Mackie SWA1501

[J M Fahey]

The schematic says 12 ohms, which is a non-standard value.
I'd use a 16 ohm one , because besides being easier to find, it will lower power output a bit, which is good; the brute power that hits that poor woofer is insane.
Measure the magnet and plate thickness, maybe the backplate is bumped , that will give you an idea about Xdamage and help you choose a replacement coil.
If possible post a couple pictures, specially from the magnet, and also from the (burnt) voice coil, with measurements (base length, wiring length, diameter, type of wire, base material).

[Enzo]

I'd use a 16 ohm speaker too. In fact if I recall correctly, that is what they sent me last time I ordered one.

1 ohm? I'd say the voice coil is melted also, does the cone move when you push on it?

Aside from protecting the speaker, I'd say a 16 ohm driver will be more likely to let the amp circuit survive as well. You won't miss the few decibel reduction.

[MarkusBass]

Thanks guys. My multimeter does not measure resistances below 1 Ohm well. I can only estimate that it shows something like 0.7 Ohm. The cone moves correctly when I push it. I also suspect that it is melted. One of the wires to the cone looks like it got some high temperature for a moment. The power transistors were shorted so the speaker most probably got a power supply voltage (at least for a while).

Mark

[J M Fahey]

so the speaker most probably got a power supply voltage (at least for a while).

Which in this case means deadly 140V DC
So far it's the highest DC voltage I have ever seen in an SS power amp. Ugh !!
Even worse than plugging the speaker straight into the 120V wall socket, which at least is AC.

[MarkusBass]

While waiting for the speaker being reconned, here is a photo of the amp. What do you think about two blue capacitors that almost touch the black element that holds the transistors? Isn't it a potential short circuit (which the amp cannot handle well as we know)?

Mark

[MarkusBass]

Someone wanted to see the coil. Here it is:

It was 8 Ohms.
Now the speaker is fixed and everything seems to be OK except a scratchy sound (<1 second) when I turn off the sub. Is it normal or should I still worry about the amp?

Mark

[J M Fahey]

Thanks a lot.
On first sight it looked like Kapton (because of the colour) but squinting my eyes it seems to have an embedded cloth texture; that would make it fiberglass (much more approppriate for that brutal use)
What do you mean by 8 ohms?
Is that the DC resistance? Because the schematic states 12 ohms, consistent with an 8 or 9 ohms DC resistance.
What impedance VC did you use to repair it?
Is it also fiberglass?
The wire sure looks toasted; is it round or flat wire?
Maybe you will need to use a loupe to be certain.
Thanks again.
EDIT: I forgot. That "scratchy sound" is probably nothing, specially if low level (meaning your cone does not shoot itself across the room), just a second of instability when the +/-15V Op Amp supply dies.

[MarkusBass]

It's fiberglass, round wire. The wire (at least 20% of it) was toased as you can see.
I know that on the schematic the speaker is listed as 12 Ohms and you are recommending 16 Ohms but the speaker is Mackie LC15/3007-8 so it's clearly 8 Ohms and it was rewired to the same impedance (it was also the easiest way to fix it). I told the guys not to expect ground shaking effects from the amp so maybe the speaker will last a little longer. The sound at the turn off is very low level and the guys told me that this is typical with this amp.
As it turned out the amp is not that difficult to be fixed - thanks guys .

Mark

[MarkusBass]

I've just got information that the sub with fixed amp and rewounded speaker (8 Ohms) was tested on stage at full power and everything is OK. I hope it will last a year or two

Mark

[J M Fahey]

Congratulations.
Now it's on the DJ's hands.
EDIT: just out of curiosity I googled the speaker code, Mackie LC15/3007.
Clearly, they burn so much that there is a full cottage industry based just on reconing them.
The huge market floored me.
Incredible.
Just check:
Mackie LC15/3007 - Google Search
1030 pages !!!!
They speak of original Italian (RCF?) and later Eminence versions, as well of "originally 8 ohms .... later changed to 16 ohms to tame their incendiary(sic) tendencies"

[MarkusBass]

EDIT: just out of curiosity I googled the speaker code, Mackie LC15/3007.
Clearly, they burn so much that there is a full cottage industry based just on reconing them.
...
They speak of original Italian (RCF?) and later Eminence versions, as well of "originally 8 ohms .... later changed to 16 ohms to tame their incendiary(sic) tendencies"

I know about it (this was the first thing that I checked). But I think that the problem is not with the speaker, not with the amp but with people who don't hear low frequencies good enough and they turn the knob in the amp all the way up .

Mark

[SVDJ]

Many thanks to all the guys that took time to post information here.
My SWA1501 stopped working in the middle of a gig (RED THERMAL LED came on)
To try to help others this is what i have found (so far)

Resistor R25 had burnt out & F2 Blown. Replaced R25, R26, C15, C16, D17 & D18 thinking i was safe.... Now for the warning!!

I'm not sure if anything else had blow at this point but i powered up with the board not secured to the frame. I read after that the board is earthed threw the frame so this could have caused the following damage or perhaps i'm just unlucky.

R72 burnt out
Q14 Blown short
Q17 Blown Short
D26, D27, D28 & D29 all short cct
Track between Q17 Base and R31 vaporised
F1, F2 and F3 Blown.

Again, as mentioned before CHECK ALL THE SILICON FOR SHORTS BEFORE POWERING UP

Everything replaced and Board repaired just waiting to test (Picked up 4A quick blow fuses by mistake, so just ordered the slow blow).

Incidently the above items seem to be a bit difficult to come by, but Farnell Farnell United Kingdom | world-leading distributor of electronic and maintenance, repair and operations products. stock them all with free next day delivery (minimum order is £20 though)

Fingers crossed for power on and i hope this helps

[Jazz P Bass]

Light Bulb Limiter.
Use it.
Solid state amps will draw huge amounts of current when things are (go) bad.
Yeah, you have to check all the sillycone.

[SVDJ]

Ok All powered on ok, No Smoke, no blown fuses, but the -15V_SW is at -10.5v.

Any ideas why this may be??

My orgiginal fault was on the +15v_sw with a burnt out R25
R25, R26, C15, C16, D17 and D18 all been replaced.

Any help appreceated

[MarkusBass]

Ok All powered on ok, No Smoke, no blown fuses, but the -15V_SW is at -10.5v.
Any ideas why this may be??
My orginal fault was on the +15v_sw with a burnt out R25
R25, R26, C15, C16, D17 and D18 all been replaced.
Any help appreciated

This is power supply for U2 (NE5532) so maybe U2 is shorted? Measure voltage drop on R25 and R26.

Mark