Visonik V900XD causes radio interference

[spooney]

I just did a rebuild of the power supply and output section of this amp. On cd's or mp3's the amp plays with no issues. When I play fm radio though it seems as though the louder I turn it up the more static it causes in the fm radio. What are some problems in amps that could cause this issue? Is there a known failure in these amps that causes this? Between secondary ground and primary ground I am reading only 47 ohms, this number seems low. Should I start my search here?

[Perry Babin]

47 ohms... Was that with no RCAs plugged in?

RFI is a problem with some amps but it's generally from the class D section. If the amp is interfering with the radio reception, check the shield on the antenna cable. The shield (unplugged from the head unit) should read 0 ohms to ground (or at least they did on older vehicles). An open shield could cause this problem.

[spooney]

It's causing the fm interference both in my home on the test bench and in my vehicle. I will have to double check but I am pretty sure it is 47 ohms with no rcas plugged in.

[spooney]

Definitely 47 ohms with no rcas plugged in.

[Perry Babin]

What's the resistance from the negative speaker terminal to the RCA shield?

[spooney]

Negative speaker terminal to rca shield is also 47 ohms. Not sure why but I checked resistance between the amps ground input terminal and the negative speaker output terminal and got a 0 ohm reading so somewhere they are shorted together.

[spooney]

Is the short between the negative speaker terminal and ground most likely the cause of the interference in the fm band?

[spooney]

I've looked over the bottom and top side of the board again and I have not been able to find any shorts/ solder bridges. Is there a component that would cause this kind of short between the negative speaker terminal and the ground terminal? Is this even a concern in this particular amp? I guess at this point I am more concerned with the apparent short than the interference. Hoping if I find the short the interference will go away.

[Perry Babin]

For an amp that uses an active noise canceling input (balanced input or similar), the non-bridging speaker terminals (or the negative speaker terminal for some mono amps) is supposed to read 0 ohms to the main ground. The 47 ohms to the main ground seems very low. If you're not having a problem with engine noise, the 47 ohms may be normal for this amp.

Some (poorly designed) class D amps produce a lot of RFI. This may be normal for this amp.

Have you tried plugging in another antenna to see whether it's better or worse?

[spooney]

I have not tried any other antennas. I tried the amp both in my home on the test bench and in the car in my own install and both had radio interference. I can try a different type of antenna to see if it changes anything. It would appear I am chasing my tail with the speaker terminal shorted to ground thing and that 47 ohms between shield ground and primary ground may be right as I had zero noise or problems of any other kind besides the RFI. On amps that you have seen with RFI was the interference so bad that it made the radio unlistenable?