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Old 6th June 2006, 01:47 AM   #1
Tenson is offline Tenson  United Kingdom
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Default Alesis RA500 Mods

Hi,

I bought a pair of Alesis RA500 amps which when bridged put out 500watts RMS. I was going to use them for bass driver duties on my speakers but I have since decided to change the bass driver I am going to use to one which happens to be 4Ohm. This means the Alesis will not drive it bridged and doesn't have enough power un-bridged.

So.. I thought I would use them on the main drivers which are 8Ohm but for the more sensitive area of 50Hz-1KHz I feel it would be nice to mod the Alesis amps to get the last bit of performance from them.

Getting to the point now, has anybody got some suggestions of what could be done with this amp?

My first impression was that for a 500Watt RMS amp, its PSU caps are very small. Is it possible to just plop in bigger/more caps to improve power reserve, or is it more complex than that?

I'm not sure what else is in there I will take a look tomorrow. I guess maybe there are some op-amps which could be changed to better ones. Maybe the actual transformer could be swapped for a torroidal (though the current one is big, at least!).

Just a silly question here, but if chip-amps are so easy to make and sound so good, why are they hardly used in good hi-fi/pro-audio?
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Old 6th June 2006, 02:41 AM   #2
Leolabs is offline Leolabs  Malaysia
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Quote:
PSU caps are very small
what are the values of them???

Quote:
if chip-amps are so easy to make and sound so good, why are they hardly used in good hi-fi/pro-audio?
do a search,you will notice that not few are actually using them.
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Old 6th June 2006, 02:45 AM   #3
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What's an Alesis amp schematic looks like?
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Old 6th June 2006, 11:14 AM   #4
Tenson is offline Tenson  United Kingdom
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Hi,

I have asked Alesis for a schematic I'll let you know if they reply.

In the mean time here are some pictures I took. I'm afraid they are poor quality as done on my mobile. Will be getting a good camera in the next few days though (Nikon 5700 ).

I don't know if these are of any use.

http://simon-ashton.magix.net/userwe...2?act=15&pos=0

I see two op-amps. One near the RCA input and another on the board near it which the gain controls connect to. (maybe un-balancing?)

The two PSU caps are each only 10,000uF! I am put that much in my DAC PSU!

Thanks!
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Old 6th June 2006, 03:56 PM   #5
Tenson is offline Tenson  United Kingdom
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I have uploaded some much better pictures which I took on my Dad's camera.

What does that little daughter board do with all the little transistors or whatever on it?

http://simon-ashton.magix.net/userwe...?act=12&mode=o

Click on the image you want to see, then click on the magnifying glass icon to see it uncompressed full-screen. If you just click on the picture you want to see it shows a small-ish very compressed version
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Old 6th June 2006, 07:07 PM   #6
Tenson is offline Tenson  United Kingdom
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Okay I have a service manual for the RA500 which has every detail one could ask for. I'll post a link to it, but I would like to ask that this not be used for the purposes of building a replica of such an amp as Alesis have been kind enough to give this to me on the understanding that it is just for making modifications.

These amps already sound brilliant for the money and if someone can help me with some modification suggestions it will be even better value!

http://www.smokeitndie.co.uk/RA500.pdf
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Old 6th June 2006, 08:28 PM   #7
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Hi, Tenson,

Alesis are usually used in pro-audio/studios. They sounds "correct" as it is used for standards.
What do you want with the existing sound?
For experimenting, try if you can hear difference if the servo is removed (R68/33k in R schematic). Usually removing the servo adds something to the highs.
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Old 6th June 2006, 08:38 PM   #8
Tenson is offline Tenson  United Kingdom
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What does the servo do?

I can't say there is anything wrong with the sound, but I have not yet had a proper listen to them. I only used them on some DIY speakers that are mid-end.

That will change though. I use Bryston amps at the moment, which I have to sell with my active PMC rig, so I can't help but feel there is some room for improvement in the budget Alesis.

As I said I imagine it could do with more power reserve as the caps are piddling for a 500watt amp (and I will be needing that!) I see a few cheap op-amps. Maybe there are a few stages that are unnecessarily complex and could be simplified with some good quality components for example... Maybe the low voltage supply could do with being better regulated. I donít know, it needs someone with more experience to look at the detail of it.
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Old 6th June 2006, 09:09 PM   #9
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Hi out there,

I am sitting here in Germany with a nice Alesis RA500. Best buy for the money- so how hotrodding this device. Excellent parts in there-so why out they went?
I think the only thing is to remove the Pots and the light show what a friend did and of course upgrade the caps a little bit which is hard to do because of the space inside-I will do both mods when the warranty is gone.
Mine is a little sick when you switch the power on some times one channel is not playing-I think there is a ******* rlais inside and not switching however? May be someone can give me a hint or have the same failure-otherwise back to the dealer and replace-but this device is beautiful.

I have built all the elektor stuff/ELRAD stuff and have some Rotel(harsh harsh) amps and plenty of tubes so I may compare the alesis to a hell of a lot stuff.

Basically leave it asis.

Regards

Peter
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Old 6th June 2006, 09:22 PM   #10
Tenson is offline Tenson  United Kingdom
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There is lots of room for caps Put them along the inside of the front, a lot of small caps parallel.
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