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Old 7th January 2006, 01:19 PM   #1381
Geoff is offline Geoff  United Kingdom
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Quote:
Originally posted by deduikertjes
I understand that you suggest to use differtent star points for different kind of earth's (signal/ other). I'm not enough of an engineer to determine which parts in the circuitry belong to which star point. Is there eny reference for that or can you explain?
See:

http://www.tcaas.btinternet.co.uk/jlhearthing.htm

The wiring arrangement shown is for a 1996 version but the principle is just the same for the 1969 original when operated from dual supply rails.
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Old 7th January 2006, 02:45 PM   #1382
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Wink a21 vs ljhood class a

thanks for the response to my question rmvgs.I have the circuit
diagram of the original a21 sugden from hifinews cir.1970 one day I will get around to building it ,and comparing to my hart electronics 1996(published in electronics world) 10w class a amp.If one looks at the circiut diagram the sugden is much more complicated and uses a kind of push-pull drive to npn output
stage.
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Old 8th January 2006, 11:46 AM   #1383
rmgvs is offline rmgvs  Netherlands
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Default not that more complicated

P Robertson, I wouldn't say the Sugden is that more complicated than the JLH. In essence I think the Sugden has also 3 gain stages if the output is seen as a Darlington-pair. For the jlh-2003, which has some extra transistors for regulating bias and offset, the differences in components-count vis-a-vis the sugden is again smaller. The Sugden is more efficient and can put out 2 times the idle-current, where the jlh has a figure of around 1,3-1,5. In other words: for 20 Watts RMS you need 1,1 Amps for the Sugden and around 1,7-2,0 Amps for the jlh (depending on the version you choose). Of course, both amps are inefficient as you compare it to for example a Hiraga which can still work in class-AB when choosing a small idle current. Another point: the Sugden article is written after the original jlh-article (1970 and 1969) and James Sugden explicitly refers to the article of John Linsley-Hood. The picture shows you a hard-wired version with all components (excluding power transformer and bridge) for one channel Sugden.
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Old 11th January 2006, 09:19 AM   #1384
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Default sugden class a

thanks for showing the pic of your amp rmvgs.I my try to consruct it on stripboard.Also from what you say the sugden is much more efficient than the jlh,which is a point in its favour.
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Old 11th January 2006, 10:32 AM   #1385
kesrmk is offline kesrmk  Lithuania
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Default CCS on LED/transistor? Why not?

Dear Geoff,
maybe I missed somth, but why not to use simplified CCS based on one transistor and one LED?

This is much simplier way compared to 2 transistors and 2 pots?
It is no easy to bias such thing...

Even Marantz using leds/diodes in power amp schematics for that purpose...
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Old 11th January 2006, 10:37 AM   #1386
kesrmk is offline kesrmk  Lithuania
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Default CCS on LED/transistor? Why not?

One more sample
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Old 11th January 2006, 12:17 PM   #1387
Geoff is offline Geoff  United Kingdom
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Default Re: CCS on LED/transistor? Why not?

Quote:
Originally posted by kesrmk
maybe I missed somth, but why not to use simplified CCS based on one transistor and one LED?
Hi kesrmk

In terms of component count, there is not much difference between the two transistor ccs and the LED/transistor version. I chose the former for several reasons.

In the dc offset ccs (Q5/Q6), the Vbe variation with temperature of Q5 alters the ccs current in such a way as to negate some of the output dc offset change due to temperature variations in Q3 and Q4. Thus there is less output dc offset drift with changing ambient temperatures and during warm up.

Also, JLH himself used this ccs arrangement in the input stage of another of his power amp designs and so I was keeping with something that the original designer had used.

The advantage with using the two transistor ccs to set the output stage quiescent current is that the reference voltage is the Vbe of Q7 (~0.6V). This is less than that for an LED ccs so the peak output voltage swing, for a given rail voltage, will be higher thus giving a (slightly) greater efficiency.

Geoff
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Old 4th February 2006, 08:13 AM   #1388
coffin is offline coffin  Taiwan
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Hi
I'm a newbie of JLH.
I'd like to try to bulld one of my own, so I spend a little time to draw a driver for it.....

The Q1/Q2 and R10 will mount on heatsink, using hard wire to connect the driver.

please kindly check if there's anything goes wrong or oscilate.
If all of you think it is OK, I'll post the solder PCB.

Click the image to open in full size.

cheers

Coffin
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Old 7th February 2006, 09:45 AM   #1389
rclarke is offline rclarke  Australia
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Coffin
Thanks for the PC layout. Where does VR3 fit in? What is its purpose? What value?
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Old 7th February 2006, 11:43 AM   #1390
coffin is offline coffin  Taiwan
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Hi

Please check this schematic, from JLH update:

Click the image to open in full size.

cheers

coffin
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