 10 Watt class A amplifier
Thanks ! - - pitty you didn't use 2N3055's but overall the results are a vote in favour of discrete Darlington!
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Old Today, 01:05 AM   #5154
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by nigel pearson View Post
For years I have wondered why the Peter Blomley 1971 amplifier design never attracted comment. All the sage and intellectual advisors seem to have avoided it. I suspect it is simply soar grapes.
I think also because the architecture never made it into the text books - as an EE student in the eighties I designed and built a similar (but fatally flawed) amplifier that my supervisors considered completely novel.

And this was in a university at the cutting edge of microelectronics design.

I wish I'd seen Blomley's paper before hand!

Last edited by thoglette; Today at 01:07 AM.
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Old Today, 09:10 AM   #5155
nigel pearson is offline nigel pearson  United Kingdom
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Very good points raised. The Blomley seems worth tying if the supporters comments are true.

I find it a miracle the JLH can drive the output transistors as well as it does. I take the point about > 20 kHz working. As Lars at Nordost says " Humans do not hear to 20 kHz usually, However they do detect waveform shape of a filtered signal that rolls off above 20 kHz", that's as best as I remember.

Although we talked about it before. My BC327/337-40 2N3055 Indian JLH needed to drop at 160 kHz -3dB full power. Before fitting 33 pF that I suspect could have been smaller ( 10 to 22 pF ? ) a small rise in output was seen between 500 kHz and 2 MHz in the noise floor with no 33 pF fitted. It was about 3 dB at perhaps 1.5 MHz peak, it was mildly modulated. The drop at 2 MHz was steep which I took to be the ft plus other factors. I didn't try the unlimited version. Some say mildly unstable amps sound better, maybe? The argument is music is different and appreciates not having the corner removed. A slightly overshooting square wave ( no output choke ) in that theory is best as long as the amplifier recovers quickly. I have no idea if that is right.

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