[friendswithdave]

Hello All, first time poster, woo hoo!

I just bought a used AV123 MFW-15 subwoofer and noted it appears to have a bad amp. When turned on it produces a pretty loud hum, louder than a ground loop hum I think. I was going to search for this on here to see if others had this issue and knew how to fix it, but I need three posts to get to that, so HELLO! If anyone has a thread they can point me to, I would appreciate it. I actually have an unused powerful amp, but just need a little guidance to connect it to the sub.

Thanks - friendswithdave

[HAL]

Get ahold of sandbagger here on AC.  He maybe able to help with the new MFW-15 amps.

[Doublej]

Replacement amp - https://seatonsound.net/product/mfw-15-mk2-amp/

Possibly helpful for repair tips though not exactly the problem you describe:

https://www.reddit.com/r/audio/comments/4qvoqk/av123_mfw15_humming_fix/
https://www.avsforum.com/threads/advice-on-broken-av123-mfw-15-subwoofers.2545897/

Connecting an external amp - You need to disconnect the existing amp from the subwoofer driver terminals and then connect the external amplifier output (just use one channel if it is a stereo amp) to the driver terminals. If your amplifier is not a subwoofer amplifier you'll lose the ability to adjust output level, crossover point, phase etc.

Here are some external amplifiers designed specifically for subwoofer duty from $99. I know nothing about them:

https://www.outdoorspeakerdepot.com/amplifiers/subwoofer.html

Lastly if you have a local repair shop you could take it to them and see how much it will cost to repair.


Good luck!

[sandbagger]

there is a fix that might work, its 4-5 caps as I remember off the top of my head and a bourbon in my hands so....
they are easy to replace.

If that does not work, its dead, do not spend any more time fixing the amp. PERIOD

Mark Seaton does get drop in replacement amps from time to time, he does them in batches though.  They are DSP programable for the stock driver or the Turbo driver.   

PM me an email or google and you should be able to find the directions

[friendswithdave]

Thanks everyone for the great info. I may attempt to change out the capacitors. If not (or if that doesn't work), it sounds like an external amp is the next step. I've bought used pro amps before so that may be my next step. I've never changed capacitors or amps before but I did find directions for changing capacitors and changing the amp as a whole should be even easier.

Thanks yall!

[Early B.]

Don't replace one cheap plate amp with another cheap plate amp. Instead, buy this one: 

https://www.parts-express.com/dayton-audio-sa230-230w-subwoofer-amplifier--300-813?gclid=CjwKCAiA4o79BRBvEiwAjteoYDUEpgY7I4boxoepoBzVE9cymusFip23T7Yy5bQSuA5jgG_V_LgXXBoCu9AQAvD_BwE

I own an MFW-15 and my amp went bad many years ago. I replaced it with the one linked above. Far superior in sound and much higher build quality. 

[petemoss]

I did the same thing and the difference was incredible.   the Dayton amp is so much better.

[soundofrockets]

How easy or difficult it is to replace the stock plate amp with the external Dayton amp?

Additionally, can I split the signal from the processor and share it with the MFW 15 and the Triple OB servo subwoofer?

[Early B.]

How easy or difficult it is to replace the stock plate amp with the external Dayton amp?

Additionally, can I split the signal from the processor and share it with the MFW 15 and the Triple OB servo subwoofer?

Very easy --

Step 1: remove plate amp and disconnect speaker wire from it.
Step 2: unscrew one of the RCA inputs on the plate amp and feed the speaker wire through the hole. Use putty, duct tape, or whatever you have available to seal the hole(s). Reattach plate amp.
Step 3: connect the speaker wire from the driver to the binding posts on the Dayton amp. Connect a subwoofer cable.
Step 4: grab your favorite beverage, turn on some bass heavy music, and dial in your settings. 

Yes, you can split the signal from the processor and share it with multiple subs.   

[soundofrockets]

Thanks Early B - is the power from Dayton amp adequate for the MFW15? 
I checked the PE website - there is another subwoofer amp rated at 1000watts - any experience or recommendation for this one with MFW 15?

I have two dysfunctional MFW 15 that needs new life.

[Early B.]

Thanks Early B - is the power from Dayton amp adequate for the MFW15? 
I checked the PE website - there is another subwoofer amp rated at 1000watts - any experience or recommendation for this one with MFW 15?

I have two dysfunctional MFW 15 that needs new life.

Yeah, you'll have plenty of power. Of course, you can never go wrong with a bigger amp.

[soundofrockets]

Good to know - what about other features - will the MFW 15 woofer compatible with SA1000?

[SoCalWJS]

Get ahold of sandbagger here on AC.  He maybe able to help with the new MFW-15 amps.

I'll second this (if he's still around).

Upgraded my MFW 15 to his "Turbo" version with the external "Seaton" (Modified) Amp.

HIGHLY recommended. If it's still available, DO IT! New Woofer as well. HUGE difference. 

[soundofrockets]

Thanks John - just wrote sandbagged a PM. 

What woofers are you using?  I have the default woofers in my pair.

[SoCalWJS]

Thanks John - just wrote sandbagged a PM. 

What woofers are you using?  I have the default woofers in my pair.

I don't know if I can find exactly - I know I commented here on AC many years ago when I did the upgrade. Still have photos in the gallery.





Quite a difference. Guess which one is which? 

[Early B.]

New Woofer as well. HUGE difference. 

Yeah, I replaced the woofer many years ago. Substantial improvement. Try one of these:  https://www.parts-express.com/dayton-audio-rss390hf-4-15-reference-hf-subwoofer-4-ohm--295-468

The beauty of the cabinet alone was worth what I paid for the sub, but the amp and driver are low quality. Change those out and you've got a helluva sub.   

[soundofrockets]

My woofers are good for now - but if there is substantial improvements by replacing both the amp and the woofer - I will strongly consider swapping them both.

The SA 1000 amp is out of stock at the moment at PE.

[soundofrockets]

Hi John - is the upgraded woofer on the left?

[SoCalWJS]

Hi John - is the upgraded woofer on the left?

[friendswithdave]

I have been having trouble identifying and finding the exact capacitors required. I'm leaning towards replacing the entire amp or selling it as is. Is there a market for these subs with bad amps?