Alesis Matica 900

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A

Audio Tech

Member
Joined 2004
Hello Netlist,

I checked only the bias of both channels and its the same. I think that I have something broken immidiately after the inputs. Because on "bad" channel the sinewave looks nice as on the good one. If I want to make them clip at the same time I have to set gain potis (scale 1-10) for good one on 7 for bad one to 10.

I just ask for schematics because is much more easier to find what is causing this difference. If I wont get it, as it looks, I have to go on on the hard way. But is very strange the amp was produced in 1996 and there are no free serv. manuals to find.

Regards,

AT
 
Zero Cool

Zero Cool

Member
Joined 2004
I just worked on one of these as well and noticed very bad tracking of the input controls. when the controls are wide open. both channels are the same, but with the controls half way, one channel is quieter then the other. I didn't take measurements but noted on the scope the discrepancy.


Also. I found MANY bad solder joints in these amps. these are not built very well mechanically. check everything for bad solder joints. I found some 25-30 bad joints in one amp!
 
A

Audio Tech

Member
Joined 2004
Hello ACD,

Thanks for the link. It has been a while that later one channel break down and I didn't have time to repair it. One channel is completelly destroyed. I think the cause of it are very bad quality diodes in voltage amplification stage 1N4148. These diodes are realy a piece of sh... They become sometimes more resistive and current limit transistors are most times too small to protect the current amplification stage. During repair I will modify all these.

Regards,

AT
 
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