High Speed Diodes

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R

rljones

Member
Joined 2001
(I'll try to keep my head down to avoid the arrows...)

Mr. Dieckmann,

In looking over the snubber references and doing a little googling on my own, I came this reference:

http://www.steward.com/techinfo/subsystems.html

about 2/3 down, the article discusses using ferrite beads in the power supply section, both on AC lines, between the bridge and rectifier diodes and even on the output DC voltage wires.

This technique, along with this article:

http://www.eherbert.com/ehtech/spcsnub1.pdf

would seem to suggest that ferrite beads are as affective as using derived RC networks for snubbing purposes.

What is your take, or anyone elses for that matter, on this?

Regards, Robert

"Always be prepared to give an answer to everyone who asks...But do this with gentleness and respect..." 1 Peter 3:15
 
Elso Kwak

Elso Kwak

Banned
Joined 2001
geocities.com/elsokwak/
Schottky vs. Soft Recovery

Hi all,
I did dome search to find out about prior art:
John Curl was using RURD460 soft recovery in the supply of the improved JC-2 preamplifier. (Positive Feedback, Vol.8, No1)
John points out the glitch is difficult to measure, as I can confirm. I never did see the ringing on my scope.
http://db.audioasylum.com/cgi/m.pl?forum=tweaks&n=56094&highlight=curl+soft+recovery&r=&session=
http://db.audioasylum.com/cgi/m.pl?forum=tweaks&n=16739&highlight=curl+soft+recovery&session=
http://db.audioasylum.com/cgi/m.pl?forum=tweaks&n=15285&highlight=curl+soft+recovery&r=&session=
Allen Wright is using BYV10 Schottky's in his Vacuum State Electronics mod. for the Sony SCD-1 SACD player.
Sony is using a whole bunch of RBA-406B bridge rectifiers in the same player. These are 4A Schottky bridges.
Giorgo Pozzoli is using soft recovery BYV27-100 is his Convertus Decima DAC.
http://www.tnt-audio.com/clinica/convertusdecima-sch_e.html
I also downloaded a preamp supply for a kit. I forgot the name. It is using MBR1100 Schottky's and 1 Ohm resistors between transformer and bridge.
Guido Tent is using 1N5819 Schottkys with 470pF snubber caps in his and Heijligers et. al. DAC.
http://members.chello.nl/~m.heijligers/DAChtml/dactop.htm
All the other references given don't use any snubber.

Concluding I can say that the Schottky diode might have found more widespread use than the soft recovery diode.
I for one was using Schottky 11DQ10's in my Philips CD650 CDP, DAC and preamp.
Now as a experiment I replaced all Schottky's by MUR120 high speed soft recovery.
It is a clear improvement! These powersupplyrectifiers have a profound influence on the sound of female voices. Soprano's and flutes and the like. Sounds like some resonance effect to my ears.
So I tempted to state that the soft recovery issue is more important than the high speed.
In the Rectifier Applications Handbook from Onsemi (HB214/D) I found that Schottky's do exhibit ringing!
Onsemi has now a few ultrasoft recovery rectifiers: MSR1560, MSR860, MSRD620CT. The latter is 6A rating, the other even higher, but I will give it a try. Will also experiment with ferrite beads, RC-snubbers and small resistors in series with the diodes.
:idea: :cool:
 
fdegrove

fdegrove

diyAudio Senior Member
Joined 2002
NOTHING'S EVER PERFECT.

Hi,

These powersupplyrectifiers have a profound influence on the sound of female voices. Soprano's and flutes and the like. Sounds like some resonance effect to my ears.
Click to expand...

I'm duly impressed, this is exactly what I hear even on the better commercial DACs .

While I agree with you entirely when you say that Schottky diodes aren't perfect, they're often a lot better than the average diodes available.

In the following thread I show shots of two identical, snubbered supplies bar the diodes:

TUBE REGULATOR

Posts #s 39 &40.

