Aleph with 2sk1058

[umut1001]

hi everyone..i wanna build an Aleph amp with only a pair of 2sk1058 transistor..i have +-40volts .. but i dont know what to do..i dont want to parallel the mosfets..because i wanna get the clearest sound..what can i do..do you have pcb or schematics Aleph with 2sk1058..i wanna use 2sk 1058 because it has better sound character i believe its the best..please help and discuss

 

[h_a]

Laterals are not 1:1 substitutes for vertical mosfets.

Undoubtly you would like to see what Nelson himself says about that:

http://www.diyaudio.com/forums/showthread.php?postid=660822#post660822

Concerning your wish to avoid paralleling fets (last paragraph in the post)

http://www.diyaudio.com/forums/showthread.php?postid=660055#post660055

Maybe you want to dig into this topic deeper?

All the best, Hannes

 

[umut1001]

hi

i can not understand completely what Nelson is talking about.. i think my English is not good enough I understand that verticals and latherals have some advantages and disadvantages..I made a PLH amplifier..i used IRF240 IRFP240 and 2sk1058..IRF240 has a more natural sound than IRFP..but they burned..i think i had a problem with bias..now i am using IRFP as a current source and 2sk1058 as a signal transistor now it sounds good..but i want to make a output capacitorless single ended amplifier..because of disadvantages of capacitors.IRF240 is expensive here in my country.its about 10dollars.i dont know what to do

 

[h_a]

Well, you have basically 2 issues to deal with: a different temperature coefficient, which should not be a problem since you want to use laterals which have a negative one (self-protecting) in contrast to the positive of the verticals.

However a circuit for vertical mosfets will have some sort of temperature compensation, like a junction (bipolar transistor). This compensation will continue to reduce the bias current when the amp warms up. This you would need to manage.

2nd the transconductance of the laterals is usually lower and for source-followers this would not be any problem at all. As far as I know at least the Aleph3 uses the mosfets in common-source mode, so you get a reduce voltage gain.

If this is a problem in your setup, I do not know.

However I do not have any practical experiences with such subsitutions, so I can only advice you strongly to wait for advice from more knowlegeable people.

All the best, Hannes

 

[umut1001]

thank you..now i am using 2sk1058 on PLH amplifier..hum is more than IRFP240..but mid and treble is better..I think sound is better with 2sk..but i will buy and try IRF240 metal mosfet..the metal mosfet sounds better than plastic ones..hasnt anyone have idea ?

 

[GRollins]

Using a lateral MOSFET as the output device in one of the Aleph variants can lead to difficulties. The lower transconductance means that the front end is running very lopsided in an attempt to get the lateral device to bias properly and you're facing higher distortion and lower bandwidth than you would have if you were using a vertical MOSFET. The differential is having to run very heavy current on the back side and light on the front. The front end will clip much sooner than it should on a positive input signal.
The bottom MOSFET in the Aleph output stage is unusual in that it supplies voltage gain. With a lower transconductance device, the gain will be lower. Since the gain is lower the gain available for negative feedback will be lower and the performance won't be as good as you might wish.

Grey

 

[umut1001]

For PLH amp nelson said that you can use Lateral mosfet too..But i have no idea for Aleph.. i just wanna have clear and better sound..

 

[GRollins]

In a classic Aleph front end, the left side of the differential has a 392 Ohm load resistor. To bias a vertical MOSFET such as the IRF parts, you'll need to see something like 4V across that resistor, or around 10mA. The differential as a whole is biased with about 20mA, 10mA of which goes through each side of the differential.
To bias a lateral MOSFET requires something on the order of 2V, so the differential adjusts itself as best it can, putting something like 5mA across the 392 Ohms.
But...
This leaves the other 15mA intended to bias the front end with no place to go except up the other side of the differential. This is why I say the differential is lopsided. Under normal circumstances a differential will have approximately half the current flowing through each side. But in a case such as I have described, the current is roughly 25%/75%. It's not an optimal circumstance.

Grey

 

[Nelson Pass]

Your choice is to roughly halve the bias current or the resistor.

 

[umut1001]

hi Mr Pass.. I am trying different transistors.. IRF240 is very good transistor it sounds good..but I accidentally burned them..I wanna use 2sk 1058 on aleph..i dont know how to make differences on aleph amplifier..how to change the resistors ?

 

[MikeW]

It is R14 on the schematic for thr Aleph 5. From the minus rail to the Drain of Q1.