Wonky Wheels

[Kipper4]

Guy I've been having one of my brain waves.

Could I wobble the lfo with a variable cap and um sneak some ldrs in place of pot 1 ?




What problems might I run into please ?

I really hope my wheels don't drop off.

[antonis]

Rich, plz get some rest... 

(you're in a potentially dangerous mind-trouble if you contemplate cannibalizing antenna tuners overnight..) 

[EBK]

Variable caps are usually in the pF range, right?

Edit: It is very possible that I misunderstood the question.....  I think you may be asking if C1, C2, and POT1 can together act like a variable cap.  Is that right?

[GibsonGM]

Variable caps are usually in the pF range, right?

Because of this, you might get a variable LFO but wouldn't be able to hear the frequency change as it would be so slight (?)

[EBK]

Variable caps are usually in the pF range, right?

Because of this, you might get a variable LFO but wouldn't be able to hear the frequency change as it would be so slight (?)

Edit: Ignore all of this if I misunderstood the original question.

Or, perhaps you can throw in a few more parts...
http://www.radio-electronics.com/info/circuits/transistor/capacitance-multiplier-circuit.php
I'm always in favor of adding more parts for the sake of academic enrichment, but the results are not always the most elegant or efficient solutions for a particular problem.  Depends on what your goals and priorities are.  I'd personally go for it, but only if I already had a variable cap in my parts bin and I wasn't aiming to produce something for eventual commercial sale.

Note that with an op amp capacitance multiplier, you could turn an LDR into a variable cap.  Just sayin'.    (again, not a serious suggestion, but it does sound like fun.)

[duck_arse]

Rich, plz get some rest... 

(you're in a potentially dangerous mind-trouble if you contemplate cannibalizing antenna tuners overnight..) 

probably no, if you are thinking "fuzzface input cap blend". why wouldn't you just add some range-switched (fixed value) caps, and then sling yer ldr across the SPEED pot// R23?

[anotherjim]

I think Rich was seeing C1 via the pot across C2 as a variable cap. Then I think the values shown should be reversed? 100nF to 101nF isn't doing much

...but, in the LFO, this is setting amplitude. Done by varying the reference DC back to the op-amp -in so the Schmitt trigger thresholds can be varied. I'm not sure what capacitive coupling of that will achieve.

[Kipper4]

Well the original lfo had a 10nf cap for C1 I cannibalised mine cause I realised with the help of the cro that the output wave was less triangle and more sine shaped.
Duck didn't like this at all IIRC.

So my thinking was that if I was to pan between the two caps with a pot or ldr and series resistors that the wave would sort of make a shape that was sometimes more triangle than sine and vice versa. To make a phaser sound more like a rotary cab than a plain phase..

So what do we think now?

I got the idea from looking at lfo with a glide feature and a thread I was reading here.
Later on I'll post a link.

I'm a hungry man right now and the chippy is about to open.
Soon come.

Rich

[anotherjim]

...if I was to pan between the two caps with a pot or ldr

Ah, then pot1 wiper to pin 8 and each cap at the pot ends, yes?

[Kipper4]

lfo with glide

http://www.cgs.synth.net/modules/psycho_lfo.html

swing and sway thread

http://www.diystompboxes.com/smfforum/index.php?topic=20237.0

[Kipper4]

I think this is an lfo with glide

http://youtu.be/Guvc03nBd_k

[duck_arse]

didn't like? you know my taste is in my name, kipper.

IIRC, the 10nF cap was on a single oppy osc, to help round-off the triangle peaks, in an effort to prevent the dreaded tix. and yes, as A.J. says, no, and you've got the caps that won't work in the wrong spots.

[Kipper4]

Any suggestions as to what cap values would work please.
If this is not worth it (variable caps) what else is worth the punt.

I might have to investigate further the glide in ken stones lfo drawings.

[pinkjimiphoton]

rich,
hell yah it should be doable. you can replace any pot with an ldr, but if ya want other than a variable resistance, get a center tapped one or use a vactrol..

a variable resistance is a variable resistance. to fake a variable cap you need a center tapped ldr tho. hook one cap to one side, the other to the other, join their unused sides as your input and the center tap to the output.

thinking about it tho, you could likely just stick one cap on each side of an ldr and just let the resistance change act like a pot

i think i'm gonna sit and make some popcorn, i love watching rich's mind implode...

that said, no reason why you can't use an ldr. a variable resistance is a variable resistance. i think ...

[deadastronaut]

god knows what this dude is doing, no schemo etc...but it does change the nf range..

https://www.youtube.com/watch?v=cohCRhIcd3k


he can nibble sweetcorn through a fence too..

[Kipper4]

Haha thanks guys.

The corn is nearly ready to crop here.

I'll get around to breadboarding some soon, IF the chips get here.

[EBK]

I'm going to start putting "stabilitrons" in everything I build just so I can start casually throwing that word around.