This is just a quicky, inbetween major writes.
Nice little amps these. A bit susceptible to mains noise (Beer pumps, Flourescent lighting, lighting control systems) as many smaller amps are. The bigger the mains transformer in an amp, the more the filtering effect it has. It’s a property of something called ‘Inductance’ that is inherent in a transformer (or any coil of wire, for that matter), and this presents a high impedance (sort of like resistance; but not) to high frequencies; the higher the frequency the more the filtering effect, and the cleaner (less noisy) the outcome. Switching noise, of the sort that starts with beer pumps etc., is often way up there in mega hertz (MHz) range, whereas the mains frequency is way down around 50Hz or 60 Hz, depending on where you are.
Anyway, there’s a whole blog that could be written, on not much more than mains noise and how to minimise it; but that’s for another time, probably.
This little Mesa was described as being intermittent, the output just disappearing altogether sometimes, no speaker hiss, no nothing. The first time I came across this problem it was a big head-scratching job. It turned out to be very simple.
It was the jack in the back of the amp, on the end of the short lead to the speaker. This gets us to quality jacks. The Marshall jack was total trash as is the Mesa Boogie, although it looks a lot better.
There are two distinctly different ways to make a jack plug. If you buy say a good Neutrix, or Switchcraft or Amphenol, for instance, the soldered wiring is directly to the rod for the hot terminal, and onto the case for the ground/cold terminal. These are machined very well, and should last a very long time, unless you for some reason say, play underwater. Or decide to use one as a towrope.
The other sort, which don’t usually have any manufacturer’s name on them (wonder why not?) Have solder tags for the wiring, and these are pressed together. If you turn the end of one of these between your finger and thumb, and it rotates, your next move is to find a good recycling place because the plug/lead is worse than a liability.
This is what is on the end of the Mesa Boogie internal speaker lead, and also what was on the end of the Marshall speaker lead. I’d like to Fender speaker leads are better, but although the centre contact is solid, the outer relies, again, on two bits of metal pressing together.
Worse than that, the centres of cheap jacks can spin round and short. And that can be death for your amp. Valve amps don’t like open circuit loads, so your speakers should always be connected, but most semiconductor amps don’t bother about that problem at all. But a shorted jack will very likely wipe out your nice power amp stage, and replace it with nasty black smoking things that used to be transistors.
It’s one thing using cheap stuff at the guitar end of things. That is unlikely to be much more than an annoyance, but it’s big bucks at the speaker end.