Behringer Acoustic Amp ACX1800

[Trevor Gore]

I came upon one of these (Behringer Acoustic Amp ACX1800, http://www.behringer.com/EN/Products/ACX1800.aspx) the other day - not bad for the bucks. The intention was to try out a whole stack of ideas regarding acoustic sound reinforcement by wiring different stuff (speakers, EQ, sensors, etc.) in. The problem is getting access to the electronics. Having removed all the obvious screws etc. I still can't get the amp. chassis to slide out. Any ideas anyone?

Thanks in anticipation.

[kiwigeo]

One of these would do the job

[Trevor Gore]

That's just one step away...!

[Matt Bach]

Amp chassis can stick really well to the enclosure covering/tolex, especially if you're taking it apart for the first time ever.

Make doubly sure you've got all those screws out (sometimes the handle bolts to the chassis too but not sure on your amp) and give it a bit of a heavier hand and it should come out.

[Trevor Gore]

Thanks, Matt.

I had my suspicions about the handle. I'll have another go and see if I can get the plastic covers off the handle mountings. I've had a go already. The plastic covers seem to snap on in someway, with no obvious ways to snap them off, without literally doing that. Any hints greatly appreciated.

Thanks again.

[Kim]

Have the control knobs and input jacks been released from the fascia? Most times the fascia comes out with the chassis but not always, sometimes the fascia is used to align the chassis so the knobs and securing nuts need to come off the pots and jacks to allow the pot shafts to come through the fascia as chassis is removed from the back.

If the chassis is loose in the cabinet now but is still stuck, look inside carefully with a torch for any hardware such as "T" nuts etc that may have dropped down and causing things to catch up. Sometimes you need to pull back and up a bit so the front edge of the facia can clear what ever is causing the issue. If all is removed yet the chassis is 'still' rock solid, just be aware that they really throw these things together now days and sometimes the chassis is fitted while the glue on the tolex is still going off. It does not take much to bond in the chassis and if they have used urethane, it can be a right bastard because you don't want to force things for fear you have missed some secret squirrel fixing, but at the same time it is going to take a bit of brutality to break the gorilla's grip.

Good luck

Cheers

Kim

[Trevor Gore]

Thanks, Kim.

This thing is assembled almost like a rack mount unit (wish it was!), with the whole amp chassis just slid in like a drawer above the speaker enclosure. It is held in with 3 screws each side...and something else! There's nothing going up from the speaker enclosure into the base of the amp chassis (apart from the cabling to the drivers), so I think Matt is on the money, with screws from the handle assembly going into the amp chassis from the top. I'll just have to see if I can prise off the plastic covers to the handle fixtures without wrecking them (not that it really matters, but I try to keep things tidy!)

The first odd thing about this amp (I'm sure there'll be others) is that the two speakers are wired out of phase with each other. I've put a phase switch on one of the speakers and the whole unit is now a lot louder, when they're in phase. However, at low volumes (but fairly high on the knobs) it sounds fairly realistic when they're out of phase! I prefer the sound it gives to the AER Acousticubes I've heard for about 10x what I bought this for! When I finally get to the amp chassis and wire in a real speaker it should be interesting!

[kiwigeo]

The first odd thing about this amp (I'm sure there'll be others) is that the two speakers are wired out of phase with each other. I've put a phase switch on one of the speakers and the whole unit is now a lot louder, when they're in phase.

That's not odd.....that's just a crap wire up job on the speakers. Behringer must have built that amp on a friday after theyd come back from lunch at the local boozer.

[Tod Gilding]

Trevor, I Don't like to be telling you your business, But would'nt you be better off useing a PA Rather than an Acoustic amp that usually have circuits that shape the tone ?

[Trevor Gore]

Trevor, ... would'nt you be better off useing a PA Rather than an Acoustic amp that usually have circuits that shape the tone ?

Hi Tod. Yes, if it was just about performing. But any circuit shapes the tone, whether intentionally or not. What this thing is about is a bit of a project to figure out why acoustic amps (or amplified acoustics) sound so universally crap! The best reproduction I get is through my NAD amp and JBL speakers. Almost sounds like a guitar!

My current thinking is that you can live with just about any flat response amp that has the right input impedance and plenty of gain and power. All the commercial acoustic amps seem to go wrong by trying to get hi-fi sound out of what are essentially electric guitar speakers. Hence trying to get the amp chassis out to build it into a decent speaker cab. Then I'll see if I need a better amp.

[Trevor Gore]

I just know you're all hangin' out for this one...

...it was the handle screws. Got those out, slipped out like a good'un.

Thank you Matt!

[Matt Bach]

Good luck with the insides!

[Trevor Gore]

Here's a couple more things about this amp...

I have a mate with one; its speakers are wired out of phase too. That suggests it either intentional or totally random!

It's a two channel amp, one channel intended for instrument (guitar), one for a mic. Different frequency responses on each. The instrument channel has the tops cut off. Basic gain is about the same for both channels. Guitar sounds better on the mic channel (without the tops cut off). Funny that! Can't imagine why they just didn't go flat response both channels; it's not an electric guitar amp!

The power amp stage is mono. Yet it has separate outputs for the two speakers. Still trying to figure out how that part of the circuit it wired. Gee, I might have to get my old 'scope out!

[Trevor Gore]

Well, I was wrong! The power amp stage is twin channel, just both fed with the same input so it works like mono.

And one of the reasons acoustic amps never sound real good...the standard speakers don't push out much over 5kHz even if the amp runs up to 20kHz.

Can anyone recommend a compact full range hi-fi speak set (probably 8-10" driver plus tweater, ~40 watts RMS, ~50-20kHz, not mega bucks)?