How to make an audio console's power supply better?

[Dead_Nid]

Hi dear friends!

I've recently discovered the existence of Shotkey and Hexfred diodes which are said to be the best type used for rectification in audio PSUs. Can someone enlighten me on this as well as diodes in general? (fast,soft recovery etc)

Thanx a lot!
Nid

 

[Dead_Nid]

...by the way, is "Schottky" and "Shotkey" the same thing? What about FRED and Hexfred? Is there any difference in performance between using discrete diodes and bridges?

 

[ante1]

Hi Nid,

It depends on what you are trying to accomplish.

 

[Dead_Nid]

Hi Ante, you are right. Even though I have currently no known problems I think I am trying to accomplish the most efficient, clean energy (RF free) power supply I can make for my mixing desk. Nevertheless I've read that Hexfreds give a significant performance gain in the overall sound such as better resolution and reproduction of high frequencies and dynamics. Maybe that is another hype, that's why I am trying to get other people's opinions. Thanx a lot!

Best regards, Nid.

 

[bloki]

Comparing both regulators 1083 and 338 regarding ripple rejection parameter you can find that both has the same guaranteed value, -60dB. And it defines how much ripple you will have on output voltage.
Some types of linear regulators can oscillate if output capacitor has very low ESR.

 

[ante1]

Hi Nid,

I think the advantages of using this type of components are very limited. I would say it’s not even possible to measure the difference.

 

[Dead_Nid]

hmmm bloki, do you know if the LT1083 or LM338 will oscillate when caps have low ESR?

Ante, have you ever used all these diode types in linear regulation circuits so as to make a fair comparison?

Best regards, Nid

 

[ante1]

Hi Nid,

Nop I have not, I just can’t see why it should be that important in the rectifier stage. At least not if you already got your diodes or bridge rectifier bypassed with caps like I described earlier. 
BTW. I have not encountered any regulators which oscillate from low ESR caps.

 

[Dead_Nid]

Thanx Ante. I haven't done any mods yet...too much damned work...but I am going to start very soon.

 

[ante1]

Hi Nid,

Well, the guy here seems to be convinced why you don’t try it?

 

[Dead_Nid]

Happy new year to everyone!

Haven't tried any special diodes yet. I want to ask two very newbie things that I am curious about:
1) My PSU uses two 4700uF smoothing caps (in parallel so total capacitance is 4700x2). I am going to replace them because they are very old. But as the opportunity arises I could replace with greater capacitance. Is that better in smoothing quality (apart from space and cost issues)? Remember, this an audio mixing desk's power supply. So...I am thinking of placing 6800uF or 10000uF and that will mean a total of 13600uF or 20000uF...Even theoritically, is there any benefit as the capacitance gets higher and higher? Is there any chance that it can cause trouble instead?

2) What about voltage ratings? I was told (by Dan Lavry) to use caps with voltage ratings as low as possible. But in some manufacturers charts I have seen that the higher the voltage rating the lower the impedance. Any clue?

I am between BHC, Nichicon and perhaps Black Gate caps. Any suggestions?

Thank you! Best regards and happy,creative 2006!

 

[indulis]

More is not always better. There are dangers in making your cap's too large..... i.e. how would you limit inrush current?

For the most part, the ripple is "more" a function of ESR. Most times cap's are put in parallel to get ESR down instead of capacitance up. Lower voltage cap will give you a higher capacitance in the same size package. Depending on the voltage levels, you might be able to use cap's from Oscon.... they are VERY, VERY GOOD in terms of low ESR!!!!!

 

[Dead_Nid]

thanx indulis. please explain "inrush current". have you read the rest of the thread? It is a linear regulated psu. thanx again!

 

[ante1]

Hi Nid,

A Happy New Year to you too! ;D

The higher capacitance will lower the ripple (if any ripple exists), that’s the benefit.
Yes, as indulis says: inrush current can get you in trouble (maybe) depends on the rest of the circuit and how much higher value caps you use. However it is not the capacitance itself which is the issue, it is the ESR since this decides the level of the current. In other words; same uF but lower ESR might increase the inrush current anyway.
Inrush current is the current at powerup when the caps are drained and is “filling up” energy from the transformer through the rectifier diodes.