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Old 22nd January 2006, 09:35 AM   #11
teemuk is offline teemuk  Finland
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Location: Suomi, Finland
Funny that you mention the bass response since most of the people who have built this pedal usually want to mod it to give even more bass. Anyway, you can cut down the amount of bass by reducing values of either the 1uF coupling capacitor or the 47nF capacitor in the opamp's feedback loop.

Here are couple of mods you could try: Unless you love the clean sound of this pedal lower the value of gain potentiometer (from 1Meg to 500k, 250k or even smaller) to get a better control over distortion (you can try a reverse log potentiometer too), connect a resistor in series with diodes (1k to 10k might be a good value). Try different clipper components (ie. leds, ge, silicon or schottky diodes).

The fuzzy sound is something you can't avoid with such a simple design as this. You can either cut down the bass drastically (in the end it will just give you a very sharp tablesaw tone) or cut down the hi freq (less buzzy but too muffled tone). If you expect to get a less "fuzzy" metal tone from this pedal just forget it, this circuit is too simple for that. Most of these simple circuits are basically just fuzzboxes and if you want a more authoritive metal tone you should look from boss circuits how it's suppose to be done. Well... you could try putting a graphic eq after the distortion effect to help a bit.

Teemu K
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Old 22nd January 2006, 09:50 AM   #12
DolbyR is offline DolbyR  Finland
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several people have heard the demo recordig of this box, that i made and no one has actually liked it...general comments were the unclean sound. So i guess i'll just try the boss DS-1 clone next. I personally don't play guitar, this project is just for some friends that have bands and can't afford to buy commercial ones.
And i just love soldering

To me it sounds like the box would filter a lot of high frequences...this effect was much stronger when i tried with a 1uF NFB cap, and changing it to 10pF helped a lot, but not enough. Could i maybe try with a 1pF cap?
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Old 22nd January 2006, 10:26 AM   #13
teemuk is offline teemuk  Finland
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Join Date: Nov 2004
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Quote:
Originally posted by DolbyR
To me it sounds like the box would filter a lot of high frequences...this effect was much stronger when i tried with a 1uF NFB cap, and changing it to 10pF helped a lot, but not enough. Could i maybe try with a 1pF cap?
I think it shouldn't really make such a difference. There's a huge difference between 1uF and 10pF but not with 10pF and 1pF. 10pF should be good and most distortion circuits actually have an earshattering harsh tone without a lot of hi freq NFB. More likely the problem is that the low frequency distortion just blocks out all hi freq content. Try this: Pluck the low E string and then one of the higher strings. Did you hear the sound from the higher string with equal volume (or at all)? If not, then you have to cut down the amount of low frequency distortion.

If the sound is muffled all the time then you have to find out what cuts the HF too much. It really shouldn't be the fault of 10pF capacitor, (IMO it's even a too small value). Check out (and alter) the value of the capacitor in parallel with diodes or the capacitor from signal path to ground in the input.

Teemu K
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Old 22nd January 2006, 10:32 AM   #14
DolbyR is offline DolbyR  Finland
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ok, thanks again...will try and get back to the subject in a week or two
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Old 23rd January 2006, 08:41 AM   #15
DolbyR is offline DolbyR  Finland
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no, this distortion is just hopeless...i'll go for the Boss DS-1 clone...
I was thinking...what components would i need to change if id like to use this as a preamp for the bass?
i mean, i dont want it to distort, just to be clean...the opamp would probable need to be swapped atleast and some gain resistors lowered?
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Old 23rd January 2006, 10:33 AM   #16
teemuk is offline teemuk  Finland
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No need for opamp swap neccessarily. Just lower the gain, and remove the clipping diodes and capacitors connected from signal path to ground. Increase the capacitance of rest of the capacitors, including the one at bias and excluding the hi freq NFB capacitor.

1 Meg resistance in the feedback loop seems quite big considering the fact that the opamp is driving a (max.) 20k load. (This is also the reason why this circuit totally sucks on hi freq.) I do not have a slightest clue what the people at MXR thought when they designed a circuit that is heavily loaded by the output! I would lower these values (1Meg to 100k plus the rest of the gain set circuit respectively) and then icrease the resistance of master volume potentiometer to 500k.

The downside in all this is that these "mods" are actually a total rebuild of the circuit and if you just need a clean boost for bass some other circuits might even perform better. If you can cope with a modest boost i would ditch this circuit and go discrete: less parts, simpler design.

Teemu K
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