Something new and interesting from Keeley

[Mark Hammer]

A phaser...

http://www.robertkeeley.com/product.php?id=57

[zombiwoof]

Looks pretty cool at first glance, with the ramping feature and tap tempo.

Al

[Mark Hammer]

Reading through the manual, it appears this is a hybrid pedal, similar to the Empress Tremolo, in that the audio path is entirely analog, but a PIC or other micro-controller is included for tap tempo, and what may well be all aspects of modulation.  The net result is that current consumption (avg 50ma) tends to put it well out of the range of batteries for all but the shortest of gigs (Ed Sullivan or AGT appearances?).

It includes a ramp-up/down function between the two variable speed settings, similar to the Line 6 Roto-Machine.

The "Edge" control is different.  Tell me what you think: "Our edge knob is two things...One part depth control, changing the phase from a more subtle effect, to one that is full out spacey as the knob moves clockwise.  The other part is envelope filter, changing where the signal is phased the hardest. At the farthest setting clockwise, your highs are most enhanced.  When turned fully counter-clock, the low end of your phaser gets the boost ."

To me that sounds almost like a BMP tone control in the feedback/regen loop, except that presumably the middle setting gets you no regen.  So it may function sort of like a BMP, but isn't exactly the same.  The Marshall Edward Compressor also has a BMP-like control that adjusts the balance of high and low end feeding the rectifier, in complementary fashion, but with no middle cancellation position.

In any event, an interesting feature, and something that should be simple enough to implement in a different fashion in DIY pedals.  Just note that, as a passive control, inserting something like a BMP tone control in the feedback loop would likely require some sort of gain applied to compensate for signal loss.  That could be a simple op-amp stage set for whatever gain is needed to offset the passive loss.

Now that I think of it, if one had an inverting op-amp stage, either before or after such a feedback-tone control, the feedback resistance in the op-amp stage could be used to drop gain down to zero for zapping regen, or increased to provide suitable compensatory gain.  Plus, since it would be an inverting stage, you could feed the signal back from the last stage to the first, not unlike what was done in the early FET-based Ross phasers (the feedback signal needs to be opposite phase to what it is combined with at the mixing node).

Forgive me as I think out loud.

[joegagan]

nice work mark.  sounds like some nice innovation coming from keeley &co.

The Marshall Edward Compressor also has a BMP-like control that adjusts the balance of high and low end feeding the rectifier, in complementary fashion, but with no middle cancellation position.

wow, interesting. i really like that control on the marshall ed. doesn't mess with the mids like you said

[Mark Hammer]

Well, it's not supposed to alter the tone directly.  Rather, it alters whether the gain reduction occurs evenly across the fretboard, or whether it responds more to lower notes or higher ones.

I had actually remembered the circuit wrong, so here is the correct version:

C9 and C10 are both tied to ground through one leg of the (100k) Emphasis pot, and R18.  IC1B's gain and low frequency rolloff point are dictated by the product of C9 and R18+potportion.  Turn it fully in one direction so that the resistance between lugs 1 and the wiper = 0, and Ic1b has a gain of 2.8x and low end rolloff at 1291hz.  Turn it fully the other way and the gain of IC1B is now around 1.1x with a low end rolloff around 68hz.

The other side of the pot operates, in conjunction with C10, like a guitar tone control.  Shift more pot resistance in series with C9 and you lower the resistance to ground for C10, losing more top end.  That gets fed to TR2, and of course, everything from TR2 onward works just like a Dynacomp.

Going by Keeley's description, their Edge control works a little differently.  They're both clever in their own way.

[Processaurus]

That's an interesting idea about the BMP panning hi shelf/low shelf tone control in the feedback loop, I wonder if it alternatively it could be the tone control applied to the 100% wet, phase shifted signal, before being summed with the dry signal.  Or both, with the tone control at the start of the phase shift stages, after the regen gets mixed in with the dry.  Regardless, I bet any of those options could affect the character of a phaser in an musical way.

Looks like it may use the fancy Molten Voltage tap tempo LFO chip, from in the picture of the innards.

[Mark Hammer]

I had added two stages of fixed leading allpass to one of my Ross beasts, and noticed that if the the point where the phase shift maxima is set in the upper mids, the added stages tend to intensify the effect as the sweep goes upward.  Not so much that it sounds like a stronger effect, but rather it doesn't sound like it wimps out quite so much at the top end of the sweep.  My two added stages use a .01uf cap and 10k to ground, yielding a corner frequency of 1.6khz (i.e., 90 degrees of phase shift above that point).

That's not what Keeley is using, clearly, from the PCB shots and chip-count.

[theundeadelvis]

Sounds pretty good: http://www.youtube.com/watch?v=J7SvYDQL24E