Mark Harmmer's Woody Pedal white noise problem.

[nguitar12]

Hi everyone. I have finished building Mark Harmmer's Woody acoustic simulator Pedal

I am building the single supply version as show as the following schematic.


Everything is working quite well except this pedal is generating a high level of white noise that make it pretty unusable especially when I turn the top knob up.  I would like to know if the pedal suppose to behave like this or this are problem on my build? The white noise is far more then any high gain distortion I have built.

Also I found the the edge of the high frequency will distorted when I hit the string hard. How can I make this pedal more usable? I spent a lot of time layout this circuit but now it is really disappointing me.

[R.G.]

I highly suspect that it's oscillating. RF oscillation gets reflected back down into audio as a heterodyne or as an "angry" sounding hiss.

How's your wiring? Grounding? Is there a 0.1uF ceramic from V+ to V- on every opamp package?

[nguitar12]

I highly suspect that it's oscillating. RF oscillation gets reflected back down into audio as a heterodyne or as an "angry" sounding hiss.

How's your wiring? Grounding? Is there a 0.1uF ceramic from V+ to V- on every opamp package?

This is my schematic:



I don't see any 0.1uF ceramic from the original schematic.  I am using a dual opamp instead of two tl072.
Also since this is a single supply version so it is not supposed to have v-

[Mark Hammer]

I've made Oliver Alex's version and it is relatively quiet (I still think it could use a simple gating action on the top/treble part).  So the white noise is in your build, not the circuit.

The effect relies on producing distortion for the high end, and mixing that back in with a clean signal.  But you won't hear it as distortion unless the highpass filter just before the clipping section (with the 3 diodes) is set too low and lets more than the upper mids and treble through.  That could happen if you misread the values of the 3300pf (3n3) capacitors.

[nguitar12]

I've made Oliver Alex's version and it is relatively quiet (I still think it could use a simple gating action on the top/treble part).  So the white noise is in your build, not the circuit.

The effect relies on producing distortion for the high end, and mixing that back in with a clean signal.  But you won't hear it as distortion unless the highpass filter just before the clipping section (with the 3 diodes) is set too low and lets more than the upper mids and treble through.  That could happen if you misread the values of the 3300pf (3n3) capacitors.

I just ctake a look at those 3.3n cap. I am using a CBB cap labeled 332 for them. Is it a correct value?
How about the white noise? Which part of the circuit do you think that is messed up?

[Mark Hammer]

At least the caps are the right value,  Good,

Is the white noise there even when the "Top" control is turned down?

[nguitar12]

At least the caps are the right value,  Good,

Is the white noise there even when the "Top" control is turned down?

The noise is almost unnoticeable when the "Top" control all turned down.
I will record a clip for you to determine the problem.

[nguitar12]

OK sound clip is up.
The signal is recorded directly to sound card.
gain setting for all clip are the same and yes I know how to record without clipping so all the distortion are from the circuit.

Here is the play list for 5 clip:
https://soundcloud.com/wai-man-chan-2/sets/pedal-test

clip 1: humbucker, top knob all the way down
clip 2: single coil, top knob all the way down
clip 3: humbucker, top knob all the way up
clip 4: single coil, top knob all the way up
clip 5: single coil, top knob all the way up, strum hard

[nguitar12]

anyone can help me out on this?

[R.G.]

I highly suspect that it's oscillating. RF oscillation gets reflected back down into audio as a heterodyne or as an "angry" sounding hiss.
How's your wiring? Grounding? Is there a 0.1uF ceramic from V+ to V- on every opamp package?

This is my schematic:

I'm saying this for your education, not to be snotty - a schematic is a dramatic simplification of a circuit. It by no means puts all of the information about the circuit on paper. The actual wiring and layout may be *critical* to getting good results.

I don't see any 0.1uF ceramic from the original schematic.  I am using a dual opamp instead of two tl072.
Also since this is a single supply version so it is not supposed to have v-

The original schematic may well not have power decoupling caps on it. That does not mean that they should not be there. And in single supply circuits, ground is connected to the V- pin of the opamps. The opamps are not smart enough to know the difference. It is good practice to put a 0.1uF or 0.01uF ceramic cap from the V+ pin to the V- pin on every opamp package. Sometimes, even most times, you can get away without this. But it's never bad practice to do it.

It is possible RF/ultrasonic oscillation is not the cause of your issue, as I'm only guessing. But it's a problem that has happened to me before. Other possible causes are:
- a mistake in the schematic
- a mistake in wiring the schematic into real parts
- poor layout; getting the wrong thing too close to the wrong thing, or running wires where they shouldn't go
   As an aside, is this on a PCB? Stripboard? Perfboard? Chances for the board itself causing issues increase in that order. One screaming advantage of PCBs is that they are VERY consistent. Stripboard is less consistent, and perfboard is a handicraft, each one being different.
- construction problems, such as incorrect part values, connections to the wrong pins, broken parts, soldering issues, and so on.

[karul]

Noise is more present on single coil clips. What kind of guitar are you using, what kind of pickups - was just one pickup used for the clips, or you were in a hum canceling position.
Is your guitar shielded? How close you were to the PC while you were recording? Any other source for noise, neon light etc ?

[krulmarx86]

hey man, I had the same problem, I used 2 tl074, but I think they were fake ones, I replaced the one in which the clipping diodes were, by a tl084 from texas instruments, and the distortion when you hit the strings hard disappeared.

[antonis]

And that replacement took you almost 5 years..?? 

P.S.
Welcome..!!

[rankot]

Better than never

[Mark Hammer]

I laugh at a mere 5.  Twenty-seven years and counting for my Hyperflange.   

[rankot]

You mean this: https://www.diystompboxes.com/smfforum/index.php?topic=49040.msg364410#msg364410

[stallik]

I like it Mark, you've built a truly vintage pedal

[Mark Hammer]

You mean it's now old enough to be considered vintage?  Hmm, maybe I ought to leave other things sitting around for a few more years. 

[tubegeek]

I like it Mark, you've built a truly vintage pedal

Mark is building a truly vintage pedal!