[sdiy] upgrading my Envelope Generators

[xamboldt]

I had written up a step-by-step guide on the EFM forum, but that  
folded when Tom G pulled the plug. Stupidly, I didn't have a back up.  
It's worth mentioning that I didn't actually come up with this idea,  
from what I understand Scott Bernardi came up with the idea and Dave  
Kendall mentioned the mod a while back, and this sparked my interest  
in giving it a shot. Anyway, here's a basic version of what I did:

The re-triggering functionality is already built into the design. The  
gate signal just passes through a differentiator, which pulses the  
trigger section. To get it to retrigger, you just have to separate  
the gate and trigger signals internally.

First of all I used comparators to boost both the trigger in and gate  
in signals (I found that the unit didn't gate/trigger reliably  
without them). Then I took the gate signal and send that through the  
circuitry leading to pin 9 of the 4052 (if you use a comparator  
first, I suppose if you wanted to you could skip this aforementioned  
circuitry, which is just a buffer). I then also sent the post- 
comparator gate signal through a diode and C3, then normalled this to  
the trigger in. This way, it still works with just a gate. Then the  
trigger in ends up at pin 6 of U2. Make sure that if you use a  
comparator on the trigger in it comes before the normalization of the  
gate signal (i.e. the normalled gate signal should not pass through  
the trigger in comparator), otherwise the differentiator formed by C3  
and R17 won't work.

Obviously the Gate/Trigger switch becomes useless if you do this mod.  
If you want trigger only mode, just normal the Gate high and then the  
trigger will work by itself as long as no gate is plugged in (just  
remember to turn the sustain down).

Also, for LFO mode to work, you should use a DPDT switch and have one  
pole hooked up like before, and the other pole with the center hooked  
up to the gate in signal that goes from the panel to the PCB, the LFO  
pole hooked up to +V, and the ADSR pole hooked up to the gate in jack.

PURE SPECULATION WARNING - the LFO switch MIGHT work as it did before  
if you just keep the original SPST switch, but  then the LFO would  
only cycle when the gate is high - this could be cool if you want a  
gated LFO. THIS MIGHT NOT BE TRUE - I haven't tested this possibility  
- it could screw with some of the logic going on internally and hang  
the LFO up. I seem to remember something like that happening to me  
before, but I try to block out most of the painful memories I have  
from troubleshooting EFM stuff.

I hope that's not too rambly... Let me know if it doesn't make sense...

-Chris


On Jan 26, 2006, at 5:44 PM, elmacaco wrote:

> Do you have any records of the mods you performed?
>
> ----- Original Message -----
> From: "xamboldt" <xamboldt at earthlink.net>
> To: "Synth DIY List" <synth-diy at dropmix.xs4all.nl>
> Sent: Thursday, January 26, 2006 2:09 PM
> Subject: Re: [sdiy] upgrading my Envelope Generators
>
>
>> If you can find the schematics for Tom G's VCRADSR (VC control of
>> ADSR and Rate), I and a few other people have successfully modded it
>> to work with gates and triggers...
>>
>> -Chris
>>
>> On Jan 25, 2006, at 5:48 PM, Benjamín Velasco wrote:
>>
>>> Hi list!!
>>>
>>> I currently have 2 EG on my modular but i want to replace them
>>> basicly because i want a retrigger feature (mine only has gate). Im
>>> planning to build the EGs from Ray Wilson's site, but also im very
>>> impressed with the VCHADSR from Jurgen Haible's and the Bergfotron
>>> site. This EG has very interesting unique features and also all the
>>> parameters are VoltageControlled. I was wondering if it could be
>>> possible to add a retrigger feature to this VCHADSR in a simple
>>> way. Or maybe it has it and i don't see it :))). Thank you all
>>>
>>>
>>> Benjamín
>>>
>>>
>>
>