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KSP-400 Hum Fix/Possible Non-Powered Tower conversion?


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Yeah I noticed that as soon as I fired it up. It is LOUD. I was able to rob a super quiet fan from a PC power supply I had laying around, and now it's inaudible if youre more than 5 feet away from it. But like you said, the swap is super easy. I think it took me a total of 15 mins including the time it took me to actually find the fan and pull it from the power supply.

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Living room is still a disaster area. I've ordered/bought and recieved all of the following so far.

Crown XLS202 Amplifier

Behringer Feedback Destroyer Pro DSP1124

Behringer UltraGain MIC2200

2-Pairs of AR 10 gauge, terminated speaker cables

RCA 1M to 2F adapter

RCA 1M to 2F Cable Splitter

(2) RCA to 1/4" phono adapters

(2) 1 meter 1/4" phono jumper cables

(2) 1 meter XLR jumper cables

(2) Female RCA to Male XLR adapters

I'm waiting for my amp replacement plates to get finished before I can go any further, but right now I have it set up so that the sub output from my receiver splits into 2 signals and feeds into channels 1 and 2 of the UltraGain, From there it jumps into Channels 1 and 2 of the Feedback Destroyer, then from there to channels 1 and 2 of the Crown amp.

Having both the UltraGain and the Feedback Destroyer are probably overkill for just the two subs in the KSP towers, though they offer an insane amount of adjustability and eq capabilities.

Once I have the KSP's all back together with the amp delete plates, I'm going to set a high pass filter on their subs at 25-30 Hz, since by spec they're 3dB down at 27 Hz anyway. I'm planning to add an additional sub to handle the extra deep material. After doing a bit of reading over at the hometheatershack I'm fairly certain ill build a custom Sonosub with either a soundsplinter 18 or 15, and I'm going to route the signal for that through the UltraGain and the BFD as well like so.

Split the sub output from the receiver into 2 signals and feed them into channel 1 and 2 of the UltraGain like they are presently. And again send those to channels 1 and 2 of the BFD. From there I'll split the signal coming from channel 1 of the BFD into 2 signals which will feed channels 1 and 2 of the Crown XLS202 amp. Channel 2 from the BFD will be ran to the amp which will power the extra sub.

So that's what I'm working with/thinking about so far. Thoughts? Ideas? Concerns? Please share!

Pics of the mess:






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Edmund is THE MAN!! My subs seem to be A-OK, but should they go (blow), I'll be checking back to this ol' thread!!!

Yeah, we'll wait to see if im "the man" until after I get these back together and see how it all works. haha. Right now I'm still just waiting on the amp replacement plates to get delivered from my waterjet guy, which may happen as early as tomorrow. Updates to follow, of course.. I still cant believe nobody's tried this before.

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I just had me another ridiculous idea..Wondered to myself how the sub section of the KSP-400 would sound as a ported enclosure instead of sealed. I could create a second version of the amp replacement plate out of wood which incorporates not only banana plug terminals for the sub, but also a port.. Hmmmmmmmmmmmmm. Now the T/S params of this sub would come in really handy to model some different enclosure options.. Based on my drawings of the speaker enclosure the internal volume for the sub is roughly 2.75 cu ft. Admittedly on the small side for a ported enclosure for a 15" sub, but it sounds like it might be an interesting experiment none the less..

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Still WAAAAAAAAAAAAAITING... for the plates to come from waterjet. My own company keeps screwing me on these.. [:'(] Soon, I hope.

Some pics of other progress..

Woofer and amp(s) out.


Amp and unnecessary wires removed/tied off. Lead wires to sub installed. Cord seal applied around amp cut-out.


Woofer out. Foam out. Lead-light in.


Sub lead wires installed. Foam back in. Numerous layers of cord seal applied around woofer opening.


Sub re-installed. Cord seal applied to amp cut-out and back side of control box.


A view of the mess my living room has been for the past 2 and a half weeks. In case you're wondering, no I'm not married, so I can get away with stuff like this.


As always.. Updates will follow..

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Good news: The plates are done.

Bad news: The guy who was picking them up for me, left them in his land rover at the repair shop..

Can't win.

Looks like I'll have to go get them tonight, finish/paint
them tomorrow, and maybe install them tomorrow night.

John, yours will be in the mail tomorrow if I go pick them up tonight.

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Update # 487

I retrieved the plates and brought them home. Please ignore my hideous countertop and linoleum.


Made sure that the banana plug terminals fit the keyed hole cut-outs in the plate.


Test fit the plate to the back of the speaker. Looks good so far!


The next day at work I grinded down all the sharp corners, bead blasted them, and painted them black.

