Increasing PSU capacitor on Soundcraftsmen MA-5002A

[mazur]

Hi.

I'm recapping my Soundcraftsmen MA-5002A amp and I'm thinking of increasing the PS capacitors. This is a class H with 63V on the rails up to 125W and switches to 92V up to 250W. For the 63V it has 2 11,000uF at 60V caps and for the complement to 92V it has 2x 22,000uF at 30V. Question is: how high can I go? I was thinking 40,000uF and 60,000. Is it going to affect the in-rush current and cause problems?

Thanks.
--
Elias

[Atomicplayboy]

Originally Posted by mazur

I was thinking 40,000uF and 60,000. Is it going to affect the in-rush current and cause problems?

Yes it is going to increase inrush current, but whether it causes problems is up for discussion.

It's always I good idea IMO to fit an inrush liniter (NTC thermister) on the primary; the idea is that their resistance is high when cold, so when you cold-start the amp there's a soft-starting action. This isn't foolproof though as they take a while to cool down before they provide protection again.

For the modest increase you're talking about you might well be OK though - I think you'd need to tack the new caps on and measure it.

I wonder whether increasing these caps will actually get you anything though; what makes you think they're undersized at the moment?

Cheers,

[nigelwright7557]

I added larger capacitance to my amp and it started blowing mains fuses.
I had to increase the value of the mains fuse to the next current value upwards.

[mazur]

Originally Posted by Atomicplayboy

Yes it is going to increase inrush current, but whether it causes problems is up for discussion.

It's always I good idea IMO to fit an inrush liniter (NTC thermister) on the primary; the idea is that their resistance is high when cold, so when you cold-start the amp there's a soft-starting action. This isn't foolproof though as they take a while to cool down before they provide protection again.

For the modest increase you're talking about you might well be OK though - I think you'd need to tack the new caps on and measure it.

I wonder whether increasing these caps will actually get you anything though; what makes you think they're undersized at the moment?

Cheers,

Nothing really. I tend to agree with you that probably I won't get much improvement (the amp already sounds great) and besides I use it to drive some large Altec 1003B horns, so it's probably just using a few miliwatts I was thinking about it because people say that more capacitance gives better results, etc. I guess I'll just replace the caps with the same value because of the age. Thanks for the help.

[Atomicplayboy]

Well, I like to figure out the performance bottlenecks in a design and remove them in turn. I'm also a believer that if it isn't broken don't fix it, especially if you care about breaking it If it sounds great now, I would spend the time and effort on improving acoustics instead.

Larger inrush isn't an issue so long as it's managed correctly (NTC, delay fuse, up-rated rectifier etc) but I don't see much point adding the compexity and stressing these components without measuring some difference with and without the uprated part first.

Just my £0.02

Cheers,