Need help with spec'ing amps for Kappa 8’s

MiamiBoy

Active Member
I recently purchased a pair of Kappa 8’s in very good condition. I don’t own an adequate amp to power them and only have been playing them gently using my 100w Yamaha receiver. I’ve read a lot on this forum about Kappa 8’s and what amps folks are using to drive their Infinities. I knew when I bought the Kappa 8’s that they require lots of power and just as important amps capable of handling the low dips in impedance that the Kappa 8’s present at different frequencies.

A review of the Kappa 8’s from the October 1987 issue of Stereo Review stated that “the impedance of these speakers was a nearly constant 2.4 to 2.8 ohms over the 1800 to 20,000 hz range and was one of the lowest speaker impedance they have measured.” YIKES!

I need some guidance as to what specifically should I be looking for in amplifier specifications to not make a mistake. If a manufacturer states that the minimum recommended speaker impedance is 4 ohms should that exclude the amp from consideration? Is it necessary that the manufacturer specifically state that the amp has the capacity to handle impedance dips down below 4 ohms?

So what do I look for to ensure an amp can handle these bad girls? I likely will want to bi-amp them.
 
That's where the work starts, just like Arnie said.

You get the amps that dip real low and can handle the low ohm speakers. Then, you look at the sound characteristics.

Lots of work. But these speakers really just illustrate and reproduce the electronics you have in front of them. And your sound source. The better the electronics the better the sound. In essence, the speakers are not the caboose of your system. The other components are.
 
I thought about Kappa 8s before I got my RS-1s. Still would love to own a pair. My limited research led me to Threshold; any Nelson Pass design should work well. Carver 7t or 9t monos work well. And my present VTL 300 Deluxes would work well if you're into tubes. I'd love to hear a biamp setup with Threshold on the bottom and VTLs up top. That was my original idea but never did get the Kappas.
 
Do your 8 Kappas have the toggle on back? It puts a resistor in line to reduce the load on lesser amps at the expense of some bottom. What kinds of music do you play and how loud will you crank it?

There is a lot of testimony on what to use on 8 Kappas in the Infinity forum. Many recommendations on new and used amps that cover a wide range of cost. Well worth the time of digging back through. Some will say the load on the 8 Kappa isn't as bad as its reputation has portrayed over the years. It may be safer and better assured to go with the beefier recommendations, especially if you intend to crank the volume.

I have no experience with biamping the 8 Kappa but I've rocked them hard with Adcom GFA 555II (Adcom modified Nelson Pass GFA 555 design) and more recently Wyred4Sound ST-500 (Class D B&O ICEpower). The W4S amps are excellent mates, extremely efficient and handle the load very well but may not have the higher finesse of better class A/B amps. The Adcom GFA555II are a good example of great value at lower expense but you have to be careful to make sure they're in good working condition or be prepared to get them repaired. You can ruin your 8 Kappa if an old 555II goes out on you. Adcom is currently selling a modern version of the amp but you'll probably do better to get another recommended better performing used amp.

The 8 Kappa will sound as good as the components feeding them. They respond very well to high quality audiophile hardware. (Repeating for emphasis because you scored a set of very good cost-to-value speakers for a wide variety of music.)

Be sure to read up in the forum on care and maintenance of your Polydomes.

My $.02. :smoke:
 
I don't know your budget, but this is the time to do homework. Just considering the bass application Like above where belvedere2 says Theshold. He's right. A lot of folks like that Infinity/Threshold synergy.

But Nelson Pass also designed for other companies aside from Threshold. Forte and if memory serves, some of those models are dual mono. He did the big Nakamichi amps. A certain Denon amp, if I remember right.

Same with Dan D'Augustino from Krell. Lots of folks like Infinity w/ Krell. So aside from Krell, he designed Soundstream and the Aragon amps lots of folks use. Dual mono.

Lots of work for you to do. And that's just 2 amp designers. But right now is when it pays off. You can prevent the dreaded step A to step B in a little while thing. Purchase right the first time.

There are lots of old threads about this kind of thing and not just the Infinity forum. You literally will have a flow chart of sorts or a tree with lots of branches.

And when finished, you get to work on the next amp for the mids.

But it pays. The speakers will know the difference.
 
I've used a few amps on my 8's, carver, adcom, and an eagle 7A. None could handle the Kappa 8's at higher levels.

If your budget minded for now I can recommend the QSC GX5 as a very good amp for running these speakers. With a good preamp mine sound very good and can go stupid loud.

Until I can afford a nice a nicer upper end amp such as krell, mcintosh..etc. it does a fine job.

I will also say of all the amps I tried, if you listen at moderate levels the B&K ST-202 is a sleeper. While not mega powered it was by far the best sounding match with my kappa 8's. I really regret selling that one.
 
