debuging a simple distortion guitar effect

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Opencan
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debuging a simple distortion guitar effect

Post by Opencan » Tue Nov 08, 2005 10:54 am

I've build a distortion effect from this schematics : http://members.lycos.co.uk/driftingfuzz ... stplus.pdf (the bottom one) and i've changed the output cap. from 0.001 to 0.0033 because i didn't had the right cap at the moment, and the level pot. to 100K from the 10K because it just works better in my opinion.

Now, i've got it all working perfectly on the pre-wired board, and when i moved it to a soldering board i got something wrong probably, or burnt something, because now the Gain pot. does a very weird thing, he goes from 0 ohm up to about 260Kohm and then, when i keep on turning the pot. it goes back to 0 ohm. the result actually is, that when i turn the pot. all the way one side, it screams and create a disturbing echo. and when i turn it the other way, it does pretty much the same. one side, for a reason, have more bass.
anyone knows what may have gone wrong?

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Sambuchi
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Re: debuging a simple distortion guitar effect

Post by Sambuchi » Mon Nov 21, 2005 12:34 pm

would help to see a schematic.. or the layout of the board.

Enzo
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Re: debuging a simple distortion guitar effect

Post by Enzo » Mon Nov 21, 2005 5:16 pm

Those are on the link he provided. The pot is possibly broken in the process of construction. Also check carefully for solder bridges at the pot connections.

fripster
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Re: debuging a simple distortion guitar effect

Post by fripster » Tue Nov 22, 2005 2:57 pm

mmm check your R13 connections... did you mistakenly solder the wrong pins together?

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Edd
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Re: debuging a simple distortion guitar effect

Post by Edd » Fri Nov 25, 2005 3:23 am

“and i've changed the output cap. from 0.001 to 0.0033 because i didn't had the right cap at the moment”

Mmmm, can’t see any big variance there as the cap is shunting the clipping diode sets and acting as a high freq by pass and also a RF shunt in case the unit was used in a high RF proximity of an AM signal so that you wouldn’t have a “crystal “ set making voice/music emanate through your system if not in a grounded metal shielded casing.

“and the level pot. to 100K from the 10K because it just works better in my opinion.”

There is an imbalanced output created from the manner of utilizing the two sets of clipping diodes across the audio signal…….since one polarity of incoming signal is shunted across one diode junction…while the opposite polarity of signal is meeting a series combined pair of junctions, and the resultant higher clipping level of those junctions.
Your selection of the higher output gain pot would be parallel shunting the equivalent input impedance of the input of your amp, with a little less loading and the resultant slight extra gain. But, that is somewhat minumal by the inherent low level available of ~.7V at one polarity of signal and the ~1.4 V from the other polarity. It also might make a very slight different tonal response and voicing.

“The Gain pot. does a very weird thing, he goes from 0 ohm up to about 260Kohm and then, when i keep on turning the pot. it goes back to 0 ohm.”

Every one else also thought of a miswire here. What I am seeing here is that if you were to check from center wiper to a side terminal with the circuit you have present you would have either a single diode junction or a series diode pair, basically placing a short across the ends of the pot. When you test from center tap to a side leg with an ohmmeter, the utilized test voltage level would be adequate to conduct a junction(s) and then you would get a low ohms reading on either end and a median/center resistance at the mechanical center rotation of the pot, just as you are experiencing.
Most common ohmmeter circuits will do this except for those that are designed to test using lower voltage thresholds, that will not conduct thru a silicon semiconductor junction.
To confirm that this is what is happening in your testing, lift both the center tap of your pot and one outer leg free of the circuit and test it thru its rotational range and see if it then ohms out normally.

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Opencan
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Re: debuging a simple distortion guitar effect

Post by Opencan » Fri Nov 25, 2005 3:41 am

i pretty much got what your saying, but that was one major headache !
haha

thanks for the info

Robert Reed
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Re: debuging a simple distortion guitar effect

Post by Robert Reed » Fri Nov 25, 2005 5:31 pm

Opencan
One thought occurred to me is that a 1Megohm pot tied to ground on both ends would give you the exact same ohmeter readings (c.t. to grd.) you are getting. Check your pot value to make sure you didn't inadvertatly install the wrong one. Also check for grounds on both ends of the pot. Just a shot in the dark.

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