I think it is a lot. I can't see any advantage over 20k or 30k. The ripple starts to look more and more like a sawtooth, especially with higher loads, and we all know that saw tooth waves have a very rich set of higher harmonics.
100 (or 120) Hz ripple isn't so bad for the amp, because the power supply rejection at low frequencies is almost always quite good. But at higher frequencies it is much less so these higher harmonics of the saw tooth can get to the output easier than the basic ripple.
So my point is really why pay double for the caps unless it brings you something in terms of sound quality. I don't see that.
PSUD2 is an excellent program to get a feel for it.
And, Andrew, I always try to be nice; I sometimes don't succeed but I hope that in that case you can excuse me...
jd
Hi Jan,
I have to disagree a bit. If a large amount of reservoir capacitance is to be used, one can profit by splitting it and separating the two sides with a very small resistor, on the order of 0.1-0.3 ohms. This amount of resistance is still very small compared to the equivalent DC resistance of the power supply, but gets another pole of filtering in the path to suppress the high frequencies of the sawtooth.
Cheers,
Bob
You can try it. Take a xformer, a rectifier and a filter cap and a load resistor. Look at the ripple on the cap on your scope or on a simulator. As you increase the cap you will see that the ripple goes down in amplitude. That of course means that the topping up by the transformer takes place in smaller and smaller pulses, because the time where the xformer voltage is above the cap voltage gets smaller and smaller. Not many people realize that the xformer is effectively disconnected from the system most of the time except for the small period that the rectifier conducts. Ballpark figures for a 50Hz system (10mS period) is that the xformer is disconnected 8mS and connected (charging the caps) 2mS per period.
But you still need the same charge in the cap for that load, so smaller times means higher pulses, stressing the xformer and the rectifier.
What you also will see is because the charging time gets smaller and the discharging time (necessarily) gets longer, the ripple starts to look more and more like a sawtooth.
If you look up how a sawtooth is constructed you will see it is the sum of a base frequency (here 100 or 120Hz with two-phase rectification) plus, in theory, an infinite series of even harmonics. The sharper the sawtooth, the more higher harmonics.
There is enough material for that on the internet, google is your friend!
jd
Agreed Bob. The same effect can of course be reached with a C-L-C filter. I just wanted to present another view to the often indiscriminate increase of the capacitance after the rectifier thinking that bigger must be better. I've seen 100.000uF right after the diodes, the mind shudders!
jd
But with a properly implemented ceramic coupling cap and choke coil thats all history
You just have to careful with component selection and placement
Ceramic coupling cap? In a supply? Sorry, you lost me...
Unless you are joking of course. Yes that must be it
jd
True; just use an inductive resistor
.Actually, I do like to have at least 0.1 ohm in such an arrangement down to DC. It allows me to better isolate that first ground connection where all the current spikes sum. I then put this star on a spoke off the main star ground.
Cheers,
Bob
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Who else is got something in the works using thermal tracks ???
Kindah curios to see how many ventured to TT land
The output stage bias is very stable in this TT implementation:
http://www.diyaudio.com/forums/showthread.php?threadid=111756
Ahhh...
Insfirsit un roman
De unde esti ???
Eu am fost nascut si am copilarit in Arad, dar parinti au emigrat in canada in 96.
Back on Track
Who else is got something in the works using thermal tracks ???
Kindah curios to see how many ventured to TT land
My error correction amp uses Sanken TT darlingtons and was published in AudioXpress and Elektor USA.
jd
Ahhh...
Insfirsit un roman
De unde esti ???
Eu am fost nascut si am copilarit in Arad, dar parinti au emigrat in canada in 96.
Servus canadianule de origine romana
!Eu sunt din Campulung - Arges, insa sunt stabilit in Bucuresti de aproape 20 de ani
Hai sa continuam in engleza ca sa nu facem nota discordanta cu linia forumului. Te astept pe PM pentru orice alte intrebari
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Who else is got something in the works using thermal tracks ???
http://www.diyaudio.com/forums/showpost.php?p=1858307&postcount=98
http://www.diyaudio.com/forums/showpost.php?p=1866841&postcount=139
http://www.diyaudio.com/forums/showpost.php?p=1866838&postcount=922
Last edited:
Indeed, servus is used in many European countries:
http://en.wikipedia.org/wiki/Servus
I wasn't know that, thank you Jacco
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Who else is got something in the works using thermal tracks ???
http://www.diyaudio.com/forums/showpost.php?p=1395756&postcount=113
Ceramic coupling cap? In a supply? Sorry, you lost me...
Unless you are joking of course. Yes that must be it
jd
Like this...
Ahhh yes, not a coupling cap, it's called a snubber. Normally snubbers are a series connection of R and C, to damp any switching transients on the diode.
The problem with using a diode is that it forms a nice bridge for any mains noise into the rest of the equipment.
jd
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