Roland Jet Phaser LFO, with ramping

[Mark Hammer]

The Roland AP-7 Jet Phaser (supposedly the unit made famous in the Isley Brothers' "Who's That Lady")  has an interesting LFO that ramps from slower to faster.  I've snipped the LFO/ramping portion of the overall schematic, and cleaned it up for legibility purposes.  As near as I can tell, the two switch sections shown are halves of the same DPDT for fast/slow switching.

I've never come into contact with one of these, but the circuit is amenable to use with a P90 or P45 board.  Is the ramping any good, or was it simply a first approximation?

[StephenGiles]

Didn't the Maestro Stage Phasers have a start up circuit for the LFO, and come to think of it so did the Moog 12 stager.

[StephenGiles]

Yes the Moog uses a CA3094 to achieve this!

And the Maestro
http://www.jedistar.com/pdf/maestro_stagephaser.pdf

[Mark Hammer]

The Maestro circuit seems more complex than the Roland one, and would need to be redesigned for a 13600/700, in view of 3094 rarity.

The basic question, though, that determines what path to pursue, is how it sounds.  Is the ramp-up and ramp-down smooth? a "musical" acceleration/decelleration?  amenable to mods such as variable ramp time?  hard/easy to adapt to different control-element types? (OTA, FET, PWM, LDR)

This is the stuff I'd like to know, and presently don't.

[kristopher612]

a quick youtube search yielded this video.  if you just want to hear the ramping, FFW to about 2:45 and let it play from there.  i like it enough to maybe build the whole thing
http://www.youtube.com/watch?v=HygFy1A_hWc

[Mark Hammer]

I etched the board for the AP-7 this morning, and got most of the drilling done before I had to bring my kid to the orthodontist.  It's a nice-sounding pedal, which I think will also work well with 2N5952s (can't think of a reason why they wouldn't).

Note that the stock unit employs a Big Muff style tone circuit, and a sort-of DS-1 precursor for the distorted sound.  Unlike the BMP panning between highpass and lowpass sections, though, the AP-7 includes some switch positions that set the tone to full bass, or full treble.  If a person had the space, they could simply install a 100k tone pot instead of using a fixed 100k resistor and the rotary switch.  Probably makes the wiring less complicated too.

Thanks for the link, I'll check it out later when I get home.

[Thermionic]

Hi!

I have an old Jet Phaser (in near mint condition) though... it is broken due to a loose lockingnut for the "jet-switch". The result is that all wire solders on this switch has been torn off on the back side. I am looking everywhere after a scheme to know "which wire-color to be soldered where"...


Any tips is of highest interest!

Many many thanks in advance!