Memphis 16-ST500D

[Dr Zeus]

This amp is being repaired. It's output channel burned up as well as the entire power supply. I replaced all the power supply fets with new units.

Looking a bit closer, I noticed this amp uses 640/9640s for outputs. Can I use 540/9540s as a substitute? What about just for testing? I dont have any 640/9640s on hand yet.

Thanks!

[Perry Babin]

If the rail-rail voltage is less than 100v, the 540s 'may' work.

[Dr Zeus]

The rail voltage is measuring +-58vDC at idle but I'm not sure if it will go beyond that under heavy load. The rail caps are 80v. The power fets are 50n06.

You know what is strange about this amp; is has 2xIRF640s and 4xIRF9640 outputs.

Are the 540/9540s safe for reliable use?

[Dr Zeus]

You said rail-rail voltage. Thats meauring 116v (Twice of 58v)

[Perry Babin]

No. The rail-rail voltage is 116v.

There are generally more P-channel FETs than N-channel FETs in this type of amp.

[Dr Zeus]

OK. It looks like only one of each 640/9640 shorted so I clipped them off the PCB. I was able to power the amp us and get it to play perfectly fine with the bad outputs removed, leaving only 1x640 and 3x9640s in place.

I'll order a stack of 640/9640 as I'm starting to see a lot of high current amps use them instead of the 540/9540.

[1moreamp]

Originally Posted by Dr Zeus

You know what is strange about this amp; is has 2xIRF640s and 4xIRF9640 outputs.

If you check the current rating of both of these devices the reason why they have staggered quantities becomes evident. The N fet has a much larger current rating of the P fet....hope this helps...