16 steps staircase LFO, with schematic

[bioroids]

Hi!

I posted at my site http://www.dedalofx.com/bioroids (you may need to hit Ctrl-F5 if you visited it before) the schem for this circuit I made (with Gez contribution), along with a description.

It makes a 16-steps triangle or ramp waveform, and also has 16 different patterns with sequencer-like tones, in the style of the Vanishing Point

It's intended to be used with LM13600 or other OTA-based effects, but can be adapted easily to LED/LDR combos.

And it's pretty simple, using only 2 CMOS ICs and 2 NPN transistors.

Any comments are welcomed, and I hope it's interesting to someone.

Luck!

Miguel

[gez]

Good stuff! 

[R.G.]

You may want to read http://geofex.com/Article_Folders/LFOs/psuedorandom.htm for some other stairstepped LFO setups, including triangle and sine.

[Transmogrifox]

I like that a lot.  I was doing some thinking about how to pull it off a while back, but the binary counter chips I have don't have the carry out or the direction so it was going to require a significant amount of external logic.  I'll have to include some 4029's in my next parts order.

You managed to pull it off with just a few parts.  I like that D flip flop oscillator because I have a bunch of CMOS D flip flops that I didn't know what to do with and I bet that's a pretty low-current oscillator that contributes minimal clock tick in the ground path.

I think I know the perfect filter for this.  I have recently purchased a Korg Delta, and got the schematic from the guy who sold it to me.  I really like the sound of the filter, and I think it would make a nice guitar filter.  If anyone is interested in the Korg Delta filter, say so and I can scan it in and post it.

[bioroids]

Hi

I've read that article R.G. and found it very interesting. I just updated the page to show links to it and Tone God's Vanishing Point.

Transmogrifox:  the Flip-Flop clock generator was a contribution by Gez and it didn't introduced any clock noise, at least in this setup. That's a pretty handy trick! On the other hand, I'd like to see the schem of that filtre if you dont have trouble posting it.

Thanks!

Miguel

[Transmogrifox]

I have posted the filter here:

http://putfile.com/pic.php?pic=9/26900243581.jpg&s=x4

The input would be at the op amp right before the "LP/BP" switch.

The modulation input is at the base of the differential pair.  I suspect the purpose of the differential pair is to generate an exponential on the linear CV so that the filter sweeps more evenly across the audio range.  In the Korg Delta, this modulation input is a large summing junction taking a CV from the ADSR, a joystickc a center frequency bias pot, and an external input option.  This is where you could put the stepped LFO output, or envelope follower, or you could make an extra rad filter pedal using an envelope follower, various LFO's, a guitar trigger and ADSR.

The resonance of the filter is the pot labelled "RES".  It uses LM13600 OTA's, and the op amp flavors are non-consequential.

The filter's output is not so obvious from the window I cropped from the schematic.  The output is taken from the high end of the resonance pot (as in the contact that is not the wiper, and not the one connected to ground).

These extra obvious details are put here for people with limited electronics knowlege who may be interested in actually using this filter.  Anyone with interest in a complete schematic illustration how this filter could be used with the stepper LFO, let me know and perhaps I will find time to compile such a schematic if there seems to be interest.

EDIT:  I just noticed some other things that are not clear:

The 180k resistor with a line drawn across the input is unclear.  That is NOT a connection to the input.  This is another CV coming from the keyboard follower.

"a+" and "a-" are +15Volts and -15Volts respectively.  I think you very well get away with a 9V setup and a virtual ground so that the a+ connections are 9V, a- to ground, and the ground connections to the 4.5V virtual ground.  The filter would be likely to distort significantly on high resonance settings, so +/- 9 volts would be more ideal (for an 18 Volt total). I think that must cover it for the most part

[puretube]

free information sucks...

[gez]

[SOT]...Miguel: the curve in exp.#02 reminds me of CMOS inverter transfers...
(no wonder...); just a little more assymetric.
Maybe similar to "linear" cmos-inv. applications, try a feedback-resistor...

The 4016 Switch can be biased to work as a linear amp.  Clipping isn't that soft as there's a hidden inverter to the gate of the p-channel MOSFET (just woken up so I reserve the right to change that once my brain gets going).  Because of this inverter current consumtion is higher than a single UB stage too.

The 'Scuzz Box' at Marcos/Munky's site uses a 4016.

[bioroids]

I have posted the filter here:

http://putfile.com/pic.php?pic=9/26900243581.jpg&s=x4

Thanks! That's an interesting circuit.

[SOT]...Miguel: the curve in exp.#02 reminds me of CMOS inverter transfers...
(no wonder...); just a little more assymetric.
Maybe similar to "linear" cmos-inv. applications, try a feedback-resistor...

I've been meaning to try that for a while, but couldn't find the time.
Can distort pretty heavy anyway, as Gez points.

I was thinking in making a tremolo using only the 4 "stages" of a 4016, just for experimental purposes.

Luck!

Miguel