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JLH Headphone Amp
JLH Headphone Amp
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Old 14th December 2017, 06:35 AM   #731
EUVL is offline EUVL  Europe
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There are other TO220 devices which are more linear.
For example 2SC4883.


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Old 14th December 2017, 09:06 AM   #732
Buzzy is offline Buzzy  Singapore
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Quote:
Originally Posted by EUVL View Post
There are other TO220 devices which are more linear.
For example 2SC4883.


Patrick
When you say linear does it mean that the transistor's gain is linear over a range of Ic values (by looking at the HFE vs Ic graph) ? Is this what is meant by linear ?

I have been reading online on how to bias transistor and how it works as an amplifier. But most of the stuff I read does not show how to use datasheets and what to look for when trying to use the BJT in an amplifier.
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Old 14th December 2017, 10:16 AM   #733
EUVL is offline EUVL  Europe
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Yes, hfe vs. Ic.


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Old 14th December 2017, 09:56 PM   #734
hotiron is offline hotiron  Scotland
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Stick some Mosfets in there and see how ye get on.
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Old 15th December 2017, 02:43 AM   #735
EUVL is offline EUVL  Europe
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Done that before.
All FET JLH Class A


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Old 15th December 2017, 02:52 AM   #736
EUVL is offline EUVL  Europe
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Incidentally, people only talked about this JLH 1979 HPA as if it were the one and only HPA design from John Linsley Hood.
It is partly because of the availability of low-cost (sometimes also "cheap") kits and PCBs on the internet.
And it is essentially a low power version of the JLH1969 Power Amp.

But there are other later designs from Linsley Hood that were specifically designed as Headphone amps.
For example the complementary BJT design from 1985 (circuit 2 from the first link).
http://www.startfetch.com/jlh/jlh-1985-headphone.pdf
A Paul Kemble web page - John Linsley Hood preamp designs.

Complementary BJTs are so good these days that there is no real reason for doing quasi push-pull, except for fun.




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Old 26th December 2017, 02:56 PM   #737
wushuliu is offline wushuliu  United States
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Quote:
Originally Posted by randomlf View Post
Just stumbled across this thread and bought one of these. So small and inexpensive, i couldn't resist. I don't understand a word of the instructions though.
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Old 12th January 2018, 08:17 PM   #738
wushuliu is offline wushuliu  United States
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Originally Posted by randomlf View Post
Finally arrived. I took another look at the ebay listing and whoo boy there are some 'instructions':

Quote:
The PCB is close to 200K variable resistor two 47K resistors, use a 18K, so the more linear circuits.
Kits will be multiple two 22P compensation capacitor connected in parallel with the resistor 2K2 has two holes above.
Circuit welding is completed, access to the DC input, adjust two 200K adjustable resistance, so that half of the VL, VR two test points on the GND voltage Vcc. For example, your input voltage is 15V, then, VL, VR should be 7.5V.
If you purchased the shop supporting the chassis, the four of MJE340G ON reverse-mounted pipe shop will be presented a thermal adhesive, reference PCB rear view of the power tube chassis via thermal plastic heat dissipation.
There are two small holes next to the potentiometer, it is ground, printing a copper wire potentiometer connected to the housing
Circuit adjustment is completed, it is recommended replaced with a fixed resistor as close to 200K adjustable. Of course, this step is not to be.
Er, anyone willing to translate that?
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Old 25th January 2018, 05:35 PM   #739
wushuliu is offline wushuliu  United States
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I think I figured out the above. Next question is - what's the lowest value I can use for the JLH output cap with a single rail power supply?
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Old 26th January 2018, 03:00 AM   #740
ammel68 is offline ammel68  United States
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JLH Headphone Amp
Why would you even buy that particular kit that uses a large output coupling cap and comes with such goofy "instructions"??

Most people, including myself, go with this kit or something similar:
GZLOZONE JLH HOOD1969 Class A Headphone amplifier Kit / Pre-amplifier Kit | eBay
Best $20 I've spent.
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