Values of my IRFP 240 Mosfets

[Hydesg]

These are the values of my mosfets
do you guys think that they are suitable for my aleph 2 ?
without causing much problems?


4.2
4.2
4.21
4.21
4.22
4.22
4.23
4.23
4.27
4.29
4.29
4.33
4.35
4.37
4.38
4.39
4.4
4.4
4.41
4.42
4.42
4.44
4.46
4.47

all 24 fets
any comments?

[halojoy]

I am no expert on MOS.

But those 4.20-4.23 - 8 Devices,
are perfect match perfect for PARALLELLING.

Those 4.39-4.42 - 6 devices, also perfect!
---------------------

I would guess (Nelson has the final answer),
that a different of below <=0.05 V would not matter at all.
When we comes >= 0.20 V, I do not think it is good match.
4.20 does not match with 4.40
---------------------------------------------------

It is also imporatnt that all devices was MEASURED
under Same Conditions. Same time in cicuit, same room-temp etc.
and measured in same way.

Did you use the working condition when doing measurments?
(the current, voltage, heatsink that will be used in the amp)
If so, then your figures are 99% valid = GOOD!.
And you can make the choice based upon that data.

/halo

[Jay]

It is strange that the deviation (measured Vgs) is very large. Are you sure you have them from the same manufacturer? I’ve guessed that International Rectifier’s would not have such large deviation. When I bought them, I asked for the same batch number (may be this is why I got small deviation). Because MOSFETs have “intrinsic” parameters, I won’t parallel MOSFET from different manufacturers just because the Vgs is similar.

As stated in the SM, even if Aleph5 (3 MOSFET) had been matched for 0.01V (deviation/range?), 0.1V deviation will not impede the operation. As you need 6 in parallel, you may have to compromise. May be 0.02V with the maximum of 0.2V, which can easily be fulfilled with your MOSFETs.

I think the question is: should you put the high Vgs on the signal section? (Because hi Vgs here means hi Id). I think this issue is more important than maintaining a match between current source section and signal section. And, deviation in current source section may only mean unequal temperature sharing, while deviation in signal section do affect sound performance.

I believe MOSFETs have complex parameters such that their paralleled high performance cannot be achieved automatically with similar Vgs. But I KNOW, that matched pairs is like magic (may be only in that circuit), boosting the performance dramatically, especially in bass performance. That’s why to match them I did an “on site” swap. And I wonder, is 6 always preferable than 5?

Like Halojoy, I'm no expert either

[dshortt9]

As long as you group the ones with the closest Vgs they will be fine. The first six, second six, etc. The signal and source groups do not have to be matched with each other.

[UrSv]

Originally posted by Jay
It is strange that the deviation (measured Vgs) is very large. Are you sure you have them from the same manufacturer? I’ve guessed that International Rectifier’s would not have such large deviation. When I bought them, I asked for the same batch number (may be this is why I got small deviation). Because MOSFETs have “intrinsic” parameters, I won’t parallel MOSFET from different manufacturers just because the Vgs is similar.
--snip --

You have pretty nice groups there and the variations are not that big but rather quite normal IMHO. I would group them as the groups of the closest values as mentioned and and run it like that. Should be just fine. Only thing to think of would probably to choose groups in pairs choosing the two lowest value groups for on amp and the two highest value groups for one. Should be great.

Have fun.

[Nelson Pass]

That is a typical range off one wafer. We match as tightly as we can, but remember that .1V is still a workable tolerance in Aleph circuits, so don't get too excited.

[Hydesg]

Hi
if im not wrong
there are 2 output boards for each channel
1 is gain devices and 1 is constant current

can i use

4.2
4.2
4.21
4.21
4.22
4.22
for channel 1 constant current

4.23
4.23
4.27
4.29
4.29
4.33

for channel 1 gain devices

4.35
4.37
4.38
4.44
4.46
4.47

for channel 2 constant current

4.39
4.4
4.4
4.41
4.42
4.42



for channel 2 constant current

[halojoy]

Why not:
4.20 4.20 4.21 4.21 4.22 4.22 - for channel 1 constant current
4.23 4.23 4.27 4.29 4.29 4.33 - for channel 1 gain devices
--------
4.35 4.37 4.38 4.39 4.40 4.40 - for channel 2 constant current
4.41 4.42 4.42 4.44 4.46 4.47 - for channel 2 gain devices
------------------------------------------

That is what Nelson suggested, as I got it (with my understanding in english)

Why did you mix up the last two groups?

Most important is that each group of 6,
is as good matched as possible.
With 4.35 together with 4.47, you have 0.12 volt difference
in that group.

Secondly in importance is
that the gain-group is somewhat matched c-curr-group within one channel.
---------------------------------------------

For to minimize difference even further
I would say you should buy like 5-10 extra MOSFETs.
But buy that at the same time from same production package.
(Nelson says there is no worries if you buy 24 from same package
and take 6 lowest, 6 next and so on. And he should know.)

/halo - a bit puzzled - has Hydesg written it all right in the post

[UrSv]

Originally posted by Nelson Pass
That is a typical range off one wafer. We match as tightly as we can, but remember that .1V is still a workable tolerance in Aleph circuits, so don't get too excited.

Exactly. Do what I said and what Halo said and sort them by Vgs. Use the first 8 for current source 1 and second 8 for ouptut 1. Third group for current source 2 and last 8 for output 2. That will give you the best mathing per channel. Like NP confirmed, your spread is normal.

[nbaula]

I am aslo matching FETS for my A2, another question I have is what is the acceptable tolerance in VGS values beetwen channel.
For example, the values posted there is more than .1V difference.
Can you hear an audible difference between channel /