Multiple Output MOD

Multiple Output MOD
This page details the various multiple output MODs that I am aware of for both the Six-Trak and MAX. This is posted for informational purposes only.

Just a long note before I begin,..

Over the years of running the site I have received many questions about the various versions of this modification. I have always tried to respond to the questions but my information was always second-hand, having never done or used any of the MODs myself. In February 2000, A. Dickey was extremely kind to sell me a Six-Trak at a great price, with the provision that I perform the MOD(s) and make a web page showing how it was done. I would like to thank Mr. Dickey for his help in making this page possible.

There are also several other people that have provided me with information and suggestions over the years. They are, in no particular order, G. Montalbano, C. Roberts, C. Jones, A. Blomgren and "Moogchild." I know that I have forgotten a couple of names, please forgive me.

I encourage you to read all the MODs before opening your synth up. The photos all are of a rev_A Six-Trak. This circuit board is not exactly the same as later revisions. There are points that I have omitted in later MODs because these areas have been covered earlier in the text. This is not a step-by-step guide on how to modify your synth- if you do not know how to open the synth, read schematics, use a soldering iron or even follow proper safety procedures please do not attempt to MOD your instrument. Let me make this perfectly clear- all information is provided for informational purposes only. Proceed with caution and at your own risk. Now to the fun stuff,...

History

Perhaps the first output MOD for the Six-Trak was the "6-Channel Output Board for the SCI Six-Trak" (c) 1984 by Dan Ramsauer. Unfortunately, I have been unable to attain clear copies of the schematic, so if you know anything about this MOD please drop me a note. The next MOD was designed by G. Montalbano in 1986, with the project being sold to Polyphony but never published. Several years later, C. Jones on his site provided visitors with a passive circuit that appears to have been the most popular version of the MOD. The circuit simply takes the CEM 3394's output from PIN #19, through a switch to either an ouput or back to the synth's circuit board. Despite the current to voltage problems, this circuit seems to have worked well. There have been several active circuits designed, most relying on adding an OP amp, resistors, connectors and switches. As can be expected, these MODs have had enhancements and revisions (which I list at the bottom of the page). If you have other suggestions or have designed your own MOD please contact me. Thanks.

Passive Output

Pros: It can be done in a fairly short period of time, is inexpensive and is extremely easy to do. Used outs are removed from the MIX output. No power taps are required.

Cons: Tuning problem. Output not muted with tuning circuit is active. CEMs are not isolated.

Before starting, take a look at the schematic. Remove the circuit board and prepare the case. You will need to double socket each of the 3394s, but before doing this, bend pin #19 of the upper socket and solder a wire to the pin. On the lower socket, insert a return wire into where pin #19 would plug. Next, you must connect to a toggle switch, this will send the CEM's output to either the independent out or back to the synth for tuning and/or the MIX output [Note: the switch maybe replaced with an auto-switching jack. I did not do this because I thought having to unplug the connector every time I wanted to de-activate the input could be accomplished more easily with a switch]. A resistor is added to ground to solve the current to voltage problem of the circuit. I decided to wire the output in what appears to be reverse order when seen from the back of the Six-Trak (from left to right, voices 6 to 1). But from the front panel of the synth, the voices are ordered, from left to right, 1 to 6. I also oriented the toggle switches to operate in the horizontal plane- when toggled toward the MIX output, the signal goes to the MIX output. I also find it very easy to drag my finger along the back and toggle all the switches in one fluid motion. The MOD is clean looking and easy to use- and yes, those are red oak sides- just one of the other mods that have been performed on this Six-Trak ;)

This circuit works fairly well minus the loud click and tuning problems that might occur if the Six-Trak is inactive for 30-60 seconds (MAX users will not experience this unless they press the TUNE button while the individual outputs are active). Tuning can easily be corrected by turning off all the individual outputs and performing a MANUAL TUNE.

Active Output

Pros: Easy to perform. Fairly inexpensive to do, but will run around $20-25 to complete. Used outputs are removed from MIX output. Very hot output signal (will drive headphones with ease!).

Cons: Tuning problem. Output not muted when tuning is active. Requires knowledge of Six-Trak circuitry for ground, Vcc+ and Vcc- connections. More circuitry- more to go wrong.

This MOD has a fairly easy circuit to build. Remove the synth's circuit board, and prepare the case, and add switches and output jacks. Next build the OP amp portion of the circuit. You will need to locate a place to get the ground, as well as the Vcc+ and Vcc- voltages from the synth. I suggest a down load of the GMM directions below and/or down loading the complete Six-Trak schematics (MAX users, I don't have the schematics for the MAX, but the boards are similar and you should have no problem tracing the circuit with a DVM). Next the circuit board needs to be installed and all connections made. The final MOD (or here) looks very much the same as the passive MOD.

This MOD works well, but shares the same tuning and muting problems as the Passive MOD. Having the hot, clean output is great, but on some mixers a -20dB pad might be necessary.

GMM Active Output

Pros: No tuning problem. Output muted when tuning circuit is active. Fairly inexpensive to make, but plan on spending $20-30 depending on where parts are purchased. Great circuit design. Hot output signal. All voices are always sent to MIX output (good and bad). No toggle switches needed- less destructive.

Cons: Requires knowledge of Six-Trak circuitry for ground, Vcc+ and Vcc- connections. More circuitry- more to go wrong. All voices are always sent to MIX output (good and bad).

This non-destructive to circuit board MOD requires many hours to build and install. I suggest down loading the complete instructions before attempting this MOD. There are only two suggestions that I can add to the great directions. One, be very careful when bending the OP amp's pins- be sure that they do no NOT touch the resistor. Also, to help with circuit layout here is a photo of the layout that I used.

MOD revisions

A pan control can be added to either of the active MODs- just add the pan pots after the OP amps then to a stereo output.

Instead of using TL084s, two TL082s can be used.

C. Roberts replaced the jacks with TRS jacks- for the outputs and also an input MOD (this MOD replaces the noise circuit of the Six-Trak/MAX with an external signal. This allows running any audio signal through the VCF and VCA).

"Moogchild" added a switched minijack, sending voices 1, 3 and 5 to one output, and 2, 4 and 6 going to another after the multi-output. If single voices are being used, they "disappear" from this summed output. If the minijack switch is turned to the other position all voices are returned to the Six-Trak.

So why do this MOD?

After having waiting years to perform this MOD I wish I had done it much sooner. Why? It allows independent control over each voice of the Six-Trak/MAX. This means you can have EQ/EFFECTS/PANNING/etc.,.. control over each voice! When put into MIDI Mode 4 the MOD really shines.

Here is a tiny MP3 demo showing what the active MODs will allow. Reverb and delay were added to a couple of channels. No EQ, MOD or PITCH data was used. The lead voice had a little CC data sent to control the frequency cutoff. None of the mixer's inputs were over-driven. Since I have been asked a couple of times now, ALL sounds are from the Six-Trak- including the bassdrum and HH parts.

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