Re: Lambda + chip question

From gstopp
Sent Mon, Oct 9th 1995, 18:13

     I think....I think... the 50240 has a 50% duty cycle and the 50241 has 
     a non-square duty cycle so it can be used as the actual sound source 
     with even harmonics and not as the clock source in the upper regions 
     of the clocking circuitry.
     
     The diode-keying VCA effect is an old organ trick. It only works with 
     rectangular waves (see the schematics for the PAIA Stringz 'n Thingz).
     
     I can't believe they didn't include sound generation on the 49th key. 
     How tacky. Hey you Korg designers, if you read this, that was tacky. 
     :-)


______________________________ Reply Separator _________________________________
Subject: Lambda + chip question
Author:  Haible_Juergen#Tel2743 <redacted@example.com>
at ccrelayout
Date:    10/9/95 10:35 AM


>
>> I finally found a Korg ES-50 "Lambda". It will be shipped 
>
>Can you tell me/us more about this beast? I've never heard of it.
     
My lambda arrived on Friday, and first I was a little dissapointed. 
It didn't sound as good as I remembered. Then I found that one
of its oscillator banks didn't work. (It has 3 HF-VCO's and 3 complete 
TOS / Divider chains.) I found that one of the TOS IC's was blown.
It's an S50241, and I was quite desparately looking for it on the weekend. 
Then, after scanning loads of documentation in the archieves of TBS,
I found that I could also use a 50240, the one I got from an old Crumar 
Performer many years ago. As I have no datasheet for either I was
saved by finding one strange string synth ("String Melody", maybe
this was a Hohner) which could use either the '41 or rthe '40, according 
to its service docs. So I went home, desoldered the '41 and put
a socket and the '40 in, and everything was just fine. What a great 
sound!
================================================================
I'd really be interested in the difference of the 50240 and 50241 IC's. 
So if anybody knows something about these, please do tell! 
================================================================
Now here's a brief description of the ES-50 "Lambda".
49 Keys, but only 48 working (the 49th would have eaten up another
divider chip (;->) ). Fully polyphonic. Two (!) discrete envelope generators 
for each (!) of the 48 keys (hundreds of diodes used as voltage controlled 
resistors). 96 voltage controlled Envelope Generators !!
Mixing of different footage rectangles, supposedly to get 
staircase-type saw waves. The three oscillator chains are controlled 
by a 60 degree / 120 degree / 360 degree LFO to get the basic 
string-ensemble chorus sound. You can also manually detune two
of the HF-VCO's, and two LEDs on the front panel nicely show the 
beating of the oscillators, caused by detuning and by the complex LFO 
modulation.There are formant filters for String and Choir sounds,
and finally the wole thing can be routed thru a BBD chorus.
You can change the chorus speed by a Joystick left to the keyboard. 
This "Ensemble Section" I have described so far has also a Brass 
and an Organ Preset, but I don't think they are worth that much.
I get this great lush ensemble sound with "Chorus" (=Choir) + 
"String I" + "String II"  switched on simultanously. Attack and 
Release are switchable from fixed to variable, and unlike the 
global envelope on a Solina You get a real AR contour for each 
individual note.
In addition, there is a "Percussive" Section which uses the second 
set of envelope generators. These are AD-types with a fixed and 
switchable Sustain level and Release switchable from short to 
Release = Decay. The Presets are E-Piano, Clavi, Piano and 
Harmonics. Forget about the names - but E-Piano plus Harmonics
make a nice bell-like sound that fit to the ensemble section very well. 
There is a pot for "Key Click", but what it really does is adding a 
nice attack sound to the E-Piano preset. The Percussive section
has a nice Tremolo (AM) feature with modulation rate adjustable. 
You can route the Percussive and the Ensemble section seperately
or both thru the BBD chorus sections - Yes, it's actually two BBD's, 
one for each section, but they re modulated from a common LFO.
The reason for separate signal chains in the chorus is that You 
both sections go to VCAs and can be mixed together with an 
expression pedal.
Speaking of mixing: There are a (rather effective) tone control 
and a master volume slider for each section.
This was my brief description - sorry it was all mixed together, 
inside and outside of the beast, hope You enjoyed it anyway.
As I posted before, one of the Lamda's greatest features is its 
flat top, so it Dousn't actually take much space as You can stack 
anything above it. You shold see my nice keyboard stack:
Kawai Piano, Lambda, MS-20. Ah, and routing the Lambda thru 
the MS-20's filters is nice, too.
Besides being a great ensemble machine, the lamda will be the
main basis (sonically and physically (;->) ) for my Vocoder, when it 
will be ready.
Oh and I don't know it I will do it, but as each key just switches between 
15V and ground (Key contacts go to GND, and there are 4.7k pullups),
It would be very easy to get both, Midi In and Midi Out, with Doepfer 
kits.
     
     
JH.