Geo parapedal project op-amp

[numpty]

What is the recommended op-amp for this project please?

[Paul Marossy]

You can use a pair of any low noise dual opamps - TL072, NE5532, etc.

[numpty]

Thanks for that Paul, the next question is: what is the capacitance of C3? as I have just noticed that it doesn't appear on the layout, neither does the type of diode which is D1.

[Paul Marossy]

The exact value of C3 is still unknown, AFAIK. I used a 0.01uF cap in mine based on something I remember being told about (by RG, I think). It's been a while since I built it.

D1 is just a polarity protection diode. A 1N4148 or 1N4001 could be used for that.

[numpty]

Thanks, I'll try that then, BTW were you happy with the results?

[Paul Marossy]

Thanks, I'll try that then, BTW were you happy with the results?

Yeah, I think it sounds great. I need to break it out and start using it again.

[numpty]

my next build then!

[Paul Marossy]

Cool, good luck! 

[danielzink]

Funny - I just finished one of these up re: RG's layout - I think I even PM'd Paul about some values - I used a .01 for C3 and 4558's





Dan

[joegagan]

beautiful! in and out. 

not too sure how that dual gang will hold up, please let us know.

[Paul Marossy]

beautiful! in and out. 

not too sure how that dual gang will hold up, please let us know.

+1

[numpty]

This might seem an obvious question but are the cap values in nanofarads on RG's schematic, as I noticed that the C1 is 10n on the posted interior photo of the PCB but 103 on the schematic?

[MarcoMike]

the dual pot should work... I made an expression pedal with one of those and it works great, for almost 1 year now.

numpty, 103 is the "secret code" for capacitors. means 10x10^3 pF, which is 10n
many caps are marked that way... it took me ages to understand them... I was never sure (maybe even now, I am wrong... )

I really would like to build this pedal as well...

[danielzink]

beautiful! in and out. 

not too sure how that dual gang will hold up, please let us know.

+1

It's actually the same pot that Chicago Iron uses in their Parapedal kits. I bought one of those kits ages ago and did something silly to the pot (can't quite remember what....probably hysterical memory loss......          ) - anyhow - I called them and they were like "just run up to Radio Shack and get a blah-blah-blah pot......it's what we use...."

Dan

[flintstoned]

I need one of those -blah-blah pots! Radio crack? Hows that pinion stay on? Flat sided pot?

[numpty]

The capacitor  has a capacitance of 103 (10 x 1000 pF = 0.01 µF). So C5 is 0.1uf . It's little a bit confusing though, you might expect to see this printed on a cap but not normally in a schematic. I usually test small caps to be sure.

[danielzink]

I need one of those -blah-blah pots! Radio crack? Hows that pinion stay on? Flat sided pot?

Yup Radio Shack - if you go into the store I think it's the only dual gang they carry - 100k maybe ? (can't quite remember).

The pinion gear is the "standard" flatted circle gear. I  carefully dremeled out most of the flat so that there was still a bit of flat and was a good press fit on the shaft (that's what she said.....)

Dan

[joegagan]

oh, ok , i recall that part being for sale at radio shack, it was stocked as a fader for stereo speakers if i recall correctly. i have a few of those laying around.

the newest radio shacks that have opened here do not have any electronic parts. they are closing the old ones gradually and replacing them.

[Paul Marossy]

the newest radio shacks that have opened here do not have any electronic parts. they are closing the old ones gradually and replacing them.

Yeah, I don't even bother with them anymore. Only for special circumstances will I go to a RadioShack these days.

Anyway, those dual pots will last a while. But you'll have to replace them once in a while if you use your pedal a lot. They won't last like one of those Dunlop "Hot Potz II" pots will.

[numpty]

Are those pots linear?