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Something you might have missed which may send you down the wrong track... generally, a buzz (in audio equipment) is caused by poor earthing, but the buzz is generally 50hz. Where does the 50hz buzz come from in a DC power system (particularly on a diesel where there is no ignition circuit)?
The power units within the amplifiers generate their own higher rail voltages in order to get their (usually totally inflated) higher power outputs via inverters, which generate the noise. (I'm probably teaching grandma to suck eggs here) Therefore, in a BADLY DESIGNED or faulty power supply, there may be some internally generated noise which gets onto the DC power feed cables. However, it should be possible to filter this out in the same way you would filter motor noise.
As the frequency of the switched mode PSU is usually fairly high (I have some operating typically around 2khz) this should be quite easy to filter out as long as it is external and not leaking into audio circuitry internally. However, I'd agree with the other posters who've advised checking for good earthing. Earthing case to case is no bad thing either, though it's good practice to only have one earth from each point back to the main earth so as to avoid loop hum.
The power units within the amplifiers generate their own higher rail voltages in order to get their (usually totally inflated) higher power outputs via inverters, which generate the noise. (I'm probably teaching grandma to suck eggs here) Therefore, in a BADLY DESIGNED or faulty power supply, there may be some internally generated noise which gets onto the DC power feed cables. However, it should be possible to filter this out in the same way you would filter motor noise.
As the frequency of the switched mode PSU is usually fairly high (I have some operating typically around 2khz) this should be quite easy to filter out as long as it is external and not leaking into audio circuitry internally. However, I'd agree with the other posters who've advised checking for good earthing. Earthing case to case is no bad thing either, though it's good practice to only have one earth from each point back to the main earth so as to avoid loop hum.
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