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Changing rectifier's ..is it worthwhile??

Mynamemynaim

Mynamemynaim

38yrs a Naim owner
So I have a pair of vishay rectifier's doing the job of AC/DC conversion in my power amp (one per board from separate transformer windings)
Would it be a worthwhile investment to change to a pair of Avondale Schottky boards at £28 each...ie would I hear the difference and say "money well spent"
Anyone done it and want to comment please??
 
Mynamemynaim said:
So I have a pair of vishay rectifier's doing the job of AC/DC conversion in my power amp (one per board from separate transformer windings)
Would it be a worthwhile investment to change to a pair of Avondale Schottky boards at £28 each...ie would I hear the difference and say "money well spent"
Anyone done it and want to comment please??
Click to expand...
Hi,
If you examine Doug Self book, he recommends placing snubber capacitors across each diode, s this reduces any RF switching artefacts.

If the Avondale board includes these, then maybe purchase, else fitting to a rectifier should be easy to do.

Regards,
Shadders.
 
Not sure if Les includes caps on his rectifier's...but don't think he does
I wasn't thinking about higher out put voltage I must admit!!
I thought any gains would come from faster switching giving a smoother voltage??
 
Mynamemynaim said:
Not sure if Les includes caps on his rectifier's...but don't think he does
I wasn't thinking about higher out put voltage I must admit!!
I thought any gains would come from faster switching giving a smoother voltage??
Click to expand...
Hi,
There seems to be two approaches, standard diodes with snubber capacitors across each, or fast switching soft recovery diodes to reduce the RF at turn off time. The ultra fast slow recovery diodes do not need snubber capacitors.

You could ask Les if snubber capacitors are ok for his design, as this is a quick implementation to your existing board also.

Regards,
Shadders.
 
Mynamemynaim said:
Not sure if Les includes caps on his rectifier's...but don't think he does
I wasn't thinking about higher out put voltage I must admit!!
I thought any gains would come from faster switching giving a smoother voltage??
Click to expand...

Very, very unlikely to be any gains from changing rectifiers. The rectifiers just charge up the smoothing caps of course.... and they do it in very short sharp spikes of current towards the top of the mains waveform.
Add some snubber caps or RC networks if it makes you feel better about it:)
 
@Mynamemynaim - try a search for 'snubbing' in the DIY room for previous discussion; its easiest, perhaps best, done across the secondary of the transformer.
It's not difficult to get right, and puts the whole thing to bed more or less.

I do like fast soft rectifiers in new builds, but otherwise - the above works just as well IME
 
I can't say I've noticed any difference in sound with either snubbing or fast soft recovery rects... I can verify from my own tests the lack of RF ringing and any need for snubbing with the later though...
 
Thanks to all
The simple answer seems to be to pop some capacitors in the appropriate place and be done with it I guess...
Though this might make a reasonable difference moving away from the vishay ...but maybe not..don't want to waste money on unnecessary changes
 
If you feel it's a worthwhile endeavour then the qspeed rectifier are as quiet as it gets, snub the transformer secondaries with an appropriately measured c -rc snubber set and it's done.

I cant lend you a small 50hz share wave generator, quasimodo for just this purpose, you'll need a scope to do it correctly though.

I always do this. For the 8 quid or so it cost to eliminate any vestige of ringing it's a no brainer, though not audible is 95% of cases. I do it on every Paradise build, just cos.
 
The qspeed looks interesting and available at mouser too .
Thanks for the offer...and I do have a scope .,.but probably a step too far for me.,
Will investigate the qspeed and snubber option and take it from there!

Cheers everyone
 
I have always been wary of caps across rectifier diodes for the possibly mistaken belief that the cap must couple some AC noise across the diode. Is this not true or do the benefits of the cap out way the cost of coupling rubbish into the PSU DC circuit?


sq225917 said:
I cant lend you a small 50hz share wave generator, quasimodo for just this purpose, you'll need a scope to do it correctly though.
Click to expand...
SQ225917, how have you developed the Quasimodo transformer test rig? I have been meaning to build one but any practical insights would be really helpful.

Cheers
Ian
 
davidsrsb said:
The Qspeed datasheet shows very high Vf, around 2V in practice for the 600 V, 1.5 V for the 300 V part
Click to expand...

Yes, they do, and it's borne-out in practice.

Just checked the 6A/300v Qspeeds in the psu for my headphone amp next to me - at c.300mA dc out/rail, Vf is c.1.6v per diode. Pretty rough measurement: but notably more than using any plain old silicon thing. And that means more dissipation - but the TO220 format means they're good for a watt or so without any added heatsink (rather more, obviously, with) and at this level they're barely warm to the touch.
 
Yes I actually pick between different version to help trim the voltage between dual mono supplies when the transformers are a little awry
 
It's a non subject IMO.... nothing to be gained or lost through choice of rectifier.

If we were talking efficiency and switching losses in the rectifiers of a SMPS then that's another thing entirely...
 
IDM said:
I have always been wary of caps across rectifier diodes for the possibly mistaken belief that the cap must couple some AC noise across the diode. Is this not true or do the benefits of the cap out way the cost of coupling rubbish into the PSU DC circuit?
Click to expand...

One of the reasons to fit small caps across each individual diode in a 4-diode bridge is that it 'clamps together' at RF all the connections. Thus helps reduce or prevent any RF coming in from mains to become an RF event between the power lines and ground.

So although they can help reduce 'snap noise' from the diodes, they may also help reduce any tendency for the unit to pick up crap from the mains.
 
There's huge electrolytic caps to ground after the rectifier anyway and in most modern amps there are smaller film caps across these for lower RF impedance.
A few turns of the mains lead on a ferrite toroid just before entering the equipment is about the most effective way of dealing with RF it is an issue IMO. I've got rid of RF breakthrough from a radio ham using 1000W RF amp 100 yards away in the past!
 
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