pulsar !!!!!!!!!!!!!!

[casey]

does anyone have the electro-harmonix pulsar schematic...?
i am interested in the chop feature....

thanks.   :lol:

[Jason D]

www.tonepad.com    has a layout and schem. of the Pulsar.

[Mark Hammer]

Every 2 op-amp Schmitt-trigger-plus-integrator LFO (i.e., what you see in just about every damn phaser, chorus and flanger) has both a square and triangle output.  Essentially they all are square-wave generators, and the integrator half makes the circuit stupid so that it takes a while for the square wave to rise and fall again, which is what the triangle wave is.  Having the volume change fade in then out is the traditional tremolo.  Having the volume go straight from on to off is the "chop" function.

The Pulsar uses a different way of generating the LFO wave, and the "chop" switch simply selects between a lower and higher value capacitor.  My guess is that the large value one introduces enough lag to produce a triangle wave from the squarish one coming in.

[casey]

thanks for the replies....i never noticed it at tonepad.


thanks for the explanation mark

[puretube]

not to be mixed up with the new one:

http://namm.harmony-central.com/WNAMM04/Content/EH/PR/Pulsar.html

[Jason D]

Hey, does anyone know (Mark?) how the variable wave shape control works on that (the NEW Pulsar)? Or, how you could modified any tremolo to do that?

[Dan N]

not to be mixed up with the new one:

http://namm.harmony-central.com/WNAMM04/Content/EH/PR/Pulsar.html

Isn't this your design puretube? Congrads!

[puretube]

the answer lies here:
http://www.puretube.com/link-page.htm

(scroll down a little...)

[Mark Hammer]

I couldn't explain how to do it, but continuously variable and switch-selectable waveshapes have been around for ages in the synth DIY community.  The simplest arrangement is to use a 3rd op-amp stage between comparator and integrator that splits the LFO waveform into ascending and descending portions using a pair of diodes.  These can then be varied independently to produce ascending and descending ramp waves in addition to the equal-slope triangle waves.  Look at the "simple square-wave shaper" on Tim Escobedo's site for an example of how this works.  A more advanced example can be found here: http://www.aleph.co.jp/~takeda/radio/img/LFOII-scheme.gif

I posted an Elektor article from 1978 on my site that describes construction of a multi-waveform sweep generator.  It can provide swept HF clocks for BBD-based effects, but it can also provide non-typical LFO waveform for sweeping non-BBD-based devices.  There is a PC-layout in the article, although you'll have to use software to flip it for press-n-peel purposes.

[puretube]

yes, Mark, there`s no "big" magic to it.
I`m sure there are a couple of similar circuits s.w. `round the web.
The more tricky thing is to do it with  2 opamps, 1 Ub, and "tick-free"...

since this is most obviously a pedal currently in production,
the ethics of this forum (and other reasons...) don`t allow me to go
much further...

[Mark Hammer]

I actually don't WANT you to go any farther, Ton.  If we had it handed to us on a plate all the time, how would we ever stumble on to new ideas, right?  :wink:

Judging from all the postings in past, if you can make a tick-free *anything* that uses an LFO, that puts you on the short-list for the Nobel Peace Prize!!

[puretube]

o.k.: little hint helping for "tick-free-ness" with PCB-based LFOs:
keep the LFO-ground separate from the audio-ground, and let both get into contact at the big PS cap only.
Same goals for +Ub.
("star-grounding" & "star-supplying").
(s.th. we all learned...).

De-coupling the B+ of the LFO with a small R and an extra load-cap from the audio-plus. (obvious, and done in a lot of projects...).

Another cause for "ticking": long free-running wires from the Schmitt-trigger`s output to "speed/rate"-pots or LEDs are x-mitting antennas
for the sharp spikes that will induce into the audio-path when criss-crossed
through the box. Especially high impedance parts of the circuit are potential receivers. (we learned that, too...).

and there is more...

P.S.: I`d be afraid to be on the same list with Bu.. and Bl...

[bioark]

here: http://www.aleph.co.jp/~takeda/radio/img/LFOII-scheme.gif

broken link

[nordine]

some weeks ago i built a tremolo that runs nice and everything, but has the con of heavy ticking at first ....then fading out (the ticking) till almost completely dissapear.

i mean, the effect is ready to use past -at least- half minute after switched on, before has that nasty ticking. any guessings?

should i upload the circuit?

[bioroids]

i mean, the effect is ready to use past -at least- half minute after switched on, before has that nasty ticking. any guessings?

should i upload the circuit?

I have the same problem with a tremolo of my design, but using the LFO from the EA tremolo.

Miguel

[Paul Perry (Frostwave)]

has the con of heavy ticking at first ....then fading out (the ticking) till almost completely dissapear. i mean, the effect is ready to use past -at least- half minute after switched on, before has that nasty ticking. any guessings?

The only thing that I can think of that can change over half a minute, and then stop changing, is a charging capacitor.
Maybe the 1/2 Vcc bias voltage source has very large R and/or very very large C and doesn't get to 1/2  Vcc for a while?

By all means post the circuit!

[nordine]

here is it: