Lowrider - Clean Signal Good, Octave Downs are sporadic, Upper is questionable

[hardstatic]

Hi all,

I just got my Lowrider put together and am having some issues.  The clean is spot on, upper just sounds like a dirtier version of the clean, and both of the lower octaves are simply acting very strange - as if they are quickly turning on and off.  I was very careful during assembly with resistor and cap values (or perhaps not!).  I did not do the C10/C12 modification and I used 2n5457's instead of the 2SK30's.  I have a few ideas as to what could be wrong:

1.  The 100K trimpot was absent from my stash so I used a 500K temporarily - I wouldn't think this would cause a whole lot of problems if it was dialed way down, but i'm not totally sure and I believe the trimpot only affects the octave up, correct?
2.  Capacitor polarity - I only had electrolytic caps at 1microFarad.  I checked the schematic and tried to figure out the polarity for these during assembly (bit new at this).  In particular C3, C14, and C18.  If we look at the PCB layout diagram in the PDF file, I have C3 with the positive facing down, C14 with the positive facing left, and C18 with the positive facing left.  My feeling is one or all of these may be incorrectly polarized.
3.  IC's - I order IC's from Tayda and they all have slightly different things appended to the chip type:  My TL072 is designated "TL072CN".  My LM324 is designated "LM324N".  My CD4013 is designated "CD4013BE".  And my TL074 is designated "TL074CN". 

I am currently going through every resistor to verify the correct values (after reading another user's post regarding incorrectly labeled resistors), and I am verifying all caps as well.  The other issue I am having seems to be a grounding problem with the metal 9VDC jack I am using.  Everything powers correctly when it's not touching the box; however, when I attach the jack to the box things get wonky... plus i'm short the 9V battery adapter, but I wouldn't think that would cause a grounding problem?

Of course I boxed it before testing!  Here are some pictures as it currently rests:

[hardstatic]

I just tediously double checked all resistors and caps, everything looks correct.  I'm leaning towards the cap polarity on C3, C14, and C18...

[alanp]

You've got C3, C14, and C18 populated by electrolytics. The schematic shows them as non-polarised, and the silkscreen on the PCB shows that a polyester film box type was probably intended there. Polarised capacitors, like electrolytics, have one of the bars drawn hollow on the schematic to show the positive side, and nonpolar just have two straight bars.

Don't know how much difference that makes, but that's what I noticed.

[Vintageman]

Hello

When you say that the lower octaves are turning on and off...Did you noticed this behaviour playing open strings?

The Low Rider isn't perfect, this behaviour that you're experiencing, playing open strings is more or less common in this circuit (I think that the bug has to be in the circuit). I've read about it, I don't remember where, and my own Low rider has the issue. I haven't found a solution for this issue. I think that maybe the problem is caused by the CD4013, that is confusing the main tone with the first harmonic, I don't really know, but it makes sense, given the fact that the open string has the strongest first harmonic.

Play the same riff in the fifth fret, if the problem disappears, don't worry no more about it.

About the gain and fuzziness of the upper octave, you can tweak it to your own taste, playing with the values of C10 and C12, I did this mod and works really fine.

[hardstatic]

Thanks Vintageman, I think you are right.  I replaced the electrolytic caps with non-polarized and it made no difference in the behavior (go me for reading the schematic right!).  I went ahead and boxed it up, replaced the DC jack with the typical plastic one (I figured out the metal was grounding the whole thing out, being center negative and all), and gave it to my bass player.  It seems to work quite well and she is happy with it, as long as she doesn't play multiple notes at the same time!