SpeakerTalk

audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

It looks about right apart from C5 which on later 105s should be 80 uF non polarised at least 50V working.

The series bass capacitor is made up to 480 uF on early 105 2s and I believe 450 uF on late 105 2s so I'm not sure if your 900uF made up of two 450s is absolutely correct. Maybe Guru can clarify?

Dev · Posted: Fri Nov 16, 2012 7:30 pm Post subject:

speakerguru · Posted: Sat Nov 17, 2012 9:43 am Post subject:

Where both sides are within 1% of each other and within +/-10% of their nominal values, I would leave them alone. Where they fall outside these limits, without the original factory build charts, you will have to decide whether to replace with nominal or some other values. In any case, I would recommend that maintaining good pair matching should be your primary aim.

Dev · Posted: Sun Nov 18, 2012 7:03 pm Post subject:

speakerguru · Posted: Sun Nov 18, 2012 11:24 pm Post subject:

KEF bought +/-10 or sometimes even 20% capacitors. They were all measured in the factory and sorted into 1% bands. For Reference series all the inductors were wound +/-1% to complement the stock and spread of capacitors. If the capacitors were high then the inductors would be wound low, etc. This together with drive unit matching, would keep all the critical crossover and eq frequencies within 1% and the frequency response within tight limits.

I have no idea how capacitors (and drive units) drift after all this time. That's why you'll have to make your own decision re absolute values. But you won't go far wrong if you major on keeping the pair matching of crossover components close.

Don't change reversible electrolytics caps to polypropylene, because the loss factor difference will result in audible frequency response changes. You would need to add series resistance if you do and you want to maintain the original frequency response.

Have you checked loss/dissipation factor? Electrolytic capacitors can dry out and become high resistance......

clubsport911 · Posted: Thu Nov 22, 2012 9:13 pm Post subject:

Ref adding polypropylene caps etc... Is there a formula for the series reisistor you need to add? There are as many theories as there are Internet forums. I feel the one closest to my mind is 0.1ohm / 5 uf

audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

You can work it out from R=d/2pifC where d is around 0.04 for small caps and around 0.08 for large ones. Of course it is frequency dependant so I calculated around the crossover frequencies. For a single 3.3uF at 2.5kHz it was around 0.77 ohm, but at 5 kHz for example it would be around 0.4 ohm. I found a high power 1 ohm at the output of T52 and B110 around right, but it may depend what your room and position is doing to the bass response. Whether right or wrong I did not fancy putting series resistance to the B300.