CE2 LFO with "shape" control

[fuzzo]

Hi,

I've built a tremolo with the LFO from the BOSS CE2 , I decided to put a "slope" control like the one presents on the EHX pulsar .

the original CE2 :


and the modified version I made :



(I changed the cap's value on the second AOP to have a faster speed)

The square/triangle LFO drives correctly  the LED but the new "shape" control doesn't have the same impact on the  led  as it acts on the Pulsar . I've put on breadboard that kind of LFO (square/triangle) (but with different values) and they worked good . I cheked and cheked again , my verobaord looks fine .

Do you have any ideas about what I did wrong ? 

[fuzzo]

I've just put again the circuit on breadboard with the "slope" and still non-working .

What could be wrong ? the value of the pot with the diodes ?

[teej212]

awesome! looks great, the CE2 LFO is pretty great for being so simple.

[daverdave]

I'd put the diode symm section before the speed control, and wire it the other way around, with the output of the schmitt trigger going to lug 2 of the symm pot, then lugs 1 and 3 going to either reversed diode. That might do the trick.

[Thomeeque]

Do you have any ideas about what I did wrong ?  

Yes, you have chosen wrong values of used parts. Pulsar's trick is in using differrent value of integrator resistor (made by 1k resistor plus one "half" of SLOPE 100k pot) for ramp-up and ramp-down (diodes do the switching). Value of this resistor varies in Pulsar from 1k to 100k+1k (1:100!). In your schemo it varies from 1k+1M to 1k+100k+1M which makes very small difference (1:1.1). What is important as well is fact, that Pulsar has much stronger square signal at RATE pot's central lug (thanks to very strong V_CC/2 source it can use 1k pot for RATE), so it can use low values. You would have to use much bigger (100-times theoretically) values of "1k" resistors and SLOPE pot (btw. 1M resistor is redundant, "1k" resistors do it's work), which makes all your concept not as easy as it looked at first sight..

T.

But you may try to experiment. What is the biggest linear pot you can get? If it is 10M, use it for SLOPE, 100k instead of 1k rsistors (and jumper for 1M) and you may get close enough. I hope diodes will still work there.. Best would be to copy Pulsar's LFO 1:1 (including V_CC/2 source), that's for sure

[fuzzo]

I'd put the diode symm section before the speed control, and wire it the other way around, with the output of the schmitt trigger going to lug 2 of the symm pot, then lugs 1 and 3 going to either reversed diode. That might do the trick.

I tried with no success .

Yes, you have chosen wrong values of used parts. Pulsar's trick is in using differrent value of integrator resistor (made by 1k resistor plus one "half" of SLOPE 100k pot) for ramp-up and ramp-down (diodes do the switching). Value of this resistor varies in Pulsar from 1k to 100k+1k (1:100!). In your schemo it varies from 1k+1M to 1k+100k+1M which makes very small difference (1:1.1). What is important as well is fact, that Pulsar has much stronger square signal at RATE pot's central lug (thanks to very strong VCC/2 source it can use 1k pot for RATE), so it can use low values. You would have to use much bigger (100-times theoretically) values of "1k" resistors and SLOPE pot (btw. 1M resistor is redundant, "1k" resistors do it's work), which makes all your concept not as easy as it looked at first sight..

thanks for your post and your explaination , actually I've just realized that on my breadboard right now . I switched the parts of my LFO to one from the pulsar, I've just change the cap in the feedback loop (4u7) and the speed with its reistor to V/2 for a 100KL + 47K to get a slower speed  .

now it works good, I thought the values matter for adding that control ,   and your post comfirms  that !

thanks ! 

[Thomeeque]

 Good!

Since I had LCT LTSpice IV model of CE2's LFO already, I did try it - it works


CE2_LFO_w_SLOPE.asc

T.

LTSpice is really great - it is my breadboard (not only) when I'm in work

[fuzzo]

Thanks for you graphic . I'm sure LTSpice could be a great tool but I'm  really patient to take time and learn how use it ( And I tried  )

well I made the exact same LFO on veroboard than the one on my breadboard and this little thing don't want oscillate