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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
manthik OP
20 posts
 
@roberjerman, I am using the stock value.  There is nothing to second guess here.  It is a simple high pass filter network with a primary function to block DC.  The value could be changed according to the implementation, if desired.  The designer's intention was for the unit to be used as a preamp and amp.  Since I only use it as a preamp, I can adjust the value accordingly.

Thanks Atmasphere.  I haven't let the unit run in yet, but I'll do that by this weekend and report back.
tecknik
483 posts
 
Any update on the sound evening out, you mentioned bass with texture midrange but lacked upper frequencies' has this improved with time.

I was thinking of doing this exactly with my AR Ref 3 preamp.

manthik OP
20 posts
 
No update yet.  I just plugged in the unit in the last hour.  I'm going to keep it on.  I'll recheck the sound this weekend.  Should be a solid 48hrs.
manthik OP
20 posts
 
OK, per suggestions here, I let the amp run continuous for about 48hrs.  If you add in my listening hours, the total time would be somewhere about 55hrs.  There is very little change in the sound.  The bass is still there, mids are nice, but the top end is still shelved (maybe a tad less than before the 48hrs of run time).  It sounds akin to listening to the rolled top end of Mullard tube.  I'm sure a lot of people would like this presentation.  I'm just missing top end details, presence, and bite (when the music calls for it).  All of this top end characteristic was present with the stock cap.  I'll try to use a smaller film cap in parallel and see what happens.  I like the bass and the mids enough with the Mundorf to continue experimenting to see if I can find the right overall compromise.
stevecham
3,340 posts
 
Leaving a component on continuously will NOT properly form the caps!!! They need to discharge and recharge over multiple cycles to do this. And it is not best to simply turn the component on and off in quick succession. The caps retain charge for several hours once the component is turned off and need to discharge that voltage over the same time frame, which is why cycling on-off, on a daily basis, with an overnight to discharge is by far the best way to form caps.
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