The first item of the XP Series was the XPR, the first 19' rack unit made by SR&D. It was replaced in 1991 by an updated low-noise version, the XPRa:
The basis of the XPR is just... the X100 headphone amp! In other terms, the XPR is a sort of big, programmable X100, with of course several additions that make it totally flexible:
All the parameters of these modules (compressor, pre-EQ, preamp, post-EQ, chorus and echo/reverb) are entirely programmable, and can be stored in 100 presets.
The temptation was of course to build a guitar amp that would have an XPR as a preamp section. The guitar amp would of course be stereo, and stereo called of course for separable cabs for a wider image. That was the XP100 Programmable Stereo Amp: the XPR with a 2x50W stereo amp, housed in a double enclosure with compact 6 inches Pyle speakers:
The weakness of the XP100 is clearly its small speakers: the amp in itself is excellent and loud, but these small car-audio speakers cannot handle this power the way it deserves. The other amp based on the XPR was the XP212: a 2x50W stereo combo with two 12 inches guitar speakers. This version is extremely rare: probably a dozen of XP212 only were made.
The ad for the XP212 shows discretely another XP Series product, without even naming it! This is the more-than-rare Rockman Superhead: it is in fact the electronics of an XP100, presented in a head format. I have myself transformed an XP100 into a Superhead Replica, certainly because I will never cross a real one: Boston owns one of them, and a second Superhead was sold on eBay in January 2006: that's all we know about it! Having no speaker, the Superhead must of course be connected to a pair of full-range cabs: it is loud, it sounds good, and it is in my opinion the best configuration for a XPR based Rockman amp.
Usage, samples and limitations
The XPR is a contradictory product. It is programmable, and that makes it a fantastic unit, of course. The preamp and EQ's section is really great, and sounds really awesome.
The chorus and reverb sections are of course weaker: they don't have the complex circuits of the Rockmodules, and are fairly limited and noisy. For example, the reverb section is based on the same MN3011 chip as in the headphone amps, and was pushed to its limits in order to obtain a 220ms (340 in the XPRa) delay. It is noisy, and far from the plain and clean 500ms of the Stereo Echo.
All and all a good unit, the XPR delivers a wide panel of sound and atmosphere in a very compact and handy format. Had it been a preamp only, with the Autoclean and a built-in Smart Gate, it would have been almost perfect. But like every all-in-one device, it has some minor defaults.
Collectibility and conclusion
The XP products are quite rare: less than 3000 were built, most of them being basic XPR's or XP100's. The XPRa, XP100a, XP212 and Superhead are so rare that you must not plan to buy one: just catch it if you can when you see one!
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