Sequential Six-Trak

Grabbed a Six-Trak from the 'Bay for $325. I bought in in early January 2008, and had it delivered to Buffalo.

Wow, this keyboard is gorgeous. Cosmetically ... mint. It got more marks in the trunk of my car on the drive home than it sustained since its manufacture back in ... 1984? I dunno.

Turned it on to find that each of the 5 potentiometers was totally useless. Got back to the eBay seller who said that if I could find a suitable replacement, he'd order them to my address.

Wine Country wants $9 each! That's stupid expensive. Plus $8 for shipping. Um, yeah. I ran that by my seller and he was more interested in seeing a datasheet so he could try to source them himself, and I don't blame him. Unfortunatley I have no datasheet and I looked around to try to find pots shaped like this ... no luck.

So I bought 5 10K linear pots from radio shack, cut the shafts to length, put 'em in the grinder to achieve that "D" shape, mounted them (the collars were a bit skinny but the washers make up for it), then soldered them in place using some 24 gauge solid tinned copper wire. They work like a champ. One of them feels slightly wobbly because my grinder work was a bit off centre, so the knob doesn't quite sit right, but I'm actually OK with that for the next 25 years.

Pics to follow. (updated 2008/1/30)

2008/2/1: WELLLLLLL....

I got this thing home and decided to set it up with the Mackie C4 (using "C4 Commander") to control all of the synth's parameters.

The good: this synth sounds badass. It's possible to make really rude, biting tones that no other synth I own can make. That just re-affirms for me why I bought the thing.

Unique to this synth is that there is a separate EG for pitch, filter, and amp. With this it's possible to make some crazy percussive and SFX sounds.

The not-so-good: each voice's filter sounds slightly different. Bearing in mind that the entire voice is a CEM3394 supported by numerous mylar and electrolytic caps, this could be due to component variations or due to age. But I must emphasise the word slightly.

The difference in the filters is really only noticable with nasty, hi-resonance sounds, and it IS analog, so I can deal.

LFO value can be routed to pitch, pulse width, and filter cutoff. But there is only one depth control. Routing to each mod destination is strictly an on/off affair. This means you can't modulate pulse width and filter, for example, with different amounts.

The bad: The software-based envelope generators have only 15 values for each of attack, sustain, decay, release. This limits control over tweaking those punchy techno sounds to sit just perfectly. Set "decay" to anything above 4, and there is no punch left. But this is forgivable, since the sounds are so unique.

Most of the controls are pretty "steppy" sounding due to their low resolution. There are no audible steps or zipper rtifacts from the envelopes or LFOs though. So ... live front-panel tweaking is not out of the question, but it doesn't have the resolution needed to sound smooth and analog.

I had to edit the xml file provided by Mackie to make the display names understandible on the C4. With only 7 characters available per name, calling the parameters "Filter Cutoff", "Filter Resonance", "Filter Envelope Depth", "Filter Envelope Invert", "Filter Envelope Attack", "Filter Osc Mod" etc yields "Filter ", "Filter ", "Filter ", "Filter " and "Filter " on Mackie's much-ballyhood digital scribble strips. So I shortened them to more useful names.

Still, the C4 instrument definition is far from perfect, as all parameters are adjustable from 0-127, even the ones that only go from 0-31, 0-15, and on/off. So I do plan to spend a few hours to make that XML file perfect. Contact me if you'd like a copy of it once I'm done. To me it is evidence that Mackie really rushed the C4 Commander software out, and probably didn't even test half of the instrument templates they provide.

[i digress]did you know that the Mackie C4 was originally to be the Emagic Phat Channel?[/i digress]

Plan: by this summer I want to build a dedicated MIDIbox controller, as a proper front panel for this wonderful little synth.

Really long-term plan: I would love to design and build my own CEM3394-based synth, capable of making these great Six-Trak sounds, but without the limitations of the 30+ year old Z80 processor. It might give me a chance to check out those cool standalone PIC-based envelope generators.