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Jonesd90



Joined: 23/05/10
Posts: 98
Loc: United Kingdom, Manchester
Dodgy Alesis Power Amp
      #1019327 - 19/11/12 06:02 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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Richie Royale



Joined: 12/09/06
Posts: 4403
Loc: Bristol, England.
Re: Dodgy Alesis Power Amp new [Re: Jonesd90]
      #1019330 - 19/11/12 06:43 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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http://www.mixcrate.com/richieroyale


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Folderol



Joined: 15/11/08
Posts: 3736
Loc: Rochester, UK
Re: Dodgy Alesis Power Amp new [Re: Jonesd90]
      #1019355 - 19/11/12 09:33 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.

--------------------
It wasn't me!
(Well, actually, it probably was)


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hollowsun



Joined: 20/01/05
Posts: 5582
Loc: Cowbridge, South Wales
Re: Dodgy Alesis Power Amp new [Re: Jonesd90]
      #1019358 - 19/11/12 10:09 PM
I'd speak (and I mean SPEAK, not email) to Alesis...

01252 896000

--------------------
Website / Music Lab Machines / Blog


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Smellthevalve



Joined: 12/10/05
Posts: 63
Loc: Surrey, UK
Re: Dodgy Alesis Power Amp new [Re: Jonesd90]
      #1019376 - 20/11/12 02:46 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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Richie Royale



Joined: 12/09/06
Posts: 4403
Loc: Bristol, England.
Re: Dodgy Alesis Power Amp new [Re: Jonesd90]
      #1019454 - 20/11/12 02:54 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?

--------------------
http://soundcloud.com/richie-royale
http://www.mixcrate.com/richieroyale


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Folderol



Joined: 15/11/08
Posts: 3736
Loc: Rochester, UK
Re: Dodgy Alesis Power Amp new [Re: Richie Royale]
      #1019487 - 20/11/12 06:38 PM
Quote Richie Royale:

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.

--------------------
It wasn't me!
(Well, actually, it probably was)


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Richie Royale



Joined: 12/09/06
Posts: 4403
Loc: Bristol, England.
Re: Dodgy Alesis Power Amp new [Re: Jonesd90]
      #1019517 - 20/11/12 10:40 PM
Thanks Folderol. It has never been pushed or driven hard. Might get it fixed up next year.

--------------------
http://soundcloud.com/richie-royale
http://www.mixcrate.com/richieroyale


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James PerrettModerator



Joined: 10/09/01
Posts: 10826
Loc: The wilds of Hampshire
Re: Dodgy Alesis Power Amp new [Re: Jonesd90]
      #1019620 - 21/11/12 03:00 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.

--------------------
JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net


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