tr606 Waterston BD pitch sweep

[Fraser, Colin J]

> -----Original Message-----
> From: WeAreAs1 at aol.com [mailto:WeAreAs1 at aol.com]
> Sent: 01 June 1999 11:19
> To: pfperry at melbpc.org.au; synth-diy at mailhost.bpa.nl
> Subject: Re: Re: tr606 Waterston BD pitch sweep
> 
> To impose the pitch sweep on the 909 kick drum, Roland used a 
> transistor as a 
> current-controlled resistor in the RC network, for what it's 
> worth.  I don't 
> remember if the 606 kick circuit is the same as the 909's, 
> though.  I think 
> the 606 was a simple resonant bandpass filter, if I recall 
> correctly.  The 
> 909's was more complex, I think.   Still, probably worth looking at.

This description sounds more like the 808 bass drum...

The transistor on the osc capacitor in the 909 is there to sync the
oscillator so that the wave always starts at 0 degrees.
The oscillator is a simple voltage controlled triangle oscillator (re-shaped
into a sine-ish wave by a resistor and two diodes).
The sweep is generated by a capacitor that is charged by the trigger pulse
and discharged via the tune knob, which momentarily increases the frequency
of the triangle oscillator.
This is a very different circuit to the 606 - it's not a tuned twin-t
filter, the 808 is.

While we're on the subject, I have made some modifications to the 909 bass
drum circuit for improved bottom end, increased 'punch' and an extra tune
control that varies the pitch over several octaves from hi-pitched tom to
gut wrenching sub-bass - this mod was tried out recently by some friends
thru a massive club PA, and it drove the crowd wild  ;-)

I'll write up instructions and post them to my web site, if anyone's
interested.
I have a simple tune mod for the hi-hats too.


Colin f