Ensemble Circuit Configuration Questions

[Joachim Verghese]

Hi,

> 3 BBD IC's, modulated by 2 120 degree LFOs:

I guess the Roland RS-202 (1976) falls into this category, judging by
the circuit description in the service manual:

"The output from the filter is distributed into three delay circuits,
BBD, and modulated. The modulating signal oscillator comprises two
sets of unstable (!) multi-vibrators: one oscillates 2:1 three-phase,
unsymmetrical rectangular wave of 0.5 - 0.8 Hz and a triangular wave
is obtained by means of the three filters; the other set oscillates
a similar rectangular wave of 6 - 7 Hz, which chops the above signal
to produce mixed signal of both. At ensemble II and OFF positions,
the latter oscillator suspends oscillating."

The VP-330, as was mentioned, uses a multitude of BBDs. Curiously
enough, the vibrato function is implemented using BBDs, instead of
modulating the master oscillator of the tone generator.

The VP-330 ensemble section, which uses four BBDs, is one of the
best sounding, IMO. Basically, there are two almost identical
dual-BBD cirucits for each output channel (left/right). One of
the BBDs in each circuit is modulated by a slow LFO. The other BBD
is modulated by the inverse of the slow LFO, mixed with a fast LFO.
The LFO rates of the right channel differ slightly from those of
the left, hence "almost identical".

The sound is very lush, but a lot smoother than that of most 3-BBD
designs, IMO. It doesn't sound so obviously "string synth-ish".

>  Also, what devices implemented this as a stand alone effect?

I seem to recall ETI/Powertran had a chorus kit called "Black Hole
Choraliser", or something. The basic kit had only one BBD, but
the circuit board was designed to accommodate a second, "inverse-
modulated" BBD for true stereo effects, kind of like the Dimension D.

Speaking of stand-alone ensemble effects, I'd be very thankful for
any information on the Boss CE-1, and the CE-10, in particular.

cheers,

-joachim