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Old 3rd November 2007, 11:31 AM   #21
EUVL is offline EUVL  Europe
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If you allow for full swing in the diff pair without forward bias (which is unlikely to happen in normal usage), then you should use Idss=2xbias, hence approx. 9mA.
BL would be fine; V will also do. Whatever you can still get.

And any ultra bright blue LED from Reichelt will be more than happy at 0.5mA. In fact, I run them in series with a 10k resistor at 5V, and I still find them much too bright.


Patrick
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Old 3rd November 2007, 12:14 PM   #22
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I don't know what's the fuss ;

Papa already granted Babelfish J as pretty close iteration of Aleph J ;

there is not much of my merit , but more of his ......... it was possible with all crumbs he leave here and there ;

first one was where Papa strictly sez that 2SJ109 is in question ......
etc
etc


anyway here is ( pasted from Babelfish hysteric thread) original Babelfish schematic ; every aspect of that amp is chewed at least 3 times

again - kudos to Papa
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Old 3rd November 2007, 02:03 PM   #23
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Quote:
Originally posted by EUVL
If you allow for full swing in the diff pair without forward bias (which is unlikely to happen in normal usage), then you should use Idss=2xbias, hence approx. 9mA.
BL would be fine; V will also do. Whatever you can still get.

And any ultra bright blue LED from Reichelt will be more than happy at 0.5mA. In fact, I run them in series with a 10k resistor at 5V, and I still find them much too bright.


Patrick

and well matched pair of 2SJ74BL will do the job ;


just to prevent that question

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Old 3rd November 2007, 02:04 PM   #24
jrsun is offline jrsun  United States
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Umm, wonder what is the next? Aleph-JX?
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Old 3rd November 2007, 02:04 PM   #25
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Quote:
Originally posted by EUVL
If you allow for full swing in the diff pair without forward bias (which is unlikely to happen in normal usage), then you should use Idss=2xbias, hence approx. 9mA.
BL would be fine; V will also do. Whatever you can still get.

And any ultra bright blue LED from Reichelt will be more than happy at 0.5mA. In fact, I run them in series with a 10k resistor at 5V, and I still find them much too bright.


Patrick

and well matched pair of 2SJ74BL will do the job , same as 2SJ109BL;
not worse and probably even better , if they are well matched ;
but I'm pretty sure that will not result in audible difference


just to prevent that question

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Old 3rd November 2007, 02:08 PM   #26
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Quote:
Originally posted by jrsun
Umm, wonder what is the next? Aleph-JX?

why you think that

THIS

is something else ?
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Old 3rd November 2007, 03:09 PM   #27
EUVL is offline EUVL  Europe
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> I don't know what's the fuss ;

No fuss.

Just that I vaguely remembered Nelson saying he had done the Aleph somewhat differently the second time round. So I was expecting more twists than just the obvious. But I am still interesting to know what benefits there might be to take the sensing resistors out of the loop (better stability ?).

And using 2SJ109 for Aleph-X is nothing new. It was one of the circuits published on the high-power thread, WAY back. And many have built them or modified their AX to JFET frontends.

2SJ74BL will of course do. But apart from matching, you will never get the thermal coupling for the diff pair as on a single die. So I would still pay US$6 for a 2SJ109 if I were you.

If my memory still works, the XA100.5 & series have output stage similar to the Aleph 0 to allow Class AB operation, as discussed on other threads already.


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Old 3rd November 2007, 03:45 PM   #28
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Quote:
Originally posted by EUVL
> I don't know what's the fuss ;

No fuss.

Just that I vaguely remembered Nelson saying he had done the Aleph somewhat differently the second time round. So I was expecting more twists than just the obvious. But I am still interesting to know what benefits there might be to take the sensing resistors out of the loop (better stability ?).

if you mean on R24 on Papa's schematic, maybe I'm wrong , but I see it connected in usual Aleph way


Quote:
And using 2SJ109 for Aleph-X is nothing new. It was one of the circuits published on the high-power thread, WAY back. And many have built them or modified their AX to JFET frontends.
agree ; that's exactly my point .


Quote:
2SJ74BL will of course do. But apart from matching, you will never get the thermal coupling for the diff pair as on a single die. So I would still pay US$6 for a 2SJ109 if I were you.
I don't agree ; but that's our right to disagree
benefits of two-in-one packages are obvious when you use both polarities (as in UGS) and need to connect them thermally - it's easiest to do this with two dual packages than with four T092s ;
what I say is that difference in price and availability is much greater than benefits you gain ......... if any , depending of particular project

Quote:

If my memory still works, the XA100.5 & series have output stage similar to the Aleph 0 to allow Class AB operation, as discussed on other threads already.


Patrick
maybe I'm wrong - but that's another issue
XA30 - at least looking at published data , looks to me as X-d Aleph J

not that this is important to me ; what is - certainly unknown crumbs here and there
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Old 3rd November 2007, 04:01 PM   #29
EUVL is offline EUVL  Europe
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> if you mean on R24 on Papa's schematic

I meant R20-R23 in parallel.

> benefits of two-in-one packages are obvious when you use both polarities (as in UGS) and need to connect them thermally - it's easiest to do this with two dual packages than with four T092s

That is not true.

Take a TO92 device, and saw that apart. You can measure how far (mm's) the die is away from the next exposed surface. The black stuff of the TO92 is filled epoxy. Do you know what is the typicaly thermal resistance of a TO92 is from die to case (irrespective of whether it is square, flat or half round) ?

A 2SJ109 has both transistors on a same piece of silicon (which has one of the highest thermal conductivity of all materials next to silver, copper & aluminium). The distance between the two transistors is less than 1mm, so they are thermally perfectly tracked. There is simply no better thermal solution than that.

Of course you can argue how much tracking is necessarily. But JFETs ARE thermally sensitive. Just heat one up and see how much Idss changes.

> what I say is that difference in price and availability is much greater than benefits you gain

a) what percentage is US$6 in the total budget of an Aleph X or JX? Probably just enough to buy you a good XLR connector.

b) any circuit requiring a matched pair (LTP or the Curl follower, to name a couple) would benefit from perfect thermal tracking.

But we do not have to agree.




Patrick
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Old 3rd November 2007, 04:07 PM   #30
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Quote:
Originally posted by EUVL
............

I meant R20-R23 in parallel.

......

........




Patrick

those resistors are just drawn somewhat different than usual at Pap's schmtcs...... or I'm blind ........ hehe

( remember that's Choky just americanized term for 4eye in my native )


regarding thermal tracking........ I told you - I can't hear or measure difference in this circuit between 109 and 74

splitting hair issue ....... I'm just trying to be practical .... as I learned from Papa's work ...... and that is one of most important lessons, at least for me .

we agree on that?

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