Proposition Distortion : a few suspicious things, but not sure if it needs troubleshooting...

eh là bas ma

Well-known member

I built this project with a musikding's kit. Never even heard of the original circuit before, i just wanted to try it, out of curiosity. It certainly has its own singular sound, but i'm not sure if my build is all right.

Everything seems to be working, the sound is close to the few demo i could find on utube, but i couldn't find a good quality sound sample as comparison.
I can explain the weird resistors at RB1 : musikding forgot to send this 6M2 resistor, i had to build my own.

I noticed some whistling noises that can appear with the Volume, Treble, and Bass controls. It's easy to get rid of them by turning the knobs a bit, but i wonder if this is supposed to happen ?

I also noticed a narrow spot in the gain control's rotation, around 1/4 of rotation, where the signal cleans up significantly. It's a bit strange : If i turn Gain fully CCW the sound gets more distorted. From 1/4 of rotation if i turn CW it gets also more distorted, more than fully CCW too : On my build the cleaner setting is a narrow spot at 1/4 rotation of the gain control. Could it come from my home-made biasing resistor ?

Here is a sound sample to give you a better idea of what's happening :

In this sample, Bass and Treble are set at the middle of their rotation. I just turn the gain knob. At the end i turn all controls to get some whistling noises. 3PDT is a bit noisy too, just a bit.

What do you think ? Should i start troubleshooting ? Do you think the effect sounds as expected, besides these few subtle issues ?

Every suggestions and observations are welcome ! And happy new year !
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Try wiring the jacks to the 3PDT away from the rest of the circuit, use shielded wire.





Mark's Shop on Reverb:

Could your gain pot actually be defective? The wiper might lose contact with the track around some point in the rotation.

Also, as it has been said, you want to keep your input and output wiring as far away from each other as possible. Experiment by bending them around/ re-routing them while the whistling is happening. I sometimes experiment with grounded bits of aluminum or copper foil here and there to troubleshoot such issues. A good spot to try is between the in and out pins of the stomp switch. Of course, without shorting things out.
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Thanks for your replies !

So i guess that in the soundcloud sample the effect sounds as it should ?
Nothing obviously wrong, besides the weak point in the Gain pot's rotation ?

Is RB1 shorting to the enclosure?
No, i made sure the resistors in series were bent enough, to avoid any contact with the back of the enclosure.

I don't have any real shielded wires, but maybe i can cut the cable from an old broken EHX power supply, and see if it it works.

I'll use some tape to put them along the enclosure, as shown in the pictures reply #2, and report.
Could your gain pot actually be defective?
If i still have some issue after changing In and Out wires, i'll try to replace the pot.
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Using a cable from a broken EHX power supply, and some tape to make it stick along the enclosure's sides, worked.

The whistlings are much quieter and the weak spot in the gain rotation disappeared.

Thank you very much !

I didn't know the original circuit, my build sounds so bad that i am always tempted to open it up and fix the issue in the EQ section... it has some kind of nasal voice, like some frequencies are missing, and some other frequencies are too invasive. Can't find a good combination with the EQ controls, and that's a bit frustrating. Even with a GE-7 cutting as much mids as possible, it's still not very convincing.

But listening to utube demos, it sounds like the original, and it doesn't suit my tastes either... This time my curiosity isn't rewarded by a good surprise, I should have looked it up before building it.

Who knows ? maybe someday i'll have some use for this singular sound...

Edit : After a few experiments, i've noticed that Proposition is quite good in front of an other preamp circuit, used as a booster. Its singular sound is tamed by the last circuit, which will colour the signal as we see fit. I think i finally managed to find how to use it.
The gain texture is very interesting, but i need a preamp to shape the tone, or it sounds a bit weird.
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