Came home and fitted the banana plug terminals to the plates and then screwed them into place on the KSP's

I think they came out pretty good if I do say so myself.






Some preliminary listening is telling me that everything is working exactly how it should, and without any sort of EQ or calibration they sound just as good as with the original amps. I did bump my receiver's sub out crossover frequency to 100 hz from 80 hz. I started at 80 hz because thats where the upper section of the KSP tower is crossed over at but with the sub out at 80hz it sounded like there was a noticable "gap" in the response around 80hz. And I think I just won the contest for how many times someone could say 80hz in one sentence. But anyway, this weekend I will be cleaning up the mess in my living room and fine tuning the subs.

Perhaps Ill get around to posting some room response graphs at some point. There will be some better quality pics to follow at some point as well.

Thanks for following along!

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I had been meaning to update this post for a little while now. I think it's been like 2 weeks since last time. I did get around to doing some measurement and EQ work. I did a few rounds of slow, tedioius, manual measurement at various volumes, and found that I had a nasty dip at about 45hz and at 70hz, and a significant peak at 60hz. They were definitely noticeable by ear alone as certain bass notes around 45 and 70 would just seem to be "absent" in a particular piece of music or whatever. So I smoothed that out as best as I could for a first round, and I honestly think they sound better now than they did before since I now I can actually EQ them. That's not to say I couldn't have before, but regardless of the path taken, they're working now better than ever. Perhaps if I get bored again sometime soon I'll fine tune it a little more but for now its adequate. I guess if I wanted to get really crazy I could actually EQ each sub separate from the other though I'm not sure how I'd go about that. So anyways, here's a few more finished pics, and thanks for following.







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  • 5 weeks later...


New to the community. I just picked up a pair of KSP 400's, low and behold and sub hum from the right speaker. The other is fine. I opened up the lower panel to tighten on of the binding posts and found a capacitor laying in bottom of the plastic box??? Upon further inspection I found that it was empty and the filling (foil and paper) was up in the place that the cap should be and the two leads from the cap were still attached to the board. How in the %@#$ did this happen???????????? Any how I made sure the two leads were not touching themselves or anything else, hooked up the speaker and it is working. from what I can tell, there is no difference between the two speakers sonically.

Will any cap of the same value (100uf 25v ) work to replace it? It can't be good for it to be open like it is.

As far as the amp hum goes, I found a pair of KSP 400's on craigslist and the seller said he just had his amps sent in to Klipsch to be serviced regarding the infamous "hum". I was thinking about doing the same.

What are your thoughts on the outbaord amps compared to the originals? Is it worth spending the money to have the originals repaired or just cut to the chase and go for the outboard amps?

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I typed up a rather lengthy reply to this and somehow forgot to submit it. Perfect.

Anyway.. The plastic covering of the capacitor is probably what fell off. Probably should be replaced but I'd say odds are slim that it will fix your hum problem.

As for getting the KSP's fixed. Klipsch no longer does direct repair of these speakers, nor do they carry any replacement parts for them anymore. They subcontract out the repairs to a couple of electronics repair companies. If you call Klipsch Tech Support, they will guide you to one of them. Typical cost to repair the speakers is $120 to $150 per speaker. The repair may or may not last, like in my particular case. I also got tired of shipping my amplifier back and forth across the country to be without a working speaker for weeks at a time. That's part of the reason I decided to retrofit the outboard amp. Compared to the original amps, my outboard amp and processor sound just as good, if not better than before. Doing it that way, gives you a much more customizable system than what was available with the original KSP amps.

Whether you send the amp in for repair or go with the outboard amps is really a personal decision. If you have the willingness to do a little extra thinking, and fabrication, then it's an easy project. If you can go back and look through all my posts and pics and think to yourself "this is simple, I could do this easy," then I'd say go for it. Going with an outboard amp will probably be more expensive than sending the originals back in for repair, but to me it was a more dependable fix, and worth it when I can walk out to my living room and have a fully operational system instead of seeing one of my speakers gutted while the amp is halfway across the country getting fixed for weeks at a time.

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Thanks for the reply and addvice. I found a guy locally that said he can fix it if I got him a schematic, so I called up Klipsch and while I was still on the phone the guy emailed me a cut-away, schematic and instructions for dismatling the speakers. So I will be giving the repair guy a call and see how it goes.


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Going with an outboard amp will probably be more expensive than sending the originals back in for repair, but to me it was a more dependable fix, and worth it when I can walk out to my living room and have a fully operational system instead of seeing one of my speakers gutted while the amp is halfway across the country getting fixed for weeks at a time.

It's better to see your speakers gutted for weeks at a time while you're waiting for the waterjet guy to finish your parts [:P]

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