Using LFO from tremolo for other FX, while using tremolo?

[D Wagner]

If I use the LFO from the tremolo below to modulate another effect, will there be any negative impact on either effect?  Should I "tie" into the LFO before or after the 0.47uf cap at the LED?  (Above Q3)

Here is the schematic that I am looking at
http://www.runoffgroove.com/eatremolo.html

Thanks,

Derek

[gez]

If I use the LFO from the tremolo below to modulate another effect, will there be any negative impact on either effect?

Whatever you use to do the modulation (FET etc) should have high input impedance otherwise there's a danger of loading down the LFO output which will stop oscillation.  If you do things right then it's not a problem.

How the other effect is affected depends on what it is and how you do the modulation.  What effect will get the treatment and how do you intend to do this?  

[D Wagner]

Whatever you use to do the modulation (FET etc) should have high input impedance otherwise there's a danger of loading down the LFO output which will stop oscillation. If you do things right then it's not a problem.

How the other effect is affected depends on what it is and how you do the modulation.  What effect will get the treatment and how do you intend to do this?  

Thanks for the info Gez,

The tremolo will modulate a tone generated from a 555 circuit.  I want the LFO to do double duty as the LFO for a synth, as well as the tremolo.  

I am going to breadboard the circuit tonight or tomorrow, so I guess I'll have a concrete answer then.  

The tremolos that I hacked last night had a LOT of bleedthrough using a dual opamp LFO (square and triangle waves). The impedance issue you mentioned could have something to do with it.  I had the LFO stop a few times as I was playing around.

Back to the breadboards!

Derek

[gez]

You might be able to put the LED in the EA's LFO to good use and use it to turn on a LDR, this would avoid loading.  Haven't tried the LED mod so I don't know how well this would work out in practise (might be a bit clunky - how smoothly does the LED 'blink'?).

Rather than use a 555, the oscillator in a 4046 chip, wired up as a VCO, might be a better way to go for what you want to do.  The control voltage input is high impedance and would avoid loading the EA's LFO.

[puretube]

there are a lot of issues, concerning "bleedthrough",
and a lot has been said on this board about it....
try a search on "declicking"

[gez]

PT is right, try debugging the two op-amp set up.  It'll be better if you intend to use it for synth etc (larger and more linear range, fixed amplitude, less prone to loading etc).  I still think the 4046 is worth a shot though.

[puretube]

ooops, gez & me were crossing  

I assist his meaning, that a 4046-thing might be better than a 555-thing.

the latter loves to cause spikes on the power-rail, which love to spread and bleed through anything....

(which initself is a different animal than the comparator/schmitt-trigger LFO bleedthrough...)

:?:

[mikeb]

Yes - only use a CMOS 555, the renowned current 'spike' is much less on these babies. Also, if you look here:
http://commonsound.com/triwave/triwavescheme.pdf
... you'll see a cap / diode arrangement on the ground pin for the 555s that assists greatly in reducing the current 'spike'.

HTH

Mike

[gez]

I was thinking more in terms of the high input impedance of the 4046 not loading down the simple phase-shift LFO of the EA if you decide to go with it.  

Seeing as the 555 is oscillating in the audio range it doesn't make much difference whether you use this or a 4046 (I'm assuming your 555 is CMOS), just that the latter is a better chip/simpler circuit to do the job of a VCO in my opinion.

Although pin 5 (control) can be used to convert a 555 into a simple VCO, it isn't very effective in my experience.  The 4046 does a better job, so if you were wanting to modulate a tone it would give better results (better range), or just a simpler circuit if you were intending to use a FET or something as a variable resistor in a 555 circuit.

I'm assuming the bleedthrough was ticking from the dual op-amp LFO, in which case it's probably stray capacitance - pay careful attention to layout!.