LF411 Op-Amp dilemma

Brendan Heading lists at heading.demon.co.uk
Sat Jan 25 17:22:43 CET 1997

Duane R Balvage was saying:
>> but the Quartet is fully polyphonic - I think one of those top-octave
>> divide down jobbies. What sort of signal does this thing output when a
>> chord is pressed ?

> Hello Brendan -


>     I hate to be the bearer of bad news, but you cannot CV/Gate a
>  "top octave divider" (organ) synth. (I know, I have a Sequential
>   Circuits (Siel) Prelude,

The ARP Quartet is, incidentally, also a Siel synth. I actually quite like
owning it. I can't find a single bit of info about it ANYWHERE, so I presume
ARP must have been shipping it out just before they collapsed - which makes
me think there are <100 in existence (unless Siel had produced them

For those who are interested, the Quartet is something of a turkey as synths
go - like much of ARPs stuff they made during their dying throes (even though
it wasn't actually ARP made).The string sound is kind of usable (sounds a
touch like a Solina!), but the rest of the design and the electronics is
completely purile. The sustain circuit, controlled by a slider, varies very
little at the bottom but suddenly adds loads of sustain after a certain
point. The keyboard is clunky as hell and impossible to play!

>   closes CMOS analog switches across the key contacts. See, the top octave
>   divider ckt. has ALL notes ALL THE TIME. when you close a key, you
>   trigger
>   the envelope generator, and close an electronic switch that stays open as
>   long as the envelope is ON.

I don't really understand that (sorry). How the hell does it actually convey
the different notes, all at once, to the oscillator ? There is only one that
I can see in there (an LM37000 transconductance op-amp set up as an osc, ho
hum). The keyboard output bit, I notice, is quite complex. 12 TDA1008s, one
labelled as each note in the octave. Each note has a few caps and resistors
before passing thru the 1008s. There is also a tuning pot, and a wire going
out to the pitch controller on the keyboard (which seems to have been
designed for performance tuning as well, rather than to be used musically).

So, my main question is, what kind of signal (roughly) would I be getting out
of there if I hooked up a multimeter to the output and pressed a key ?
|Brendan Heading (brendan at heading.demon.co.uk) - Webpage online soon  |
|Irish Electroacoustic Music Association | JarreVangelisTomitaCarlos  |
|Synthesizer Freak |                     |ErasurePinhasTangerineDream |
|Alliance Party of Northern Ireland (www.unite.net/customers/Alliance)|

"Musak is the shit you hear in elevators and supermarkets".
          -- Jean Michel Jarre

More information about the Synth-diy mailing list