Small Clone LFO: Help needed

[Gringo]

Last night i finished a small clone using tonepad's layout & pcb. I built it with the depth mod from start, every ic and transistor socketed. I have audio through, the bias trimpot works, i can hear some chorus going on, which becomes more noticeable when i turn the depth pot.

The thing is that the rate pot has no effect whatsoever. After checking the pot itself, the wiring, solder bridges, misoriented caps/transistors, ics, component values, etc, i began audio probing the 4047 and its whereabouts, and could not find a trace of the lfo "tick".

I don't have a lm358, but i supposed any standard dual op amp would sub ok (wouldn't it?). Fist try was with a 4558. I also used an 2.2uF electro for the tant 2.2uf: should i swap it for a tant or is it ok?

After some searching, i found a an old post with a similar problem, which turned out to be a solder bridge (lucky bastard ). Rechecked the traces again, nothing i can see.

I measured the pins from the 4047 and the 4558 (also tried with a tl072 and a 4559 i had around, same thing), and here i am:

Ic2:

1 1.39
2 7.35
3 3.71
4 0.0
5 2.5
6 2.07
7 8.11
8 8.73

cd4047:

1 8.02
2 0.04
3 6.7
4 8.1
5 8.1
6 8.1
7 0.0
8 0.0
9 0.0
10 4.04
11 4.04
12 0.0
13 8.04
14 8.1

I'm using my regulated ps which gives 9.1v (i tried first with a fresh battery, works just the same).

I'll keep debuggin, any advice will be greatly appreciated

[Gringo]

Anyone?

[gez]

I can't say I'll be able to help, but could you post the schematic?  (others will chip in).  It takes time to search around the internet looking for these things, and it puts people off replying.  No offense intended (hope you get it going).  

[gez]

I don't have a lm358, but i supposed any standard dual op amp would sub ok (wouldn't it?).

No it wouldn't.  Many op-amps won't work configured as this type of oscillator.  What did you use?


PDF here:

http://www.tonepad.com/getFile.asp?id=8

There's guilt for you!  

[Gringo]

I can't say I'll be able to help, but could you post the schematic? (others will chip in). It takes time to search around the internet looking for these things, and it puts people off replying.

Guilty as charged :oops:

Been at it all day yesterday, hoping it was a simple mistake, to no avail.
Tomorrow i'll try to get a lm358 at the local store (wish me luck).

I measured the pins from the 4047 and the 4558 (also tried with a tl072 and a 4559 i had around, same thing), and here i am:

I also tried with a lf353, didn't work either. Are there any known subs for this particular opamp in this particular application?

Thanks in advance!

[gez]

I also tried with a lf353, didn't work either. Are there any known subs for this particular opamp in this particular application?

Hi Gringo.  The amps I use for this type of oscillator seem to be a little obscure outside of the UK (ICL7621).  

I've looked through a few schematics and the 1458 is used quite often (though I haven't used it).  In a text book I have the shematic calls for a TL072, but I've never been able to get this type of oscillator to work with that chip! (maybe it's the brand, who knows?).  If you look through some schematics for other chorus and phaser pedals, you should eventually come across a few with this type of LFO, see what they use.

Sorry I can't be much more help, good luck with your search for the correct chip.

[Gringo]

Well, i put a lm358 and fired right away I wonder what's so special about this dual opamp.

Now, the mods :twisted:

[gez]

Well, i put a lm358 and fired right away I wonder what's so special about this dual opamp

Many op-amps don't like to have their inputs pulled anywhere near the rails and won't operate properly when this occurs (some can even be damaged).  This is why a lot of chips don't work when wired up as this type of LFO

Glad you got it working in the end.

[puretube]

Well, i put ...

Many op-amps don't like to have their inputs pulled anywhere near the rails and won't operate properly when this occurs....

Glad you got it working in the end.

that`s why I love my good ole cheapo LM324s...

now on with vacation....

[Brian Marshall]

i tried making LFO's with TI tl072's .... i never had much luck.

the problem wasnt latching though.... it was nonlinearity.

i think the problem i may have had was that i was loading it down, but still not sure.... illhave to have another look at it.....

and maybe try some 358's

[gez]

i tried making LFO's with TI tl072's .... i never had much luck.

the problem wasnt latching though.... it was nonlinearity.

i think the problem i may have had was that i was loading it down, but still not sure.... illhave to have another look at it.....

The non-linearity was probably due to the asymmetry of the output swing.  This is why I use CMOS chips or CMOS inverters for this circuit as the rail-to-rail output swing ensures an equal charge/discharge time as the +ve & -ve voltages presented to the integrator, with respect to its input, are of equal magnitude .  Also means that the formula given for frequency calculation is more accurate as it's calculated upon the assumption that output swing is ideal.

Some TL072s must work in this circuit as I've seen schematics with them.  I think a lot of it depends upon the type of input protection circuitry (or lack of it?) used by the manufacturer, either that or you need to keep the amplitude small?