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.
Wow, that really is overkill. :) Often preamps have caps in the range of 2-10 uF. 

Strongly consider you use small film caps in that range instead. 

And yes, probably 48 - 72 hours of burn in to be safe. 

As for electrolytics, Panasonic makes some very nice one's. The FM series, but also does Elna. Pass swears by the silk electrolytic caps. 


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.
Thanks, Ralph!

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?
The best thing you can do for electrolytic is to cycle them on-off as you would normally in listening sessions. What helps caps is to form the electrolyte (the "burn in") and this is best accomplished by cycling them as you would by normal turn off and turn on of the component as in regular use.
@erik_squires , the preamp is also a 1W power amp, meant to drive 4ohm loads, thus the large cap value.  It is the LTA MZ2.  Since it was primarily designed as a smallish power amp or headphone amp, in preamp mode, it still likes to be loaded somewhat (between 50-100ohms).  Mine is loaded at 100ohms.  Therefore, I can easily get away with 1/10 of the stock cap value without an issue (a bulky film if possible).  This is something I can look into if the electrolytic doesn't perk up..  The stock cap is not Panasonic FM.  It is bluish-purple with a white negative stripe.  It is a Matsushita ("M" logo), but I just assumed this was Panasonic.. maybe its not.