Need Input Mosfet for A-75

[jritota]

Hello,
Can anyone help me with finding IRFD9110 or substitute?
Thank you for a great community.
Joe

[lineup]

I dont know
but maybe you could try IRF9510.

I am sure Nelson will know best replacement.

[BobEllis]

I've substituted IRF610 and IRF9610 for the input differential pairs on mine, without a noticeable difference in the sound. I did one channel when I blew the originals with poor workmanship and now cannot remember or tell which is which. I use a pair of A75s in a biamped setup, so that may be a factor in not being able to tell them apart.

You'll have to bend the leads to make them fit the AudioExpress boards, so it will look a bit sloppy.

Edit: Digikey has the lead free versions of the IRFD9110 in stock (the last letters in the part number are pbf) You may have trouble finding anything but the lead free versions of all of the devices these days. The original article suggests some alternatives - see www.passdiy.com If you need a plastic output device rather than the T03's consider the IRFP240/9240 or their Fairchild equivalents (available form Mouser)

[jritota]

Bob Ellis,
Thank you for your input (pun intended) and advice on the 4 Dip
IRFD9110PBF's. I think I can make them fit.
I'm finally getting started with my project.
I've got the chassis and Home made heatsinks ready to go.

I'm starting on the power supply now, and just getting a perspective on parts avail. for everything else.
I've chosen to go with a 1kva trans (Avel). and 4-60k @75v caps.

The output heatsink are 2"X4"X17" long angle Aluminum mounted together vertically like normal sinks 12 on each side of the amp and drilled for 2 TO-3's per (IRF130, IRF9130 outputs 100 ea. for matching )

I'll keep you posted as things progress.
Thanks again,
Joe Ritota

[BobEllis]

If I understand you you will have a case that is 17" high and 24" deep. I know that sounds like a lot of heat sink, but you really don't have a lot of radiating area. I used one of these 2"x4" foot long sections for a mini-A with about 30W dissipated (like each section of your heatsink will see) and got a 20C rise. You may get away with it, but keep an eye on the sink temperature when you fire it up.

The good news is you can reduce the bias and stay in class A for most music with little if any impact on the sound. I run mine at reduced bias because I couldn't stand 800W of waste heat in poorly ventilated end of the room.