Tremolo+ Envelope Controlled Filter = Phaser (almost)

[Jason M.]

All this discussion about Anderton's EPFM reminded me of a something I stumbled upon...

If you have a tremolo and an envelope filter and don't have a phaser, but want one, try this:

Hook up your tremolo in front of your envelope filter.
The change in amplitude the trem creates makes the filter sweep up and down.
You get amplitude AND frequency modulation.

I tried it with my Dunlop tremolo into the Anderton Super Tone Control w/Envelope Follower, but it should work with most combinations.

This idea may be old or obvious to everyone, but it kept me playin' for a while and isn't that what all these things we build are about?

J.

[mattv]

That does sound cool. I like it the other way around too.

[Mark Hammer]

This is why I keep going on about the "phase-filter" mod to OTA-based phasers like the Small Stone, Ross, and DOD FX20.  When the LFO is sweeping both a pair of allpass stages and a lowpass filter you get both a sort of modulated wah AND vibrato.  The result, ESPECIALLY if you bypass the dry signal for wet-only mode, is about as swampy as you can get when you set it to medium-slow speeds (not bubbly, just wobbly); a sort of very restrained evil that conjures sweaty nights, wrinkly old men, and dark rituals.

I like your improvised version, though, Jason.  Wonder how it would sound as you dicker with attack/decay times on the envelope follower.

[mattv]

This is why I keep going on about the "phase-filter" mod to OTA-based phasers like the Small Stone, Ross, and DOD FX20.  When the LFO is sweeping both a pair of allpass stages and a lowpass filter you get both a sort of modulated wah AND vibrato.  The result, ESPECIALLY if you bypass the dry signal for wet-only mode, is about as swampy as you can get when you set it to medium-slow speeds (not bubbly, just wobbly); a sort of very restrained evil that conjures sweaty nights, wrinkly old men, and dark rituals.

Please do go on about the phase-filter, I love it! Unfortunately, as i learned through a tip from you, I can't subtract the dry signal from my DOD, without killing it in bypass as well. This should be no problem though once I true-bypass it.

[gez]

a sort of very restrained evil that conjures sweaty nights, wrinkly old men, and dark rituals

Ah, so you too know the hell they call 'Croydon'!?
http://www.transportimages.com/gallery/Croydon-Tramlink/cabview

[ExpAnonColin]

You'd definitely want a way to make the amplitute of the signal greater, instead of just making it cut out periodically, so you could change the frequency that the env. filter got, probably you'd want a pre- and post- envelope filter level knob.

-Colin

[Mark Hammer]

Matt,

Glad to hear things are working out in the swamp.  :wink:  About the I-lose-everything-when-I-bypass problem, consider the following.

The overwhelming majority of manufacturers that use solid-state switching in their pedals use either a discrete (e.g., Boss) or chip-based (e.g., DOD) flip-flop circuit to alternately turn on and turn off a set of FETs.

As it happens, the "effect" produced by a chorus, phaser, or flanger (and probably by some other dry+wet effects types too, like octave-down units) only occurs when wet/effected signal is mixed in with dry.  Unlike distortion units and some other types of effects where you have to do more switching to go back from a dirty to clean sound, when it comes to the sorts of modulated effects noted, all you have to do to kill the "effect" is lift the wet signal connection without having to do anything at all to the dry signal.

The result is that although a flip-flop circuit is incorporated for switching, only the flip (or is it the flop?) is used to activate a FET.  Step on the switch again and the circuit deactivates the FET but has nothing else to do since it doesn't need to do anything to the dry signal that is hardwired up to the mixing stage.

What does this mean for you the consumer?  What it means is that if you know how and have the parts and space, you can whip up the same sort of FET circuit currently in place for the wet signal, stick the 2nd FET between the input buffer stage and mixing stage, and tie its control line to the other half of the flip-flop.

Look at the schematic for the Boss CE-2.  You can see that the FET Q9 has a diode (D4) at its gate, a cap (C28) to ground for decoupling, and a current-limiting resister (R48).  The control signal comes from the collector of Q7.

Now take a look at the schematic for the Boss DS-2.  In the lower right hand corner you see the exact same flip-flop circuit, except complementary signals from the collectors of each of the transistors in the flip-flop drive two sets of FETs to switch back and forth from dirty to clean/bypass.

*IF* you could insert/install a FET retrofit like what I suggested, then one step on the momentary switch would get you wet-only, and a second step would turn the wet off and the dry on, yielding nice unperturbed clean/dry signal.  But how do I get conventional phase (wet+dry) in "effect mode" if I have this FET retrofit, you ask (and well you may ask)?  Easy, stick in a simple SPST mini-toggle to bridge the drain and source of the added FET and your pedal won't care what state the FET is in; you go back to the dry-is-always-in-circuit state.

How do you do this on a DOD pedal?  Another excellent question (don't know how you do it but you ask all the right ones).  Look at the scanned article called dodswitch.gif at http:/hammer.ampage.org/ (you'll need to scroll down a few pages), and you'll see the standard DOD equivalent of the Boss flip-flop, only using a 4007 CMOS chip.  Flip and flop are available from pins 1/5/6 and 8/13, according to the diagram.  Whichever one is sitting doing nothing in your pedal is the one you want.

I'm not promising that you DO have room for this in your pedal.  However, you don't necessarily HAVE to yank the guts out, find a new home for them and wire up a stompswitch to be able to go from wet-only to dry-only.  You CAN keep the traditional solid-state switching convenience.  And again, this can be applied to just about any commercial modulation pedal out there that uses solid-state switching and a momentary switch.

Hope it was clear enough.  We now return you to "The Swamp", already in progress.

[mattv]

Well, I hadn't thought to check for extra flip-flops left over. Thanks for the crystal clear instructions. It should be easy enough.
Now I have a bit of a decision to make. I was looking forward to housing it in a larger enclosure to add switchable caps, etc. Though for experience sake, I should still re-enclose, just using a momentary stompswitch...
You're posts always get me thinkin'.

This could definitely fit in the archive.