I have a brand new diezel vh4. The amp itself makes a mechanical hum
Mechanical hum—usually from a vibrating power transformer—does happen. It sucks. It's typically caused by the laminations in the transformer vibrating from eddy currents. It can happen in literally any transformer. Typically, the only fix is to either re-pot/re-varnish the transformer or replace it with a new unit.
but once i turn on the cab it becomes louder and it's coming out through the cab.
If you mean once you take the amp out of standby, you're hearing the same mechanical vibration come through the speaker as audible audio of the same frequency (probably 60Hz or 120Hz hum), then there are a few possibilities:
1. A bad ground connection somewhere. Either in the amp or you have a ground loop from your signal chain. To troubleshoot this, make sure you just have the amp plugged in. No pedals. No guitar. Just amp and cab.
2. If the hum is 60Hz, you know it's mains hum from the wall power, which
can be from the transformer vibrating, but also bad preamp or power tubes, or a bad ground connection, or the heater circuit.
3. If the hum is 120Hz, it's coming from rectified B+. i.e. it's from the preamp somewhere. Usually a bad filter cap or bad ground connection. The fix is to replace the filter caps. I doubt a brand new amp will have bad filter caps. But it can happen.
I thought at first it could have been vibrations from the amp, but i have seperated them across the room. It's really hard to record clean guitar stuff without the mic picking up the noise.
A vibrating transformer can couple to the audio circuit and make its way to the speaker. So it has nothing to do with separating the head and cab. But the hum you're hearing through the speakers might not be the same hum from the transformer vibrating, if it's actually the transformer.
The hum stays the same volume no matter 0 or 11. I know the Diezel man says it's a normal hum and it's been like that since 1993. But i never got a reply is it normal that it's coming through the speaker as well, and even louder?
Most amps have
some audible hum. But not all. It really comes down to what you're willing to put up with. That said, I had a 2005 VH4 that was dead quiet. And an older Einstein combo that hummed. But once I replaced the faulty filter caps, it was quiet.