If money is tight look more for the good deal than a particular amp. Most quality mosfet type amps from the '80s and '90's in good working order will sound very close to the same (imho). Example: theres been a Hafler dh500 for peanuts on my local cl. That would drive those 8 kappa for weeks on end...plenty of good quality used gear for sale for not too much cash everywhere, you just need to look every day and maybe twice a day on the weekends in cl...
Jim
 
Used acurus a 250 are around

Available for. 400- 500 dollar price range. 250 watts @ 8 ohms, 350 watts at 4 ohms. Built like a battle ship. Get one with separate power cord and one that light on switch does not blink. The power supply is so good you will hear music for 30 seconds after you shut it off.
 
Same with Dan D'Augustino from Krell. Lots of folks like Infinity w/ Krell.

I am one of those folks. I have a tried a many of amp on kappa speakers. Mostly on the 9 and 9.1, and it is the best amp I tried as a whole on the kappa line. Bass is phenomenal, and mid/highs are close to some nice tube amps I have owned/tried. But the bigger Krells were designed for such speakers, so no surprise. No need for bi-amplification with a big Krell (so look at investment in those terms, one amp or two?).

A good tube amp on top and an Aragon 4004 mkii, on bottom sound pretty good on kappas, Audio Research big tube amps sound really good on them as well. Another smaller Krell, the KAV250a is a good amp as well, and quite a good price on the used market.

The amps stable to pretty much a dead short makes a world of difference on the low end though, that's for sure. But they come with a price.
 
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Most pro amps are rated for operation with 2 ohm loads. Some Crown pro amps can be used in parallel mono mode with continuous ratings at 1 ohm.

Not long ago I purchased a pair of Crown Microtech 1200s specifically to experiment with the parallel mono mode and my Thiel CS3.6 speakers that also present a fairly consistent 2-something ohm load. In parallel mono they're rated:

1300W @ 1 ohm
965W @ 2 ohm
620W @ 4 ohm

The fans are a little noisy though in them.

While they sounded fine, I didn't notice any particular performance or sonic advantage over other high power amps I used like a QSC PL236 in just normal stereo operation.
 
Thanks to all for your valuable input. In researching the specs of the brands mentioned above I can see what I should be looking for.

I am in the process of remodeling a new home and these speakers will go in the main living room that measures 28’ x 16’ with a two story vaulted ceiling and adjoining open rooms. I mainly listen to jazz, acoustic rock and classical. While I am not into loudness for loudness sake, I am into whatever volume is necessary to fill a room and hear all the details.

My budget is more a goal rather than a dollar limit. I am willing to spend what I need to in order to drive these speakers to their full sonic potential…with room to spare. Right now I am thinking in the range of $2,500 to $3,500 total for a good quality pre-owned amp and preamp in very good condition. But if it turns out I can achieve my goal by spending less I will. Or if I find an exceptional value from a reliable source but need to spend more to get it, I will.
 
I don't have K8's, but I have experience with big Infinities. Watts into a low impedance load, like the K8/9's, is good, but my experience tells me that it's more about current than watts. I was shocked to read that "7.62"
was not happy with the Eagle 7. I've tried a handful of amps on my Gamma's woofers. Hafler 220, NAD 2400 Power Envelope, Mackie FR800, and my current favorite: Crest Audio FA901.
My speakers laughed at the Hafler. The NAD was surprisingly competent, as was the Mackie, but the Crest won out hands down. It controlled the woofers WAY better than the other amps. The down side of the pro audio amps is the fan noise.

Happy shopping!

D
 
I think you might be getting the Kappa 8's confused with the Kappa 9's, I don't find the Kappa 8's to be a real problem, and I own pairs of both. I ran a pair of Crowns on them with no problems, and the fans on mine rarely came on. Crest are also a very good amp, along with the Yamaha pro amps, any of which are quite neutral and dead quite. I am not sure about the Crest or the Yamaha's but the Crowns claim they are safe for any impedance.
 
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I am one of those folks. I have a tried a many of amp on kappa speakers. Mostly on the 9 and 9.1, and it is the best amp I tried as a whole on the kappa line. Bass is phenomenal, and mid/highs are close to some nice tube amps I have owned/tried. But the bigger Krells were designed for such speakers, so no surprise. No need for bi-amplification with a big Krell (so look at investment in those terms, one amp or two?).

A good tube amp on top and an Aragon 4004 mkii, on bottom sound pretty good on kappas, Audio Research big tube amps sound really good on them as well. Another smaller Krell, the KAV250a is a good amp as well, and quite a good price on the used market.

The amps stable to pretty much a dead short makes a world of difference on the low end though, that's for sure. But they come with a price.

