SpeakerTalk

chazzco · Posted: Tue Sep 15, 2015 6:54 pm Post subject: KEF KM1 in the US

Hello All,
My name is Charlie and I am a new member to Speaker Talk.
I have a pair of KM1's that I have been trying to get information on. Most of my searches bring me here to your forum. From what I have been able find this may be the only pair in North America and nobody here even knows what they are.
We have had the pleasure of getting them operational and they sound unbelievable. There is a problem with one of the amps though. There is a dip in the mid range response. We switch the amps and the problem follows the amp. Does anyone know of a place in the Seattle area who may be able to check this out for me?

speakerguru · Posted: Tue Sep 15, 2015 10:30 pm Post subject:

Hi chazzco,

I designed the KM1 together with Dave Smith. I am in the UK, Dave is in the US. He sometimes contributes here. He is on Linkedin.

The 8 power amps per side are all Quad 405s and the crossover filters and eq are all active, so I'm puzzled by "There is a problem with one of the amps though. There is a dip in the mid range response". The power amps should be "flat", if they are not faulty. I'm wondering how a "dip in the mid" could occur due to some electronics malfunction. It's very unlikely. There are some d.c. blocking bipolar electrolytic capacitors in series with the midrange and tweeters. Maybe the mid ones have dried out and gone high resistance or open circuit?

chazzco · Posted: Wed Sep 16, 2015 6:01 pm Post subject: Thank You Speakerguru

Would the capacitors you mention be on the crossover or are they the large ones mounted on the bottom of the amp? Are the capacitors common or are they just for the KM1's? I do have a set of blue prints if that helps my cause any. I am not knowledgeable about electronics but I would like to know a little so I can explain to the repair person.

speakerguru · Posted: Wed Sep 16, 2015 9:22 pm Post subject:

They are the large blue ones near the relays on the large pcb are the rear of the amplifier. There are no passive "crossover" components in any of the speaker cabinets.

By "common", I assume you mean readily available, in which case, yes, common enough.

Bipolar electrolytic capacitors are also known as reversible electrolytic capacitors. In this case, as they are just used for d.c. blocking, the value is not critical, as long as they are not much smaller in value. +50/-10% on capacitance is OK. Make sure replacements have a similar or higher voltage rating. They should also, obviously, fit the pcb.