Favorite 9v powered LFOs? For Escobedo's PWM

[spectraljulian]

I built Tim Escobedo's PWM and I really love it, hate the LFO.  The clock noise is really intolerable, and though I can change the value of the cap to ground in order to slow/speed up the LFO speed, the filter and transistor used for smoothing out the wave form don't get anywhere near sine/triangle.  

Can anyone suggest something a bit less horrible? I'm thinking something based on a 555, or better yet op-amp or fet based because I have a small assortment of those, and I'd have to order a 555 (not a huge deal because I'll be doing a parts order soon, though if I could play with something today, that'd be ideal)

BTW. . . I read someone suggesting that running two more schmitt triggers off of the signal out of phase that a dual oscillator sound could be had.  Has anyone tried this, is it worth trying? 

[tiges_ tendres]

If you dont like clock noise you should probably avoid a 555.

Frequency Central has a number of schematics posted for low parts counts LFO's.  Search for those.

[daverdave]

My favourite LFO for effects is the schmitt trigger / integrator design, two opamps and both square wave and triangle outputs. That's pretty easy to make.

[spectraljulian]

frequency central, I googled but couldn't find.  Link?

I do have an extra 40106, I could try that.  It's a shame that I couldn't simply do it on the same chip, but the clock noise is horrible. 

[oldschoolanalog]

My favourite LFO for effects is the schmitt trigger / integrator design, two opamps and both square wave and triangle outputs. That's pretty easy to make.

+1.  
Easy to alter min/max speed, amplitude & offset.
Nice.

Good reading:
http://www.piclist.com/images/www/hobby_elec/e_ckt16.htm
http://www.ti.com/sc/docs/apps/msp/journal/aug2000/aug_07.pdf

[spectraljulian]

I'll check that out. 

By the way I decided to try splitting the signal after the 386.  I put one half into a TL081 set up as an all pass filter with a pot for R so that the phase change would be variable.  That then went into the 40106 in the PWM fashion.  The signal that didn't go into the TL081 went into the 40106 and used two of the unused Schmitts.  Each signal path had it's own pulse width knob as well.  Then I mixed them back together right before the volume. 

I have to play with it at a more appropriate hour for turning stuff up loud, but I like it.  The phase shift and two pulse width knobs are super interactive, and I'm not sure if it would be worth making a Seven Knob pedal (or 9 knob if I decided to use the extra two unused ones and add another op-amp ) but I'll have to play with it some more. 

[tiges_ tendres]

frequency central, I googled but couldn't find.  Link?

I do have an extra 40106, I could try that.  It's a shame that I couldn't simply do it on the same chip, but the clock noise is horrible. 

I'm sorry, Frequency Central (Rick) is a poster here. He has extensive layouts, circuit snippets and schematics for synth circuits, including LFO's if I'm not mistaken.

[spectraljulian]

My favourite LFO for effects is the schmitt trigger / integrator design, two opamps and both square wave and triangle outputs. That's pretty easy to make.

+1.  
Easy to alter min/max speed, amplitude & offset.
Nice.

Good reading:
http://www.piclist.com/images/www/hobby_elec/e_ckt16.htm
http://www.ti.com/sc/docs/apps/msp/journal/aug2000/aug_07.pdf

Looking at the TL082 oscillator LFO. . . I'm assuming:
1.  Best way to control rate is via R1, since R2 and R3 need to be near in frequency.  
2.  Depth would be controlled by fading the output to ground
3.  I need to convert 9v to bipolar 4.5v

correct?  

I'm sorry, Frequency Central (Rick) is a poster here. He has extensive layouts, circuit snippets and schematics for synth circuits, including LFO's if I'm not mistaken.

Oh, ok, on Aron's gallery page.  Got it!  Err well he's got stuff in Aron's gallery, but no LFOs.  I'll search here.

[spectraljulian]

http://www.diystompboxes.com/smfforum/index.php?topic=81072.0


something to play with tomorrow!

[auden100]

By the way I decided to try splitting the signal after the 386.  I put one half into a TL081 set up as an all pass filter with a pot for R so that the phase change would be variable.  That then went into the 40106 in the PWM fashion.  The signal that didn't go into the TL081 went into the 40106 and used two of the unused Schmitts.  Each signal path had it's own pulse width knob as well.  Then I mixed them back together right before the volume.  

Any chance you'd be willing to post a simple schematic? I've been planning on putting together the PWM for bit, and having some mods in mind beforehand would be great!

[spectraljulian]

wire the top Pulse Width pot and the bottom one the same, unless you want each pot to have the opposite sweep.  

You could use a dual pot for them, but then you couldn't set them in two unique positions.  Well, technically you could wire the terminals so they'd be opposite, but that wouldn't give you the full spectrum.  

The phase could also be replaced by a resistor at whatever value you like best.

Of course, breadboard it before you commit, and breadboard the original design.  Sometimes simplicity is best. 

[alex frias]

I used the Luna Tremolo LFO in a couple of other projects with some good results...

[Top Top]

Weird, I never had problems with ticking on the PWM LFO, BUT I wouldn't mind a triangle LFO on it either. I have used this LFO on other things with good results:

http://home1.gte.net/res0658s/fatman/4069_lfo.html



Using the stock 100K resistor between 1&6 did not work for me though - it would latch and stop oscillating. The value that worked best for me is about 90k Ohms. I also had to put a 2.2K resistor between the output (depth) knob and the rest of the circuit to keep the LFO from slowing down when the depth was up all the way.

