VIntage KEF speaker Impedance issue

Discussion in 'DIY Discussion' started by AlvaroAtelus, Apr 7, 2024.

  1. AlvaroAtelus


    Apr 7, 2024
    Likes Received:
    I bought a pair of KEF C40s for the cheap price of 40$, however one of them was dead silent, hence the price. I took the broken speaker apart and heated all the solder joints on the crossover. This solved the issue and both speakers are playing. Even tho they play I have to turn the volume up to unprecedented levels to run them normally. For example, with my KEF C30s a little smaller with only woofer however still a 100w I would only have to turn the volume knob to 30% to have it running at a volume where you can hear all the tones clearly. However on the C40s I have to turn the volume up almost 100% to get close to the C30. Before anyone wonders the stereo I am using is capable of running large and power hungry speakers so I still believe the issue lies with the speakers.

    Using a multimeter on the C30s I measured 6.3ohms and on the C40s I measured 6.3 miliohms. I believe this explains why I had to turn the gain so high to get a response from the speakers. I get this reading on both of the speakers but have only taken apart one of them. On the crossover I reheated the solder joint and tested all the capacitors with a multimeter. They all gave readings far above the specified farads on them. I have tested the speakers too, which is why I believe the inductors are at fault. I found a video on converting farad readings from inductors into henrys.

    I just have a few questions:

    How does something like this happen?

    Ive checked all over the internet and cant find anyone with the same issue. How did this happen and with two speakers at the same time?! My theory now is that some previous stereo it was connected to somehow decreased its impedance.

    Is there any way I can be 100% sure the inductors are the problem?

    Again could there be a more common issue that is a little easier to resolve.

    Can I repair the inductors somehow?

    I dont have a lot of money which is why I wait for a good deal on something online and then strike a bargain. Replacing both of the inductors seem very costly, especially on both the speakers. Is there a way to "reform" the inductors?

    Well, the speakers are in working order however I find it peculiar that I have to run them at so high gain to get preformance. It might also affect the sound as Ive felt like the c30s have better sound than the c40s but that could maybe be caused by this issue.
    Had photo of the crossover but the file was too big for the website.

    Thanks for the engagement!

    Attached Files:

    AlvaroAtelus, Apr 7, 2024
  2. AlvaroAtelus


    Mar 6, 2024
    Likes Received:
    One can't accurately measure such low resistance values with a multi-meter; the meter leads themselves are probably greater than that. Simply put - you have short circuit. So if we are talking about inductors - and the loudspeakers are old, the "Shellac"/varnish on the windings had probably broken down - insulation break - down is not uncommon, particularly if they absorb moisture due to being unused for a while.

    If you are that keen, you will probably have to re-wind the inductors with some new wire.

    However, don't run your amplifier into such a low impedance, otherwise you will be looking at having to repair that too!
    Hodges, Apr 20, 2024
Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.