Flapjack od

[Marbles]

Hey there!

After trying to build the hotcake, which failed (sounded great, but oscillation on some pickup settings and rolling off volume gave oscillation), I decided to build the Flapjack, since I understood it is very alike.

Unfortunately, didn't turn out that great either. It sounds ok (though not as good as the Hotcake), but there is a funny thing going on with rolling off the volume.

It's like an octaving effect when I roll off the volume. It's subtle at full guitarvolume, but by rolling off it is more pronounced. Like a slightly more more distorted synth like tone. Could be cool, but not for what I want out of it this time ;)


I used a TL071 chip instead of the lm741. Could that be it? Or could it be the fact that there are 2 different TL071 (TL071IP en TL071CP)?


I  measured the following voltages (hope I did it ok):


0.15    0.00
4.66    8.46
2.27    4.65
0.00    0.14


Anyone an idea what could be the problem?


Thanks in advance!

[Marbles]

Forgot to mention, build from this link: http://tagboardeffects.blogspot.nl/2014/09/effdub-flapjack-od.html

Maybe these are a bit better:

[Frank_NH]

I built this a while back (sounded good to me) and posted my experience in the comments.  You need to use an LM741 because this effect relies on op amp clipping.  Per my comments:

Yes, the LM741 is the one to use, and is available in the states at good ol' Radio Shack :)

I should note that this circuit makes use of op amp clipping - no diodes in either the op amp feedback loop or after the op amp output. It sounds good too, and I wonder if this has to do with the LM741 itself.

I would also use an IC socket, which would permit you to audition different chips if you so desired.

[Marbles]

Thanks a lot!

I'll try that. I thought I read that they were both an option. Because I thought the lm471 sounded a bit harsher, I used the other.
I always socket them, but ofcourse this time, I stupidly ordered 50 ic sockets for 6 legs instead of 8 haha.


While on the subject of Flapjack/Crowther... I read somewhere to cure the oscillation of the Hotcake, it helps to put a 68nf cap on the 100r feedback resistor. Worth a shot I thought, but which one is the feedback resistor, and do i just solder it in the same holes s the resistor?

Hope you can find the time to answer!

[Frank_NH]

First, I would definitely check all your connections and solder joints.  I didn't notice any problems with the volume control on mine.

The feedback resistor is 100K and is located to the right of the 10 uF cap (just to the left of the chip).  You can experiment with a cap here, but I would start small (1 nF) and go larger to taste.  You may roll off some highs if it's too large.  You could also experiment with diodes to get some clipping going.  Have fun!

[Marbles]

Thanks!
I'm sorry, I wasn't clear. the volume pot of the pedal isn't a problem, it's the volume pot of the guitar that can't roll off. When I do that, it oscillates. It's like a function of a Dwarftcraft pedal: Play with the volume knob of your guitar and it oscillates.

I changed the IC of the Flapjack and it did improve a bit. But still the same problem as the Hotcake: Rolling of guitar volume gives weid noises/octaving/slight oscillating.

For the knowledge I have now, theyre probably a bit too hard to make it work for me. Maybe if I learn some more I'll try again.

For now, I built a Timmy, cause I was tired of me failing haha. Very happy with it. It works and sounds awesome.

Don't get me wrong, I'm sure it's not the layouts, but I read other people have problems with the circuits, especially the Hotcake. I think those layouts are the ones that need expertise and experience to make them work (instead of the 'paint by numbers'-approach I'm doing now). I guess I'm not at that level yet. Maybe later.

Thanks for your time!

[Frank_NH]

Try this.  If you have a pedal with buffered bypass (any Boss pedal will do) run your guitar into the  pedal's buffer then into the flapjack.  The buffer should isolate the guitar from the flapjack.  If it works, you can make a standalone buffer on a separate vero and wire that to the flapjack's input.  Let me know if that works.