Alesis RA-150 amplifier

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TPT
Posts: 656
Joined: Mon Dec 03, 2007 3:18 pm
Location: St. Marys, WV

Alesis RA-150 amplifier

Post by TPT » Sun Jun 12, 2016 1:02 pm

I have two of these--both failed after 5 years. One channel goes out (more or less). However, not sure whether it is the output transistors or lower stage--the "clip" indicator doesn't show any input until the level control is wide open--which could indicate a lower stage failure, or output failure depending on what drives this indicator.

Anyone had similar experience with these amps?

kcbooboo
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Joined: Sat Dec 10, 2011 4:53 pm
Location: East of the Mississippi

Re: Alesis RA-150 amplifier

Post by kcbooboo » Mon Jun 13, 2016 4:36 am

If only one channel is bad, feed a sinewave into both channels and use a scope to verify the various gain stages. Compare the two channels. You should be able to find out what's different pretty quick.

That amp seems similar to the Crown D-75 or D-150 amps. The output transistors should be easy to test with an ohm-meter.

Bob M.

jammerdave
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Location: West Sacramento, CA

Re: Alesis RA-150 amplifier

Post by jammerdave » Mon Jun 13, 2016 9:53 am

TPT wrote:I have two of these--both failed after 5 years. One channel goes out (more or less). However, not sure whether it is the output transistors or lower stage--the "clip" indicator doesn't show any input until the level control is wide open--which could indicate a lower stage failure, or output failure depending on what drives this indicator.

Anyone had similar experience with these amps?

We've had a couple of those that burned up the power supply board. Beyond repair, so we had ordered new boards... Still waiting after a month. I would avoid those units.

df

TPT
Posts: 656
Joined: Mon Dec 03, 2007 3:18 pm
Location: St. Marys, WV

Re: Alesis RA-150 amplifier

Post by TPT » Mon Jun 13, 2016 3:00 pm

Yes, I replaced both of these with Chinese Crowns. Will see how long they last.

I was hoping that there was some common failure mode to narrow in on...if I take the time to repair these units, they're going to Ebay anyway.

kcbooboo
Posts: 448
Joined: Sat Dec 10, 2011 4:53 pm
Location: East of the Mississippi

Re: Alesis RA-150 amplifier

Post by kcbooboo » Tue Jun 14, 2016 4:52 am

It would be interesting to find out if both have exactly the same failed part.

I perused an RS-150 service manual I found on the web. Things would be much easier if they identified the various signals on the connectors used between the boards. Way too many interconnection wires. Probably makes module replacement easier though.

I've fixed a dozen Crown D-75s. Once you replace the 2w resistors and 1/2w 10V zener diodes that fail, and repair the burnt up foils that disappear from the ensuing flame, they come right back to factory specs. Replacing the dead NE-2H power bulb gets rid of that "doesn't power up" symptom. $5 in parts and an hour of labor produces a decent amplifier, if you can buy it cheap enough off ebay.

Bob M.

kcbooboo
Posts: 448
Joined: Sat Dec 10, 2011 4:53 pm
Location: East of the Mississippi

Re: Alesis RA-150 amplifier

Post by kcbooboo » Sat Jun 18, 2016 7:34 am

There's a supposedly brand new in box RA-150 on fleabay for $74.95 with free shipping from California. Assuming it's an accurate description, probably worth buying rather than fixing one of yours. Comes with power cord (such a deal)!

Bob M.

M7H
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Joined: Fri Mar 17, 2017 12:42 pm

Re: Alesis RA-150 amplifier

Post by M7H » Fri Mar 17, 2017 1:23 pm

Been there. Those are loaded with cheap electrolytic capacitors and I ended up replacing a bunch of them and got it working. It might not be worth your time and effort at that price point. Should have bought the Hafler.

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