input mosfet matching (aleph)

hifi · 26th July 2001, 08:28 AM

if i have understand correctly the input current sorce delivers 20ma ? and that is split up by the input mosfets to 10ma each?...cuz i have just read mark finnis "cloning manual" where he matches his input mosfet att 20ma each..that must be wrong??

/micke

tschrama · 26th July 2001, 10:09 AM

Hi...

mark finnis "cloning manual" ... ????

can you post a link to that so I can have a look ?

greets,
thijs

hifi · 26th July 2001, 05:01 PM

maybe i excagerated he has a description of how he made his diy aleph 4 it is found on http://www.passlabs.com under galleries

GRollins · 27th July 2001, 01:11 AM

Micke,
Match devices at the current that you intend to use in the circuit. I'm relying on memory, but I believe that you're correct--the front end of an Aleph runs at 20mA for the pair, hence 10mA each device. So you should test them at 10mA.

Grey

mefinnis · 27th July 2001, 04:40 AM

This is quite correct. Test them at 10mA .... the original description I used was wrong.

Fortunately, when I looked at the remainder at 10mA cf the 20mA it didn't actually make any appreciable difference to the ranking ......

Yes, I should get around to altering the construction notes :-(

Sorry ...... Mark

hifi · 27th July 2001, 03:58 PM

no sweat....i tried both and i didnt find much of a difference anyway....

/micke

vdi_nenna · 27th July 2001, 04:47 PM

What do you guys think about using low-level dual mosfets for an input stage. It looks like a TO-39 can w/ six leads. I think I read in an old Audio Electronics mag that Erno Borbley uses these in the input stage of his amps. It negated the need for matching since it's on the same chip. Any ideas on this??

Petter · 27th July 2001, 09:02 PM

Are these MOSFET's from Linear Systems? In which case, last time I checked they did not have the power rating to suit my taste. For low power stuff, consider using JFET's which probably perform better (unless your circuit is sensitive to input leakage current or you need more quiescent current before device saturation).

What are the names of the units you mention?

You can find a list of devices used by Borbely at his website http://www.borbely.com. Check out schematics and note heavy use of cascoding -- sometimes with J-FET's other times with FETs (when he needs more power dissipation?)

In my humble opinion, I think his designs have not changed much from what he published in Audio Electronics around 1990, but I am perhaps being a little cynical.

Petter

vdi_nenna · 27th July 2001, 10:39 PM

Don't know what they are. Iwas on his site today, but I was reading about JFETs, I didn't take not of make or model.

JFET come in the dual monolithic state also.

Just thought I'd ask.

27th July 2001, 04:40 AM	#5
mefinnis diyAudio Member Join Date: Feb 2001 Location: Adelaide, Australia	Err ... YES This is quite correct. Test them at 10mA .... the original description I used was wrong. Fortunately, when I looked at the remainder at 10mA cf the 20mA it didn't actually make any appreciable difference to the ranking ...... Yes, I should get around to altering the construction notes :-( Sorry ...... Mark

27th July 2001, 09:02 PM	#8
Petter diyAudio Member Join Date: Jan 2001 Location: Scandinavia	What are they? Are these MOSFET's from Linear Systems? In which case, last time I checked they did not have the power rating to suit my taste. For low power stuff, consider using JFET's which probably perform better (unless your circuit is sensitive to input leakage current or you need more quiescent current before device saturation). What are the names of the units you mention? You can find a list of devices used by Borbely at his website http://www.borbely.com. Check out schematics and note heavy use of cascoding -- sometimes with J-FET's other times with FETs (when he needs more power dissipation?) In my humble opinion, I think his designs have not changed much from what he published in Audio Electronics around 1990, but I am perhaps being a little cynical. Petter

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26th July 2001, 08:28 AM	#1
hifi diyAudio Member Join Date: Mar 2001 Location: sweden	if i have understand correctly the input current sorce delivers 20ma ? and that is split up by the input mosfets to 10ma each?...cuz i have just read mark finnis "cloning manual" where he matches his input mosfet att 20ma each..that must be wrong?? /micke

26th July 2001, 10:09 AM	#2
tschrama diyAudio Member Join Date: Jul 2001 Location: The Netherlands	Hi... mark finnis "cloning manual" ... ???? can you post a link to that so I can have a look ? greets, thijs

26th July 2001, 05:01 PM	#3
hifi diyAudio Member Join Date: Mar 2001 Location: sweden	maybe i excagerated he has a description of how he made his diy aleph 4 it is found on http://www.passlabs.com under galleries

27th July 2001, 01:11 AM	#4
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	Micke, Match devices at the current that you intend to use in the circuit. I'm relying on memory, but I believe that you're correct--the front end of an Aleph runs at 20mA for the pair, hence 10mA each device. So you should test them at 10mA. Grey

27th July 2001, 03:58 PM	#6
hifi diyAudio Member Join Date: Mar 2001 Location: sweden	no sweat....i tried both and i didnt find much of a difference anyway.... /micke

27th July 2001, 04:47 PM	#7
vdi_nenna diyAudio Member Join Date: Oct 2000 Location: PA, USA	What do you guys think about using low-level dual mosfets for an input stage. It looks like a TO-39 can w/ six leads. I think I read in an old Audio Electronics mag that Erno Borbley uses these in the input stage of his amps. It negated the need for matching since it's on the same chip. Any ideas on this??

27th July 2001, 10:39 PM	#9
vdi_nenna diyAudio Member Join Date: Oct 2000 Location: PA, USA	Don't know what they are. Iwas on his site today, but I was reading about JFETs, I didn't take not of make or model. JFET come in the dual monolithic state also. Just thought I'd ask.

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