'LIGHTWAH'

deadastronaut · April 28, 2011, 05:21:18 AM

hi guys,

is it possible to get an lfo out of one side of a tl072...?

so the wah is out of the one side?.and the lfo is out the other side.....or do i absolutely need a whole tl072 for lfo?....hmmm....

~arph · April 28, 2011, 05:32:37 AM

You can try to make a single op amp phase shift oscillator (PSO) never seen one with opamps though. But if it works with a transistor it might also work with an opamp. Look for the heartthrob tremolo, or the schaller tremolo. Or one of frequency centrals tube tremolo/panners. There are some PSO oscillators there.

deadastronaut · April 28, 2011, 05:57:08 AM

cheers!... the hearthrob sounds good....

aha, found this...one of ricks...figure 1. is a 1 op amp lfo...i'll give it a try n see...

http://circuitworkshop.com/forum/index.php?topic=215.0

~arph · April 28, 2011, 06:06:37 AM

Be aware that it can't drive an LED directly, you need a transitor or fet as in one of the other LFO's you tried.

deadastronaut · April 28, 2011, 06:11:04 AM

right...ok...hmmm..

looks like i'll have to add that on the end then...cheers.

will this lfo be too choppy do you think?...(it says its from the phaze 45...whch is quite smooth)

or should i just go with the phozer lfo?..that seems quite smooth up n down...

~arph · April 28, 2011, 06:21:31 AM

It's your pick

deadastronaut · April 28, 2011, 06:30:06 AM

yeah right...

i'll try this simple 1 op version first....could be what i'm after...it''ll make things more compact too...

deadastronaut · April 28, 2011, 07:13:36 AM

ok got it going...but its way too fast..

i changed c2 to a 470uf..still fast... $:-\$

edit:

ok got it going slow...but now it wont go fast and no real control on the pot....hmmm...

frequencycentral · April 28, 2011, 10:56:46 AM

The Tone God's Bullitt uses a single opamp PSO: http://tech.thetonegod.com/bullitt/bullitt.html It uses a second opamp for buffered vref, but would probably work just as well (?) with just a voltage divider plus cap vref.

~arph · April 28, 2011, 11:12:34 AM

Ha cool, so I have seen one before..

deadastronaut · April 28, 2011, 11:24:58 AM

aha.cheers rick....so im guessing i'm looking at the lower left section of that...then adding the 2n3904 and led onto it..

: the earlier lfo is working much better now..btw!..

frequencycentral · April 28, 2011, 11:34:23 AM

Quote from: deadastronaut on April 28, 2011, 11:24:58 AM
aha.cheers rick....so im guessing i'm looking at the lower left section of that...then adding the 2n3904 and led onto it..

Yup, the C3/C4/C5 part. PSO's can be identified by the three caps. You'll see PSO's made using a tube (usually 12AX7 IIR) in old tremolo tube amps, though they have to be high voltage to work in that case. You can also make PSO's using a transistor or opamp. The three caps need to be non-polarised as I understand it, though TTG's labelling doesn't make that clear. The three caps don't all need to be the same value, you can tweak values to alter the range. I'm guessing that the opamp PSO might well run a LED without having to use a 2n3904 to buffer it. But do let me know either way.....

deadastronaut · April 28, 2011, 11:39:50 AM

cheers man...

i'll crack on with it...much appreciated..i'll break out my other breadboard...

btw, just changed the led in that other lfo from an orange to a blue (brights) even better...

i'll keep you posted!..

deadastronaut · April 28, 2011, 12:18:12 PM

ok , i'm a little confused...

do i take the voltage divider off the other op amp and connect it to this?...and how?...or use it as is?...without it?..

frequencycentral · April 28, 2011, 01:03:13 PM

deadastronaut · April 28, 2011, 01:07:20 PM

awww nice one..cheers rick your a diamond.

i'll give it a go!. thanks man.

deadastronaut · April 30, 2011, 08:42:35 PM

hmmm tried the pso isnt doing anything, just lights up....

tried different variations of caps... $:-\$

frequencycentral · May 01, 2011, 05:23:00 AM

Hmm, did you try both polarised and non-polarised caps? It could be that the LED is stopping the LFO working if hooked up directly, so you might need that 2n3904 after all. Or an opamp unity gain buffer. It's also worth trying the opamp buffered vref TTG used in the original schematic, or alternatively try different values for the resistors in the passive vref. When trying to design something to work with a minimum amount of parts it's often best to use a maximum amount of parts first to get the circuit working. Then take stuff away and see what happens. You'll learn what's essential and what's not.

deadastronaut · May 01, 2011, 05:31:17 AM

cheers rick, yep tried different caps (polar) etc, i did try the 2n3904 out of curiosity,

one thing i noticed was when i took the 9v off the ic the led had a wobble to it then faded...so it looks like its trying

to oscillate, bu not quite there... i was up till 3 in the morning trying to get the bugger working...

i'll give it another crack today with your suggestions... cheers rob.

frequencycentral · May 01, 2011, 05:35:09 AM

BTW, are you wedded to using the LED/LDR? I assume what you're after here is a dual opamp swept twin t filter, one half of the opamp an LFO, the other half the filter? You should be able to do this with a BJT or possibly a FET in place of the LED/LDR. Hvae a look at how the Dr.Q/Nurse Quacky implements env control of it's filter using a BJT - maybe you could try similar, but using the P45 type LFO?

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