FWIW  I was also using +12V and ended up with a 2.2uF cap rather than the 1.3uF. It can do a really nice slow sweep on up to near audio rate.

May work as shown with 9v. Might have to breadboard it to get the right values for 9V.

It works great for me now though... and just think of what you can do with the other three inverters on the other side of the 4069!

[merlinb]

My contribution to the list of LFOs. A single opamp jobbie giving square and dirty-triangle outputs. Output usually needs to be buffered since the max load is 1M before it cuts out.


And here's the classic square/triangle LFO using two opamps, courtesy of stomboxology:
http://moosapotamus.net/IDEAS/stompboxology/Vol4No4/Page_02.gif

[spectraljulian]

I tried figure 4e but the voltage is varying between 3 and 5.  I guess I'll plug it in and see how it performs. 

[spectraljulian]

LFO 4 seems to work OK, but without a depth knob, it's got one setting- SUPER CHOP.  I'll have to fix that.  There's also a little bit of clock bleed, but not nearly as much.  I'll see if I can tame it, but I'm definitely going to try some other suggestions out too. 

BTW. . . I got to try out my revision of the PWM at full volume today and it's pretty awesome sounding.  Thickens the sound up a lot to not only be able to set two different pulse-width settings, but also to have one of them be out of phase.  I also got this weird bloom thing going on where chords would grow in volume after hitting them.  I'm wondering what's causing that.  It suspect that it's how the circuit reacts to acoustic feedback, or maybe the phase shift becomes more dramatic as the chords ring out, since I'm pretty sure that the phase shift isn't unified in amount. 

[spectraljulian]

On my final build I think I definitely want to do my revision though, but I want a joystick to control pulse width.

I can't seem to find 500k joysticks anywhere though. 

[daverdave]

My favourite LFO for effects is the schmitt trigger / integrator design, two opamps and both square wave and triangle outputs. That's pretty easy to make.

+1.  
Easy to alter min/max speed, amplitude & offset.
Nice.

Good reading:
http://www.piclist.com/images/www/hobby_elec/e_ckt16.htm
http://www.ti.com/sc/docs/apps/msp/journal/aug2000/aug_07.pdf

Looking at the TL082 oscillator LFO. . . I'm assuming:
1.  Best way to control rate is via R1, since R2 and R3 need to be near in frequency.  
2.  Depth would be controlled by fading the output to ground
3.  I need to convert 9v to bipolar 4.5v

correct?  

I'm sorry, Frequency Central (Rick) is a poster here. He has extensive layouts, circuit snippets and schematics for synth circuits, including LFO's if I'm not mistaken.

Oh, ok, on Aron's gallery page.  Got it!  Err well he's got stuff in Aron's gallery, but no LFOs.  I'll search here.

R1 would be best to control frequency as R2 and R3 make up part of the schmitt trigger, so changing them would also changing the ratio between them would also change the amplitude of the output waveforms. You'd need bipolar 4.5V yes, but in my experience it's a very stable circuit. If you use a depth on the output just remember that ground would be the 4.5V midpoint, other wise the waveform will be pulled to ground when you decrease the depth.

You could also include a pot setup with the output of the schmitt trigger going to pin 2 and then pin 1 and 3 going through oppositely orientated diodes them combined going into the integrator, this would give oyu decent control of the mark / space ratio, but will affect the frequency.

[oldschoolanalog]

Get out the breadboard & build the one in this:
http://moosapotamus.net/IDEAS/ADAflanger/ADA_MN3007/FlangerClone_SCH_rev5_MN3007_jan2010.gif
Single supply (try different supply V's when testing), easy to build, and easy to adjust parameters (fastest/slowest speed, amplitude, etc.).
It can be set up to go from so slow you hardly notice it to audible fast.
Plus it's tried & verified in loads of builds.

[spectraljulian]

My favourite LFO for effects is the schmitt trigger / integrator design, two opamps and both square wave and triangle outputs. That's pretty easy to make.

+1.  
Easy to alter min/max speed, amplitude & offset.
Nice.

Good reading:
http://www.piclist.com/images/www/hobby_elec/e_ckt16.htm
http://www.ti.com/sc/docs/apps/msp/journal/aug2000/aug_07.pdf

Looking at the TL082 oscillator LFO. . . I'm assuming:
1.  Best way to control rate is via R1, since R2 and R3 need to be near in frequency.  
2.  Depth would be controlled by fading the output to ground
3.  I need to convert 9v to bipolar 4.5v

correct?  

I'm sorry, Frequency Central (Rick) is a poster here. He has extensive layouts, circuit snippets and schematics for synth circuits, including LFO's if I'm not mistaken.

Oh, ok, on Aron's gallery page.  Got it!  Err well he's got stuff in Aron's gallery, but no LFOs.  I'll search here.

R1 would be best to control frequency as R2 and R3 make up part of the schmitt trigger, so changing them would also changing the ratio between them would also change the amplitude of the output waveforms. You'd need bipolar 4.5V yes, but in my experience it's a very stable circuit. If you use a depth on the output just remember that ground would be the 4.5V midpoint, other wise the waveform will be pulled to ground when you decrease the depth.

You could also include a pot setup with the output of the schmitt trigger going to pin 2 and then pin 1 and 3 going through oppositely orientated diodes them combined going into the integrator, this would give oyu decent control of the mark / space ratio, but will affect the frequency.

Btw, I can't seem to find a good schem to turn 9v to +/- 4.5v.  know of one?