Me too. And that Krell KSA series can be had for not a lot of money right now. Just watch out if repairs are needed.

I've used a Krell KSA 100 for bass on 4.5's for 15 years now. Audio Research for the 15 years before that. What an amp. I just had it serviced this year and the shop owner said the thing is really a Tasmanian devil trying to get out and work hard. They like being pushed and can certainly handle it. 600 watts it draws at idle and he thought there was something wrong drawing that much. Nope. Just a beast.

And those KSA amps sure do have tight bass. Me, I stick with Audio names/designers for purchases.....Dan D'Augustino is one of them I'll buy what he designs. Arnie Nudell is another.
 
Krell Amp Warm Up Time?

I am considering a Krell KAV-250a but one thing that concerns me is a review I found online by an owner who said it takes up to 1 hour to warm them up properly. But the Krell manual says only 5 minute warm up time is needed.

What is your experience with Krell warm up times?
 
I am considering a Krell KAV-250a but one thing that concerns me is a review I found online by an owner who said it takes up to 1 hour to warm them up properly. But the Krell manual says only 5 minute warm up time is needed.

What is your experience with Krell warm up times?

The Krell KAV-250a is a different kind of amp than most other Krells. It does not require the kind of time to warm up, as some of Krell's larger Class A amplifiers. Or atleast the one I have experience with didn't. I would agree with the manual myself.

Owning the KSA-250, I think it begins to sound it's best after about 30min. But it is a minute amount imo. So little that I do not really think on it much.
 
Bingo. Minute. not like a tube amp.

Some folks have had good luck with even the KST series for Infinity speakers. At the end of the day, that stuff costs about the same as KSA.

But driving these things kind of parallels the big model Accoustat owners. Or Apogee. Tough tough loads and then you get into the various sound characteristics of the equipment chosen.

But miami boy, we've all been through what you are going through now. The worst thing is to end up going through 3 amps or something until you are satisfied. Very expensive way to go. Then the dreaded what amp works with what pre-amp issue.

But the search feature should help to a degree. And room size is a big factor as well....they like room and open space. Next, the type of music you listen to.

And I like the way Infinity handles dynamics & that becomes a factor in amp choices. Lots of variables to have to consider. But you'll be glad you did.
 
Well after owning these Kappa 8’s for about three weeks now I can’t fully express how impressed I am with these speakers. They are the best sounding speakers I have ever owned. I keep hearing levels of detail and fidelity that were absent in my previous speakers which are Infinity RS/6b’s that I had just recapped and they were sounding as good as they ever did. To think that I almost didn’t buy these Kappa 8’s because I had read on this forum how hard they were to drive. Not so!

My 80’s Yamaha receiver (HTR-5599) is rated at 100w per channel and reports a dynamic power spec of 140/170/205/245 Watts at 8/6/4/2 Ohms respectively. I am getting great sound out of these speakers with the Yamaha.

There is a “bass load reduction” toggle switch on each speaker next to the crossover controls to reduce the bass load and I have had this engaged. When I turned the bypass switch off, the bass just sounded boomy, not tight and controlled so I put it back into bypass until I can upgrade to a more powerful amp. Still, I am getting much more bass out of these Kappas than my prior RS/6b’s with bass turned up.

These speakers were on craigslist from a seller who lived just 15 minute drive from my home. I let them sit there for two weeks before I finally called him and went to see them because he was hard to reach and I wasn’t sure I wanted these speakers “so difficult to power.” He was the original owner and said he didn’t like to play loud music. The speakers looked new sitting in his living room and after one look I fell in love and had to have them. $625 for the pair.

When I got them home I opened them up to look at the crossovers. Capacitors are all original but they still look new. Clean and shiny. (Don’t know if you can judge a capacitor by its cover but they look good.) And these Kappa crossovers are impressive. All internal speaker wiring is 12 awg gauge. I now realize that if you want to determine how much a manufacturer cares about their speaker line look at the crossovers.

Instinct told me to remove the woofers and inspect them because the owner had told me that he had them re-foamed. When I pulled one woofer out the slide on electrical clips were so loose they just fell off of the +/- terminals. And someone had cut the two wires to the woofers to remove them and when they reconnected them they just hand twisted them and wrapped the connection in scotch tape. So I repaired that with proper connections and I replaced the dust covers while the woofers were out.

Also the Polydome was yellowed and looked a little chaulky but was still very soft. I bought some 303protectant from Amazon and applied it gently. The 303protectant does not make the Polydome material clear but it does restore the pliability and softness to the material. I recommend it and will continue to periodically apply it. Thanks to member Loquatios for recommending it in another thread.
 
I bi-amp my Kappa 9 with a pair of Dbx Bx3 amps. I think they are 960 amps into 2 ohms. They don't even get warm at very high listening levels.
 
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