Easyvibe LFO guidance

[Mr Eastwood]

Hi Eb7+9  thanks     well initially i tried the bright white leds then i wanted to try some bulbs, so rather than try and build a circuit to manage the offset i just output a signal from my function gen straight into the base of a mosfet and powered the bulb straight from there;  what i found with the function gen was there is a sweet spot of bias where it sounded nice;  I recall when i was playing around with the rate I seemed to have to tweak the depth - hence the pic approach where i could adjust the offset based on the rate;   shortly afterwards I put the pic LFO on hold until version 2 and I kept the original LFO and switched the mosfet out for a npn;  this weekend I need to verify the depth is working correctly as it's seems like I have less control than i recall from my breadboard version, maybe I fried the cheap pots soldering them.   the only mistakes on the PCB were the +caps footprints were all backwards, the ldr routing was messed up and the bypass switch holes were about 2mm off along the x axis;  luckily it didn't need any trace cuts or bodge wires to resolve.  But once I resolve the depth mystery i'll post a final update.

[Eb7+9]

... what i found with the function gen was there is a sweet spot of bias where it sounded nice

that's a pretty typical thing to hunt for in any phasor (the so-called bias adjustment) ... and if there's some non-linearity somewhere in the control path that is frequency dependent - could be the driver circuit or devices, could be the bulb's thermal latency preventing from turning off enough and then limiting upper cell range - we can end up missing the fast-action zone near the turn-off point ... and end up having a dull sounding effect // why some phasors have an external color (manual offset) control

well done!
I'm sure the empirical steps would make an interesting study ...

if you don't mind, pls explain to me one thing if you will ...

what is the reason for going thru a DAC ?
have you tried driving the bulb by PWM directly ? ...

I'm just asking out of curiosity,
it's not like there's any risk of inducing zipper noise in the system

maybe there's an advantage I'm not aware of ...

cheers and thx for the detailed reply

[Kevin Mitchell]

Aww late to the party.

I would only use a bulb if the LFO was a replica of the original Uni Vibe - that way you get the same behavior to the original which is what the LED based easy vibe LFO is trying to do with LEDs. Very similar to the Micro Vibe.

What I mean is - a bulb takes longer to dim than it does to light. This is a signature trait of a Uni Vibe. Even though the bulb is getting a steady sine wave, between the photocells and bulb we get slightly different result.


My favorite Easy Vibe is one with six stages. Lush AF 


Ah I'm rambling. Neat project here!!!
-KM

[Mr Eastwood]

what is the reason for going thru a DAC ?
have you tried driving the bulb by PWM directly ? ...

I guess I just wanted a really smooth waveform without having to worry about filtering, pwm would be interesting though.

I would only use a bulb if the LFO was a replica of the original Uni Vibe - that way you get the same behavior to the original which is what the LED based easy vibe LFO is trying to do with LEDs. Very similar to the Micro Vibe.

yes sawtooth did sound the best to my ears for the leds - that's a nice explanatory pic

[Eb7+9]

pwm would be interesting though.

a couple of things to note when driving analogue parts directly from a digital (pwm) port ... current draw being the first, so a series resistor (trimmer) should be used here - I think 40mA continuous is the limit on an Arduino digital port if I recall correctly ... as far as directly applied voltage goes, the turn-on voltage of, say, an NSL-32 opto-coupler/3mm red LED is around 1.3v and that of a 1.5v/25mA grain of wheat bulb maybe around 1volt ... in a 5-volt system either of these light source choices lead to turn-on voltages (w resistors included) corresponding to duty-cycle values that are far enough away from the beginning zero duty limit, the zipper-noise zone ... in both cases the turn-on threshold forces the system to operate in the more continuous-like part of the digital control range ...

[ElectricDruid]

what is the reason for going thru a DAC ?
have you tried driving the bulb by PWM directly ? ...

I guess I just wanted a really smooth waveform without having to worry about filtering, pwm would be interesting though.

If you use PWM, you *don't* have to filter. The LED/bulb/LDR response will do that for you. PWM gives a more linear relationship between signal and brightness when compared to voltage, especially with LEDs - bulbs I'm not so sure, don't use 19th century tech myself
Just make sure the PWM frequency is fast enough that the LDR response is enough to smooth it and off you go.

[Mr Eastwood]

Hi,   just an update to my circuit / pedal;  i left it for a while then came back it late last year and re-spun the board with some minor changes and then this year I finally got around to soak testing it for 120 hrs and then making a nice case for it to go in.   I was very pleased with the results and look forward to looking at making some other types of pedals.   

[Eb7+9]

Hi,  i'm in the process of building my first pedal which is the Easyvibe ...

"not bad" for your first pedal ...
congrats!