Oscillation problems

[Arno van der Heijden]

I'm having terrible oscillation problems with my SansAmp GT-2. I originaly planned to use shielded wire, but I didn't have enough room to connect the shield (I crammed it in a 1590BB :mrgreen:), so I used just plain wire.

I do however have some ferrite beads. Will those also work as a measure against oscillation?

And what if I use shielded wire without connecting the shield? Would it be of any use or just a waste?

[Paul Perry (Frostwave)]

Stick some beads on (right at the ends) can't hurt.
And, if you use shielded wire, you have to ground the shield at one end only.

[Arno van der Heijden]

Yes, I know I have to connect the shield at one end only. But what if I don't connect it at all (because of space restrictions)?
Will it be of any help, or just a waste of shielded wire?

[Joep]

Hi Arno,

I used non shielded wire everywhere and no problems there.

Try moving around the wires a bit. See if the oscillation changes.

Bye,

Joep

[Arno van der Heijden]

Hi Joep,

I guess it worked for you because you used a bigger enclosure.

I already tried to move the wires, in every possible way, but it didn't help...  Also there isn't a lot of room to move wires...

[smoguzbenjamin]

By a bigger enclosure

[Joep]

Yeah, I used a bigger enclosure, but the wiring is a mess. Try to keep input and output wires as far away as possible from each other.

If moving the wires doesn't change the oscillation at all, it may be something else that causes the oscillation.

Have you tried the TLC2262 already? I received mine a few days ago.

Bye,

Joep

[Arno van der Heijden]

If moving the wires doesn't change the oscillation at all, it may be something else that causes the oscillation.  

Like what? Could the wiring for the LED be the cause? Can wires carrying DC cause such problems?

I cut the wires pretty short, so there's not much to move anyway...

TLC2262 ic's are already in their sockets. I had to desolder the 3 original ic's first  
I haven't been able to get a good sound out of it because of the oscillations, but my first impression is that it cleans up a little better.

[Joep]

Can you post a picture? Or send me one?

Thanks,

Joep

[spongebob]

If you still have room on your board, you could try to bypass the power supply pins of each opamp with a small cap (0,1uF ceramic for example).

Also check your grounding, ground loops can often be the cause of oscillations, try to use star grounding if possible (don't "daisy-chain" ground connections).

[Jason Stout]

Arno van der Heijden, you may be able to find the source of the problem by taking a small value pF capacitor (try 22-47 pF) and connect one end to ground with a length of wire, now take the free end and touch various points in your circuit, until (hopefully) you find a point that stops the oscillation. Try all the pot lugs first. If this works it will let you know what wires are coupling.

As for the shield working if it is not grounded, I know that i really don't know, but I don’t think it will do anything predictable, its a floating open circuit.

What could it do? Does anyone know?
:?