LF411 Op-Amp dilemma

[Brendan Heading]

Duane R Balvage was saying:
>> 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).

>       Sorry about the kinda tecchy description in my last post - I forget
> that not everyone is an electronics engineer! ;)

No problem, though I suppose I ask for it by joining a techie list :) I have
an interest in the science though. I'm hoping to do it at Uni.

> A top-octave divider string/organ synth has 1 chip that produces the top
> octave  (where have i heard that before), all 12 notes, by dividing a
> master clock  to  get C, C#, D, Eb ... etc. As you know, one octave down is
> 1/2 the  frequency,  so to get the rest of the notes on the keyboard, it
> divides the 12 top octave  pitches by 2, to get thenext octave , divide
> that by 2, and so on, until  you  have all the keys. That is how it is
> fully polyphonic - all notes are derived  (divided down) from a master
> oscillator, and they are all available AT THE  SAME TIME! (like an organ)

<this may be testing your patience :) >

So there are basically 12 notes being produced by the synth, and each one is
divided ? That would imply that there are twelve oscillators producing an
entire octave's worth of sounds. I think I get it now.

> The LM37000 transconductance op-amp is not the  oscillator!
> It is used in the 2-pole low pass filter used for the BRASS
> patches.

(Unscrews Quartet) ho hum. Yes, you're right (do you know about Quartets ?!).
I tried removing the LM37000, and indeed, the brass sound died. So, what is
doing the oscillating then ?

For the information of other synth-diy-ists, these are all the ICs used in
the Quartet....

7 (yes, 7!!) MC1458s.

5 4016 CMOS analogue switches

1 LM 13600 (sorry, not a 37000)

3 TDA 1022 Bucket Brigade delay lines

2 CMOS 4013 2x D flipflop (what for ??)

2 weird chips, both FUA 3302DC

2 CMOS 4071 4x2in OR

CMOS 4069 6 inverters

CMOS 4082 2x 4in AND

3 CMOS 4011 4x2in NAND

2 4049 6 inverters

How do ye make an oscillator out of that ?!?!

> Yes, IT ONLY HAS 1 (one) OSCILLATOR! The 12 TDA1008s are the
> divide  by 2 (4, 8, 16) frequency dividers. THAT'S WHY THEYE MARKED WITH
> THE NOTE  NAMES.

Kool indeed.

>> 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 ?


>  To the output of...? at the Audio out, you get lotsa different things -
>  strings give you "almost" sawtooths, organ gives you pulse or saw,
>  depending
>  on the setting ...  What is it that yoou are trying to do?

Ah, right. What I meant was the output on the keyboard, going to the voltage
input on the oscillator. I'm trying to see if I can hook it up some way to a
personally built synth (or even one like Gene's).

--
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|Brendan Heading (brendan at heading.demon.co.uk) - Webpage online soon  |
|Irish Electroacoustic Music Association | JarreVangelisTomitaCarlos  |
|Synthesizer Freak |                     |ErasurePinhasTangerineDream |
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"Musak is the shit you hear in elevators and supermarkets".
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