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Good capacitors for opamp power rails?
Good capacitors for opamp power rails?
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Old 21st January 2012, 03:25 PM   #1
Sype is offline Sype  Finland
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Default Good capacitors for opamp power rails?

I'm building headphoneamp using LM6171. Power supply rails are +/- 15V (LM317/337 regulated) and I'm looking for good caps for power supply, for each opamp's bypass. Schematic is Jan Meiers HeadWize - Project: A DIY Headphone-Amplifier with Natural Crossfeed by Jan Meier with some "upgrades", like more stiffer power supply.
Sanyo OsCon 47F/16V are my first choise, but do these need any ceramic/plastic caps in paraller? Are there any better alternatives for less money..? Is 15V too high supply voltage for 16V OsCon's?
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Old 21st January 2012, 03:31 PM   #2
Pano is offline Pano  United States
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Good capacitors for opamp power rails?
The OsCon are well liked and a very good choice. It's easier and cheaper for me to get the Panasonic FM series which are also very low ESR and well made. They may not be available in Finland, I don't know.
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Old 21st January 2012, 03:42 PM   #3
qusp is offline qusp  Australia
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are you opposed to SMD? actually the oscons are not even so great by todays standards, but they have a good name. the nichicon polymers are MUCH cheaper for the 47uf/16 you have part number PCG1C470MCL1GS at digikey which come in a leaded part as wel

but i much prefer the panasonic special polymer (SP-Cap), which is lower ESR and a better part overall than either the sanyo, or the nichicon. a bit pricier, but not as much as the sanyo and actually this range has some of the lowest esr caps of any polymer at <5mOhms however they are not rated as high in voltage. the murata polymer are rated for 12.5v in the 47uf and are actually lower ESR than the panasonic in that voltage rating. its only the lower voltage higher capacitance panasonics that are so obscenely low

may i ask why you want such high rails? would not +/-7.5-10v suffice? that would open up your options
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Old 21st January 2012, 03:47 PM   #4
Sype is offline Sype  Finland
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Well, Panasonic FC, FR and FM cap's are available in my favorite local shop and OsCon's from eBay.. FM series are cheaper than OsCon's but how about (sound) quality? I'd gladly spend little more money to get top quality.
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Old 21st January 2012, 04:00 PM   #5
Sype is offline Sype  Finland
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PCB is not yet designed, so SMD is possible. By the way, are tantalum caps obsolete, I have some 10F 35V SMD caps. How about sound, is tantalum cap good for audio circuit?
Voltage rails are 15 volts to get some headroom for high impedance headphones while playing loud.
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Old 21st January 2012, 08:00 PM   #6
GLooP is offline GLooP  Bulgaria
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If you aim for perfection, it's NFM21PC104R closest to the chip, followed by a film cap close by, followed by low value resistor (0.47 R-2 R), followed by Electrolytic cap. Anything goes, among the best - Panasonic FM/FC/FR/etc, Nichicon PW/HE/LG/etc, Rubycon ZLG/ZL*.
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Old 21st January 2012, 08:18 PM   #7
nezbleu is offline nezbleu  Canada
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I would not use a 16V-rated cap on a 15V rail, I think that is asking for trouble. You want at least a 25V part there. I second the Pana FM/FR recommendation.
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Old 21st January 2012, 08:40 PM   #8
jcx is offline jcx  United States
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Default just how "optimum" do you want?

LM317/336 have different output bypass optimums, if you have dual sec xfmr that provide all 4 wires then use 2 bridges, and a LM317 on both with identical parts

then the LM317 likes some ESR in the large electro output bypass to control noise, output impedance peaking - oscon/polymer electrolytic are "too good" - you should add a series damping R
old ~10uF tantalum electros were the default rec because they had ~1 Ohm ESR, often 25-50 uF Al eletros were given as alternatives - but modern Caps of both types now come with way too low ESR

http://web.archive.org/web/200808291.../files/f10.pdf shows the issue can be complicated

http://www.tnt-audio.com/clinica/reg..._noise2_e.html shows ref bypass, without big cap on output is fine with LM317 - if your load is ony inches from the reg, same pcb, broad traces then just skip the high uF output bypass cap

"insane" measurement based thread: http://www.diyaudio.com/forums/power...egulators.html

Last edited by jcx; 21st January 2012 at 09:02 PM.
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Old 21st January 2012, 08:44 PM   #9
theAnonymous1 is offline theAnonymous1  United States
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I've pretty much used Panasonic FC/FM for every project I have ever done. They don't dissapoint.
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Old 21st January 2012, 08:47 PM   #10
Xoc1 is offline Xoc1  United Kingdom
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16V caps should be fine on a 15V regulated rail. The advantage of using a higher voltage rating is a lower ESR component. Some prefer 100V rated electrolytics.
I breadboarded my headphone amp and ended up with 2 x 100uf 16V oscons per rail for each op amp, 8 caps in total. It was interesting to try different caps in the circuit. Other caps I tried were Panasomic FC, Elna Silmic and some 100V 100uf caps.
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