Powertran Digital Delay
Designed by Tim Orr (who also designed the Transcendent 2000 monophonic synthesiser and for the EMS company) in the late 70s, this delay was (I believe) available as a DIY kit, like the synth. For your money, you got a 1.6 seconds delay at 4Khz sampling rate or .64 seconds at 10Khz.
From left to right, you get, high and low level inputs, input volume and repeat level, a series of push switches to set the basic delay time, a pot to vary the chosen delay time, a mix and output volume knob. A further switch alternated between the sampling rates and yet another brought in the VCO, which had its own depth and sweep rate. To add to the fun, there was a "freeze" switch (and associated jack socket for a footswitch) - this set repeat to infinite for whatever was in memory at the time.
I've used this beast since the early 80s and have to say, I've yet to find a more creative and organic delay-based tool. The low sampling rate makes your loops good and grainy, far removed from today's pristine and lifeless repeats. The sampling rate button allows you to drop your samples to the depths - harmonics become beautiful bell tones and low notes descend into the depths, almost unrecognisable from the original. Working the other way, notes move up the octaves instead. The VCO gives lots of room for "moving" the sound. Switching the mix to fully wet and using a high depth, low rate of modulation, your notes come back slowly pitch shifted. A faster rate and lower depth gives a chiming vibrato effect.
You can capture a full-length loop, then shorten the delay time, effectively losing part of your sample. You can latter bring it back, even after you've altered the shorter section - unpredictable but exciting.
For those of a soldering-iron bent, most of the front controls can be extended to a footswitch - I even made a series of switches which shorted out the existing delay control, bringing in different resistances to pitch shift fixed tone drops. I also took the freeze footswitch round the back for ease of plugging in. A brilliant musical colleague called John Nicholls studied the circuit diagrams and added about 6 seconds of extra memory, alongside a "one shot trigger button" and a "tap tempo" footswitch.
I currently use the box in my "looping rack" to provide either short loops, or more often as a creative musical tool, warping the source guitar before passing it through an Alesis AirFX - an awesome combination. It is occasionally prone to picking up strong radio signals, but these are used as "found sound" and keeps you on your toes. I'd be hard pressed to replace it with anything currently available (apart from a PCM80, way out of my price range and without the switchable sampling rate option, as far as I know). I despair that none of the current effects manufacturers have yet grasped that most loopers don't just want loops, we want them as "frozen echo", so they can fade away naturally when unfrozen, rather than simply accumulate extra layers. The VCO is great for wacky effects and dropping sample rates is technically easy as well as offering creative options.
I've never met Tim Orr, but I'd like to think he was aware how much joy and gigging time his device has given me over the years. The same thanks goes to John Nicholls, without the extra delay time, I'd have fewer options.
All the best,