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Do electrolytic caps need burn in?

I tried swapping a pair of amp/preamp line output coupling capacitors (DC blocking).  The stock units were run of the mill Panasonic electrolytic.  I put in Mundorf Mlytic AG.  I know this particular Mundorf (and most large electrolytics) are for power supply use, but the application calls for a large 6800uF so that the system can be used as a small amp or preamp.  Since I'm using the unit mostly as a preamp, I guess I could go about 1/10 the size and try to use a film cap.. but anyways, that is besides the point.

The question here is, do electrolytics (specifically this Mundorf) need burn in?  I ask because I'm hearing the opposite of what most people hear on caps that are not adequately burned in.  The usual complaints with caps without proper burn in are lack of bass, shrill highs, etc.  The Mundorfs have increased the bass output and possibly added some texture to the mids (the good), but the highs have disappeared.  I'm wondering if the highs will come back over time?  I wouldn't say the top is rolled off, but it is just shelved.  Any details that are carried in the upper frequencies is obscured and recessed.  The life of the sound has been sucked out.  Hopefully this doesn't qualify as "audiophile" tuned warm sound.

I have considered putting a small Russian teflon cap in parallel to the Mundorf, but the values I have are too small to probably make a difference (820pF).  I also don't think this bypass should be required to get nominal levels of treble in the first place.

I've got about 5hrs on the caps now, and they sound exactly the same as time 0.  So are the Mundorf's going to open up the highs with time, or should I just move on to another cap?  I will try the bypass before I throw in the towel on the Mundorf.  The point of reference is the stock Panasonic caps, which are fairly neutral, with good top end extension and detail.
manthik

Showing 4 responses by atmasphere

atmasphere's avatar
atmasphere
11,567 posts
 
Once the electrolytic has formed up, it should work about as well as the film caps in a coupling cap situation, so long as its biased correctly. To this end, whatever AC voltage is being sent through it as an audio signal should never exceed the DC voltage on the cap.
I don't know how a coupling cap in a traditional solid state output could do that- The DC on the cap would be 1/2 of the power supply voltage and the output swing of the amplifier could be nearly rail to rail. So in such a circumstance the cap would make considerable distortion. I think this is one of the ways electrolytics have gotten a bad rap in audio as coupling caps.
atmasphere's avatar
atmasphere
11,567 posts
 
After sorting through all the choices, I finally settled on a huge pair of polypropylene 1000uF caps made for commercial power supply applications (solar power). I found them cheap on ebay. I got them custom mounted. All the highs and the details are there. Very well balanced cap.

The shunt film cap on the large EL never worked over the long term. Over time, the combined cap would sound more like the EL cap (I think the film caps I was using were still burning in). Also, the film cap values were too small relative to the EL cap to make a difference in the long run. As one might expect, no EL cap can stand up to a good film, and that goes for all of the best. For EL caps, I tried Mundorf, Elna Silmic II, Nichicon, etc.
The value of the part can make a difference. There is more nuance to power supply design than initially meets the eye. If the cap values are too large, the impedance curve of the output of the supply might not be a good bypass at high frequencies even though the overall output impedance might be lower. If too small, bass might not be well bypassed. This can change depending on the performance of the caps used- better caps can often be larger values. But you have to watch your timing constants (as a general rule of thumb, the TC of the power supply should be at least an octave lower than the TC of the audio circuit its supplying, and not much more!) and if you have regulation, many regulators won't be happy with larger values (and might have shorter lifespans too).
This is the tip of the iceberg! I would not write off conventional electrolytics though; if used correctly they can perform as well as film caps. If. Used. Correctly. YMMV but IME we've had terrible luck with using more exotic electrolytic capacitors; they don't seem to work as well as more middle-of-the-road parts. Quite often they wind up sounding dark.


atmasphere's avatar
atmasphere
11,567 posts
 
@manthik
If the caps needing to form up is what is happening, leaving the caps charged is the best way to do it. Cycling it takes longer- weeks or months instead of days.

@jb0194
If new caps in a PSU, will the temporary inefficiency manifest as possibly less responsiveness to peak demands by music at higher listening volumes? In other ways?
Yes, and in other ways. We won't even let our stuff out of the shop until it has at least a day on it, because it sounds so 'dead' prior to that. You can measure the form up too- as the caps get more efficient, the voltage on them goes up and they also run at a lower temperature.
atmasphere's avatar
atmasphere
11,567 posts
 
Electrolytics don't have a burn in time so much as they 'form up'.

That can take a while, until formed the cap will be less efficient. Give it some time.
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