Cheers,;)
 
Elso Kwak

Elso Kwak

Banned
Joined 2001
geocities.com/elsokwak/
Another interesting Link

Hi,
This one from AudioAsylum sounds interesting. In fact the post is a copy from the Madrigals website promotional literature.
http://db.audioasylum.com/cgi/m.pl?forum=tweaks&n=29351&highlight=soft+recovery+madrigal&r=&session=
Mark Levinson No.380 preamplifier:
http://www.marklevinson.com/preamplifiers_fr.htm

There are many more post on AA about soft recovery diodes. If you fill soft recovery [AND] into the search engine of Tweakers Asylum you will find 200 posts as this is the maximum number that can be displayed. I found the situation extremely confusing as there seems to be a party in favor of Schottky's and an other party in favor of high speed soft recovery.

The powersupply schematic with the MBR1100 was on the Hagerman site:
http://www.hagtech.com/bugle.html#powersupply
For the schematic scroll down the page where you can download the schematic.
;)
 
F

Fred Dieckmann

diyAudio Retiree
Joined 2002
back on track

Thanks Elso, Frank, and Bert for restoring the thread back to the topic. I have had better results from Soft recovery diodes than Schottkys, but think Schottkys with snubbers would probably work very well. For low current supplies I have used and seen others use the 1N4933 to 1N4933 series soft recovery type. Ferrite beads should be used with care as they are reactive (inductive or capacitive) over part of the frequency range and can saturate with large peak diode currents. One of the areas worth investigation is if even power transformer core are partially during peak diodes currents charging filter caps. The diode ringing is hard saturating to measure with a conventional (non storage) scope. I am working on an envelope detector using hot carrier RF diode to see if this might make this ringing easier to see with the usual test equipment available.

http://www.bravoelectro.com/html/stnetnsup.html
http://www.orcadpcb.com/pspice/applicationnotes/tn20.asp?bc=F
http://www.welbornelabs.com/ac.htm

Also from hagtech site for power supply scematic:
http://www.hagtech.com/pdf/snubber.pdf
 
mlloyd1

mlloyd1

Member
Joined 2001
Re: Schottky vs. Soft Recovery

Elso:
Good info!
I have played around a bit with the On Semi MSR (860 and 1560) series rectifiers recently. My initial impression sound-wise, is that they sound better than schottkys I have played around with in my applications. (Peter, have you tried yours out yet?;) ) I also like them better than the MUR860 and MUR1560 I was playing around with previously. Oddly enough, my impression is somewhat similar to yours; I was listening to some of my favorite female vocalists CDs at the time.

I think the power supply circuit you pointed to was from Jim Hagerman for his Bugle RIAA preamp (oops - now I see you have already pointed that out!) . I asked him some questions about the design and he graciously gave me quite a bit of info about the whys and whats. I feel uncomfortable copying into this message what he told me without checking with him first, so I'll try to do that and see what he says. Maybe he will come over for a visit if he isn't already here.

I tried series R-C snubbers across the MSR860 and wasn't able to notice any difference, but I'm still experimenting. I haven't played with any beads yet, but Phred's (?) reference from yesterday looked interesting.

Thanks for helping get this excellent discussion back on track :nod:

And to think, (many) years ago I used to be one of those folks that said a rectifier is a rectifier is a rectifier. I saw the light (well, heard the light actually) when I was "discussing" the matter of rectifiers years ago with a equipment mfr at CES. I did as I was told and held an AM radio near the bridge in one of my old class AB amps and listened to the crap. Changed to soft recovery diodes and the radio was almost quiet. Added R-C snubbers across the rectifiers and across the transformer secondary and the radio was completely quiet. I learned my lesson - experiment and listen first, then speak. :eek:

mlloyd1

Elso Kwak said:
Hi all,
I did dome search to find out about prior art:
...I also downloaded a preamp supply for a kit. I forgot the name. It is using MBR1100 Schottky's and 1 Ohm resistors between transformer and bridge.
....Now as a experiment I replaced all Schottky's by MUR120 high speed soft recovery.It is a clear improvement!
....Onsemi has now a few ultrasoft recovery rectifiers: MSR1560, MSR860, MSRD620CT.
Click to expand...
 
