Mesa Boogie Dual Rectifier Tremoverb.
I have had a few of these amplifiers as of late. Some have had some awkward problems to sort out, mainly around failure of the LDR (light dependant resistors). These are used to alter the routing and operation of the signal paths around the various valve stages. Given the way these devices are mounted, fault finding can be time consuming and frustrating.
Luckily, the owner of this amplifier was annoyed with the way the FX send-and-return facility works. For those that are not familiar with this, it is a way of breaking part the pre amp and main amp sections in order to introduce a preferred FX pedal(s). Most amplifiers are configured (rightly so in my opinion), so that when jack plugs are plugged into the FX sockets, this automatically makes the separation, making the external FX pedal connected in series with the pre and main amp. Mesa choose, in several models, to configure the external FX pedal in a parallel fashion, retaining the amplifiers tone circuits in place. Users find that the internal and external combination of signals degrade the sound they want to hear.
A relatively simple modification can be made to make the FX loop operate in a series configuration. Unsoldering and moving a couple of wires on the underside of the chassis, see picture inserted. If you want full details, send me an email. And, of course I must add for the non technical, please be aware that valve amplifiers have significant high level of angry pixies flying about which can be lethal.
I also hear that some users find that tonal colouration takes place as the reverb levels increase. Looking at waveforms, I cannot see this happening. I would be interested if any other engineers have stumbles across anything.
I get the feeling from talking to guitarists, Mesa seems to be a little like Marmite. You either love or hate them. From a service point of view, I find some models straight forward to work on, whilst others lead to consume high levels of hard drugs. I am not a guitarist, as saxophonist which has its own hardware irritations. I find the various settings on these amps curious. I didn’t say gimmicks did I? Norm, Vintage, Spongy, Bold, Clean low gain, Valve HT, Silicon diode HT……