[mtl777]

Hi, has anybody tried bypassing a UF4007 diode with a .01uF cap? This technique is reported to work well with 1N4007's to remove RF hash in power supply circuits. I wonder if it would also work well with UF4007's which are already low noise. So I would greatly appreciate if anybody could share their experience -- whether it improved or did not make any difference or even degraded the performance.

Thanks!

 

[FallenAngel]

Generally, rectifier diodes are bypassed by small ceramic caps 100-220pF.

 

[mtl777]

Do you think it would benefit to bypass a UF4007 with a 220pF cap, considering that the UF4007 is already good?  I wonder why I don't hear about so many people doing this with a UF4007?  If it works well, it's much cheaper than buying an expensive Schottky or HexFred at $5 a pop.

 

[Pars]

http://www.hagtech.com/pdf/snubber.pdf

 

[mtl777]

Quote:

http://www.hagtech.com/pdf/snubber.pdf

Thanks, that's a great article and good info!

Unfortunately, I don't have a scope to make measurements with, so will have to rely on people's advice hoping that their recommended value is in the right ballpark. It also gets more complicated with the RC snubber, so I'm hoping a simple C will be good enough even if it's not as good as RC. If I take the simple C approach, what C value would you suggest as a bypass to be placed across each UF4007 diode in a typical bridge rectifier circuit that has 4 such diodes? No need to be super accurate, I just want a value that would work for most circuits.

Thanks!

 

[Pars]

I personally wouldn't bypass them. That is supposed to be the point to ultra-fast or more importantly, soft recovery diodes.
 
I normally use Schottkys when it makes sense to do so, typically either 11DQ10 or 31DQ10.

 

[Leny]

I vaguely remember that bypass caps for standard diodes used in Elektor designs were in the region of 22 - 47 nF. However, if you have no scope then you are whirling in the dark. I would say consider changing to Scottky diodes. If not then try your diodes un-bypassed, then subjectively assess the sound of the system, then add RC snubbers if you perceive a problem.

 

[mtl777]

Quote:

I personally wouldn't bypass them. That is supposed to be the point to ultra-fast or more importantly, soft recovery diodes.
 
I normally use Schottkys when it makes sense to do so, typically either 11DQ10 or 31DQ10.

Yeah, I should probably just use Schottkys.  I heard they are very good.  What Schottky part number would you recommend in place of the UF4007? I also want to know what electrical parameters should you match up when cross-referencing to find substitute diodes so that I could do this on my own in the future.
 
Thanks!

 

[Pars]

I already told you what I use. You will have to evaluate the electrical parameters required (voltage and current, probably surge (inrush) voltage and current, etc.) to determine what might be suitable for your application. I use the 11DQ10s in stuff like CD players, etc. The 31DQ10s I use in something needing higher current (3A). Not suitable for stuff like power amps, etc. I've never used any of the expensive Schottkys you alluded to.
 
Like Leny said, try the UF4007s with no bypass. That is more or less what they are for.

 

[Leny]

Quote:

...what electrical parameters should you match up when cross-referencing to find substitute diodes so that I could do this on my own in the future.
 

 
Forward current (often called Average Rectified Forward Current)
Reverse voltage (often called Peak Repetitive Reverse Voltage)
 
:  )

 

[mtl777]

Hey guys, you are so awesome!  Thank you so much for your help!!!

 

[mtl777]

Oh, one more thing:  What parameters or other info from the data sheet do you consider in judging a diode's performance for audio use?

 

[Paul J.]

On the advice of others, both of my tube amps run UF4007's bypassed with .01uf caps.  Do be sure you are using caps with a high enough voltage rating.  Folks usually suggest 1kv or more for ceramic (I used 2kv).  600V rated film should do it (mine are doing fine).  Schottkys are expensive.  UF4007s are cheap.  I wouldn't use 1N4007's unless I was really in a bind, as the UF's are so little additional $$.
 
Paul

 

[mtl777]

Quote:

On the advice of others, both of my tube amps run UF4007's bypassed with .01uf caps.  Do be sure you are using caps with a high enough voltage rating.  Folks usually suggest 1kv or more for ceramic (I used 2kv).  600V rated film should do it (mine are doing fine).  Schottkys are expensive.  UF4007s are cheap.  I wouldn't use 1N4007's unless I was really in a bind, as the UF's are so little additional $$.
 
Paul

Thanks for sharing!  Looks like bypassing a UF4007 is a cheap and possibly good alternative to Schottkys.  I'll try it with and without bypass and see what sounds better.
 
BTW, does anybody know what parameters or other info from the data sheet should be considered when comparing and choosing diodes for audio gear?  Like, is faster reverse recovery time better?  Or how about "soft recovery" -- how is it quantified in the data sheet?