FRED Rectifiers

[Structo]

Do any of you use the FRED diode rectifiers in your ODS style amps?

For instance, this diode in TO-220 package is an 8 ampere 600v Fred.
16ns recovery time.

[img:150:150]http://www.mouser.com/images/vishay/ima ... tl06fp.jpg[/img]

http://www.mouser.com/ProductDetail/Vis ... 9rYr%252bY

In theory would one of these on each side of the HT handle the current for a 100w ODS?

Or is two in series on each side a better option for safety?

I have read a few accounts where guys have stated their amps sounded better with these compared to the old 1N4007 or similar diodes.
Anything to this?

Do you need to put snubber caps on these diodes? ( I would guess not)

Just curious if any of you use these?

[67plexi]

Tom, This ???

[XgamerGt03]

The FREDs do not require a snubber capacitor.

Some people would suggest using two in series on each side just to increase the overall power handling of each side. 600V is more than enough for most amplifiers though.

[paulster]

You don't need to go with TO-220 packages either. I don't know why everyone tries to shoehorn these in when there are plenty of fast recovery diodes available in regular DO-201AD packages.

Take a look at the SR503 (or MS503) and UF5408 for example. And there are loads of others.

[Hellhammer]

The FREDs do not require a snubber capacitor.

Some people would suggest using two in series on each side just to increase the overall power handling of each side. 600V is more than enough for most amplifiers though.

In a fullwave rectifier you often need more than that:

When using silicon rectifiers, they must have a peak inverse voltage (PIV) rating of 2.8 times (2 * root 2) the RMS voltage being delivered by the transformer. (This is a higher PIV rating than necessary with a bridge rectifier.)
For example; with a transformer rated at 300-0-300Vrms the diodes must be rated at:
2.8 * 300 = 849V PIV

http://www.freewebs.com/valvewizard/fullwave.html

[Structo]

Yes Steve just like those.
Which ones did you use?

Paul, on my D'lite when I rebuilt the rectifier board I used the UF5408's

The problem with those is that the lead diameter is so large it's hard to fit more than two of those plus a snubber in an eyelet.
In fact I had to drill out the eyelets just a bit to be able to fit them.

On my latest 100w ODS build, I used a diode called a STTH110.
It is spec'd as a Ultra Fast Recovery Rectifier.
1000v 1A 75ns.
These are the size of the 1N4007. DO-41 package.

http://www.mouser.com/Search/ProductDet ... 11-STTH110

I used three in a series like the stock supply.


So have any of you determined any sonic or audible improvement in using the FRED's over the common general purpose diodes? (1N4007)

[David Root]

The hi-fi guys say soft recovery (less voltage spiking) is more important than high speed switching. I have used quite a few Fairchild Stealth soft recovery FREDs which I think are very good and combine both characteristics.

I would still use two in series for 1200V in this specific example though. I normally use two single 1200V FREDs or a double 1200V FRED, which takes up less space. I even have some 1800V FREDs which I'm holding for a Music Man iron ODS (700Vp).

[heisthl]

at $0.60 I like these:
http://www.mouser.com/ProductDetail/ON- ... ttp3Ufs%3d

I use 4 of them though for redundancy in case of a short. No caps required.

[butwhatif]

They're good for hi power hi fi sound, i'd never put one in my guitar amp.

[Structo]

Why is that?

[butwhatif]

Subtle dynamic feel is an important part of playing. As you might know-too mushy feels dead, too quick feels cold.

[ampdork]

Curious how they would affect the feel or speed of an amp?

I am under the impression that the only thing these do faster is stop conducting....leaving less of a sonic "ping" artifact...

Other then that added noise with the normal ones I would assume they would sound and respond very much the same??

They are not like tube rectos where actual sag can occur....wonder what about them would alter the feel or speed....

[David Root]

I don't share whatif's fears, again I recommend the soft recovery types, don't get seduced by the nanosecond switching times, that is irrelevant at audio frequencies. Soft non voltage-spikey recovery is most important.

Compared with 1N4007s they are so far ahead of 1N4007s it's not worth talking about. Capability, both voltage spikes and current, and most importantly, clean tone and no noise, is light years ahead.

At the currents we use none of the 220 package units really need heatsinking I think, although I do use small ones anyway, headroom is good!

And the additional cost is small and getting smaller every 12 months.

[glasman]

I would still use two in series for 1200V in this specific example though. I normally use two single 1200V FREDs or a double 1200V FRED, which takes up less space. I even have some 1800V FREDs which I'm holding for a Music Man iron ODS (700Vp).

I agree, the rule of thumb is that you want a PIV of 3x your DC voltage. 1200 would be about the minimum I would use.

In my amps I use 3 UF4007's (1000V PIV / 1 AMP) on a side.

Gary

[bluesfendermanblues]

I also use UF4007 in my amps, which a hifi friend hinted me towards.

No sure I can really hear any difference between regular 1N4007s and the UF4007s.