Sharkfin problem

[giantrobot]

Hi Guys! I just finished my Sharkfin build and I have an issue. The sample/hold mode works fine and sounds awesome but I can't get the filter mode to sweep. I get cocked wah sound but no auto wah. The only sub I made was Bat41s instead of Bat46s. Can anyone point me where to start poking around? Any help would be much appreciated.

Thanks

[fair.child]

Hi Guys! I just finished my Sharkfin build and I have an issue. The sample/hold mode works fine and sounds awesome but I can't get the filter mode to sweep. I get cocked wah sound but no auto wah. The only sub I made was Bat41s instead of Bat46s. Can anyone point me where to start poking around? Any help would be much appreciated.

Thanks

Have you tried to debug it ? Yours are really good if it works, mine it seems not work at all, still confuse with the wiring. Maybe some pictures will help to find out the problem

[giantrobot]

Hey ya'll! I finally got back around to trying to get this thing working. I tried swapping out the ICs and diodes plus a handful of caps & resistor and I'm still not getting anything out of the filter side. The sample hold side works great and sounds killer. Anybody have any ideas?

[icecycle66]

Unless someone has hit this specific problem already, we (they, not me) will probably need a little more information.

Do you have experience using an audio probe?
An audio probe and about an hour of tracing should be able to tell you exactly where it is the sound is dying.

[giantrobot]

Thanks! I'm getting a signal in filter mode but it's not quacking like in the demo I've seen. It's more of a notched wah sound. Should I still probe it even though I'm getting signal?

[giantrobot]

So I got a new Sharkfin pcb and tried this again and have the exact same problem. I double checked all values before soldering. The only thing I used from the old board was the charge pump and the 2 CA3080s. The only thing I can think of is the J201s I got from Tayda. I just saw the thread stating a lot of these are fake. Could this be causing this problem? Would the Sample/Hold still work if so?

I've built several projects but this one by far is the biggest pain. Any help would be very much appreciated.

[jivedanson]

So I got a new Sharkfin pcb and tried this again and have the exact same problem. I double checked all values before soldering. The only thing I used from the old board was the charge pump and the 2 CA3080s. The only thing I can think of is the J201s I got from Tayda. I just saw the thread stating a lot of these are fake. Could this be causing this problem? Would the Sample/Hold still work if so?

I've built several projects but this one by far is the biggest pain. Any help would be very much appreciated.

In fact, I am having this exact same issue.  Mine Sample/Holds like a champ with a full range of tone, but the Filter mode is just a cocked wah.  It quacks a bit, but only with ear-shrieking treble, no matter how you dial in the controls.  So, not so good.

Does anyone know what voltage readings I should be seeing in T1 and T2?  Are there specific parts to the Filter section of the schematic I should be scrutinizing?   Not quite confident enough in my skills with this one, alas.

[Cortexturizer]

Look at this topic guys
http://www.madbeanpedals.com/forum/index.php?topic=12486.msg113288#msg113288

I had the opposite problem with mine, too much sweep and the problem was the peculiar relationship of type and strength of pickups with one of the resistors involved [you'll find it in the topic] That changed everything for me. Try that first. Also, I could get what you're describing by flipping one of the transistors the wrong way, so that also might be something you have done. Try it.

Hope you guys resolve your problems quickly, it's a very nice circuit.

[madbean]

The entire envelope section goes from the Filter pot to R20, so that is where you should focus your debugging efforts (assuming it is working in sample/hold mode). R21 and everything else on the right side of the schem is the Sample/Hold area.

I'm not aware that Q2 needs to be withing a certain Vgs spec, but it won't hurt to swap in a J201 from a different batch if you have one.

----------------------------
I just noticed a difference in the Tonepad and GGG versions: C6 pulls to +9v in the GGG and ground in the Tonepad. The Sharkfin has it going to ground which is what I prototyped without issue. It is probably more ideal to have a non-polarized cap with it going to ground.

If you can desolder easily, try removing C6 then temporarily run a wire from the round pad to your breadboard. Then connect a 4u7 polarized cap with the negative end to the wire and the positive end to +9v to see if it corrects your problem. I can try this on my build too to see if there is any difference (I may have already done this when I prototyped it but I honestly don't remember) but probably not until tomorrow.

[jivedanson]

If you can desolder easily, try removing C6 then temporarily run a wire from the round pad to your breadboard. Then connect a 4u7 polarized cap with the negative end to the wire and the positive end to +9v to see if it corrects your problem. I can try this on my build too to see if there is any difference (I may have already done this when I prototyped it but I honestly don't remember) but probably not until tomorrow.

Thank you for the suggestion!  Unfortunately, no difference either way--sounds the same +9v as into ground.  Also swapped out the J201 in Q2 w/ no change.  Everything else seems to check out: transistor values & positions, resistor/cap values, no cuts or cold solders, etc. etc.

Is it possible to be tripped up by the CA3080 ICs?  I've heard tell of how cheap eBay purchases of this chip have led other builders into trouble w/ other projects.  (Guess where I got mine?)  Or is that just paranoia? 

[giantrobot]

This thing drove me crazy. I tried to build it two times. Then one day I was pokin around at it and disconnected wire 8 from the mode switch and it started working fine. I'm not to sure why but it worked for me. It's worth a try

[jivedanson]

This thing drove me crazy. I tried to build it two times. Then one day I was pokin around at it and disconnected wire 8 from the mode switch and it started working fine. I'm not to sure why but it worked for me. It's worth a try

Didn't work for me, unfortunately.

Shelving this for now.  Bought some CA3080s from Smallbear to swap in for the cheap eBay ones, will see if it solves the issue.  After that... well, best not to dwell on it.  Haha.

Either way, appreciate the assistance from all--thanks!

[jivedanson]

Update: working.  It always ends up being something dumb.  R21 was 100K, not 1M like it should have been.  Missed it during my first part check pass.  Works like a champ now. 

Next stop: partyin' on the Mothership.  WHEEE