BillFitzmaurice.info

I know there are literally hundreds of threads on this site and many of them deviate wildly off topic when it comes to amps. I require an amp which will power 2x T39s for now, I'm building some tops soon but I'd like to make sure the amp is capable of driving both the subs and the tops with relative ease.

Is there a forum approved 'general' amp for this or are opinions divided? I have a DCX2496 to take care of crossovers/limiting so all I'm looking at is a good solid amp to do the work, I can buy further ones later when other kit gets built.

Crown are fairly well received, Peavey seem to get nods of approval, QSC and even Behringer's Europower amps seem fairly well rated. I'm aware digital amps claim outputs they're simply not capable of so I'm cool with sticking with the heavier old school options as long as it'll work quite happily at driving my speakers.

How much power would an amp need to power a pair of T39s and a set of tops? Any advice appreciated, I don't want to buy something crap.

First thing is which drivers?

Each driver is rated for a maximum input before limiting. Measured in volts this is a safety value as well as a point where you get no more from your driver/cab combination.

Beware of Behringers output ratings as they tend to be peak rather than RMS. The other amps you have mentioned are all fine.

An example would be that the 3012LF will take 60V, so given that Power = Voltage * Voltage / Resistance, that is 450W at 8 ohms or at 10 Ohms (the horn will at 2 ohms of impedence) is 360W. To drive two off one channel, 5Ohms impedence, you would need around 720W.

We prefer not to push amps to the limit, so anything around 500Watts RMS value should be fine for a pair of T39's loaded with 3012LF's or Lab12's or 900W if you want to drive two off one channel.

Sorry, the T39s have Lab12 drivers. What about limiting the tops or is this not really an issue?

88h88 wrote:Sorry, the T39s have Lab12 drivers. What about limiting the tops or is this not really an issue?

I slightly edited the above post. I think that the Lab should also take 60V - you probably won't get anymore sound above that, probably just heat. The Lab may also be a 6 ohm driver.

Hopefully my math on this is correct someone will no doubt correct me if I've made a cock up.

The Lab12 is indeed a 6ohm driver, I recall reading that the cabinet on a T39 works to bring that up to 8ohm equivalent. I know about not pushing amps too hard which is why I've got no issues buying another at a later date to spread the load. I'm not ordering just yet so if anyone else feels the need to step in and say something else feel free.

The annoying thing about all this is I'm not exactly surrounded by music stores that stock any serious equipment and those places in the next nearest large city are essentially just shop fronts for warehouses... I've seen a reasonably priced Samson SX2800 which claims 900W per channel at 4ohms but of course there's no way for me to see if that's bollocks or not. Amps are easily the most annoying part of building these speakers as with the drivers the specs can't really lie, same with crossovers etc but amplifiers are a completely different kettle of fish.

Chris_Allen wrote:I think that the Lab should also take 60V

Should be about 49 V.

The new XTI-2 series are nice. The new limiters can be set according to output voltage and are more tweakable than the 01 series. If you don't mind weight Face Audio makes some nice amps for which I am a dealer

Thanks Greg.

So 49V *49V / 8 is about 300W per cab into 8 ohms, 600W into 4 ohms if you used one channel.

My first choice would be the GX5 for subs:

http://www.thomann.de/gb/qsc_gx_5.htm

and GX3 for tops:

http://www.thomann.de/gb/qsc_gx_3.htm

Remember you will still need an EQ.

EQ for now I can deal with using an old 31 band we've got sitting about at work until I can grab a DEQ. I think there's also some old(ish) amps there which claim to be 4/500w that I'll take a look at to get things up and running with the tops when they're built. GX5 on the list thus far then.

Those Face Audio amps look really nice, pity I'm over the wrong side of the world and not quite minted otherwise I'd take a look. I'll keep an eye out to see if they come to market over here.

Thanks chaps, really appreciate it.

Final point that wasn't answered - don't normally limit the tops as you can hear when they have had too much! but if you are lending it to someone else, then its a good idea.

I"m a bit late to the game here, but I have been VERY impressed with the Peavey IPR amps. The 3000 should power your T39s very nicely, and there is a version with DSP. Check with Full Compass (Cal Mazzara is my rep) for some excellent pricing on these (or anything, really). The 3000s are about 8 pounds... way less than the GX, and they run super cool.

I picked up the GX5 at the weekend from an audio store in the next city over for a not too bad £334. I had a play with it set up through my DCX2496 and was fiddling with the limiter, the 49V Greg said the Lab12 is capable of running is the absolute top end before it starts to frazzle itself, correct? If so what sort of level should the voltage be at to make sure my driver is well and truly protected?

That's the peak voltage. So long as you aren't running extremely compressed music as loud as possible the average voltage is well below that. Some people do want absolute max volume on full all the time hence the need for the limiter to hold them back from smoking their drivers. Hopefully then they notice their music sounds weird with loss of big bass hits and settle for less to get their dynamics back, but if not they don't toast drivers.

At least not in one session.

The other argument is 49V is barely any louder than say 40V so why not just limit at 40V and feel extra safe.

During the play session we had yesterday I limited it at 30 just to be safe as I knew it could take more, I just wasn't sure how much. Not that it got above 13/14V on tracks anyway. Nice that I can raise the level to offer more headroom if required.

I now need to teach the people who'll be playing with these about gain structure. This should prove entertaining.

Thanks again!

Stupid question time. I have the GX 5 and am wondering if it's a good idea to run 2 T39 cabs off each output in parallel or I need to go grab another amp. The GX5 seems quite content hitting the 2x T39s currently connected up to it at a decent voltage but I'm unsure as to how it'd handle twice the cabs.

Thanks.

Two cabs single loaded I presume? Should be a walk in the park. I'm not sure if GX5 is rated below 4ohm, so you could be relying on some horn impedance to not over (under) load it.