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dtm1962 19th August 2006 11:27 PM

40A 250V Schottky Power Diodes- Has anyone use in Power Amp to replace Diode Bridge?
I have a bunch of ON-Semi Schottky Power Diodes (MBR40250)that I was going to replace the 15A 400V diode bridge with.

The DC Rails are + & -70VDC (so the secondaries are 50VAC).

Has anyone tried these and what were the effects in sound quality if any.

My amp is a Rotel RB991 rated at 200/300 WPC RMS (at 8/4 ohms respectively).

Can you see any issues other than I have to heatsink them and the DC Rail Voltage will increase by 1 to 1.5 VDC as result of the 0.6VDC drop versus the Diode Bridge that drops up to 2 VDC.

My PS Caps are rated for 80VDC as well.

These diodes have the 250VDC rating so I am thinking I am OK.

Any comments or experience would be appreciated.


poobah 19th August 2006 11:42 PM

Why change at all?

dtm1962 19th August 2006 11:45 PM

I figure they must generate less rfi noise than a standard bridge.

But it probably has less effect than used in a CD player or preamp?

Do you agree?

Any improvements or detrimental effects on sound?


poobah 19th August 2006 11:58 PM

Schottkys are fast...very fast. While they make less noise, they do so at higher frequencies... more energy in the higher spectra. This may or may not slip through your filtering.

I guess I'm not too keen on them for line rectification because they are fragile; The voltage spec on a schottky is a line you don't pass... not for a picosecond.

Breakdown of silicon diode is an avalanche process. The spike tolerance is based on thermal issues. Different deal in a schottky I believe.

I guess I'm old school here... if you can hear your diodes, you have other issues.


grataku 20th August 2006 01:43 PM

the rating seems to be fine, just make sure the heatsinking is adequate and that you wire your brigde correctly. You should be in good shape.

Booyeah Poobah!
are you kidding around or are you trying to be controversially old fashion here?
I don't think there's anything new or wrong here. Diode replacement has been one of the standard mods done by thousands of people for the past 15 years (at least) with great results. I am one of these thousands. I just recently completed an update/restoration on an accuphase e-202 and the results have been tremendous. I made the updates in stages to try to isolate the most beneficial and gain a better understanding of works and what doesn't. I must say the diode replacement produced very audible changes.

dtm1962 20th August 2006 03:01 PM

Question for grataku:
Did you use Schottkys or High Speed - Soft Recovery Diodes like OnSemi MSR1560 in your projects?

Let me know as I had ordered some heatsinks to implement these changes.


poobah 20th August 2006 05:40 PM

and these changes were???


The fact that thousands do it means little... look at cables for example. Swapping diodes is popular because, like cables, it is safe.

I am not saying that swapping to schottkys won't change the sound. I am saying that unless you have the equipment to quantify the before and after noise in your power supply supply, and its spectral distribution; you will be relying on your ears for proof. Your ears will likely prefer the "upgrade"... for better or worse.

The point remains... if you can hear your diodes; you have filtering problems.

bassmax 20th August 2006 07:17 PM

I generally agree with poobah : shottcky diode are most fast than others for redressment. they 're too less strong, and by construction (tiny silicium layer) heat so much.
For the sound, I think that not change anything if the filtering is good ( higher frequencies must be appear with this sort of diode but i don't know).

EWorkshop1708 21st August 2006 01:07 AM

Would these Diodes work good in a high frequency SMPS powered amplifier?

poobah 21st August 2006 01:18 AM

YES... that is one place Schottkys shine. Especially on low-voltage outputs like 3.3 and 5 Volts. Aside from synchronous rectification... Schottkys are the only real choice.

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