Dr. Boogey Oscillation?? Please Help (Waveform included)!!

[sphinx]

Hi all,

I am a newbie here and this forum really great~!!
Recently I have built 2 Dr. Boogey.
The 1st one I have used 2SK304 (Sanyo) for all JFET and the 2nd one I have used J201 instead.
However, they have the same problem.......
Would you guys can give me some suggestions?? Thanks a lot.

The problems are:
1. Palm muted, high freq. tone heard 
2. connect nothing at the input, high freq. also heard (is it so called oscillation??) 

But when playing the boogey with a guitar, its sound great and got no problems.

P.S. I also added 2N5088 buffers at the input and the output.

Therefore, I have captured some waveforms at each JFET output (Drain) and the finally output.
Here are the waveform:

Drain @ 1st JFET (J201) <-- You can see that some ripple here....


Drain @ 2nd JFET (J201) <-- those ripple are being amplified....


Drain @ 3rd JFET (J201) <-- and amplified....


Drain @ 4th JFET (J201)<-- and amplified.........


Finally the Output (Gain, Presence, Vol., Bass, Treb. & Mid all Max.) <-- finally those ripple becomes that.....


Any suggestions are welcome.

If you need more information, please let me know.
Thanks again.

[Bernardduur]

rebias the first transistor until no oscillation is heard. I had the same problem and this solved a lot (I biased all J201 transistors at 6.8V)

[sphinx]

Bernardduur, Thanks~!!
I have tried to re-bias all the JFET to 6.8V. However, the problems still here......

P.S. Before all JFET are bias to 4.5V and shielding cables were used at the input, output and the gain pot

Here 2 more captures:

Input Waveform (input connected nothing <-- before input buffer)


Gate @ 1st J201 (input connected nothing)


Any suggestions are welcom~!! 

[RDV]

I'm having the same problem!

It's making me crazy!

I'm going to remove it from the box tonight and try it again.

I'm getting extremely low output and almost nothing but squeal.

I may have to skip on the 1590BB and use a chassis so I can spread the wires out.

I'm also going to try twisting the wires to each separate pot together so I can route them better.

When I 1st got mine going it sounded great, but it's been all downhill from there. 

RDV