which envelope filter / auto filter to build?

[the3secondrule]

Hey all,

looking for a bit of advice on an envelope/auto filter to build.

I don't have PCB etching skills, so I'm either looking for a PCB for sale (ie GGG) or a vero layout...

I'm looking for something that can sweep in either direction, and has an attack speed. I used to have a EHX microsynth, and I like the sound / function of that guy.

I also like the sound of these:

http://www.effectsdatabase.com/model/ibanez/9/af9 Ibanez AF9

But I'm open to suggestions...

[Processaurus]

I enjoy the sound of the Mu-Tron, a nice squishy character.  Modifying it to have a different attack speed on the envelope would be within the realm of possibility.

[FunkyGibbon]

I love Chunk Systems' Agent OOFunk, but I've not seen a schematic for this.

Christopher

[petemoore]

  Neutron Filter, I only know a few of these, this one is 'deluxe' featured.

[Mark Hammer]

The Nurse Quacky is the quickest route to autowah.  Is it the "best"?  Nah.  But it's decent, easy to build on perf, doesn't need special parts, and wide open to interesting mods.  Once you've lived with it for a while and figured out what more you need (and honed your PCB-making skills), you can aim higher.

[nocentelli]

The snow white autowah is a fantastic sounding filter, but it doesn't have a "downsweep" mode (I personally don't use that sound on guitar anyway). I would say, however, that it produces more of an "autowah" than an "envelope filter" sound: With nice dynamic playing, it can be made to sound alot like a normal pedal wah, without that squelchy, synthy, rippling sound I tend to associate with envelope filters. This may be a good thing or bad in your book. With the resonance up high, it can do fairly squelchy also.

You can get a great pcb from http://www.guitarpcb.com

[StephenGiles]

It does depend on whether you want "squelchy, synthy, rippling sounds" or  smooth wah sounds. For the former they are all out there but for the latter, I'm still working on it - although the Craig Anderton Bi Filter Follower was very good. There will be moans about needing 2 batteries of course, but it's all a question of a box big enough for the project or a project small enough for the box

[Mark Hammer]

The BFF is a nice filter.

If 3secondrule is leaning towards something that does what his Microsynth or an AF9 does, then the BFF will come up a little short, despite its other virtues.  So, a few questions...

1) Does it need to sweep down as well as up?
2) Is something other than bandpass a must?
3) Does it need variable resonance?

[the3secondrule]

Thanks for all the advice guys 

I've decided to go with the Neutron, and I've ordered a board from GGG. I have a nicely tricked out crybaby, so I don't need a "proper" wah sound. Checked out a few sound samples and the Neutron looked quite nicely tweakable - as well as having the up & down sweep - and a nicely squelchy, synthy sound. Just wondering now, whether it would be possible to mod the neutron for control over the attack rate, because the slower attack of the Microsynth is something  I really dug ...

The BFF is a nice filter.
If 3secondrule is leaning towards something that does what his Microsynth or an AF9 does, then the BFF will come up a little short, despite its other virtues.  So, a few questions...
1) Does it need to sweep down as well as up?
2) Is something other than bandpass a must?
3) Does it need variable resonance?

[Mark Hammer]

Attack time can certainly be altered, but not anywhere near the extent which the Microsynth can.  Different sort of envelope extraction/generation in each.

[the3secondrule]

cool.

Yeah I figured I wouldn't get anything close to the tweakability of the microsynth. I guess being able to toggle between 2 settings would be good enough - for stock attack, and a slow setting...

thanks for the help ... where would I look to alter the attack time?

Cheers!

Jeremy

[Mark Hammer]

where would I look to alter the attack time?

You can look here: http://www.geofex.com/Article_Folders/ECFtech/ecftech.htm  in the section that talks about the envelope follower near the end.

[the3secondrule]

You can look here: http://www.geofex.com/Article_Folders/ECFtech/ecftech.htm  in the section that talks about the envelope follower near the end.

Excellent - Cheers Mark. Thats exactly what I was looking for. I'm at the stage now where I have built a few effects, and this sort of information is no longer going right over my head - its starting to make sense. I'm starting realise I'd rather be told how to find my own answer, rather than just "replace component X with value Y to increase parameter Z". Bout time I sat down and read my way through the all the "technology of" articles.

[the3secondrule]

So, for instance, I could replace the 330r attack resistor with, say, a 1k pot, and the 47k release with a 100k pot for more control over attack and release?

or have attack and release switches to toggle between say 2 settings for each...

[Mark Hammer]

Yes.

Although initially a strong proponent of the variable attack mod, over time and builds, I came to realize that aiming for longer attack times was simply asking for too much from the circuit.  That series resistance that slows down the chargeup of the averaging cap places a limit on current (which is, after all, how it works).  This makes the unit behave like the sensitivity is too low, so you end up having to adjust the sensitivity when you increase the attack time.  This is even more problematic with the Mu-tron/Neutron, because the sensitivity control is the same as the overall gain control, such that you can't offset the unresponsiveness of a longer attack time without having to increase the output volume.  Now, you could add an output volume control, but now you've been forced to adjust two other controls all for the sake of tweaking a third one.  As my grandmother would have said: "Feh!!".

You CAN provide longer attack times if the resulting envelope is suitably buffered.  That would involve adding enough to the circuit that you couldn't use any existing layouts.  Consequently, the less problematic control to add for simple envelope feel is a variable decay via the bleed resistance in parallel with the averaging capcitor.  In this case, that's the 47k resistor in parallel with the 4.7uf cap.  Making it higher in value slows down the time for the charge in the cap to drain off, and making it smaller speeds things up for a faster decay.  This mod does not require any adjustment to sensitivity of the envelope follower stage.  You'll find that faster decay times tend to provide a more "synth-like" sound.  The Mu-tron already comes with a reasonably quick decay, which is probably one of the reasons why bass players like it so much.  Longer decay times are more suitable for rhythm guitar than they are for bass.

That being said, a switch that flips in a 100R resistor in parallel with the 330R should provide an audibly faster attack than stock, and give yet one more sonic option without too much intrusion and complication.