Can I get full power from my combo without adding a cab?

[cameltoe]

I posted another thread up about adding a cab to my newly aquired Trace Elliott GP7 SM combo.

It's 150w RMS, with a 1x15 driver.

It has two speaker outputs, with the print 'SPEAKER OUTPUT 4ohms' between them.

I was told on the other thread, that currently the combo will only be kicking out about 80w (ish) using just the internal driver, (which I was told would be 8 ohms) and to get full power from the amp I'd need to connect another cab to get 4 ohms and the full 150w power output.

I gigged it last night, and it was just loud enough, but I didn't have much headroom to be honest, and the venue wasn't that busy.


I have a Hartke vx3500 combo amp for my big gigs, so really if I was going to bother to buy a cab to go with the Trace, I might as well just take the Hartke.

However, knowing absolutely nothing about amps, I wondered if it was possible to get the full 150w from my Trace WITHOUT adding a cab? Could I, for instance, swap the 8 ohm driver for the appropriate 4 ohm driver to acheive max volume?

My AC Euro 200w 1x15 combo is quite a bit louder than my Trace. This amp, though, doesn't have any speaker outputs. I'm wondering if this amp has a 4 ohm driver already and hence puts out the full 200w? I would think the Trace with it's full 150w would kick it's ass though!!


Anyway, If there's a way to do this and someone could point me in the right direction I'd be grateful!!

[Bill Fitzmaurice]

[quote name='cameltoe' post='857309' date='Jun 4 2010, 09:46 AM']However, knowing absolutely nothing about amps, I wondered if it was possible to get the full 150w from my Trace WITHOUT adding a cab? Could I, for instance, swap the 8 ohm driver for the appropriate 4 ohm driver to acheive max volume?[/quote]
Full power is moot; the difference between what you might get with a 4 ohm driver versus 8 ohm is 2dB, and that's best case. Adding a second identical speaker gets you 6dB, which should do the trick.

[cameltoe]

Ah so not such good news then.

Bringing another cab is what I want to avoid really, as the Hartke will be the easier (and louder) option then anyway.

So with the RMS output almost doubled from going 8ohm to 4ohm, through a speaker that can handle the power, I'd really see no extra (real world) volume?

[Mr. Foxen]

[quote name='cameltoe' post='857651' date='Jun 4 2010, 08:29 PM']Ah so not such good news then.

Bringing another cab is what I want to avoid really, as the Hartke will be the easier (and louder) option then anyway.

So with the RMS output almost doubled from going 8ohm to 4ohm, through a speaker that can handle the power, I'd really see no extra (real world) volume?[/quote]

If you are changing speaker, you could put in one with a higher sensitivity, which would give a few more db, but that would screw the tuning (such as it is) and change the sound. All in all more effort than its worth.

[Bill Fitzmaurice]

[quote name='cameltoe' post='857651' date='Jun 4 2010, 03:29 PM']So with the RMS output almost doubled from going 8ohm to 4ohm, through a speaker that can handle the power, I'd really see no extra (real world) volume?[/quote]Not enough to make it a worthwhile venture. What would work if you must stay as small as possible is a high powered compact amp, at least 300 watts into 8 ohms, and a fifteen with high sensitivity and long excursion, such as an Eminence 3015. With a low powered amp the only way to get high output is with at least two drivers.

[bumnote]

Ive done it and its not worth the expense or hassle

Get another cab

[Phil Starr]

There's a problem with most 4ohm drivers as well. they are usually made by just changing the voice coil for a shorter one which makes them less than optimum. typically the low level efficiency goes up at the expense of a much reduces excursion (Xmax) which means running out of grunt at higher sound levels. Another reason for not doing it.

[Bill Fitzmaurice]

[quote name='Phil Starr' post='857859' date='Jun 4 2010, 07:10 PM']There's a problem with most 4ohm drivers as well. they are usually made by just changing the voice coil for a shorter one which ...reduces excursion (Xmax)[/quote]Not if they do it the right way, by reducing the number of windings on the same former. But your point is valid, not every driver manufacturer does things the right way, and you must pay attention to all the driver specs, not just impedance.

[JTUK]

interesting discussion but just not worth the hassle to go down this route.
If that compact combo isn't loud enough to be useful on gigs, then move it on or use it as a practice/rehearsal amp.

There is loud enough in terms of sheer volume and there is pushing the thing too hard that all sound is compromised because you have to dig out all the plus EQ making the sound unusable. Saw this last night when a guy had a small combo but drove the mids so it would be loud enough. He ended up with an unplayable sound which was frankly awful.

HEADROOM

Edited June 5, 2010 by JTUK

[Delberthot]

back in the day I ran a 7210H GP7 combo with a 1048H. It was only putting out 200w put it was plenty.

More recently I ran a series V AH150 at 8ohms so it would've been putting out about the same as your combo on its own - I was using a 4x12" however so I actually had far more volume available than I needed.

[Phil Starr]

[quote name='Bill Fitzmaurice' post='857879' date='Jun 5 2010, 12:46 AM']Not if they do it the right way, by reducing the number of windings on the same former. But your point is valid, not every driver manufacturer does things the right way, and you must pay attention to all the driver specs, not just impedance.[/quote]
You're right Bill, there is no reason for this to be a problem other than keeping the cost of manufacture down by a few pence/cents but all the drivers I have looked at by Celestion/Eminence/Fane have gone down this route, more exotic manufacturers may have done this properly. I simply don't have the data to know if the 4/16 ohm units in commercially made cabs have been properly engineered.

It is something I can get very grumpy about, the manufacturers must know they are selling these speakers which are sometimes not fit for purpose and usually to someone who thinks they are getting the same speaker but just in 4ohms.

[cameltoe]

Ok guys, thanks for the advice.

The combo IS loud enough for my smaller gigs, which is all I really need to use it for, but I had noticed that at a couple of recent gigs I didn't have the headroom i'm used to.

Not a problem though, I'll take the Hartke out for the larger gigs.

My little AC Euro 200w combo never really needed to be pushed above 4 or 5 on the master volume, BUT this amp didn't hava an input gain like the Trace does, which obviously needs to be set at optimum each time it's used.

The input gain has been freaking me out a little bit too, I don't know if there is a problem here, but last night (and the gig I used it at on Thursday) I ran the input gain (at first) up around level 8 without the clipping LED coming on hardly at all, but as the gig progressed, I had to turn the input gain down a bit more each time as the LED kept flickering on more.

This isn't me just digging in more as the gig progressed- I made sure I gave it a really good clank when initially setting it up, but last night it went from 8 to begin with down to almost 2 or 3 by the end of the night! and The LED was still flickering! I had to ignore it in the end.

Any ideas here?