[sdiy] Korg Lambda envelope

[David Moylan]

Ah, this makes some sense, I'm used to thinking of positive envelopes. 
So D102 is the drainage path for the cap but when the key is up D101 is 
forward biased and D102 is then off. And similarly if the key is down 
D103 is biased on turning off D104 (or stealing current depending on 
your perspective) and it's path.

So the attack and release controls...  They're just voltages, right.  If 
the Attack is set really low (which I think would be faster) and we 
press a key we have a discharge of the cap through R11.  If the Attack 
is set high then we have the discharge path but only until the voltage 
on the cap is a diode drop above the attack voltage right?  Then the 
only path is through R12.  It is safe to say that the attack and release 
are each 2 stages with the tails having a set time constant dominated by 
R12/C11?

Thanks.

Dave




Florian Anwander wrote:
> Hi
> 
> I am not too deep in that kind of circuitry, but as far as I understand 
> it works like the following (all the gurus: please correct me if I am 
> wrong):
> 
> Lets take the most upper key in this diagram. As long as the input of 
> the gate/divider chip is +V the corresponding note is off. A keypress 
> enables a connection via R8 and the transistor (on on the left side of 
> the diagram) to -V. This causes a (negative) voltage at R12 and 
> following on the Gate-Chip, with the consequence, that the note is on. 
> The rise of this voltage is depending on the loading of C11. This 
> loading can be slowed down, by a partial current flowing over to the 
> attack bus which depends on the setting of the attack pot.
> If you release the key again then the capacitor will be unloaded again 
> via a current over the release bus which depends on the setting of the 
> release pot.
> 
> All the best, Florian
> 
> 
> David Moylan wrote:
> 
>> What I'm talking about is the envelope generation not the VCA section, 
>> that's taken care of elsewhere in a chip.  The envelopes (per key) use 
>> a global Attack and Release setting.  It's a strange topology with 
>> reversed diodes and I can't quite figure out how to decode it.  I 
>> think the diode resistance is being modulated
>>
>> Have a look.
>>
>> Dave
>>
>> Paul Perry wrote:
>>
>>> This has nothing to do with the present case, but.. it occurs to me 
>>> that in
>>> the case of audio frequency square waves, you could modulate the 
>>> amplitude
>>> with a simple diode 'minimum' circuit.
>>>
>>> Could be useful somewhere sometime.
>>>
>>> paul perry Melbouurne Australia
>>>
>>>
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>>
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