SHO Help

[spfautz]

Building this SHO clone based on http://tagboardeffects.blogspot.com/2010/07/zvex-super-hard-on-updated-version.html

I've got a problem with my build. I've got signal passing through the circuit, and the crackle is indeed OK. When my pot is fully clockwise (all the way up) I get a boosted, some added dirt, signal that sounds pretty good. When the knob is turned back down (counter-clockwise), I get an aweful squelch, feedback, oscillation even, type sound. This isnt the crackle from the pot, its continuous.

I dont currently have an LED connected, but I didnt think this could cause this.

Any thoughts?

[Jazznoise]

It's not the LED. Mine is without one, stock on vero with a BS170 as the transistor.

Is your wiring shielded? And can you post the layout/schematic you worked from? Does any signal come through when it's oscillating?

[timd]

Did you build on Vero? Could you take some pictures of the underside of the board? Sometimes accidental connections are made with solder. These solder bridges can do weird things in a circuit.

[spfautz]

Here is the layout I'm using.



Wiring is shielded.
There is some underlying signal beneath the oscillation.

[spfautz]

Here is an under pic.  its a little out of focus.



I used a probe to trace the signal all the way to the output.

[Arcane Analog]

Are you sure you have sheilded wire? Your wiring might way be too long and 'spaghetti' for that small box without sheilded wiring.

[timd]

Are you sure you have sheilded wire? Your wiring might way be too long and 'spaghetti' for that small box without sheilded wiring.

Could be. The build itself looks good.

[spfautz]

This is the wire.  The box is tight, but I've been doing all of the testing without packing it in yet so I know the components aren't inadvertently touching something.


http://www.mammothelectronics.com/CHANDLER-CHND-100-2407-p/1100-600-1.htm

[Arcane Analog]

That's not sheilded wire.

Spaghetti and long leads can cause problems when wires cross over each other. I think that was what was in mind when the sheilded wire question was mentioned above.

[timd]

I should have worded that differently. I meant to say that the veroboard itself looked good from a solder standpoint and I can't see anything wrong there.

[spfautz]

Not shielded good to know.  I've made lots of projects with this wire though. Is there something about this circuit that would make it more prone to this problem?  If this was the culprit, would I be noticing Chang in the sound as I move wires apart?  And why does it only happen when the pot is partially closed?

[Arcane Analog]

Not shielded good to know.  I've made lots of projects with this wire though. Is there something about this circuit that would make it more prone to this problem?  If this was the culprit, would I be noticing Chang in the sound as I move wires apart?  And why does it only happen when the pot is partially closed?

Yes. Move the wires about to see if there are any changes.

[Eric.nail]

I'v used this layout many times. Ran into problems only in my own faulty wiring. Never used shielded wire either...so i don't think your wire's the problem. Try shooting an image of the topside of the board. The other thing is it might be the transistor. I'v had weird things happen with those transistors...Or the cap. You could always swap the cap too.

[timd]

And why does it only happen when the pot is partially closed?

The circuit is affected "negatively" by that resistance area. You could measure that on a multimeter to see exactly where on the 5K pot the problem arises. You could look into the shielded wire idea, or look into building another SHO veroboard of you have the parts. Then solder the old board and solder in the new one. This will tell you if the problem is the vero or the wires.

[spfautz]

I just checked again, couldn't get any change to happen when wiggling wires around.  I measured the pot with a multi-meter.  The problem appears to be gone when the pot is wide open, with no resistance.  When any resistance is added (turning the knob down) I'm getting the feedback, and the feedback escalates from almost fuzz like oscilation at first, to full buzz feedback when turned all the way down. 

The circuit has the pot changing the resistance between ground and the source pin of the transistor.  Tomorrow, I'm going to try and re-do all of my ground connections.  Any other suggestions?  Does it make sense that based on what I've said the problem lies somewhere within the ground circuit?

[timd]

Is the transistor in the right way?

[ode2no1]

i actually had the same problem recently with a SHO build that was working perfectly fine until i finally got the correct taper 5K pot in there. i was getting this weird oscillation with the pot turned down. are you getting this problem with a battery or a power supply? i had mine connected to an electro-harmonix 9v power supply at home when i got the oscillation, but when i took it to my rehearsal studio and used it with a one-spot it was fine. i figure it's probably the wiring in my apartment, which was built in 1960 that was causing the problem. it seems like a one-spot, which was daisy chained to 8 pedals would be more of a problem that a power supply connected directly to the SHO...but like i said, this was in an old building. have you tried it anywhere other than where you're getting this problem?

[IvIark]

Try reflowing the joints, some look a little suspect (although it may be the light in the pic).

[Eric.nail]

Try reflowing the joints, some look a little suspect (although it may be the light in the pic).

Waohhhh The man himself! IvIark, I use your layouts all the time! I LOVE what you do...Props to the master.