1982 Marshall JCM800 2210 Split Channel

Overview

I’ve been looking for an early-circuit revision split channel JCM800 for quite some time, and although I probably overpaid, I finally took the plunge on this early ‘82 100 watter. It had a recent recap job by a tech and was working 100%, so I figured it’d be a great comparison against my ‘85 and ‘86 split channel amps, both of which have the later circuit design.

Unlike some amps where a circuit revision is a few value changes, transformer changes, or some other change that keeps the main design intact (such as Mesa Marks or Rectifier revisions), this amp may as well be a completely different amp that just happens to share the same controls as the later versions.

So while visually, and functionally, this amp is the same as the later models, it is completely different inside. For example, this amp has two channels, a “normal” and “boost” each with their own set of controls. The Normal channel is clean-ish, and has a simple volume, treble, and bass layout. The Boost channel gets a lot gainier, with a full 3-band treble/middle/bass EQ section, a channel volume control for balancing, plus a preamp gain control. The master section contains an overall presence, overall volume, and control over the amp’s footswitchable spring reverb. On the rear panel, it has an effects loop, a DI out taken off the speaker tap, and a jack for the two-button footswitch.

That’s where the similarities end though. This amp’s master volume is a dual-gang pot (controls two values at once) set up in a post phase inverter master style. Other substantial changes are the location of the clipping diodes on the boost channel, where this amp has only two tube gain stages on that channel, which feed into a cathode follower pushing the signal through a quad of diodes just before the channel volume control. Even more interesting, the EQ stack is located immediately after the first gain stage, almost similar to a Mesa Mark, but this amp is substantially less aggressive sounding. The normal channel only has a single input gain stage, followed by its EQ section. Technically both channels go through another tube stage called “mix,” just before the reverb drive and recovery tube stages. Some say they have issues with channel bleed on these amps at high volume, for example turning up the normal channel very high bleeds into the gain channel, but mine does not have this issue - I suspect this is due to the cap job. As components wear out of spec, the bleed starts to come through.

It’s not exactly what I expected, it is a lot darker than my other Marshalls, and the master volume needs to be turned way up to really get the goods due to its location in the circuit - not necessarily that “louder is better” if that makes sense. On the plus side, the master is much more useful here - it tapers nicely and makes every setting on the knob a different level of loudness, so it’s much better at tweaking lower volume levels too. The later circuit’s master volume isn’t a PPIMV type, and is much more finnicky - incredibly loud by “2” on the knob and doesn’t get any louder at all after about “4.” Both this ‘82 model and the later amps are the same volume when fully cranked up, in my studio the dB meter registers about 115dB each from about 15 feet away.