TS - oszillation, when Gain is turned up..... plz help

[Oliver]

Hello,

my TS Circuit is modified with an 1M Pot as Gainpoti.
When i turn it up the Gain and turn the TonePot up to the Hights, the Circuit oscillates and has a "feeeeeeeeeeeeeeeeeeeep" in the Signal.

Added on i have a Switch to go on CleanBoost (like the CompCut)
That the Clipping Diodes AND the 50p Cap is removed from the feedbackloop of the OPamp.

In CleanBoost it makes the same "feeeeeeeeeeeeeeeeeeeeeep"....

Both only, with much Gain and much Treblesettings.

What can i do to prevent this effect?

Thanx and bye

Oliver

[Oliver]

no idea? anyone?  :cry:

[puretube]

maybe put the diodes and cap back in there?

[csj]

Oliver,
I've built 6 of these over the last month or so.
PTP not PCB.
3 worked right out the gate. No squeals at high levels.
2 oscillated in exactly the same way you describe.
1 is just the board itself and not put into a box. I use it as a kind of wiring template.

I used the same kind of design for the diode switching... except that it was an on/off/on arrangement to either go with the silicon/diode lift/LED configurations.
I gave those first three pedals away to people who have helped me out  in some way or another. They worked great and I didn't think too much about them. Just built them, listened to them, liked what I heard and passed them on.

The 2 pedals left over are here...





These were for me... 1 set up with a 4558 and 1n4148, the other with a 5532 and LEDs.

Unlike the first 3 these worked great up to that certain point you described.

I put my earplugs in...
plugged both into  a Princeton...
turned the amp and pedals up to get the squeals...
took my toothpick and started poking and pushing wires...
both were simple fixes but one more work than the other...
The one on the left had output signal feeding back to the input.
Fix...Shielded the output and moved the input.
The one on the right was a PITA.
Fix... rewired most of the underside of the board.

Lessons learned for me.

1. Wiring layout/lead dress is crucial.
2. Since I use PTP when I get a board to work the first time...take pictures of everything if I plan to build that one again.

Clay

edited for spelling errors.

[Oliver]

Hi Clay,

thanx for Your reply!!
Your Boxes look very good !!! - nice Work.

Yesterday Night i worked on my Pedal for 3 Hours.

I added a 100p Cap parallel to the 50p one.
Added one Diode into the FeedbackLoop.
Changed two Diodes in the HardClipping Stage.

Now in Overdrive Modus there are 4 Diodes in the FeedbackLoop:
2 1N914 in Series and one 1N914 in Series with a 1N4004, in
antiparallel with the two 1N914 (slightly asymetrical).
In OverdriveModus the Stock 50P Cap is now Parallel with
the added 100p Cap and in CleanBoost Modus there is the
100p Cap in the Feedbackloop.
In DistortionModus in the Feedbackloop are 2 100p Caps parallel
and after the OP Amp sektion 2 1N914 and 1 1N4004 (antiparallel)
from Signal to Ground.

The Feeeeeeeeeeeeeeeeeeep is gone!!!! (the 100p Cap made it)

The Overdrive Sound is better now (from the added Diode)
More Output

Now the Circuit acts as a TrebleBooster, when Tone is Turned up
with Treble....

The Only Thing is, that in DistortionMode, with lowest Gainsetting and normal setted Tone (at Half f.eg.) the Sound comes a little bit gated.

The TS can be boosted by a preconnected Booster or other Overdrive.
And it sounds great - no more Muddy, when kicked into its face.

im happy now!!

bye
Oliver

mine one is not so tidy...