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Capacitor Questions Modular Synthesizers
Old 4th September 2007
  #1
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Capacitor Questions

Hi, I have some questions on capacitors:

1. I have a Delta 1010 soundcard that has a proliferation of "En" marked caps (the "En" being inside an elipse). Sorry I have no picture, but the color is black with white negative stripe. Do you know who is the manufacturer of these caps? Are they good quality? How do they compare with Panasonic?

2. What caps would you recommend for power supply filtering/decoupling in a soundcard? I've heard lots of praises for Black Gate caps (Rubycon mfg) but they're too expensive. Are they worth the price? Alternatively, are the Panasonic FC's good enough? Or how about Panasonic FM? Are they better than the FC?

3. My soundcard is using electrolytics for coupling, which is not their ideal application. Why are electrolytics being used here? Is this because of cost considerations only? Can these be safely replaced with polypropylene caps? If so, what brands would you recommend?

If they can't be replaced with polypropylenes, what electrolytics would you recommend for coupling then?

4. I read that replacing a filter cap with two caps in parallel (each cap half the value of the original and the same voltage rating) will give you the same cap value and voltage rating of the original but with the benefit of lower ESR and higher ripple current rating. Is there any downside to doing this, such as increasing the heat, or is the heat more or less going to be the same?

5. In general, how long is the shelf life of electrolytics? I have an old unused motherboard that's been in storage for 5 years whose capacitors I'm thinking of salvaging for a project. Not worth it?

Your help is greatly appreciated. Thanks in advance!

Michael
Old 4th September 2007
  #2
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ulysses's Avatar
Quote:
Originally Posted by mtl777 View Post
2. What caps would you recommend for power supply filtering/decoupling in a soundcard? I've heard lots of praises for Black Gate caps (Rubycon mfg) but they're too expensive. Are they worth the price? Alternatively, are the Panasonic FC's good enough? Or how about Panasonic FM? Are they better than the FC?
I think that Panasonic FM and Nichicon HE are the best reasonably available electrolytic caps you can get. Other people swear by special "audio" caps such as the Nichicon Muse etc, but I think they're just marketing hype. Try comparing the data on these caps, it appears that "audio" caps are just general-purpose caps (like NHG or VZ) but with fancy gold lettering and a higher price. Still, people will imagine that they sound different if they're so inclined.

Quote:
Originally Posted by mtl777 View Post
3. My soundcard is using electrolytics for coupling, which is not their ideal application. Why are electrolytics being used here? Is this because of cost considerations only? Can these be safely replaced with polypropylene caps? If so, what brands would you recommend?
The primary reason is usually that the circuit requires a large value of capacitance, and electrolytics are the only reasonably-priced, reasonably-sized, and readily-available parts with that high capacitance. Changing to film caps usually requires reverse-engineering the circuit to reduce the amount of capacitance needed (such as by capacitively-coupling an internal stage, removing DC offset from the outputs, so that the outputs can be DC coupled). A computer soundcard is not likely to lend itself to this kind of work, and may not be worth the effort. Trying to shoehorn big film caps into a spot that used to contain a compact electrolytic may create more problems than it solves, especially if the larger part has higher inductance (as physics will dictate). Besides, it's highly unlikely that the capacitors are the weakest link in the audio quality of your soundcard.

Quote:
Originally Posted by mtl777 View Post
If they can't be replaced with polypropylenes, what electrolytics would you recommend for coupling then?
Panasonic FM or Nichicon HE. If you're worried about having electrolytics in the audio path, you could bypass them with small film or NPO ceramic caps. It's usually not difficult to solder a surface-mount capacitor across the solder pads of the electrolytic cap (on the underside of the PCB). There are people who swear by this. It probably can't hurt anyway. The ceramic or film cap will have a lower impedance at higher frequencies than the electrolytic, and you can calculate the crossover frequency.

Quote:
Originally Posted by mtl777 View Post
4. I read that replacing a filter cap with two caps in parallel (each cap half the value of the original and the same voltage rating) will give you the same cap value and voltage rating of the original but with the benefit of lower ESR and higher ripple current rating. Is there any downside to doing this, such as increasing the heat, or is the heat more or less going to be the same?
The downside is that the circuitboard you're dealing with is designed to hold a single larger cap, and trying to stuff two smaller caps in there will be a pain in the ass and result in longer leads going to these caps. Those longer leads will have a higher impedance than the single big cap you're trying to replace.

