Does JFET Input Apply to All Alephs?

[Jay]

I haven't seen or read a thread where the bigger Alephs are built using JFET front end (Aleph-J). Can anyone let me know the thread if there is one?

Is there any precaution regarding to applying JFET to the bigger Alephs? I'm thinking of building Aleph 2, but with JFET input (like Aleph J).

I have only a pair of big heatsink suitable for high power class-A. This heatsink is used to be used for Moskido 60W. So I have to choose between Aleph 2 and Moskido (to use the heatsink). What is the wattage of the Aleph 2? Where can I find pdf file related to Aleph 2?

Now a question regarding use of fan for cooling down the heatsink. As a guideline, what is the minimum size of a heatsink if sufficient cooling (at least 3 fans) is applied to the heatsink? 40% of normal size (without fan)?

Thanks

[generg]

for bigger Alephs most people suggest to double the number of J-Fets in the input and to double the current through the input stage to about 16mA to drive more pairs.....

[AndrewT]

Some heatsink lose 90% of their dissipation capability when the fan fails. (horizontal tunnels are likely to be much worse).
But, that does not equate to getting ten times the performance by adding fan/s.
Expect at least double and possibly quadruple the dissipation performance by blowing.

[Jay]

Originally Posted by generg

for bigger Alephs most people suggest to double the number of J-Fets in the input and to double the current through the input stage to about 16mA to drive more pairs.....

I don't have 8x PJFET. I have many JFETs but 4X for each type. If the requirement is the 16mA may be I have to use the standard IRF9610, but buffered by B1. Who knows the buffer will help. But if the quality is not good enough, I will use BJT input.

[Jay]

Originally Posted by AndrewT

Some heatsink lose 90% of their dissipation capability when the fan fails.

It seems I will need that device that will cut off the supply when the heatsink reach certain temperature (due to fan failure). Never used this device before.

Heatsinks are expensive and difficult to find, so this fan cooling idea looks interesting, if it is not too noisy.

[generg]

If the requirement is the 16mA may be I have to use the standard IRF9610

I heard for some time both input stages wit J-Fets and 9610s and .....

I liked both...... J-Fets were more airy and they sounded great with violins and classic music and the 9610s darker, I had the impression of more dynamics for Pop and Rock...

For me really a matter of taste and .....weather inside the soul....

[Jay]

Originally Posted by generg

I liked both...... J-Fets were more airy and they sounded great with violins and classic music and the 9610s darker, I had the impression of more dynamics for Pop and Rock... For me really a matter of taste and .....weather inside the soul....

I like the sound character of a MOSFET than a JFET. But IRF9610 has too high capacitance, which I believe is the thing responsible with the poor quality of the higher frequency sound (and very low level signal?). I want a MOSFET sound, but with a clean high frequency sound. I think a MOSFET with low Ciss (and high gfs) will be the King... (I believe such device exists, but may be very expensive).

[generg]

o.k. I understand....

I have looked once for such devices, there are some SMD types, still manageable to solder in a normal way that have,, with a bit cooling area, about 1,5 Watt

I look for the data.....

[nar]

Originally Posted by generg

o.k. I understand....

I have looked once for such devices, there are some SMD types, still manageable to solder in a normal way that have,, with a bit cooling area, about 1,5 Watt

I look for the data.....

Am also in search for that kind of SMD data / can build micro circuit board to act as adapter to TO 92 regular pinouts on DIY boards

Best,

nAr

[AndrewT]

The all FET amp Threads have been looking at and getting good results with ZVN2110 and ZVP2110 in both through hole and SMD. This is being used in the VAS stage, but may translate across to input.