Matching Aleph-X

I’m currently trying to understand witch transistors should be matched in my Aleph-X.
BC 550C
IRF 9610
IRFP 240

My guess is IRF 9610 and IRFP 240 not BC 550C but I’m not sure. And what current should I use? Nelson Pass is using 5mA for some unspecified mosfet in his matching article but I don’t understand why. Why not use 50mA, 0,5mA or even 1 A?

Please enlighten me.
 

Netlist

diyAudio Moderator Emeritus
2003-01-18 9:50 am
The diffpair is the most important to match closely as this greatly effect offset voltage.
Then comes the output mosfets, and if you can also match output resistors. BC550C don't have to be matched but high beta is preferred (I think). Matching with real life currents is top notch.

/Hugo :)
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
No need to match the biploars, but it doesn't hurt.

The 9610's you want to match around 10 mA or so because
that's where we run them. (just match the two input devices)

The 240's you want to match when they are connected in
parallel, so that they share the current equally. Matching all
transistors throughout the amp is fine, but not usually practical,
although when you're dealing with thousands, matching them
all to high precision is easier than not.
 
Nelson Pass said:
No need to match the biploars, but it doesn't hurt.

The 9610's you want to match around 10 mA or so because
that's where we run them. (just match the two input devices)

The 240's you want to match when they are connected in
parallel, so that they share the current equally. Matching all
transistors throughout the amp is fine, but not usually practical,
although when you're dealing with thousands, matching them
all to high precision is easier than not.


Why don't you use half as many 250's or 260's?
How many 240's do you have left? 5000000 ?
Can I have the ones that don't match (on the low side) for more mini-A's.:clown:
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
MikeW said:
Why don't you use half as many 250's or 260's?
How many 240's do you have left? 5000000 ?
Can I have the ones that don't match (on the low side) for more mini-A's.:clown:

I still have a slight preference for 240's and 244's as they give
us more dissipation versus capacitance, even though it's at
higher cost.

We keep 5 figure numbers around (that would be somewhere
between 10,000 and 99,000 ;) ) and we do have a stock of
250's but they require modification of the circuitry, so we are
saving them for the last generation.

Products are slowly going to plastic. Soon only the XA's will
have TO-3's.