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?
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?
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/userwebsite;jsessionid=427mttqiae31c.omaasp12?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!
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/userwebsite;jsessionid=427mttqiae31c.omaasp12?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!
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/userwebsite;jsessionid=23e5lkrfh6pg.omaasp32?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
What does that little daughter board do with all the little transistors or whatever on it?
http://simon-ashton.magix.net/userwebsite;jsessionid=23e5lkrfh6pg.omaasp32?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
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
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
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.
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.
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 don’t know, it needs someone with more experience to look at the detail of it.
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 don’t know, it needs someone with more experience to look at the detail of it.
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
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
Hi, Tenson,
It's not clear what you want with this amp. You mentioned more power, it is difficult to do so, because power is related to rail voltages, this will change everything, need to recalculate heat dissipation etc.
You can try (with carefull monitoring) change opamps and caps. Sometimes changing these "not harmfull" things can lead to dangerous oscilation.
It's not clear what you want with this amp. You mentioned more power, it is difficult to do so, because power is related to rail voltages, this will change everything, need to recalculate heat dissipation etc.
You can try (with carefull monitoring) change opamps and caps. Sometimes changing these "not harmfull" things can lead to dangerous oscilation.
well its a very standard amplifier, very much from the japanese design school of power amplifiers.
Triple emitter follower output stage with current limiting
Balanced input stages to eliminate 2nd harmonic distortions,
looking at things, its been quite well optimised with emitter degeneration on the input stage and good matching arrangements.
Made in the wei-phon electronics factory in china.
Nice big mains transformer, but....
troulbe is, doesn't sound so good to me now, I had one of these and a behringer.
Whilst they worked, the be was pretty poor,
the alesis less so.
Output power is closer to around 70 watts into 8 rather than 150.
Power supply clips very easily, and you can tell upon transients.
Whether bigger capacitors would cure this, who knows, but don't touch the mains tx, EL cores are superior to toroids in numerous ways.
watch you don't blow the bridge rectifier.
or wreck the boards which no doubt is quite easy.
Bridged, you are only incresing the voltage capability, and they won't like varying loads, only happy really with 8 ohms.
nice amps tho for the cash.
Better off with a big mosfet pa amp.
5532 opamps are very good indeed, low noise, they are hard to beat, I wouldn't bother as you can't really drop in opamps, without possible attention to some factors.
some opams are subject of great hype, don't believe a word of it.
The servo cancels out dc, instead of just a basic passive capacitor.
I am undecided which is best.
Evox caps are the best small ones, nichicons and panasonics, some elnas, and siemens go for the biggest you can get for the psu.
If musical fidelity use jamicon and naim and graham slee and tom evans use tantalums then they are good enough for anyone.
Triple emitter follower output stage with current limiting
Balanced input stages to eliminate 2nd harmonic distortions,
looking at things, its been quite well optimised with emitter degeneration on the input stage and good matching arrangements.
Made in the wei-phon electronics factory in china.
Nice big mains transformer, but....
troulbe is, doesn't sound so good to me now, I had one of these and a behringer.
Whilst they worked, the be was pretty poor,
the alesis less so.
Output power is closer to around 70 watts into 8 rather than 150.
Power supply clips very easily, and you can tell upon transients.
Whether bigger capacitors would cure this, who knows, but don't touch the mains tx, EL cores are superior to toroids in numerous ways.
watch you don't blow the bridge rectifier.
or wreck the boards which no doubt is quite easy.
Bridged, you are only incresing the voltage capability, and they won't like varying loads, only happy really with 8 ohms.
nice amps tho for the cash.
Better off with a big mosfet pa amp.
5532 opamps are very good indeed, low noise, they are hard to beat, I wouldn't bother as you can't really drop in opamps, without possible attention to some factors.
some opams are subject of great hype, don't believe a word of it.
The servo cancels out dc, instead of just a basic passive capacitor.
I am undecided which is best.
Evox caps are the best small ones, nichicons and panasonics, some elnas, and siemens go for the biggest you can get for the psu.
If musical fidelity use jamicon and naim and graham slee and tom evans use tantalums then they are good enough for anyone.
yes once you start splitting amps and using different ones for treble and mid duties it makes you realise that the current and power drawn by them isn't neglible, it makes a huge difference.
go for active tri amping, the only way to go.
even a phonostage can benefit from using 2 units instead of one.
I found contrary to my intuition that an amp for bass and treble is much better than 1 on each speaker, which previously I preferred.
this was in someone else's rig tho', it may or may not be speaker/amp dependant, only way is to try.
personally, I am past the modding phase, I only do what needs doing when it does, and just concentrate more on music now instead of gear.
after all that's all its for, isn't it?
go for active tri amping, the only way to go.
even a phonostage can benefit from using 2 units instead of one.
I found contrary to my intuition that an amp for bass and treble is much better than 1 on each speaker, which previously I preferred.
this was in someone else's rig tho', it may or may not be speaker/amp dependant, only way is to try.
personally, I am past the modding phase, I only do what needs doing when it does, and just concentrate more on music now instead of gear.
after all that's all its for, isn't it?
lt cdr data said:
Not quite: degeneration is insufficient with respect to the values of compensating caps. used.
The thing tends to oscillate if turned on after the source; this is heralded by the heatsinks running very hot for a short period.
Be that as it may, the modular nature of this design makes it amenable to sweeping changes in circuitry.
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