Quote:
Originally Posted by mtl777 View Post
5. In general, how long is the shelf life of electrolytics? I have an old unused motherboard that's been in storage for 5 years whose capacitors I'm thinking of salvaging for a project. Not worth it?
Shelf life of electrolytic caps varies dramatically, and depends on how they're stored. The biggest consideration is their temperature, followed closely by the DC voltage across them and the AC current through them. Even the humidity will have some effect. Caps last much longer when they're kept with a polarizing voltage on them, and will go bad much more quickly if they don't. The data sheets for any decent cap will tell you their rated life, which is usually measured in thousands of hours. But that's under rated voltage, and at maximum rated temperature. They last much longer if they're not kept at that max temp; when operated at reasonable temperatures, high-temp caps (105C) last much longer than general-purpose caps (85C). There is tube gear that's been in continuous operation in radio stations for decades, and their electrolytic caps are still healthy. This is because they've remained powered up and have been operated in a climate-controlled environment. Take one of those units out of service, leave it on the shelf in the garage for a year, and then power it up - the main filter caps will probably short out, and fry the power transformer.

Finally, it's important to note that the cost of any reasonable capacitor is insignificant in comparison to the labor (time, skill, frustration) required to replace them. Therefore, it would be rather foolish to replace capacitors with other second-hand capacitors for anything other than an emergency repair. I don't even buy electrolytics from the surplus store, not even for hobby projects. Buy fresh new caps - not only will they have more of their lifespan ahead of them, but caps are constantly being improved. The current standard "low impedance" caps (FM and HE) are significantly better than the low impedance caps of just a few years ago. That's exactly why they've introduced new lines to replace the old ones - the FMs are replacing the FCs, which replaced the HFQs, and so on.
Old 4th September 2007
  #3
Gear Addict
 

Hey, thanks for the great info!

Quote:
Originally Posted by ulysses View Post
I think that Panasonic FM and Nichicon HE are the best reasonably available electrolytic caps you can get. Other people swear by special "audio" caps such as the Nichicon Muse etc, but I think they're just marketing hype. Try comparing the data on these caps, it appears that "audio" caps are just general-purpose caps (like NHG or VZ) but with fancy gold lettering and a higher price. Still, people will imagine that they sound different if they're so inclined.
I heard the black gate has been discontinued. They're recommending Rubycon ZA/ZL instead, which they say is even better than black gate:

Rubycon ZL/ZA Capacitors: Reference Audio Mods

I think I want to try these, especially in the critical areas. They'll work great whether for coupling or decoupling, right?

Quote:
The downside is that the circuitboard you're dealing with is designed to hold a single larger cap, and trying to stuff two smaller caps in there will be a pain in the ass and result in longer leads going to these caps. Those longer leads will have a higher impedance than the single big cap you're trying to replace.
What are the bad effects of higher impedance? (Sorry I'm ignorant about this.) If you're using only two caps in parallel, would the increase in lead length cause a significant increase in impedance that makes it not worth doing?

Thanks again!

Michael
Old 5th September 2007
  #4
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ulysses's Avatar
Quote:
Originally Posted by mtl777 View Post
What are the bad effects of higher impedance? (Sorry I'm ignorant about this.)
Higher imedance (due to inductance or ESR) causes a capacitor to act less like a capacitor. Ideal capacitors have impedance that contiously decreases as frequency increases. Real-world capacitors have inductance that eventually causes the impedance to go back up at some point as frequency increases. In the case of decoupling capacitors, it will cause less decoupling to occur at higher frequencies, where the decoupling is needed to keep the circuit stable. That's why we tend to use small ceramic capacitors right near the pins of op amps - to maximize HF decoupling. Large caps with long leads, placed further away so that there are longer circuitboard traces connecting them to the op amps - these are the things that cause oscillation in wideband amplifiers. In the case of coupling capacitors, this would tend to cause a peak in response somewhere between where the capacitive reactance rolls off the low end and the inductive reactance rolls off the high end. It's why "modders" often put small film caps in parallel with electrolytic coupling caps.

Quote:
Originally Posted by mtl777 View Post
If you're using only two caps in parallel, would the increase in lead length cause a significant increase in impedance that makes it not worth doing?
Yes, that's the question. It all depends. It depends on the inductance, on the other circuit impedances, on the sensitivity of the circuit to HF problems, and on how particular you want to be about the accuracy of the circuit.
Old 6th September 2007
  #5
Gear Addict
 

Thanks for the great info!

Now let's turn our focus on non-electrolytic caps for coupling. Are polypropylenes the best? What brands would you recommend?

Michael
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