Burt Baccarach's Korg CCO core in the TB 303 essay!

[>>>marjan<<<]

Hi all,

It seems that some of you weren't inhaling regular doses of
solder fumes lately :)

Let's be little bit more tolerant. Some think "cool" nickanames
are err... cool, some don't. And if we don't agree on some topic,
like what happens inside TB filter or Minuteman ICBMs, we can
find what REALLY happens if DISCUSS. This may sound lame but that's
how it is (otherwise, be warned, I still have those 3 Tomahawk
missilles ;) ...

Now, switch back to the regular geeking:

I've played with TB303 ccts some time ago but when Tony A. brought up
his
version I found it unecessary to investigate any further, as I'm not
very interested in "drug" music (as BJ stated :) rather find it little
but fun synth. It be nice to ask Tony for tech opinions as he surely
spent 
much time over it.
My guess on VCA cct is that you'll get similar results with any other
decent VCA with some right biasing and final discrete stage that
original uses (I don't have TB cct in front of me nor much time).
VCO section is indeed ms20/polysix clone, why?, it's ingenious korg
vco, simple, low parts count but effective. TB seems overall like
cheap attempt, all cct gives that impression, and mine is that it's
constructed by some other than standard Roland eng. of the time.
My first TB vco used BF245, while it worked, later I've found
it's NOT as with 2SK30 (or whatever it is) FET which I later got.
This seemed as stupid feature, it's not CEM or SSM to be obligatory.
I've tried to use some LF opapmp and some biasing, little caps in 
feedback and so on and got pretty much (to me) close results. 
With some more experimenting (and patience which I lack of :)
and better opamps (I had very limited resorts) it should be possible
to eliminate FET. Or use some standard fet in audio path with some
clever opapmp feedback to simulate original.
VCF section is surely exception for Roland, they used OTA based filters
in those times. One must not forget what TB was ment for in the first
place.
Cheap (!!!) bass player substitute. Let's make cheap analog bass
emulator,
with some nice programmable features (which seemed to be more
important).
Probably to Roland engs it sounded as good electronic bass. "Strange"
features
found in it (I guess) emanate from attempt to emulate bass, slap bass,
this
and that playing style... So you get strange "square" wave, which wasn't
ment to be "synth" square, rather "bass" one. Obviously they failed to 
sell it as bass sub. Simple as it was it had to have some controls
integrated-shared, so some unusual things that we all see in the schems
like resonance pot or cutoff had to be done, as all that you can patch
on modular, but you need lots of pots and jacks. I belive Roland guys
hadn't expect to be used as "acid" grail. I mean, you could get such
results with modular and sequencer, but hey, MOST of the "DJs" are...
Well let's stop there. My opinion for myself, enough of strong words on
this list. 
Also, I was in doubt why they used transistors as diodes instead plain
diodes. My guess is that they needed _some_ matching for ladder
diodes, and those transistors had better specs than stock diodes (as
in 2 tranies from the box would match better than two diodes).
Or the boss wanted "moog alike but still different from it" so
engs draw this filter "you see it's moog filter (and we all know
how good for bass it is) but it's connected somewhat differently
so no problems with patent"?
MY undertanding of 18/24 dB mess is that that with diodes
you get lousy buffering and all the previous stages affect the
next stage impedance so the last pole (cause there are 4 caps) is
kicked so far that it has no practical effect on the sound.

So, the "mystery" around TB is from many aspects. We could get
all the comments, and put it up online, like BJ's, or he could
update his. You learn all the time. For years I wondered why
my VCS3 filter clone doesn't sound like Jarres plinks and plonks,
then Mr. Sponton scans an article which says Jarre got all his
EMS stuff retrofitted with Moog filters. Blast!

BTW there was TR series which was intended to sub drummers. Ha!
If you ever had real band, you KNOW that NOTHING can sub real
drummer (especially when he's not palying :)))



Cheers,


marjan