[sdiy] Tama TechStar TS306 mods

[Metrophage]

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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