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Kenwood KA-8100 driving 4 ohm speakers (MMG')?

D

donberry

Super Member
thanks to johninct, I am the owner of a Kenwood KA-8100. It will be used in my family room where my wife only allows a pair of DCM TF-400 for aesthetic purposes (let;s not get into the wife debate thingy).
While the TF-400 are decent speakers, I did not plan on a KA-8100 and it seems like i should have a little bit better speaker to go with it....enter the Magnepan MMG which is similar in looks and i just happen to have a Martinlogan Abyss sub that should do quite well with a pair of those.
But,
Looking at the specs of the KA-8100, it is rated at 75 wpc from 20hz-20khz but at 4 ohms they rate it at 90wpc but that is only at 1khz...so I am not too sure if it was really made to be driving a 4 ohm speaker.....

From only looking at the specs, I am of a mind it may run pretty warm at 4 ohms and since they only rated it at 1khz, does not seem like they had 4 ohm speakers mated with this in mind....
but......again, the magnepan is an easy 4 ohm load. I know they like power, but they do not really require high current as it will be 4 ohms across the freq. spectrum, no nasty phase angles to worry about like an esl will give u.

anyone have any experience with this amp and 4 ohm speakers, or any good thoughts on the subject ?
 
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The Kenwoods have always been happy with low impedance speakers as far as I could remember, I've had a few and they were built like elephants. I think you'll be fine.
 
I don't think you're going to have a problem with the 8100 but I have never had Magnepans. FWIW, I had my 8150 driving 4 ohm Klipsch and some other speakers with lower impedance and the Kenwood did a good job.
 
I have never run any 4 ohm speakers with my 8100 but my MMG really eat the watts. My MMG's have been reparied so they may less efficient than normal. Still they would clip my Adcom 545II and a Hafler 280XL at moderate listening levels. At low listening levels you might be able to use the 8100 but I think it would be push beyond that. I will be interested in your results though to see if you have success.
 
I'd say that if the Maggies had a fairly flat impedance response without nasty peaks, dips and phase angles you would probably be okay.

The Magneplanars usually have very low sensitivity, so I'd expect that if you wanted high SPLs you'd need to go to different higher powered amp. If however, you don't listen loudly - give it a try.
 
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I agree with theophile. Give it a try, check the heat sink temperatures to make sure that things don't get too warm, and be prepared to buy a bigger power amp if you like your music loud. The KA-8100 has pre-outs, so you can use its preamp section to drive a separate power amp.
 
The amp was probably fully tested at 8 Ohms, but only tested at 1KHz into 4 Ohms at just before or just a bit into clipping. Since the 4 Ohm wattage is not really that much greater than with 8 Ohms tells me the power supply sags quite a bit under load.

The output devices will be warmer on 4 ohms, but not a whole lot because of the voltage sag. In my younger days, I ran a receiver on 4 ohms at high volume for a few hours. While the heatsinks stayed cool with the help of a fan, the power transformer became too hot to touch. No more of that!

For an amplifier to be considered 4 ohm worthy, I like to see the output wattage of at least 50% more than the 8 ohm wattage. If not, the PSU is too weak. This is my personal opinion, not something set in stone. If you choose to run the amp with 4 ohm loads, I would not operate it at high volumes for extended periods.
 
1 - I appreciate all the responses - thanks. My thoughts (which are usually not very accurate or coherent)

johnr66 - that is pretty much my thinking and i normally don;t even look at amps without high current, BUT, I am normally thinking whether an amp can put up with an inductive load from speakers for any nasty phase angles that may occur. I was actually really only looking for something like a KA-5700 or KA-7100 to drive the TF-400 , but johninct made me such an awesome deal, I could not refuse (if I am not mistaken, I believe the KA-8100 was the amp I ended up with when I was in Germany in the late 70's - driving a pair of HPM-150 - which I also own a pair of those. No, wife has kicked those out of the tv room a few times. They are just a bit too big for her tastes in that room)

as for the low efficiency - I am in total agreement that magnepans sound much better with bunches of power. For me, is one of those speakers where they sound much better the more good clean power u give them.

My thoughts were tho - this is basically a "tv system" but as it is in the room i am in the most, I would like to have some decent sound in there. Volume wise it would never really be cranked at all, I could get by with not very loud, IF it were a good not very loud - quality over volume on this one.

The magnepans are pretty much a purely resistive load so it is pretty much 4 ohms throughout the freq. range - basically an easy load for a 4 ohm rated amp
just not too sure if the KA-8100 is actually a 4 ohm rated amp due to the way they rated it.
I could see it driving the Klipsch easily as the Klipsch are so efficient. While the MMG are an easy resistive load, it is going to still be taking 50-70 watts of power for a not very loud experience - so how long could the amp put out that 50-70 watts at 4 ohms and not stress it out to bad ?

I am not worried about "loud" - if I want loud and good, I can just walk down the hallway and crank up the main system - but I would be using it for background music a good 5-6 hours a day, if not more.
I guess it comes down to could it do 50-70 watts of power for a couple of hours at a time at 4 ohms ?

Is just something I am looking into. Was just thinking that since I did get a better amp(for me) than anticipated, while the TF-400 are some decent speakers, just seems the KA-8100 should have something a little higher up the food chain - and the MMG resemble the TF-400 looks wise so the wife could not complain about them being in that room.
But then I looked at the spec sheet and saw that 90 watts at 1Khz..........
 
Don,
Kenwood's published ratings are lower than what the amp can deliver, probably by 10-20%. I ran the 8150 with two pairs of speakers, a pair of JBL Studio Monitors and a pair of big floor standing Yamahas for a party in a hall. The kids used it for dance music until 2:00 AM, when we shut down the show. It pushed those two pairs of speakers to deafening levels and didn't blink. The best thing, for me, was when the lead singer in the band (had live music, too) was looking at the amp and had to turn the volume knob a little past 1/2 volume to investigate. The look on his face made the whole night a success.
If it was me, I'd hook up the Maggies and keep an eye on the 8100 but I think you'll be happy with what it does. FWIW, I sold my Kenwood Supreme but still have the 8150.
 
If Kenwood labeled it to handle 4 Ohm loads, then so be it. Just remember that the heavier loads will stress the amplifier more than with 8 ohm loads. For background music where the amp rarely puts out more than a watt, this is not an issue. For loud extended playing, I would pop the top and check the temp on the transformers after a couple hours.

If you love hifi and music, why ruin the most important piece in the chain, your ears! Listening to music at high levels is not healthy for them.
 
The Maggies are supposed to be a pretty steady 4 ohms, but the low efficiency means higher output levels and the amp will work harder than it might otherwise.

Keep an eye on temps, and you should be fine.
 
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