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Discussion Starter · #1 ·
Hi,

I own two Kef PSW4000 subwoofers (12" woofer, 500W amp, bass reflex, amp cutout dimensions are: 16.5" w x 10") and with one of them I have been having a lot of problems. There's an intermittent hum that either doesn't show up for days or sometimes it happens within minutes. The sub has been serviced by both Kef itself as well as Analogique (Kef repair center) in Manhattan. I have spend hundreds of dollars and countless miles trying to have this fixed, but at this point I am considering replacing the Amp since Kef doesn't offer a replacement amp.

These are two amps that I found which would be a good fit:
Bash 500W Digital Subwoofer Plate Amplifier
Dayton Audio SPA500 500W Subwoofer Plate Amplifier

My questions are (and I apologize if this not the correct forum):
- Would replace the amp with an aftermarket work? I realize I probably need to add some thick board since it won't be a perfect fit, but the inside cabling should be pretty straight foward and the only thing I'm giving up is the front LED?
- I am leaning towards the Dayton, since it fits better in the cutout dimensions, has a LFE input and the electronics are covered. I just need to figure out if it fits in the inside (which I think it will). Any thoughts on the amps or any other recommendations?
- I am also considering an external amp - I would just need to route the speaker cable to the outside
- Any other thoughts?

Thank you,
Mark
 

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- Any other thoughts?
I'm wondering if it's worth the time/effort/money/hassle for a sub that old. Isn't that sub 8-10 years old by now? If so, the issue you're having may be related to age and usage. You might want to consider putting that same money towards a new sub, instead of forestalling the inevitable. If one of your units is having an issue the other may not be far behind, so you could be throwing good money after bad.
 

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Discussion Starter · #3 ·
I'm wondering if it's worth the time/effort/money/hassle for a sub that old. Isn't that sub 8-10 years old by now? If so, the issue you're having may be related to age and usage. You might want to consider putting that same money towards a new sub, instead of forestalling the inevitable. If one of your units is having an issue the other may not be far behind, so you could be throwing good money after bad.
That's a valid concern. However, we're talking about a two subwoofers worth over $2,000 each. Beautifully build, nothing wrong with the woofer. So if I can spend a few hundred dollars to 'fix', why not do the fix instead of spending a few thousand to replace?
 

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That's a valid concern. However, we're talking about a two subwoofers worth over $2,000 each. Beautifully build, nothing wrong with the woofer. So if I can spend a few hundred dollars to 'fix', why not do the fix instead of spending a few thousand to replace?
Fair enough. In that case, you might want to consider an external amplifier. That way you don't have to cut the cabinet at all. It would probably look cleaner that way.
 

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Discussion Starter · #5 ·
Fair enough. In that case, you might want to consider an external amplifier. That way you don't have to cut the cabinet at all. It would probably look cleaner that way.
Thank you for your input. Do you have any recommendations (looking at 500W) or would any amplifier work? Could I simply extend the woofer cable and router it outside of the cabinet to the amp?
 

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Thank you for your input. Do you have any recommendations (looking at 500W) or would any amplifier work? Could I simply extend the woofer cable and router it outside of the cabinet to the amp?
Most of the external amps will be more powerful than 500 watts, but if you're judicious with the volume knob everything should be OK. Some of the more popular amplifiers are made by iNuke, Lab Gruppen and Crown. Virtually any one of their subwoofer amps should be more then sufficient.
 

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Discussion Starter · #7 ·
Thanks again. I've been doing a lot or reading and I think this one would be a good fit: "iNUKE NU3000"

A few follow-up questions:
1. I don't know any specs (Ohms) about my Kef woofer (and the broken old amplifier for that matter), just this:
Model: PSW4000
Type: Bass reflex, downward firing
LF Drive Unit: 300 mm (12 in.) long-throw
Crossover Frequency L+R variable: 40 Hz - 140 Hz
LFE fixed: 250 Hz
Frequency range (± 3 dB): 25 Hz - 250 Hz
Amplifier: 500 Watts
Sensitivity: Active system
Maximum Output (SPL): 113 dB
Impedance: Active system
Magnetic Shielding: Yes
Weigh:t 38 kg (83.6 lbs)
Dimensions (H x W x D): mm 465 x 495 x 495 in. 18.3 x 19.5 x 19.5
Full Kef Manual

The iNUKE NU3000 should provide plenty, if not more, of comparable power and I might actually hook the second sub also up to the unit if I like the sound of the amp (so no bridging).

Would that sound about right? Or would you recommend a lower/higher model?

2. Now about the connections - bear with me.

Kef Sub -> iNuke
I will need to open the Kef, disconnect the speaker wire from the old amp. Ok hopefully easy enough.

Next, a cable from the sub to the amp. Something like this?
Bare cable to speakon

What is the recommended way to connect the internal Kef speaker wire to the 'external' cable?

The cable will be about 15 feet, since I plan to have the amp close to my other amps (I am using Parasound A51/2 x A23 for my normal speakers). This enables me to use my auto-switcher to switch the unit on/off.

iNuke -> Pre-amp
My Pre-Amp is a Marantz AV7005 so I can use XLR connections to the Marantz sub 1/2 XLR Out. Do I need to do anything to 'boost' the signal? I've seen mixed replies about this.

