Aleph 2 Power R

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To the extent that the banks of MOSFETs are matched, it's nice to have everything as predictable as possible further on down the line. If you can find tight-tolerance resistors, by all means use them. It will reduce the variations in current through each output/current source pair, hence lowering the distortion and ensuring more equal load sharing.
That said, I used the blue Panasonic (Matsushita) resistors from Digikey. They are, I believe, 5% tolerance parts.
They are in the signal path. The better quality you use, the better your results will be.

Regarding power requirement, someone correct me, but I think it goes something like:

P = I^2.R = 0.5 x 0.5 x 1 = 0.25W

Now, the dynamic current source can double its bias, so we take 2xI = 1W maximum dissipation.

Everyone I have ever spoken to will say allow at least 2x maximum power requirement, so we are now at 2W.

I suspect the 6W resistors I just bought are "way over the top" .......

Which brings me to the point: IF my calculations are correct, then why not just use a number of metal film devices in parallel. They are cheap, easy to come by, have excellent tolerance and have near zero ESL ??

What say the EE-types ....... have I missed something here ??????

cheers, mark :)
Aleph power resistors

Hi Mark.I can see you intend to tune up your A 4 !!
I think the modification will perfectly work.I would do the same,but running 4 resistors in parallel /0.25W 1% from Welwyn
at each power resistor initial place.
Maybe Nelson can light us up,but I think he may not have same interest than ours in this precise point.

And ..... while I'm on this bent:

The output stage resistors. Lets assume an Aleph5, which is what I am currently building.

Output = 4x 0.47 = 0.12ohm

Output current up to 2x idle. Now, source resistors show 3x 0.5amp, but description states slightly above 2amps at idle (never could work that out ???). We'll take 4amps peak output for argument.

So, P = 16 x 0.12 = 1.92W

So, we need about 4W rating to be quite safe. This section could be easily made from 10x 0.4W metal films ...... it would probably take even less space on the PCB ;)

cheers, mark

PS: Nelson, if your about, is this reasonable?
As long as you've got sufficient heat dissipation capability in the resistors and the total value works out right, you'll be fine.
As a fringe benefit, paralleling resistors will tend to average out the values, leading to an even closer match to the calculated value.

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