Small Clone Rate debugging

[potul]

Hi all,

It's been a while since my last visit here... I've been dedicated more to digital stuff lately (midi, dsp, etc...), but last month I decided to go back to "analog" setup, so I'm using now my old pedals.

the topic is related to my Small Clone (built from a tonepad PCB)...  It sounds great, but since I built it 2 or more years ago, the rate pot is not behaving as expected. I have it modded with a blinking LED so I can see the rate of the LFO, and during 75% of the pot sweep, nothing happens. Only at the very end the LED starts to blink and the chorus comes up.

First thing I did was verify the pot, suspecting it might be wrong (it's supposed to be 1M Anti-log). But the pot is ok,,... I even desoldered it and measured the pot at different positions... everything fine.
I also verified the values of all resistors in the LFO area and they seem to be good.

Any idea of what can be wrong?....

hint: The rate pot behaves differently when powered with a battery or power supply. When using battery it starts to do something around mid position. With power supply its' more arount 75/80% position. So it seems to be affected by the voltage.

Regards,

Mat

[Cozybuilder]

Just a WAG since you gave almost nothing to go on, but what kind of LED did you use? If its something standard, try replacing it with a low current super bright red, green (or anything but blue), and use a current limiting resistor.

[potul]

Thanks for the suggestion, it's worth to try. I will try as well to remove completely the LED and see if this makes any difference.

Mat

[Scruffie]

What Opamp did you use? The Small clone is picky, should really be a LM358 and not a substitute.

[potul]

I think I used the good one, but I will verify tonight...

[potul]

After some months......

Today I finally fixed the damn thing. I left the Small Clone aside for some time, but this weekend I decided to revamp my pedalboard and paint some of the enclosures of my pedals, including this one. So I said to myself: "You need to take all the guts out anyway, let's try again to fix it".

At last, it was one of the obvious things that could fail, the Tantalum capacitor of 2.2uF had something goofy. I changed it for an electrolytic I had in a drawer and now it works like a charm.

By the way, does someone know if the Tonepad layout asks for a tantalum one for any specific reason? I could not see any difference after changing it for an electrolytic (apart from the fact that now the LFO works as it should)

Regards,

Mat

[mcknib]

Never use them and never will they are supposed to last longer because of the dielectric set up, have better ESR qualities and it is of course smaller than an alu can type from wiki:

Because of its very thin and relatively high permittivity dielectric layer, the tantalum capacitor distinguishes itself from other conventional and electrolytic capacitors in having high capacitance per volume (high volumetric efficiency) and lower weight.

but as far as I know there's no audio performance reason to use them in stompboxes.

[potul]

Great, thanks for the confirmation. I will leave the electo in.

Thanks everyone for all your suggestions during the thread, it really helped me debugging.

Mat

[potul]

In fact.... looking at the tantalum cap, I suspect I reversed the polarity. It has a vertical line, that I assumed it was a "-" (minus sign)... but it might be indeed identifying the positive  leg.

Nevermind... it's working fine with the electrolytic.

[bluebunny]

The vertical line (or dashes) point to a "+" sign, and it's the longer of the two legs:

[potul]

In my cap, there is not visible "+" sign, just a vertical line.
So it looks like I wired it reversed..... Probably that was the issue.

Thanks all for the help. Now I need to work on the artwork....

Mat

[mcknib]

You're a lucky individual then Potul because they have a very high potential to destroy your circuit if put in the wrong way round.....so what's this weeks lottery numbers then? haha