Elso Kwak

Elso Kwak

Banned
Joined 2001
geocities.com/elsokwak/
Re: Re: Schottky vs. Soft Recovery

mlloyd1 said:
Elso:
Good info!
I have played around a bit with the On Semi MSR (860 and 1560) series rectifiers recently. My initial impression sound-wise, is that they sound better than schottkys I have played around with in my applications. (Peter, have you tried yours out yet?;) ) I also like them better than the MUR860 and MUR1560 I was playing around with previously. Oddly enough, my impression is somewhat similar to yours; I was listening to some of my favorite female vocalists CDs at the time.

I think the power supply circuit you pointed to was from Jim Hagerman for his Bugle RIAA preamp. I asked him some questions about the design and he graciously gave me quite a bit of info about the whys and whats. I feel uncomfortable copying into this message what he told me without checking with him first, so I'll try to do that and see what he says. Maybe he will come over for a visit if he isn't already here.

I tried series R-C snubbers across the MSR860 and wasn't able to notice any difference, but I'm still experimenting. I haven't played with any beads yet, but Phred's (?) reference from yesterday looked interesting.

Thanks for helping get this excellent discussion back on track :nod:

And to think, (many) years ago I used to be one of those folks that said a rectifier is a rectifier is a rectifier. I saw the light (well, heard the light actually) when I was "discussing" the matter of rectifiers years ago with a equipment mfr at CES. I did as I was told and held an AM radio near the bridge in one of my old class AB amps and listened to the crap. Changed to soft recovery diodes and the radio was almost quiet. Added R-C snubbers across the rectifiers and across the transformer secondary and the radio was completely quiet. I learned my lesson - experiment and listen first, then speak. :eek:

mlloyd1
Click to expand...
Michael,
Well, what can I say... You are one step ahead of me....;)
I just received the MSR860's this morning. The other types are in backorder.
I am confident in trying these.
Thus far my experiments are confined to low current supplies as my Ampzilla needs rather high voltage diodes not yet available in Schottky. I have some MBR20200CT but I think the 200V voltage rating is a bit on the low side for a +/- 80V supply. Also I wanted to await the outcome of my experiment with the supply for the CDP and the DAC.


;)
 
fdegrove

fdegrove

diyAudio Senior Member
Joined 2002
SiC Schottkys.

Hi Elso,

as my Ampzilla needs rather high voltage diodes not yet available in Schottky. I have some MBR20200CT but I think the 200V voltage rating is a bit on the low side for a +/- 80V supply.
Click to expand...

600V high enough?

Basically the new Silicon Carbide Schottkys promise the possiblity to go as high as 2KV, i.e. 100 x higher than the regular ones.

MICROSEMI

Cheers,;)
 
A

ALW

Member
Joined 2001
Snubbed again

Thanks Elso, Frank, and Bert for restoring the thread back to the topic. I have had better results from Soft recovery diodes than Schottkys, but think Schottkys with snubbers would probably work very well.
Click to expand...

Had a little play with this yesterday, as I had some time to fill.

Seeing the resonance of the transformer is not to difficult to do with a reasonable 'scope. Use the ripple waveform for triggering on one trace, then look at the transformer waveform on the other trace.

You can then zoom into the area of the sinusoid where the diod turns off, and some small-amplitude ringing was clearly visible.

A few minutes later and the leakage inductance of the transformer, it's self-resonant frequency, and thereby it's capacitance were calculated.

Add diode capacitance to the end result and we can then calculate an optimised RC snubber with a target damping of 0.5, as per Hagerman article above.

Another look with the scope and the snubber fitted and I can't resolve it anymore, and listening tests do seem to have resolved something - not night and day, but subtle and definitely better.

That was in a low current supply using some 50SQ080 Schottkies - chosen 'cos they were lying around, rather than through any specialised selection process ;)

I'll now dig deeper into th contents of this thread, thanks for keeping my spare time usefully occupied Fred :)

Andy.
 
