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Dodgy Alesis Power Amp

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Dodgy Alesis Power Amp

Postby Jonesd90 » Mon Nov 19, 2012 6:02 pm

Hi, I recently bought an Alesis RA300 secondhand.

Seemed all fine when I first tested for 5/10 minutes. Today however I finally got round to properly testing it and after about 15 minutes of use the amp stopped outputting from the right channel. Occasionally I would get a crackle of something and then gone again.

To me it sounds as if an internal cable is loose and intermittently becoming loose etc so I'm pondering whether to open it up and have a look. I thought I'd ask here first though; so long as I have the amp unplugged from the mains and nothing attached should I be ok to open up and have a look? Or am I going to get a nasty shock from a capacitor which is holding charge or something like that?

My electronics knowledge is admittedly average to (very) poor but I can stop a lose cable and my soldering skills are good enough (recently swapped XLRs to 1/4 inch balanced jacks on a 48 way multicore).

Any advice really appreciated.

Thanks, Dave
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Re: Dodgy Alesis Power Amp

Postby Richie Royale » Mon Nov 19, 2012 6:43 pm

Happy Birthday Dave!

Before you open it up, give the connectors a clean up with some contact cleaner and make sure it isn't the cables.

I think amps do have a potential to harm you if you don't know what you are doing, so I would be cautious of poking around unless you know what to stay away from.
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Re: Dodgy Alesis Power Amp

Postby Folderol » Mon Nov 19, 2012 9:33 pm

And a happy birthday from me too

You're not really going to get a shock off the caps, but they will hold a lot of charge at around + and - 30V so would be able to create quite a savage spark if shorted, so just leave the amp switched off (and unplugged) while you go and have a cup of tea.

Although it could simply be dirty pots/switches or plug connections, the fault sounds fairly typical of a bad soldered joint on the PCB somewhere. Look particularly closely where any components of any size meet the PCB, and especially any plugs or sockets. Strong light and a good magnifier make this a lot easier.
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Re: Dodgy Alesis Power Amp

Postby hollowsun » Mon Nov 19, 2012 10:09 pm

I'd speak (and I mean SPEAK, not email) to Alesis...

01252 896000
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Re: Dodgy Alesis Power Amp

Postby Smellthevalve » Tue Nov 20, 2012 2:46 am

I've seen some posts on other sites about this.
Some alesis and samson amps can have problems with relay switches making the sound cut out.
If you take a look at community.alesis.com/alesis/topics/ra300_amplifier_cutting_out there is a bit of advice from FCTRdotNET about it.
Not a good idea to try fixing it yourself unless you really know what you are doing though...
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Re: Dodgy Alesis Power Amp

Postby Richie Royale » Tue Nov 20, 2012 2:54 pm

Not quite related to this, but I have an Alesis, which blows the fuse immediately. Needs a professional I think, but it is now pretty much redundant, so I'm loathe to spend money on it, any possible suggestions as to what is causing it to blow the internal fuse, without any signal?
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Re: Dodgy Alesis Power Amp

Postby Folderol » Tue Nov 20, 2012 6:38 pm

Richie Royale wrote:Not quite related to this, but I have an Alesis, which blows the fuse immediately. Needs a professional I think, but it is now pretty much redundant, so I'm loathe to spend money on it, any possible suggestions as to what is causing it to blow the internal fuse, without any signal?
Rectifier or main smoothing caps possibly. If it's been mistreated, output transistors/chip more likely.
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Re: Dodgy Alesis Power Amp

Postby Richie Royale » Tue Nov 20, 2012 10:40 pm

Thanks Folderol. It has never been pushed or driven hard. Might get it fixed up next year.
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Re: Dodgy Alesis Power Amp

Postby James Perrett » Wed Nov 21, 2012 3:00 pm

What happens if you give the amp a sharp tap while it is misbehaving? If it is a dodgy relay (which is very likely), a sharp tap will be enough to get it going again for a while.

James.
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