KR MegaVibe speed problem HELP

[rama claproth]

I have a MegaVibe which I mod it to original UniVibe specs, at high speed settings it speeds up for 2 seconds then it goes weak and then it slows and it stops and would only work at medium settings only.

The resistors for the high speed are 1K8's as used at the original UniVibes and also many Vibe clones.

If I decrease the value to 4K7, it works...but still not enough speed for me.

What could be wrong with it? Why the 1K8's doesn't want to work?

Really confused...help

[R.G.]

OK, had a chance to look at this (from your PMs). I can't quite tell from the photo exactly what the KR does with the extra transistor, diode and the resistor changes. If you can send me a photo of the bottom (copper traces) side of the KR circuit board similar to the component side board, I can trace down what he did.

From the description, I believe that he mucked around with the bias settings on the LFO, but I'll have to trace out what he did to be sure.

The LFO on the Univibe is touchy, and has barely enough gain to oscillate. I think your problems with the LFO stopping at some speeds is related to this, and that increasing the gain of one of the transistors will fix it, but without the changes to the PCB, I'm guessing.

The KR PCB looks similar to the original PCB, but the circuit is not the same, so I think the actual PCB traces may be different. So your changes to have it be "original univibe specs" may not be what you think.

That's my best guess in the face of not quite enough information.

[rama claproth]

Thank you RG! YOU DA MAN!!!

Yes I did changed the transistor C828 that connects with the 2M2 resistor with a higher gain BC549C.

Now it works!

Gracias RG!!!!!

BTW here is the layout of the stock KR MEGAVIBE:

http://img855.imageshack.us/img855/8632/megavibelayout.jpg

[rama claproth]

Ooopsss the link above for the MegaVibe layout is wrong (it should NOT have those "Wattson" tracing value ---> 10nf C13 and 6nf C16)  this one is CORRECT! ---> http://img844.imageshack.us/img844/8632/megavibelayout.jpg     

[rama claproth]

2N2484 for Q1 (Hfe 300 - 350), the rest for Q2 to Q13 all are C828's (Hfe 150 - 200)...yup, they're that low!