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Old 12th February 2005, 07:47 PM   #1101
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Talking Thanks a lot!

thanks a lot for the pcb!
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Old 23rd February 2005, 07:51 AM   #1102
RKH is offline RKH  United States
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Default Q3 Substitute?

I'm collecting parts to build an updated- JLH. Both the updated and high-power ESL versions call for a 2SC3421 for Q3. Mouser.com shows a TIP47 as a cross-reference match for the 2sc3421. Are there any opinions out there as to the suitability of this substitute?


Cheers.

Ryan
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Old 23rd February 2005, 08:14 AM   #1103
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Hi RKH,

Don't use a TIP for the phase splitter, its internal junction capacitances are too high.

It will work, but use the 2SC3421 or BD139 for reliably good results.

Genuine Toshiba 2SC3421 are available from Cricklewood Electronics London. They are reliable.


Cheers ......... Graham.
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Old 23rd February 2005, 02:17 PM   #1104
RKH is offline RKH  United States
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Default Thanks!

Graham,
Thanks for the advice. BD139s are easier to source here in the states so I'll go that route as a first attempt. If anyone knows where to find genuine 2SC3421s in North America, please give me a shout.

Cheers!

Ryan
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Old 24th February 2005, 07:02 AM   #1105
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hello,

after building my amp a jlh variation , the DoZ

using as output devices a pair of tip3055, i decided to improve it by puting another pair of tip3055 (so now we have 2 pairs of tip3055)

as i found the improvement was so great i even decided to put another paraleled pair, wich has improved the "precision" of the sound even more.

today i will probably try another pair, but this is getting expensive...

do you thik that if i try with 10 paraleled pairs of ..lets say bd139
the sound will be even more precise, since those are faster and there will be more of them so they will work "lighter"??

thanks for the answer, see you later!
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Old 24th February 2005, 07:31 AM   #1106
mikelm is offline mikelm  England
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this sounds interesting - graham maynard is doing something similar right now as well here...

Class-AABB output stage.

can you tell us what the total o/p bias current was doing ?

did it increase a little with each addition or did you adjust it down to the original level ?

mike
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Old 24th February 2005, 07:37 AM   #1107
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I built a headphone amplifier in class A with BD139/BD140.

Based on an Elektor class A headphone amplifier, but with 8 output devices.
After the first design Elektor came up with a second edition of the headphone amplifier a number of years later with 4 output devices instead of the original 2.

Mine delivered the entire output in class A, i used the amplifier on my DIY loudspeakers for some time.
I used the BD versions with the highest Ft for the amp.
It was my first class A amplifier and the sound was astonishing, even with only a 24va transformer and double LM regulators.

Seemed to me that part of the sonic quality was due to the extreme bandwidth of the BD devices.
Graham has the 3281 in his design. Very hard to come by, pretty expensive, and BD bandwidth is 4 times higher.
Sounds like a great idea to me.
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Old 24th February 2005, 07:53 AM   #1108
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wel the current in the DoZ version of jlh is controlled by a transistor so the shift in quiescent current was really very little if there is any, furthermore im doing no matching at all with transistors.
may be if you use a lot of transistors in the output , statistically the mean Hfe are very alike because of the large number used it tends more to a gaussian dsitribution.
may be there is a "chorus effect" , after all its more nice to hear a chorus of 20 singers tan only one (well i know it depends of....),
anyway i like the chorus of 8 transistors i have created

i'm using 30v at 1,5A , a little more than the recommended , because i think there is a small difference in sound definition.

the high ft of the bd139 is good for the resolution of the sound, but i'm afraid that the stability of the amp will be severely damaged...

i have heard of some expensive "faked" a class that claims to have 16 output transistors, but those are mosfets, and i didn't like that sound at all.

reading more i find that there is a builder that has constructed the jlh for esl but that used it actually for non electrostatic loudpseakers, common 8ohm speakers, and he has compared that with his friend version that uses 4 mj15003 instead of the 6 he actually uses , he has reported an improved sound too.

i wonder if geoff still reads this forum mey be he could bring to us some light .

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Old 24th February 2005, 08:06 AM   #1109
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Hola,

There is company here in Holland that builds amplifiers under the name Array.

The amplifiers have an encridible number of paralleled small power devices, they claim sonic benefit.

For my headphone amp i selected BD's from one batch, turned out there were only a couple that had a large deviation in Hfe.
With 0.50 ohm emitter resistors( 2*1 Ohm parallel) i thought it good enough to use the rest, with even average Hfe for the 140 and 139.
Mosfets in full class A are ok, class AB Mosfet stages are not.
(only my opinion)
BD's are so small that many can be placed close to eachother and signal traces are still small.
Threshold made solo amplifiers with 64 output Mosfets.

Hasta.
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Old 24th February 2005, 09:22 PM   #1110
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Good News!

i've finished the first test with 11 pairs of bd 139,after the whole day cuting wires and soldering...

The result is incredible!!! i have not listen to something like that long time ago...
much more precision in the voice, the bass are perfectly defined,an incredible improvement, no sign of unstability, increased sensibility...
this amp is a dream... mi final goal are 24 pairs (yes 48!!)
bd139, to give a good safety margin, because i think that the sound i so smooth and well defined that i don't think that the increased number qill give a sound improvement.

and this is cheaper , since an tip3055 equals more less 10 bd139

and the bd139 are more tan 10 times cheaper ....well i cant see any shortcommgs.

the sensitivity of the amp is greatly improved, this has to be treated carefully, for example if i put my hand 1 cm near the heatsink or the pcb some hum pases the loudspeakear, but i know how tu cut this pb out... so for now i am extremelly happy....

so i recommend you to give a try to this mod ( replacing hiagher power transistors by a lot of small ones)

i repaet the improvement is real , and very noticeable, i whish you could hear the diff on my amp!!!

if someone is interested in a more precise description of how this mod has improved the voice playback, just ask for it , i will be very happy to explain so.

bye , and i hope you can try it some day ....
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