variable stuttering pedal

[benfox]

I'm searching someone who did this one.... http://www.geofex.com/FX_images/stutter.pdf 
Is it a simple tremolo or is it a really variable duty  cycle of stuttering ?

[RLBJR65]

I've never built it but think it could be described as a choppy tremolo.
Try doing a search cause I'm sure I have seem this come up in previous thread(s).

[R.G.]

It is really a volume chopper, with a variable duty cycle. The amount of chop is variable.

[John Lyons]

I was hot to make this one a while back but got sidetracked. I started a PCB layout for it but haven't been back to finish it.
I don't think I've seen a thread about anyone here making it...I may be wrong.

R.G.
I know I've heard about making the speed of the EH Pulsar circuit faster and how you can get close to a ring modulated sound...I assume this is the case with this circuit..?  can you reccomend how to go about changing the speed to be able to chopp faster...or does the speed work fast as it is layed out now?

[Transmogrifox]

It would certainly sound interesting to do ring modulation with a variable duty cycle pulse--particularly if you were modulating the duty cycle with a separate LFO.  I have been wanting to try something of this nature for some time.  It's by no means unheard of in the DIY synth community. 

[col]

I built this and the effect is fantastic but I can't get rid of the ticking noise as mentioned in other threads on this forum. I don't know how to post links so unfortunately you'll have to do a search. For some reason the noise starts quite loud and diminishes with time as you leave the effect on. I have tried all the things mentioned on other posts but nothing has removed the ticking to a useable level for recording. For practice it's fine if a little annoying.
I have tried various caps on different parts of the circuit and none have made any difference withiout affecting the sound adversely. The silly thing is I dind't notice it before I boxed it up. When it was just on my test rig it sounded fine. Has anyone actually solved the problem on this circuit as apart from the tick it is superb!

Col

[Processaurus]

http://geofex.com/FX_images/stutter.pdf
If you right click the Geo links and say properties, it gives the URL.
Would a photo-FET be a good idea for this effect, to electrically isolate the audio section from the LFO?  I built it and it ticked badly too, even with a cap on the gate of the JFET to ground to slow down the transition from off to on.  The LFO design is great on its own, though.

[gez]

Trapezoid...no click stutter.

One day I might be generous enough to post a schemo...

[Paul Perry (Frostwave)]

Trapezoid...no click stutter.
One day I might be generous enough to post a schemo...

In the meantime, at the cost of some complexity, a 'slew limiter' circuit will convert a square to a trapezoid.
But if the question is just how to get a LFO that is flat topped, but doesn't have a vertical edge, then what about a triangle wave going to a grossly overdriven LM13700 or other OTA amp stage? First the triangle goes to a sine & then with more signal, the top flattens, you get a round shouldered square at some stage, could be OK?

[gez]

In the meantime, at the cost of some complexity, a 'slew limiter' circuit will convert a square to a trapezoid.
But if the question is just how to get a LFO that is flat topped, but doesn't have a vertical edge, then what about a triangle wave going to a grossly overdriven LM13700 or other OTA amp stage? First the triangle goes to a sine & then with more signal, the top flattens, you get a round shouldered square at some stage, could be OK?

It's quite easy to do; I think what you proposed with the 'slew limiter' is where I'm comming from (though I prefer to think of it as an integrator stopped in its tracks).

Feed an OTA set up as a follower with your square, stick a cap at the output of the OTA (not it's buffer) and the output ramps up till the -ve input is same as +ve.  This gives you your trapezoid.  Adjusting the amplitude of the square (stop resistor and variable resistor from Square output to centre of bias divider) and you have variable depth.  You'd think that the feedback to the -ve input would cause distortion of the ramp up/down, but it doesn't (nothing that's visible/audible).

If you use half a LM13700 for the trapezoid shaping, the other half can be used for the modulation.  Might sound kamikaze, but if you provide separate ground paths for the square LFO and all bias resistors/cap etc associated with the trapezoid shaping circuit, it works out fine and click free.

No schematic, but all the info's there...can't get fairer than that!

[Paul Perry (Frostwave)]

No schematic, but all the info's there...can't get fairer than that!

Aw, c'mon Gez, where's the stripboard layout for me?? (seriously, I was wondering what to do with the other half of the LM13700.... DOH!)

[R.G.]

Try this one:
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=6294

[gez]

RG, you're just showing off now! 

I'll stick to my cheap and cheerful (read 'hack') way of doing things for now...

[R.G.]

Hey - that's not mine, it's right out of a magazine.

I simm'ed it with a 2N5485 in shunt chopping, drain and source held to 5.1V on a zener and a 100K series res. Looks good, and very little feedthrough with 70mV signal

Bread board it will you?

[gaussmarkov]

Try this one:
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=6294

[gez]

Hey - that's not mine, it's right out of a magazine.

Whoops, I don't know what happened there.  I must have accidentally clicked on one of those ad links as the thing I first saw was a microprocessor chip that limited slew, not the article you've just linked to.   

Dr Who is about to start, so the article will have to wait for the moment! 

[gez]

I simm'ed it with a 2N5485 in shunt chopping, drain and source held to 5.1V on a zener and a 100K series res. Looks good, and very little feedthrough with 70mV signal

Bread board it will you?

Probably not, now that I've actually looked at the right link (sorry for the confusion  ).  It's a clever circuit, but what I outlined suits my needs better as I can use the other half of the LM13700 for modulation, there's none of the rounding off mentioned in the article, I can vary slope by varying Iabc and vary depth around a central (or off-centre) axis - this gives choppy trem as well as on/off stutter.   Apart from anything, I don't have a spare board free, sorry.

It's a really clever circuit though.  I think a suitable op-amp would have to be specified as the inputs get pulled to the rails.

Someone here should give it a go mind, I'm sure it would cure the click...

[donald stringer]

Would you put that circuit R G mentioned before the variable stuttering circuit.?

[R.G.]

Would you put that circuit R G mentioned before the variable stuttering circuit.?

It would be the voltage that drives the JFET gate. The PWM stuff would drive the slew rate limiter, and the slew rate limiter slows down the gate waveform until you can't hear transients.

[gez]

RG, can't promise anything, but I found a fix for the circuit I was working on so should be able to strip a board this afternoon.

I've downloaded your schemo and I think I've got some switching FETs somewhere.  I'll report back if I get it up and running.