Display MoreAs quick and simple as I can explain it, 99% certain this is all correct (I think don't hold me to it) as I'm a keen modded Marshall enthusiast.
- Mark Cameron is an amp tech who used to work in a guitar shop in the USA, the shop purchased a lot of amps from Jose Arrendondo's sister I believe after his death that were left in his shop or uncollected by rock stars after he'd modded them. Mark had a keen interest in the 80's hot rodded Marshall tone of his heros. To him this was like finding a goldmine of great information. He opened up these amps to see what magic was in there and traced/remembered/learned what made it all work. One amp in particular was a Marshall with the badge missing with Atomica sprayed on the front which sounded to him and everyone who heard it as a holy grail of EVH/80's Marshall tone. The rumours were that this was an amp Eddie was working on with Jose before his death that was never finished. Other rumours were it belonged to an LA band called Atomica. But obviously the EVH connection and story makes it all the better haha.
- Jose Arredondo owned a shop called Arrco Electronics, which fixed electrical appliances like vancuum cleaners etc. He also modded and repaired amplifiers on the side.
- A little known guy called Eddie Van Halen was friends with Jose and had him service (or mod depending on what you believe) his Marshalls. To help Jose out he "leaked" in a guitar magazine that Jose tweaked his amps.....next thing you know, every LA guitarist is down at Arrco asking for their Marshall's modded.
Typical Jose mods included:- Pre amp tweaking for more gain and tighter more modern gain structure
- Diode clipping via zenner diodes or transistors
- Post phase invertor master volume
- Valve fx loops
- Insert loops before the cathode follower to be able to act as an extra gain stage if you inserted something like a cranked Lexicon Rack unit in there.
- Negatve Feedback tweaks
- Extra master volume control with zenner diode clipping volume positioned before the tone stack rather the typical Marshall post tone stack pre phase invertor
- Mark Cameron then started to offer his own mods primarily based on Jose's work, giving guitarists the chance to obtain these tones again.
- Now to your actual question - I'm pretty certain the "Aldrich Mod" is a Marshall JCM/JMP circuit with the pre amp tweaked for more gain and a 4th gain stage added by doing away with the cathode follower and using that side of the 2nd pre amp valve for the 4th gain stage. No cathode follower anymore in the circuit it is now a plate driven tone network. It also has a resonance control added. What I'm not 100% certain on is if it used any diode clipping. If the base for the mod is a non master volume Marshall Super Lead like I'm certain Doug's was the gain stages will need to be cascaded and a master volume added making it basically a JMP Master Volume/JCM 800 amp with tweaks. It is supposed to sound half way between a Mesa and a Marshall.
There are also John Suhr and Martin Golub versions of the Aldrich mod, which I believe is slightly different, which Doug has used at different times. I think Golub's version uses and extra valve for the forth gain stage and keeps the cathode follower intact although I couldn't swear by this at all.
Wow, Liam...amazing write-up. Thank you for the background and history on this...much appreciated, mate. 
