M50 ULTIMATE AMP build- help

[BigBrent]

I have been at my quest to rebuild the "ultimate" M50 for awhile now. I have used the excellent posts here, like Eric D's resistor flush with the heatsink method, as well as the cap replacement and some Burr Brown op amps.

This leads to my next question. I saw a post some where on here that said something to the effect of replacing the ZR44 FETS with the ZR48 model. They mentioned this is because the devices can handle more current, so it would be an upgrade. Does anyone have any ideas or feedback about this?

Brent

[Eric D]

I replaced the FETs in one of my M50s with STP80NF55 FETs. These are rated for 80A each. They do not have even close specs to the original FETs though, so you run the risk of the PWM driver not handling them well. In my case they worked just fine.

[BigBrent]

Can you tell me more about these "PWM" drivers? Are these the items that have the "DII 42" reference? I noticed on mine, they don't match like they seem to on some repairs that you have done. Is it important for those to match? Thanks for your patience...

Brent

[Eric D]

The SG3525 DIP device (10 or 12 pin, can't remember off hand) is what I am talking about.

[KUB3]

I thought the general consensus was it's a total waste of time 'upgrading' these as you can't even hear it.

[BigBrent]

I thought the general consensus was it's a total waste of time 'upgrading' these as you can't even hear it.

In my case, I like to "indvidualize" my car, my computer, almost anything I tinker with. While you are right that you probably can't "hear" it. If it makes it more bullet proof, or even different, that is what I am going for.

I am also into old cars and have an old garden tractor on the back burner.. components for these amps are inexpensive compared to having a hobby with that stuff!!!

Brent

[BigBrent]

Eric D- you continue to be a big help to me, and everyone in this forum.. I have another question. The devices to the left of the FET's are what devices? I know one is labled "SF163", "SF163A" and look like they have a difference in polarity labeled as: ~+~ and ~-~ respectively.

I am also noticing on mine, the top indicators are different ie ":DII 42" and ":DII 43". In the posting where you replaced the FET's, I noticed you had replaced these and both of the ":DII" numbers matched. Is this important or does this need to be changed? If so, I'd like to try my hand at replacing these too, now that I am this far into rebuilding.

Thanks for all your patience and all you do for us forum members

Brent

[KUB3]

I have also improved my MS 275, but in areas it will make a difference - to reliability and cosmetics. I had considered mounting chip holders, but while it's working perfectly I see no point.

[BigBrent]

Right now I have a pair of BB OPA627AU SMD chips on 2 single 8-pin adapters for the Op amps. This is for the uniqueness factor. I found a cheaper alternative to the more expensive brown dog adapters. If it doesn't work, I'll change it back to a more widely accepted op amp solution.

Brent

[Eric D]

KUB3, this thread is not about op-amps. With op-amps, you are correct, a lot of people agree there is no point in changing them, as you won't hear a difference.

We are talking about power supply FETs, and going from a factory FET rated for 30A maybe to one rated for 80A will get you more power out of the amp at lower impedance loads (in theory). Since the M50 only has 4 FETs, that is not a lot of current capability. Upgrading these to more modern parts may significantly gain current capability for the whole power supply.

The devices to the left of the FETs are the rectifiers. Each is a pair of diodes. Unless broken, I don't see any reason to change these.

[KUB3]

Oh right, I got the wrong end of the stick here