3. Guess that I'll also need to replace the iNuke fan. Thinking of the Noctua fan

Am I missing something? This actually looks like it might be an upgrade. :)

Bottom (woofer and port) view
http://i26.tinypic.com/345lbhc.jpg


Amp view
http://i26.tinypic.com/mcsprp.jpg


This is actually a picture of one of my subs (Cherry color)
http://farm4.static.flickr.com/3439/3840541246_0b6398c1b6.jpg
 

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Next, a cable from the sub to the amp. Something like this?

That seems like it would do the trick.


What is the recommended way to connect the internal Kef speaker wire to the 'external' cable?

Frankly, I would go directly to the driver. The new cable you have will more than likely use a thicker gauge wire then what Kef did, so it would be better to bypass that part entirely and just use the new cable.


My Pre-Amp is a Marantz AV7005 so I can use XLR connections to the Marantz sub 1/2 XLR Out. Do I need to do anything to 'boost' the signal? I've seen mixed replies about this.

I'm not certain why you would need to boost the signal. The type of configuration you're trying to create is becoming increasingly more common, so there's probably not going to be an inter-operability issue.


Am I missing something?

Perhaps, but it's because I forgot to mention it. Make sure whatever amp you buy has a High Pass Filter (HPF) that you can set yourself. The current amp will limit how much content is sent to the driver below what it was designed for. Based upon the specifications you posted that would probably be 25Hz. An external amp has no such artificial limit built in because the manufacturer has no idea what driver you will be using. An adjustable HPF allows you to dial in that limit yourself, effectively protecting the driver in the same manner as the original amp. If you don't enable a HPF you can be pretty certain that the driver will get damaged.
 

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Discussion Starter · #9 ·
Am I missing something?

Perhaps, but it's because I forgot to mention it. Make sure whatever amp you buy has a High Pass Filter (HPF) that you can set yourself. The current amp will limit how much content is sent to the driver below what it was designed for. Based upon the specifications you posted that would probably be 25Hz. An external amp has no such artificial limit built in because the manufacturer has no idea what driver you will be using. An adjustable HPF allows you to dial in that limit yourself, effectively protecting the driver in the same manner as the original amp. If you don't enable a HPF you can be pretty certain that the driver will get damaged.
Thanks for the reminder. It looks like I should spend the extra $60 to get the 3000DSP. It looks like the 3000DSP has a HPF built in. I am not sure if I can set it 25 Hz exactly, but 20Hz should do.

It looks like the woofer in my Kef is 4 Ω, so running this in stereo gives me 820W (compared to 500W with the Kef amp). What are your thoughts about having both Kefs running through the amp (if the first project is successful of course)? This is probably a better amp, and I'm getting 60% more power as well.

Thanks so much for all your information.
 

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You can run both subs from a two channel amp. You just need to get a Y to run the sub mono signal into both channels. I do that with my Behringer EP4000 driving dual 12's in my tapped horn sub.

In the past, I have replaced the built in amp to a B&K with one from parts express and used an external amp to drive a pair of Carver subs. It's all good.
 

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Discussion Starter · #11 ·
You can run both subs from a two channel amp. You just need to get a Y to run the sub mono signal into both channels. I do that with my Behringer EP4000 driving dual 12's in my tapped horn sub.

In the past, I have replaced the built in amp to a B&K with one from parts express and used an external amp to drive a pair of Carver subs. It's all good.
Thanks! My amp actually has a dual sub output, so I don't need the Y cable :)
 

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Discussion Starter · #12 · (Edited)
Here's a picture of the driver. Quick question: is there actually a positive (red) and a negative (white) to a speaker? The only 'identification' would be the red dot near the blue cable, but I don't see anything else indication + or -.

Edit: someone else noticed that "it looks an awful lot like your sub has a Peerless XLS/XXLS driver. Also, I can't help but notice a six-digit number starting with 830, which is what Peerless uses for the XLS12/XXLS12.Peerless uses for the XLS12/XXLS12."

 

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Here's a picture of the driver. Quick question: is there actually a positive (red) and a negative (white) to a speaker? The only 'identification' would be the red dot near the blue cable, but I don't see anything else indication + or -.
Speakers most definitely have a + and -, and in your case the blue lead is indeed the + side. Even though it's not marked the spade lug for the blue lead is bigger then the other one, which is how they designate the positive connection.
 

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Discussion Starter · #14 ·
Just wanted to tell you guys... MISSION successful! It works great!

I have my HPF set to 25Hz and my LPF to 100Hz (HPT as per the original specs). Would you guys recommend a Peak Limiter? The original amp was rated 500W. I am considering setting it at -0.8 dBfs (outputting [email protected]). What is your opinion: too high, too low, not needed?

Any other recommended settings? Next up will be to disable the amp in my second sub :)
 

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Congrats! I'm glad everything worked out for you. :T

So long as you're judicious with the volume knob I wouldn't worry about adding a limiter. However, if there's a chance you -- or anyone else -- is going to be driving the sub hard you may want drop it to 500 watts, equivalent to the original amps output. That will help ensure no damage occurs.
 
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