Replacing JBL EON 518S amplifier

[xtian]

I have a JBL EON 518S subwoofer with blown power amplifier. However, the switch mode power supply still works, with three terminals, putting out +45/gnd/-45VDC. Fortunately, the SMPS and the amplifier are separate units, and it was easy to remove the amplifier.

I'm looking at replacing the amplifier with this Shure unit. The datasheet says input voltage of 36-60vDC.

So, my question: Do you think I can use only the positive half of the power supply? Or would this put stress on the SMPS because I'm only loading the positive rail?

[glebert]

It seems like you might run into a current limitation of the SMPS if you try to get full power out of half of the PS. Do you need it to do 2 ohm load? There are tons of cheap class D modules on Ebay that will take +/-45V for 4 ohm loads.

[xtian]

Yes, woofer is 4ohm. I just started searching eBay. Can you point to any? I'm getting lost.

[glebert]

Many of the class D amp modules are based on the IRS2092 driver chip so if you search for that on Ebay you should find something. 45V rails you would probably want the 250W amp modules, although I think the 500W would work even though you are a little below the voltage rail specs.

FYI, one thing to watch for is if the speaker has a piezo tweeter sometimes class D amps see that as a capacitive load and won't work or will have odd behavior. I've found some have used a small matching circuit with resistors and inductors for this.

[Jazz P Bass]

Have you tried to repair the unit?

[xtian]

Have you tried to repair the unit?

No, not interested. I can smell burnt VOCs. Too much disassembly is required to even meter the FETs, and there's heat sink paste everywhere. You want it?

[xtian]

I ordered one of these. We shall see what we see!

https://www.amazon.com/gp/product/B0893MBTW6

I mean, $18. Come on.

[J M Fahey]

It should work,why not?

Just one doubt: do you still have a separate input/processing module doing all the EQ/limiting/whatever job?

[xtian]

There is a preamp board, yes. It was powered by a bipolar 15vDC supply generated on the SMPS. I just found a schem, so there is a good chance I can rig it to work. Otherwise, I imagine I can easily generate 1.5vRMS signal from my digital mixer to reach full volume.

Does one need to use a ~600R resistive load when testing line level output?

[xtian]

I take it back, the schematic was one JassPBass posted for the JRX line, not specific enough for the EON518S.

[xtian]

OK, never mind on the preamp board--it has a visibly flamed-out, surface mount IC.

[J M Fahey]

Ok, then you can still mount a new power amp, it just will be flat.

To use it as a basic active subwoofer, you can build a simple active crossover on perfboard so it just gets signal beteween, 40 Hz and 120Hz.
1 or 2 TL072 should be enough and it can be fed from existing +/-15V (which I hope still works) or quite probably you can get such a crossover board assembled and working from EBay.

Hereīs one, all that $2.38 can buy, itīs probably designed for car subwoofer duty, so it asks for +12V only, I bet it will work perfectly from +15V:
https://www.aliexpress.com/i/32964758895.html


You will miss all the sophisticated EQ/processing/enhancing/whatever JBL must have certainly addded, but it will work.
You will still have the cake, just without the cherry on top

I wouldnīt put this simpler no-limiter Subwoofer into the hands of a DJ, or at a headbanger Metal festival, but for milder PA use it should be fine.
Pity the processing board was lost, but hey, you have what you have.

I have already mentioned that here in Argentina lately I see lots of small/neighbourhood/school PA operators showing up with a random mixup of various brand and model cabinets, on inspection they show back panels with a piece of plywood and couple speakon connectors covering the hole where the original plate amp used to be.
Racks show an equal mishmash of various rack amps, from trusty old PVY CS800 to cheap no brand Numark and Pyramid class "DJ amps" driving the cabinets.

Guys build up a quite usable and whatīs incredible: good sounding PA system with what amounts to pawnshop or Craigslist finds for peanuts.

[xtian]

Thanks, JM! This subwoof will be sent a signal from a digital mixer, so I can do my own low-pass EQ there. And, as I discovered today, no need for any preamp.

So, package from Amazon arrived today...amazingly fast. I got the unit plugged in and tested it with music from my iPhone, all good. Next, I wanted to hook it up to my 1000w 4-ohm dummy load and test with sine wave, and things went pear shaped. As soon as I attached my signal generator to the input, power consumption shot up from 16w at idle, to well over 120 watts, and smoke started to come out of the new power amp. I quickly determined that I cannot connect the -ve pole of the audio input to earth. And, well, my signal generator is earthed.

WTF? Is this going to be a problem with any grounded audio source I try to plug in?

[g1]

Next, I wanted to hook it up to my 1000w 4-ohm dummy load and test with sine wave, and things went pear shaped. As soon as I attached my signal generator to the input, power consumption shot up from 16w at idle, to well over 120 watts, and smoke started to come out

I wouldn't think grounding the input should be a problem if using a 'floating' speaker in real life conditions. Where did you have your scope ground?

[xtian]

Scope ground was not attached!