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Post by spendorspain on Sept 4, 2006 18:10:24 GMT
Hi
I’m going to upgrade the reservoir capacitors in a 2 x 24 VDC PSU (for my headphone amplifier) with two Nichicon KG snap-in 4700uF/35v electrolytic caps (I’ve read very favourable reviews and they are very sensible priced). My doubt is regarding the use of bypass caps in parallel with them. I have two 0.1 uF/400V axial polypropylene film and tin foil and two 4.7 uF/250V metallized polypropylene (radial “box” type, as the axial ones are too big) capacitors. I’ve searched a little and there is a general agreement about the improvements made by bypassing the reservoir caps with a smaller cap, or caps if the bypassed electrolytic has a high value (of course, the bypassing of a DC-blocking cap in series with signal is another matter). I’m going to use the 0.1 uF cap in parallel with the 4700 uF, but I doubt if I need to use also the 4.7 uF cap. I have read that a combined “triple” cap (4700+4.7+0.1 uF in parallel) is better in shunting unwanted noise to ground, as each bypass cap deals with different frequencies; but I have also read that mixing caps can create harmful resonances when they combine and interact in the real circuit. Therefore my question is if the use of the 0.1 uF bypass cap would be enough to clean the supply (so I don’t have to worry about the complex interactions that the combination of 4.7 uf + 0.1 uF probably would generate), or if the double bypass is always better.
I hope you can help me with your advice. Thanks in advance.
Best regards
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rickcr42
Fully Modded
Rest in peace my good friend.
Posts: 4,514
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Post by rickcr42 on Sept 4, 2006 18:43:07 GMT
With solid state gear I personally have had good luck with the "Triple Cap" like you describe with the middle cap (in your case the 4.7uF) being either as big as I can squeeeze in or afford.
The last bit due to how fast both the price and size increase as you go up the scale in size with film caps.
When room is limited I go with a 1-2uf and when there is more 4.7-10uf with the reason being to get the film cap as far down into the audible range as possible with the ideal being all mid-to-high aubible frequencies covered by the far superior capacitor while the areas of less audibility-the RF range and the low bass taken care of by large electrolytic and fractional uf bypass cap.
Unless you are willing to build a bypass cap box the size of a shoe box and that costs several Hundred dollars there is no getting around using an electrolytic with SS gear even with a low current/low voltage power supply
Oh yeah-the nichicons are a great capacitor for the price
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Post by spendorspain on Sept 6, 2006 20:41:48 GMT
Thank you Rick, for your advice. I've used the "double" bypass (4.7uF+0.1uF) with the big 4700uF Nichicon KG caps and a single bypass (0.1uF) with the Cerafine 470uF caps. I've just reconnected the PSU and I hope there will be an audible improvement.
BTW, what is recommended for bypassing a 100uF/35v Cerafine capacitor?. Taking into account PCB size constraints, a single 0.1uF WIMA polypropylene bypass cap in parallel (small box-type with 5mm lead spacing ) would be ideal. I hope good electrolytics like Elna Cerafines are less slow and better behaved at high frequencies, and perhaps 0.1uF is enough for this relatively low capacitance (100uF) el-caps. What do you think?
Thanks again. Regards
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rickcr42
Fully Modded
Rest in peace my good friend.
Posts: 4,514
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Post by rickcr42 on Sept 6, 2006 23:36:20 GMT
is this for signal coupling ? If yes then I am against the grain/common beleif of using a multiole capacitor for signal coupling though 100% a minority view and rather prefer the single best capacitor I can fit/afford in that spot so that everything entering leaves as a whole rather than in "frequency selective parts" re-assembled at the output of the multiple capacitor. In the signal path as a "coupler" everything passes through the capacitor because it is a SERIES connection instead of like in a power supply where nothing actually passes directly through from end of the part to the other end but has one side SHUNT connected to a ground. As for the Cerfines,not too shabby and I have a HUGE one on the output of my Single Ended MOSFET Class-A amp but I find the Elna Silmics are maybe a better choice from use in other circuits. Bypassing 100uf with 0.1uf : 1-if audio coupling no-Being only 0.1uf the effect will likely be inaudible but will depend on next stage input impedance just exactly where the frequency crossover to the cap will take place,Higher impedance next stage means lower down the cap will operate though even a 100K input the audible results will be minimal at best. The main problem with good caps is size with the best ones always being big in size.Better to squeeze in something good or if no room forego something that will not be any real improvement. At least in my own personal opinion 2-if power supply then YES ! As many as you can fit in as many places as you can get them ! RFI,rectifier noise,mixed signal circuits.ALL radiate into any active amplifying stage so need to be "shunted away" before these signal can enter the circuit at the power supply pins and be treated as just another signal by the device hence amplified as well Quick and dirty would be signal path cap bypass as big as you can get it with each jump in size meaning further down in the audible range the new cap will dominate power suopply the tiny RF bypass has more importance than the larger 2-10 electrolytic bypass cap.One may or may not be audible,the other can prevent signal contamination so always a good idea and in multiple positions with solid state gear.Why solid state ? Because of the bandwidth.Those data sheets/ad copy that says "flat to 200Khz" also means it will react to any ultrasonic garbage as well. hope this helps man Rick
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