Singing the Neovibe Blues

[fretbuzz2003]

Hi,
I am going insane trying to figure out why my Neovibe isn't working correctly. I'll try to explain this the best I can.

When I plug it in, with the speed pot all the way up and the depth pot halfway up, I get this really quick vibe which sounds great. For about 30 seconds. Then the bulb randomly mixes in bright flashes, which interrupt the quick vibe with a deep pulse. Then the quick vibe stops altogether and I get slow, deep ugly phasing. If I touch the board anywhere, the quick vibe comes back, then when I take my finger off it goes back to the slow vibe.

I have checked everything at least twice. All part values, polarity, pinouts, wiring, etc. I can't find any shorts anywhere. The voltages at the transistors all seem reasonable.

Any ideas?

Two thoughts I have are the power supply and R.G.'s input buffer mod from the Technology of the Univibe:

I'm using a 24VDC 15W wall wart with a max current of 0.63A. Could this be supplying too much current?

For the input buffer, I took R1 out and ran wires to perfboard where I put R1 and the rest of the input buffer circuit. I'm using a J201 FET. Is this the wrong JFET to use?

Any help would be greatly appreciated.

[jrc4558]

I think the problem is with one of the capacitors in the LFO. When you touch the board you're disturbing the electrical potential with the "ground" of your body. Capacitors store the potential and charge-discharge in the LFO operation. So my guess is that the bug is in LFO.

[fretbuzz2003]

Is there any way to tell if a cap is bad or should I just replace all of them in the LFO circuit?

[jrc4558]

WEll, I know one thing. If you switch your DMM to resistance and measure a cap, it should read as a slowly growing resistance. If it reads 0 - it's shorted.
I'm not really familiar with that type of oscillator though. I build EZ Vibes.