My MCA5 has developed a crackling noise on a single channel (left main) recently. The sound to the speaker sounds like it's cutting in/out. I disassembled and checked all connections. Reassembled, and everything sounded just fine. But, a few days later the noise continued.
This amp is most likely the same design as the MCA50, but I've read that the MCA50 upped the rated power to 225 WPC vs 200 for the MCA5. They also increased heat sink sizing. I've owned the MCA5 for abotu 17 years and I've used it regularly for years. The only real difference lately is that I'm using the balanced inputs lately. For many years I used the coax inputs.
I have the tools and capability to replace PCB components, but I'm not entirely sure where to start. Any help would be appreciated.
This amp is most likely the same design as the MCA50, but I've read that the MCA50 upped the rated power to 225 WPC vs 200 for the MCA5. They also increased heat sink sizing. I've owned the MCA5 for abotu 17 years and I've used it regularly for years. The only real difference lately is that I'm using the balanced inputs lately. For many years I used the coax inputs.
I have the tools and capability to replace PCB components, but I'm not entirely sure where to start. Any help would be appreciated.
I'd start by checking for DC at the output, first, to be safe. Then opening up the amp, hooking up a speaker I don't care too much about, and running some test signal through the amp while tapping and prodding boards, components, cables, etc, to see if there is a mechanical source to the "cutting in and out". Maybe bad solder, a bad connection, or a cracked trace... Use a dowel, or the plastic end of a small screwdriver (i.e. something non-conductive) to tap with.
@SQLGuy Thanks for the reply! I've had the amp channel out of the chassis for inspection a month ago. I looked at it under the microscope and didn't see anything that looked suspicious. Although, I think the main FETs are all covered up by heat sink. I too am wondering about a mechanical issue. I read a note about an NAD amp developing an intermittent cutout due to burnout of the relay. That would be an easy fix, but I'm not sure there is a discreet relay for each channel.
I'm considering bench testing with a DC power supply, function generator, and oscilloscope. If I put a ceramic power resistor across the outputs and read a frequency sweep, maybe I can at least reproduce the issue.
Questions in my mind:
I'm considering bench testing with a DC power supply, function generator, and oscilloscope. If I put a ceramic power resistor across the outputs and read a frequency sweep, maybe I can at least reproduce the issue.
Questions in my mind:
- What is the DC bus voltage? ( guess I can test it, but what is common?)
- What is the reference level input voltage amplitude?
- What is the output amplitude?
Attachments
I'm wondering about the adjustment potentiometer. I assume it's bias voltage. Maybe spray some deoxit on it. I think that style might be prone to issues but I'm new at this stuff. Any idea what the bias is supposed to be? Have you tried Anthem customer support?
I've not yet reached out to Anthem because they don't even post a phone number that I could find. When I called Outlaw years ago for a pre/pro issue, I was told I should just throw it in the trash and buy a new one. I guess I didn't want to have that kind of frustration with this amp.
Due to covid they don't answer phones anymore. I haven't had much luck with them either but I saw that a few others have.