[sdiy] Tama TechStar TS306 mods

[gregory zifcak]

yeah, these are great! do you know which opamp would be a good replacement 
for the 4558?

unless something is broken, you should get a downward bend by turning the 
bend knob clockwise. there is a center detent for no bend, and 
counter-clockwise is bend up.

one neat mod for the synth circuit is to bring the modulation speed trim pot 
out to the front panel. it's 5k, so i just used the sensitivity pot; i 
always use the trigger input anyway.

also, the emphasis circuit is not that cool, but it's a dual opamp at the 
end of the signal chain. i turned it into overdrive.

some other things i've done:
-add a switch to route the oscillator through the filter and attack vca 
instead of the noise.
-connect env of tom 1 to vca of tom 2 for independent pitch and amp decay 
times.
-vco cross modulation.
-lots and lots of resistor swapping for different tune and filter ranges, 
bend depth, decay times, etc.
-fixed hpf on noise.

you probably already have the schematics, if not:

http://fa.utfs.org/diy/tama305/schem.htm


>
>I bought a few Tama drum synth circuits over the past month. I really
>like these modules! Unlike the CEM based Simmons units, these tama
>units are "discrete" op-amps and OTAs. Layout is great, very much fun
>for tweaking! The 4558 amps result in some constant background hiss.
>Nicely fixed by replacing (all but the trigger comparator ic) with low
>noise types.
>
>The headphone amplifier ics are flamed. Found no info about these
>"TA7336P" chips, but I did find a cheep source for them, so I can
>replace them this week (baby permitting).
>
>The sounds of the handclap and synth modules are great. The toms are
>not bad, but beg to be tweaked. I swapped a few resistors in the "tune"
>and noise filter areas to make more bassy.
>
>I succeeded in messing up a few things...
>I was trying to jumper some of the noise output to the VCO for
>modulation, but somehow "blew up" the noise output. Noise was still
>there in all of it's subcircuits, including the post noise/tone mix
>"attack" (stick crack) portion. There are FETs for switching the knobs
>to a preset value, I am guessing I broke those since everything else
>works.
>Other thing which went wrong was when I was trying to get either the
>noise or VCO to modulate the "bend" portion. The bend is, if I recall,
>always "up", but I wanted to get a "down" bend. I was wondering if I
>could break traces to swap the inverting/non-inverting inputs of two
>opamps, but as I wasn't sure I didn't want to do so right away. I was
>able to do a neat downward stab by bridging one of the trigger
>comparator pins to one of the bend pins. But then I accidently bridged
>the wire to something else, and the triggering has gone, leaving a sort
>of "drone instrument"! I doubt if anything else on the board is so
>sensitive to this jumpering as the FETs. I will try to replace them
>eventually, see if this restires the boards missing functions.
>
>These FETs also interest be for other reasons! The preset feature is a
>switch labeled "memory". Basically, there are resistors of certain
>values off to the side. If you hit the memory switch, all of these FETs
>switch from the pot values to the preset resistors. (I can just imagine
>some baked '80s drummer playing a show, terrified at how far from
>reality the drum sound settings have gone... relieved to be able to hit
>the 'memory' switch to restore a semblance of normality!) I think the
>switch is a DPDT. I would love to replace the switch with yet more FETs
>so I can trigger the preset to switch in resistors or pots of my
>choosing. Maybe a trigger bus, so it can be it's own trigger, or even a
>trigger which fires another drum voice- changing the voice of an
>already sounding drum. Alas, I have little transistor experience as of
>yet.
>
>It seems that the more elegantly functional a circuit is, the more
>difficult for me to discern what the subcircuit functions are! The Tama
>boxes and my DR110 are far more baffling and mysterious to me than is
>the MG-1 or Juno106
>
>This unit is also inspiring me to learn to translate a few of my crude
>synth module ideas via CAD/CAM software, so I can make PCBs which fit
>these cases. Cheep rack cases pre-drilled with a large array of
>usefully laid-out holes and a bipolar 15v supply is kind of handy.

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