Improve DOD EF 440 envelope filter

[reeko81]

I've recently built a dod EF 440 and i found it fantastic...terrific...
just one disappointment...it's too trebly...i like its dinamic,it's so soft due to the VTL5C4/2, but it is too trebly...what can i do to improve it?
Please answer me!

[Rafa]

Hii:
A high pass filter
Here theres something
http://privatewww.essex.ac.uk/~mpthak/Distortion/
the article is for ditortion but it should work, i think
Rafa
t

[Mark Hammer]

It's not clear what you mean by "too trebly".  Do you mean that it sweeps toohigh? that it sounds too thin and peaky when it goes high? that the overall range of sweep is fine but there is too much trebly content relative to the fundamental as it sweeps up?

I am less familiar with this sort of filter topography than I am with others, but following this schematic - http://www.generalguitargadgets.com/pdf/ggg_ef440_sc.pdf - my gut sense is that increasing C7 or maybe experimenting with tacking on another 2200-3300pf in parallel with it might reduce some of the treble.  Alternatively, maybe you just need to stick a little lowpass network on the output after C8.

[reeko81]

Yes...I mean that it sweeps too high and there is too much trebly content, because it sweeps too high.
But the dinamic is fantastic, it's soft!

[reeko81]

Could you explain me better how to do a little lowpass network after C8?

[Transmogrifox]

If it just sweeps too high, then turn the range knob down until it doesn't sweep very high.  If you can't adjust the range down low enough, then bring "Level" down too.  If it still sweeps too high then change the range pot to 250k.

On the schematic linked by Mark Hammer, there's a 10k resistor going to pin3 on IC1a, and a 100k from that junction to what is essentially the filter input.

At the junction with the 10k, 100k, and IC1a you may experiment with some different value capacitors.  I'd start with a 10nF (.01uF), and start increasing values until you like what you hear.   This will effect the envelope follower, but probably not dramatically unless you put a dramatic value capacitor in there.  You can compensate for the loss in the IC1a op amp feedback loop leg to ground if necessary.  We probably would be able to add a capacitor to IC1b output to inverting terminal, but with the caution that it may go unstable.  I haven't examined the circuit closely enough to tell for sure.  give it a try, as you can always desolder the part if it screams at you.

[Mark Hammer]

Here's another strategy to try.

While you *can* simply turn down the sensitivity, there is the issue of producing an envelope signal that has a large enough voltage swing to get past D2.  That diode not only makes sure that only one half cycle of the audio signal passes, but that NOTHING passes unless it is greater than the forward voltage of the diode (which will be 500-600mv).  In a sense, you want the sensitivity to remain the same, but the sweep to be a little narrower, whie still including subtle sweep with softer picking.  Turning down the sensitivity may not get you all of that.
Happily, there is an LED in the mix, and the effect of large voltage changes on the LED brightness can be altered by simply increasing the current limiting resistor, which in this case is R6 (2k2).  Consider trying slightly largely resistor values, like 2k4 or 2k7 or maybe even as high as 3k3 to see if you can retain the ability to produce modest sweeps when you pick soft, but acceptably wider ones when you pick hard.

[reeko81]

Ok! I've put a 500k linear pot for range (in ggg project called improperly level) instead of the original 100k and change R6 to 4,7k.
Then to work with a lower range i've changed C6 and C7 values to 33nf...now it's good to my ears! Maybe should be better with a 500k log pot..
Should be better increase C8 value???

[Transmogrifox]

Should be better increase C8 value???

If it's good to your ears, there's nothing more to change 

[Meanderthal]

 Hey! Now I have a use for that VTL5C4/2 I ordered thinking that's what I needed for a mutron... You pretty much just described how to mod this for bass, and it's so simple! One question though, is that really TL022, or do they mean TL072?

[Indoor Fireworks]

Ok! I've put a 500k linear pot for range (in ggg project called improperly level) instead of the original 100k and change R6 to 4,7k.
Then to work with a lower range i've changed C6 and C7 values to 33nf...now it's good to my ears! Maybe should be better with a 500k log pot..
Should be better increase C8 value???

I know this is an old topic and this is probably a dumb question but what would happen if I replaced R6, C6, and C7 but kept the original 100k pot?