Question about Alesis RA-150 Amplifier

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Amp not powering up

I recently got an alesis ra300 but like many others there was a faulty relay unit. I replaced this with an 8 a instead of the 10 a one. However I think when I replugged the cables I plugged the right input into the output section and vice versa. When I turned it on it started to power up for about 2 seconds before the fuse went. I replaced the fuse and switched the cables to how they should be but it's still not powering up at all now.I'm wondering where the fault may lie is it in the transformer? if so how can I fix this problem?

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Chek transfomer with a multi meter set on continuity,check primary input across wires AMPLIFIER MUST NOT BE PLUGGED INTO WALL SOCKET...check outputs low readings in ohms are good no readings mean open transformer(buggered

I suspect outpuit stage short as this probably buggered relay in first place

Posted on Jan 08, 2009

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Alesis RA150 overheat.


You first need to check whether the relay you have used as a replacement has the same voltage on the coil as the original. You have wisely chosen one with a higher current rating on the switch contacts, which is a very good idea, but I suspect you've not looked at the coil voltage to ensure it's the same. For example, you may have installed a with a relay with a 12 volt coil, while the original had a 24 volt coil. Result? the new relay coil will overheat, as will the driver transistor.
A simple test is to operate the amp until it feels hot, TURN IT OFF, quickly remove the top cover and see if the new relay feels hot. If it does, you need to source a replacement relay with the correct coil voltage. Usually the coil voltage is written on the body of the relay somewhere, so you should be able to identify it on the original unit airly easily

Apr 08, 2014 | Alesis Amplifiers & Preamps

1 Answer

Hello. RA300 used only in a studio environment, never pushed hard. During a mastering project we lost one side of the amp. Thanks!


The first things to check are the devices on the heatsink. They do all the work so tend to go when pushed! Remember stereo amps are just two amps put together, so at least you have a good channel (which is the same as the bad one) to do tests with say an ohmeter.

Apr 27, 2011 | Alesis RA-150 Amplifier

1 Answer

I have an elesis RA 500 it blows the slow blow fuse when i plug it in .any ideas what is wrong?


hi there,
it sounds like the internal transformer has gone.
It's not user replaceable and will require you to take to an electronics store to be repaired.

SAME THING RECENTLY HAPPEN WITH ONE OF MY BITS OF KIT ...... for heavens sake don't just keep changing the fuse time and time again.

Jan 07, 2011 | Alesis RA300 Amplifier

3 Answers

Alesis RA 500 makes a "clicking" sound and no more sound. later it will "click" on again


Clicking sound is a protection relay. This means one of the power amp sections have failed. Or that your speakers connections are faulty

Sep 24, 2010 | Alesis RA300 Amplifier

1 Answer

Alesis RS300 Reference Amplifier Channel malfunction...


You say "it seems like". Do you mean to say it is intermitent, or did it start cutting out and then finally fail? If that is the case I would look first to replacing the relay in contention in this thread.
http://www.fixya.com/support/t224708-amp_cuts_out_after_while

It's a cheap fix and will eliminate one potential cause. The Radio Shack part is widely available.
http://www.radioshack.com/product/index.jsp?productId=2062483

My RS-300 had started dropping the left channel, but occasionally both. It is possible that the relay has failed on one side and thus you have a dead channel...I did the fix and am now quite happy with the amp

Steve

Dec 26, 2009 | Alesis RA-150 Amplifier

1 Answer

Took my RA300 and Tannoy Reveal X speakers to a cellar party for halloween. No drinks were spilled or anything but it had an ipod plugged into it most of the night and the volume on the amp turned to max,...


Normally when people bring their HI-FI to a party they tend to fix up the leads to the speakers in a flimsy manner ( as it is only temp) . With the crowd mulling around these leads(wires) could very well come loose or even short out. This leads to your Final Drive ( Output Amp) to short out. It is not an expensive repair. Check your final amp & replace any shorted/blown items. To get full satisfaction the job best be handled by the local agents of the amp.

Nov 19, 2009 | Alesis RA-150 Amplifier

2 Answers

Power up problem with alesis rs300 (ra300)


you have more than likely damaged some transistors.
the resistors have burned because of excessive current.
there are 2 typesof transistors,bipolar and mosfet
a bipolar transistor has 3 pins.1) base 2)emitter 3)collector.
an NPN is tested with the + meter lead on the base , and a PNP transistor with the - lead on the base.
TESTING
base to collector should read .5 to .6 v drop in one direction and open in the other with a digital meter on the diode check function.
base to emitter about the same,but slightly higher than the collector.
if base to collector is .5v then base to emitter is .52 or so.it is always higher than the base collector number.
between emitter and collector will read open in both directions.
if there is a short on any lead combination,the transistor is blown.
npn transistors operate on the positive rail power supply,and pnp on the negative rail.
typically a 150 watt amp will run + - 65vdc.
the transistors running on the plus side are npn and on the negative pnp.
most pnp output transistors are green.,but some are black,
so we must go by the numbers on the transistors, eg.A1076 is a pnp,B755 is a pnp and all transistors that have a C or D eg. D424 are NPN transistors. all A and B numbers are PNP and all C and D numbers are NPN.
MOSFET transistors have 3 pins 1)gate 2)drain 3)source
the source goes to power like the collector does. the drain is like the emitter,and the gate switches it on like the base does.
testing a mosfet is a different procedure.
a mosfet with k then a number e.g. k135 is a positive device like npn.
a mosfet with j and a number e.g. J50 is a negative device like pnp.
a mosfet reads open source to drain both directions.
for a positive (k number device) the plus meter lead goes on the source.,the black meter lead on the drain. on the diode test function.
jump a wire from the source to the gate for 1/2 second and remove the jumper while leaving the other two meter leads connected to the source and drain.The mosfet should switch on and the meter should show a short.that means the mosfet switched on.About 5 seconds later,the resistance from drain to source should go open.
for a p channel mosfet,it checks the same,except that the black meter lead goes on the source and gate .
a mosfet will stay switched on longer than the voltage applied to the gate,if it is driving a high impedance device such as a meter.
a bipolar transistor will not stay on when voltage is removed from the base lead.
i hope this has been of some help.

Sep 09, 2009 | Alesis RA-150 Amplifier

2 Answers

Distortion in one channel


your right output component (transistor or integrated circuit needs to be replaced)

Nov 11, 2007 | Alesis RA-150 Amplifier

22 Answers

Amp cuts out after a while


My Alesis SA-300 started the cutting out when at moderate levels some months ago... Well, Radio Shack has instant gratificaion for those who have one in the neighborhood. Part number 275-249 will do the trick!
http://www.radioshack.com/product/index.jsp?productId=2062483

I replaced the Dong Woo part with the Radio Shack item and the amp is back to its old self... maybe even a little better. Loud, clean and steady.

Thanks to all you who have contributed to this thread.

Steve

Oct 17, 2007 | Alesis RA-150 Amplifier

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