Problem with my new echo base

[lerxst88]

SUPER COOL PEDAL first of all!!! 

I am having some issues with the LFO section. when I switch it on or off (cant really tell), it gradually shifts the delay time up or down (depending on the direction of the switch) so it sounds like the modulation works for a second (and sounds AMAZING!!!) but then it comes to an equilibrium delay time and there is no modulation.

Also Im not quite getting runaway repeats with the feedback maxxed. i know I can jumper a resistor to get it to self oscilate but Id rather put in a resistor so it will self oscillate when maxxed and ONLY when maxxed, meaning any other setting the delays will die off eventually.


Thanks guys!!!

[lerxst88]

Update!!!

I noticed that when disconnecting the LFO switch pads the status LED gets much dimmer, and when connected the LED is proper brightness

a clue?

[Taylor]

Is this on my PCB?

I just simulated the LFO in Falstad's simulator, and went through and deleted parts until I could replicate your problem. The only thing that worked (in that it properly broke the oscillator) was disconnecting the 680k resistor to the left of pin 1 of the TL072. All other deletions killed the modulation, but did not act differently whether the LFO SW was engaged or not. But removing this 680k stopped oscillation and  went to a negative voltage in one position of the LFO SW, and then ramped up to a positive value when the switch was the other way.

So check out that resistor and see if you've got it soldered properly. Even if you're not using my board it's the only 680k on the board so you should be able to find it easily.

[lerxst88]

Thanks a ton Taylor! Ill check it out!

[slacker]

Nice bit of virtual debugging Taylor   Flipping the switch would then alternately charge and discharge the 10uF cap causing the temporary modulation effect.
A short across the 1M5 resistor would do the same thing.

To answer the other question, to get runaway repeats you just need to play with the value of the resistor connected to the wiper of the Feedback pot, if you're using Taylor's layout his documentation shows which resistor this is, otherwise just trace from the wiper until you come to a resistor. With the stock values it should already do runaway repeats, unless you've done the "humbucker mod", in which case you may need to reduce the value a bit. To get runaway feedback only with the pot on max you'll need to experiment with the value, it might not be possible to get it to do that though, you might have to compromise and have it do runaway feedback only above 90% or so.