The idea of ZIM went through quite a few changes during the year prior to making them. The very first version was a basic soft-clipping amp with no input buffer and no tone control, just the absolute basics. It was a cool idea - take a great sounding overdrive, the Tube Screamer, and strip it down to just the bare essentials. And it sounded pretty damn good. I had a need for a light overdrive with just a slight amount of clipping and high frequency roll off to smooth out fuzz and octave effects when driving a clean amp, and this is it. I decided to call this guy "SCREAM". Stupid name...

Then came the idea of putting two of them in one box. I've always loved the sound of two overdrives running at the same time, and I thought that two basic clipping amps in one box would be cool. And it was - I chose to configure it so that there was a master bypass switch, and a boost-drive on/off drive switch. And three knobs, Drive 1, Drive 2, and Volume. The main volume knob controls the volume for Drive 2, which is always on when the effect is activated. When Drive 1 is kicked it, it's actual volume is controlled by a trimmer on the circuit board. This works out well, but sometimes it's hard to get the right amount of boost due to the lack of a second volume knob. The boards used are the same board I use for the Foxrox Wah Retrofit, just modified to hold the overdrive circuit. I built up quite of few of these guys - see the bottom right photo.

I wanted this thing to cut through on leads, and to possess all of the ingredients of a great rhythm and lead machine. All of the features continued to fall together, and I came up with a brainstorm for shaping the overall tone of the new ZIM...a voicing section!

VOICE - ZIM has a special voicing circuit on Channel B. After the signal is processed by the overdrive circuit, it feeds an 8 - stage phase shift circuit that consists of a series of 8 static all-pass filters. These are individual phase shift stages that stay in one spot, they don't sweep. Each filter contributes a degree of phase shift, which is then summed back with the original overdrive signal producing a unique psychoacoustic notch-filter effect. There are 8 available selections, one for each phase shift stage. And each selection can be summed with the source signal either positive or negative, giving drastically different sounds. This adds up to a total of 16 different voicings. .

ZIM's Voicing circuit can be used several different ways. Here are some examples -

- Find the right notch to tune in a room. Great for compensating for natural notches.

- Match voicing for just about any amp for consistent sounds.

- Dial in a sharp tone and use ChB for leads that cut through.

- Recording multiple guitar tracks. Use different settings to prevent frequency piling.

- Careful overdrive and voice settings can closely approximate, and even exceed many of the tube amp / mic'd cab textures found in today's amp modelers.

- Wacky sounds - dial in that raunchy grunge tone that actually sounds good

Here are pictures of the next ZIM prototype. This is one of two identical units. Like the previous ZIM prototypes, this unit also has a configuration where the switch on the left is the main bypass switch, and the switch on the right activates the second drive channel.

ZIM's features continued to come together. I came up with some great new ideas, and one not so great one..

Good ideas -

- Make it in a Foxrox - style box, like CC2 and TZF, but smaller.

- Change the switching configuration - make both channels independent, each with it's own foot switch.

- Include a front-panel volume control for Drive A. This means adding another control pot, but it makes a huge difference.

- Include individual patching jacks between the two overdrives. Since Drive A and Drive B each have their own true-bypass footswitches, it's possible to treat the two drives as separate pedals. I decided that instead of hard-wiring them together inside, it would be better to offer Drive A out and Drive B in on the rear panel using switching jacks. I chose Reann black plastic switching jacks because these jacks would have to act as switches when not in use, and they are the most reliable of this type available. Using the patching jacks you can change the order of the two drive channels, patch things between them (like a wah wah pedal!), or anything else you'd do with two overdrive pedals. You can also treat them as separate overdrives, with different people playing through each one, or processing a stereo signal.

- ZIMcard - In order to open up a world of possibilities (an save some space), all of the Overdrive circuitry is built onto a plug-in card called the ZIMcard. 2 ZIMcards plug into the back of the main board, one for channel A and one for channel B. The ZIMcard is held in place by an 8-pin connector and a 6-32 screw with a standoff and nut that tightens it in place. A ZIMcard can easily be swapped, modified, tweaked, whatever... and if it gets messed up, a new one can be installed. As time passes, different versions of the ZIMcard will be made available to address different preferences. Since ZIM acts as a "true-bypass main frame" there's a good possibility of other circuits being developed in the future. Other circuits such as treble booster, fuzz, distortion, and compression could be built onto future versions of ZIMcards...

- Dentented pots - The Volume and Drive pots each have 11 detents, making it easy to retain settings. You still have the freedom to leave the knob at any setting, but the nice little "bumps" definitely help to select a setting and stick with it. The Voice Boost/Cut knob has a single, center detent.

Bad idea -

Voice - I decided to cut it from 8 stages down to 4 stages. I was running out of space on the circuit board, and I suspected that 8 stages was too much for some people to handle. That's a lot of different sounds, and it's not easy to settle on one voice because they all sound so good. So.. I figured 4 selections would be good - that's 8 different sounds when you add together both positive and negative summing. So I went ahead and laid out the circuit boards for both the main mother board, and the individual daughter boards. I ordered small prototype quantities, without all the fancy solder mask and silkscreen stuff you see on professional circuit boards. This gave me a chance to play with a 4-stage ZIM, and to have it evaluated by a couple of other people. The general feeling when comparing the 4 stage ZIM pictured below to the 8 stage ZIM above, is that it sure would be cool to have all 8 notch selections..

So that decided it - the production version of ZIM will have all 8 voicing stages. I've had a small run of the revised circuit boards made and they work like a charm. These are pro-quality boards all the way. I designed them in IVEX Windraft and Winboard. Special attention was paid to proper signal routing and lots of ground zones for the lowest noise and bleed.

While waiting for the enclosures to be built, I decided to entertain myself by building one out of card stock. Using the metalwork drawings and the silkscreen artwork, I printed out a ZIM enclosure on my laser printer. Then I cut and taped it up - and here it is. The units will be red with white lettering, like the image on the main ZIM page.

11-12-03

I got a sample enclosure for approval. This gave me the opportunity to built up the first real ZIM! The enclosure came unpainted, so I sanded it down and applied some chrome/silver paint to make it look nice and to keep it from rusting. In the pics below it looks like aluminum, but it's cold-rolled steal.

I built it up and then removed the guts so that I could paint it. Here are the guts waiting to be returned to the enclosure.

Here's the top part of the enclosure after being painted. Nice box.. It was a relief to see that everything fit as expected.

Here's ZIM all built up.

ZIM.