Do electrolytics values stay constant ?

[Galu]

I found that some of the old Elcap electrolytic capacitors in the KEF held their values but had quite a high ESR value, while others were massively dried out and not doing much at all.

Hi!

Yes, those nasty Elcaps should always be replaced as a matter of course, as they do not age well!

 

[Galu]

The electrolytics on your crossover board certainly look in good physical condition!

Alcaps are good quality NP electrolytics and should have a long operating life.

The non-polar electrolytic capacitors in a loudspeaker crossover do not become as hot as polar electrolytics might do in an amplifier. Consequently, the damp electrolyte does not dry up as fast, which helps ensure a long working life.

If the wire lead outs still remain perfectly sealed then the Alcaps are likely to be well within spec.

 

[lolilol1975]

Ah, that should sound like good news but to my ears it sounds like bad news, as that means it's likely there may be not much improvement.

 

[waxx]

in my experience (and i did rebuild quiet a few crossovers), you stay with the original plan (replace elco's with elco's of the same values, including the ESR) or you redesign the crossover with new parts from start on measuring the speakers and often following the same effect (order and slope) of the originals. What you do depends on the situation. But just replace an elco with an film cap or so is asking for problems.

In this case i would order the replacement kit (wich is a good one) and keep it original. But when i redid the crossover of my Goodman Mezzo SL set, i started from scratch, also because in one speaker the inductor was damaged and not useable anymore and i did not have the schematic.

 

[lolilol1975]

The electrolytics on your crossover board certainly look in good physical condition!

Alcaps are good quality NP electrolytics and should have a long operating life.

The non-polar electrolytic capacitors in a loudspeaker crossover do not become as hot as polar electrolytics might do in an amplifier. Consequently, the damp electrolyte does not dry up as fast, which helps ensure a long working life.

If the wire lead outs still remain perfectly sealed then the Alcaps are likely to be well within spec.

I sent the photo to the guy at Falcon Acoustics and he told me that the KEF caps were made in the 1980s so for him these are original caps. So there is that.
I'm still waiting for the little gadget that measures ESR and my set of replacement caps, and I guess I'll start to do some soldering work.

Also, I have to say that I've replaced a pair of dodgy interconnects between preamp and amp and the sound has improved a LOT !

 

[Galu]

Also, I have to say that I've replaced a pair of dodgy interconnects between preamp and amp and the sound has improved a LOT !

That's very open of you to say so. Always a good idea to check the connections before suspecting the equipment!

Your speakers are bound to sound even better after you have fondly fettled them.

At the very least, by recapping your vintage speakers, you will have staked a claim in their ownership and can be sure that they are giving of their best.

 

[Mark Tillotson]

Select-on-test for electrolytics is bogus, they are fundamentally imprecise components
and drift loads.

 

[Galu]

Select-on-test for electrolytics is bogus, they are fundamentally imprecise components and drift loads.

Mark is absolutely correct and it may be worthwhile, in the context of this thread, to elaborate on his statement.

Despite all their advantages, wet electrolyte capacitors are subject to slow deterioration caused by gradual evaporation of the electrolyte inside.

Their ESR increases over time and their capacitance decreases.

Film capacitors do not suffer from these ageing problems and, if I were designing a loudspeaker crossover network from scratch, my choice would certainly be to use more reliable film capacitors wherever possible.

 

[trobbins]

Is there an elephant still in the room - the drivers themselves!

 

[Galu]

Falcon Acoustics is knowledgeable about the KEF drivers and has chosen the components in the replacement capacitor kit to match the original capacitors as closely as is possible.

 

[trobbins]

The driver resonances and Q's may well have shifted a bit over the decades. If KEF were measuring and tweaking each section of xover to match individual drivers, then in this day and age it seems rather simplistic and low-fi to just use default value cap kits.

 

[Galu]

True, but I don't think the OP has the facilities to account for the maturation of the drivers.

 

[Galu]

Lolilol1975 has posted this on another thread:

Woah, KEF has replied to me with the full maintenance document !
So I upload it here for anyone interested.
Attached Files

REFERENCE 105.3_201503201532[1107].pdf (535.1 KB, 13 views)

 

[trobbins]

Ok so they aren't tweaking to each driver, just to related xover part values, which have obviously been measured and binned.

 

[lolilol1975]

Falcon Acoustics is knowledgeable about the KEF drivers and has chosen the components in the replacement capacitor kit to match the original capacitors as closely as is possible.

Yeah, I've ordered the kit. However I'm not sure the current caps are in such a bad shape.
I've measured one of 20 uF with the cheap gadget that you can find on amazon and Banggood, and it was still within spec, it also had an ESR of 0.22 ohm and 1.8%. Not a specialist but it seems fair to me. Anyway, since I'll receive the new parts, I will be able to compare with new ones.

Nevertheless, I feel like replacing the 7uF, 16uF and 20 uF caps with their equivalent SCR caps, which are bigger but could still fit. The 20uF could be replaced by 2 10uF in parallel.

 

[lolilol1975]

Ok so they aren't tweaking to each driver, just to related xover part values, which have obviously been measured and binned.

For this design. From what I've read online, this series was abandoned because it was too costly to make. I don't know if they still measure and select their parts to 1% but I doubt it.