F

Fred Dieckmann

diyAudio Retiree
Joined 2002
Progress

First off thanks to Robert not Bert.......

Thanks for the additional research from everybody. I am doing some measurements on power transformer that might give and rough idea of the typical numbers for some of the parameters I measured to use in modeling.

Signal Transformer

http://www.signaltransformer.com/signal/products/pdfs/page_08.pdf
A41-175-1111 (surplus) 175VA

R primary paralleled windings 1.6 ohm
L primary 0.33 H
L leakage primary 15.8 mH

(for each secondary winding)
R secondary 0.05 ohms
L secondary 5.3 mH
L leakage secondary 0.28 mH


Plitron 225 VA
http://www.plitron.com/Pages/Products/Std/ratings.htm
06714011 #1614

R primary paralleled windings 1.5 ohm
L primary 0.65 H
L leakage primary 0.38 mH

(for each secondary winding)
R secondary 0.13 ohms
L secondary 25.4 mH
L leakage secondary 0.9 uH
 
Peter Daniel

Peter Daniel

Member
Joined 2002
audiosector.com
Paid Member
Re: Re: Schottky vs. Soft Recovery

mlloyd1 said:

I have played around a bit with the On Semi MSR (860 and 1560) series rectifiers recently. My initial impression sound-wise, is that they sound better than schottkys I have played around with in my applications. (Peter, have you tried yours out yet?;) ) I also like them better than the MUR860 and MUR1560 I was playing around with previously. Oddly enough, my impression is somewhat similar to yours; I was listening to some of my favorite female vocalists CDs at the time.
Click to expand...


I just receive the MSR860 diodes today, thanks.

I compared them to MUR860 and I must say that it seems like an improvement. More 3 dimentional sound, more detail in treble, more musical. MUR seems to be a bit flat sounding, while MSR gives more music. If I can complain about something, it would be a sort of artifact in female voice. I don't know what it really is, but it seems like some sort of haziness or glare, but nothing really big. I will see how it sounds after breaking in, but it looks very promising. Certainly the best alternative to MUR860 I checked so far.
 
R

rljones

Member
Joined 2001
Carlos,

I've purchased Shindengen devices from BDent ( http://www.bdent.com/ ). I've found that these devices are much better than usual bridge rectifers. I have not compared them to Schottky devices during any listening tests.

I can, however, provide some test bench data of sorts. I'll be brief with the data. I have an amplifier. the details of which are not pertinent, that with dual-bridged Shindengens has a freq response of -2dB at 100kHz and a THD at 1W/8R of 0.006%. I changed to 100V/8A Schottky's and the THD dropped to 0.005%, and, surprisingly, the freq. response is now -0.2dB at 100kHz. (I've checked other parameters and the amp is definitely stable and not oscillating.)

Nothing else in the power supply was changed; just the recitifiers. The topology is still dual-bridged. The power supply is an Avel 30-0-30 (500VA I think) with 0.1uF across each secondary pair, 0R1 in series from rectifiers, filtered by 6800uF per rail, another 0R1 series resistor, and finally 15,000uF per rail. I recently changed the second 0R1 series resistor to a 3mH choke and the THD dropped to 0.004% and now looks even cleaner on the scope. (Maybe I don't know what I'm doing, but when I sync the scope to 120Hz, all I see on the rails is about 3mV of sine-like ripple--the choke really smooths it out--I see no high freq ringing, etc.)

Next, I'll try some the MSR1560 and MBR20200CT (I already have the latter), but I'm looking for a source for the MSR1560; any suggestions for a source?

Regards, Robert
 
P

Petter

Member
Joined 2001
Referring to previous posts, it seems likely that Schottky can sound very good if the current pulses (power) levels are not excessive. For high power it should be advantageous to use "ordinary" soft recovery diodes.

I have tried my 15ETH06 devices but have not had the chance to compare with anything else in a meaningful way.

Petter
 
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