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Old 20th November 2007, 12:33 PM   #221
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just a idea .........

need few tests for deciding exact number of leds in input jfet source ;

CCS in source of output jfet - what else than Papa's 240 thingie

Papa ........ ?


is it newest see-saw machine?
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Old 20th November 2007, 12:35 PM   #222
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Quote:
Originally posted by EUVL
...........

Hang a 4mA constant current diode (e.g. J511) from each of the drains of the JFET diff pair to 10V below the negative rail.

The rest I should leave as mental jogging exercises.


Patrick

good one
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Old 20th November 2007, 01:05 PM   #223
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> just a idea .........

Kills too much voltage on the negative rail and hence reduce swing.

No, no. You need to come up with something more elegant.




Patrick
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Old 20th November 2007, 01:09 PM   #224
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Thanx Skt. Alex for this beautyful Aleph JJJJ... !


Greetings from Germany

Jürgen
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Old 20th November 2007, 02:11 PM   #225
Dr. ODD is offline Dr. ODD  Germany
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First : A year ago my old amp broke down and I didnd got started building my own one. I wanted to hear music and so I byed an Aleph J from Reno Hifi. I love this Amp It dond need any canges. It´s an Amp from Heaven.

But I had the following ideas:

Using 3 or 4 pairs of output Transistors ( more Damping Factor and better Head spreading)

Using the J Fets with higher output currend ( I think it was GR grade, or was it V ? anyway ) to drive the extra pair.

Bias the hell out of it ( of cours with bigger PSU and Head sinks)

The goal could be much more Power for 4 ohm Speakers. ???

Bernhard
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Old 20th November 2007, 02:53 PM   #226
EUVL is offline EUVL  Europe
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> Using 3 or 4 pairs of output Transistors

See post #215 & #217.

PS

One more tipp from me. If you use a Grade V JFET (Idss 16mA) for the diff pair, and change the drain resistors to 500 ohm, you can drive at least 3 pairs of 2SK1529 directly (without additional follower) without losing any bandwidth. Transconductance of 2SK1529 is comparable to IRFP240. They do sound different -- matter of taste.

By changing the resistor to 500R, you will reduce the open loop gain of the 1st stage by 50%, and hence also the amount of negative feedback.


Patrick
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Old 20th November 2007, 02:57 PM   #227
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Quote:
Originally posted by EUVL
> just a idea .........
No, no. You need to come up with something more elegant.




Patrick

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Old 20th November 2007, 07:34 PM   #228
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Quote:
Originally posted by sandmarc
I was thinking about building the output stage with Lu1014Ds cascoded with the IRFP240s.
One could use a separate, more negative supply on the 'J109's drain R, maybe just hooked off with a zener or TL431...

- Klaus
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Old 20th November 2007, 08:11 PM   #229
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Quote:
Originally posted by Dr. ODD
First : A year ago my old amp broke down and I didnd got started building my own one. I wanted to hear music and so I byed an Aleph J from Reno Hifi. I love this Amp It dond need any canges. It´s an Amp from Heaven.

But I had the following ideas:

Using 3 or 4 pairs of output Transistors ( more Damping Factor and better Head spreading)

Using the J Fets with higher output currend ( I think it was GR grade, or was it V ? anyway ) to drive the extra pair.

Bias the hell out of it ( of cours with bigger PSU and Head sinks)

The goal could be much more Power for 4 ohm Speakers. ???

Bernhard

Quote:
Originally posted by EUVL
> Using 3 or 4 pairs of output Transistors

See post #215 & #217.

PS

One more tipp from me. If you use a Grade V JFET (Idss 16mA) for the diff pair, and change the drain resistors to 500 ohm, you can drive at least 3 pairs of 2SK1529 directly (without additional follower) without losing any bandwidth. Transconductance of 2SK1529 is comparable to IRFP240. They do sound different -- matter of taste.

By changing the resistor to 500R, you will reduce the open loop gain of the 1st stage by 50%, and hence also the amount of negative feedback.


Patrick

This is the approach I was thinking of taking to bias more power into 4 ohms. Using a V grade jfet from the GB and irf 150 or 250's for the FET's.

-David
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Old 20th November 2007, 08:50 PM   #230
EUVL is offline EUVL  Europe
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I guess you meant IRFP250.

IRFP250N, on the other hand, has lower capacitances.


Patrick
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