Matching Aleph-X

[anders.a]

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]

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]

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.

[mastertech]

Mr Pass some people go to extreme lengths to match the dif-input-pair to give
you an example they glue the cases together to match i assume thermal charactiristics but i am somewhat like you i look at details where the match
is complete for example a pair in a single case specificly made for matching
the transistors in the first place

Nelson Bass

[anders.a]

Tank you to you all. This helps a poor beginner like me.

[MikeW]

Originally posted by Nelson Pass
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.

[mastertech]

hi guys one last note
Mr Pass is partly right in saying you dont have to match exactly the pair
there are amplifiers that have a little mismacth and when under
subjective listening they sound better than those that have a better match
it all depends on the whole circuit not just a stage

Nelson Bass

[jh6you]

Originally posted by mastertech

there are amplifiers that have a little mismacth and when under
subjective listening they sound better than those that have a better match

How come...?

Regards

[mastertech]

i guess that depends on what music you listen to

[Nelson Pass]

Originally posted by MikeW
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.

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.