Converting SWR LA12 60 Watt to 100Watts

[Rpucciano]

Hi, I have the LA 12 SWR combo, and I love the dimensions and sound, but I need more power . as I see, the LA15 has the same pre, and the same powerboard, in the schematics, only show to change two resistors between LA12-LA15. Obviusly I know that I have to put an more powerfull speaker, but I donīt know if I have to change the transformer of the source to more voltage supply.
If someone knows how to upgrade it, please let me know how to do it.
Thanx a lot
salute
Rafael

[loudthud]

What makes the LA15 100 watts? Is it the rail voltage or the speaker impedance?

[Rpucciano]

What makes the LA15 100 watts? Is it the rail voltage or the speaker impedance?

I think is the voltage , in my LA12, there is 48+48 instead the 59+59 that should be as say in electronic diagram, but I donīt know the impedance of the speaker of a LA15.
Your question, is a good one!!!
Regards.
Rafael

[loudthud]

I think is the voltage , in my LA12, there is 48+48 instead the 59+59 that should be as say in electronic diagram, but I donīt know the impedance of the speaker of a LA15.

In that case you will need another transformer. There would be no need to increase the rail voltage if the speaker impedance was lowered. My guess would be that an 8 ohm speaker was used, just measure the voice coil resistance, it will be about 6 ohms. You may also need to increase the amount of heat sinking to keep those output transistors cool. The hard part will be finding a 12 inch speaker that will work properly in that box and handle the additional power.

[Enzo]

And increasing power from 60 watts to 100 watts will only make it about 2db louder.

[Rpucciano]

There is de electronic diagram, see that the resistors R31 & R30 are to take voltage to send to the pre 32VDC, thats why for the LA15 are more resistive than the LA12 with less voltage on power source. The power transistors are able to work up to 150Volts 10 A so the may be able to handle with no problem 59VDC, the other thig I think is to try to do a 2inch hole to be able to handle a more powerfull speaker





swr la12 la15 power amp sch.pdfswr la12 la15 power amp sch.pdf

[Rpucciano]

thanx all you guys to get interested on this thread, and thanx for share your knowledge!!!!
Kindest regards

[pikleyano]

Have you worked out this mod? I've got the LA12 as well and would be interested to know how it worked for you....

[Rpucciano]

Hi, Pikleyano, I didnīt do it yet, but I will do soon. I didnīt find the speaker that I want and is the first thing I will change before do any modification, beacause I think that the eminence inside this combo is not the best one, it only cost 40 bucks. if you need further information, just ask.
regards
R

[Rpucciano]

Hi, The LA15 has 8ohm speaker too. Thanx for interesting.
Regards
Rafael

[Kitoplaysbass]

replace speaker to decrease resistance

I was wondering if you were to replace the 8ohm speaker inside the LA12 with a 4ohms speaker wouldn't that draw more power from the amp. Or would this be bad for the amp?

[J M Fahey]

Hola vecino !!!

Since the power board is the same, by definition it can handle the extra power.
You *will* need a larger transformer .... will it fit?
You will also need better cooling.
Don't think you have space to add "more fins", best option would be to add a small fan blowing across it.
Even a small 2" "CPU type" will help.
For a "better speaker" which also handles the power, and still available and at a reasonable price, you may consider one of the PA "Greek letter" Eminences (Alpha/Beta/etc.) ; the higher letter meaning higher quality and price.

That said, 100W , specially in the same small box and still with a 12" speaker won't be that much louder.

Personal opinion, in your case and considering you are willing to work, I would leave it as-is, and build an extra *powered* speaker box; power module and speaker your choice, and drive it from your line/preamp out.
You would be adding real extra power, extra cone surface, and extra box volume.
*That* would be noticeably louder.
For home/studio/small club use, you can use your original amp as-is; in larger venues (or with louder drummers) you add your powered box.

Hi Kito.
*Maybe* you could do that, and survive, but it will definitely run hotter and you wouldn't get more than 20 or 30% more power.
Not worth the risk.
And maybe your 4 ohm speaker is less efficient than the original one (which is not bad at all) and you actually *lose* volume .
Fact is, a single 12" in a small box is barely enough for bass, when playing along a drummer, it's a physical fact.
*Even* if you put an EVM12L there

[loudthud]

+1 to what J M said.

SWR does a lot of work to custom design the speakers that go in their amps. Your chances of finding a good match for that small box isn't very good.