I've just built this Distortion+ from www.generalguitargadgets.com but when i tested it, its humming so loud that you won't even hear the guitar. Everything is correctly, everything necessary is connected to ground and the opamp [UA741CP] voltages are ok.
Just to say, the led indicator was left out as i could only find a DPDT switch.
Any help would be great.
Just to say, the led indicator was left out as i could only find a DPDT switch.
Any help would be great.
A more direct link might be of some use.
http://www.generalguitargadgets.com/index.php?option=content&task=view&id=42&Itemid=74
http://www.generalguitargadgets.com/index.php?option=content&task=view&id=42&Itemid=74
Hum in DC powered circuit? I assume you are referring to oscillation instead...
Is it "humming" on high frequency: That 10pF NFB capacitor seems quite small for high gain circuit. If the oscillation is low freq instead then i'd guess you have a ground loop somewhere. Try grounding at only one point.
Teemu K
Is it "humming" on high frequency: That 10pF NFB capacitor seems quite small for high gain circuit. If the oscillation is low freq instead then i'd guess you have a ground loop somewhere. Try grounding at only one point.
Teemu K
Btw. i'm using a 9v battery to power it, not a wallwart.
Everything is grounded according to the layout, so everything, except the output pot is grounded to the same point [left top corner].
I could try with changing the output pot grounding to the same spot.
i noticed that in the DOD overdrive 250 circuit [same pcb], a 25pF cap is used, so should i try swapping the 10pF for a 25pF cap?
BTW. The humming decreases more than half when i turn the distortion pot to down, and im not using a C-taper, just a regular 1Meg linear, which is wired the same way as the C-taper in the layout...this could be wrong, i'm not sure.
Everything is grounded according to the layout, so everything, except the output pot is grounded to the same point [left top corner].
I could try with changing the output pot grounding to the same spot.
i noticed that in the DOD overdrive 250 circuit [same pcb], a 25pF cap is used, so should i try swapping the 10pF for a 25pF cap?
BTW. The humming decreases more than half when i turn the distortion pot to down, and im not using a C-taper, just a regular 1Meg linear, which is wired the same way as the C-taper in the layout...this could be wrong, i'm not sure.
Batteries do not hum so you are experiencing an oscillation problem.
The purpose of that capacitor is to attenuate high frequencies so adding more capacitance will also darken the tone. When selecting that capacitor I usually start from a value of about 47pF and sometimes go up to even 1nF. But, if components are good quality and the layout is good the amplifier is less prone to high frequency oscillation.
High gain amplifiers are quite tricky and the source of oscillation could be almost anything. The safest bet is to check the circuit wiring, component values and solder joints thoroughly - again. Usually when i encounter low frequency oscillation i eventually discover that i have either made a wiring mistake or have misread a resistor value. Try to keep wire lenghts as short as possible, especially check the wire lengths of potentiometer wiring. Also, check the input and output grounding: if the ground is lifted it could cause oscillation. Even component layout will matter!
High frequency oscillation (high pitched noise rather than "humming") will most likely occur in high gain circuits if they fail to replicate the original design 100%. Opamps for example can be quite picky about the circuit they're used in. This is why my first thought was that the 10pF cap is too small. HF Oscillation can be easily cured with the expense of brightness
Teemu K
DolbyR said:
The purpose of that capacitor is to attenuate high frequencies so adding more capacitance will also darken the tone. When selecting that capacitor I usually start from a value of about 47pF and sometimes go up to even 1nF. But, if components are good quality and the layout is good the amplifier is less prone to high frequency oscillation.
High gain amplifiers are quite tricky and the source of oscillation could be almost anything. The safest bet is to check the circuit wiring, component values and solder joints thoroughly - again. Usually when i encounter low frequency oscillation i eventually discover that i have either made a wiring mistake or have misread a resistor value. Try to keep wire lenghts as short as possible, especially check the wire lengths of potentiometer wiring. Also, check the input and output grounding: if the ground is lifted it could cause oscillation. Even component layout will matter!
High frequency oscillation (high pitched noise rather than "humming") will most likely occur in high gain circuits if they fail to replicate the original design 100%. Opamps for example can be quite picky about the circuit they're used in. This is why my first thought was that the 10pF cap is too small. HF Oscillation can be easily cured with the expense of brightness
Teemu K
Thanks, i'll remelt all the solder joints this afternoon, check the wirings [i used cat5E for the wirings, should i change them to something else..i have also some Cat5 solid core wire around, or should i just buy something better?] and then start with cap changes if necessary.
And the distortion pot, maybe i should remove for during the tests so that i'll know that its not the problem?
And the distortion pot, maybe i should remove for during the tests so that i'll know that its not the problem?
What kind of wire is Cat5? I guess almost any wire will do and it shouldn't make much difference whether it´s braided or solid. Some people like to use very thick wire but i find it clumsy and i have never experienced any degrade on performance with (even very) thin wire. This of course only applies to low current wirings.
The resistance of the potentiometer is an important part of the circuit and if you want to test whether it's faulty you can simply bypass it with wire loop to get maximum gain. You better keep the amount of working with the PCB (swapping components etc.) as minimum as possible since the foils in printed circuit boards are very fragile. Ín other words, it's better to know what to fix than to throw some wild guesses and ruin the board with exessive heating. However, redoing solder joints might help in case there is a cold solder joint somewhere.
You haven't told whether the oscillation is high or low frequency. Knowing that would be a great help in troubleshooting and fixing the circuit.
Teemu K
The resistance of the potentiometer is an important part of the circuit and if you want to test whether it's faulty you can simply bypass it with wire loop to get maximum gain. You better keep the amount of working with the PCB (swapping components etc.) as minimum as possible since the foils in printed circuit boards are very fragile. Ín other words, it's better to know what to fix than to throw some wild guesses and ruin the board with exessive heating. However, redoing solder joints might help in case there is a cold solder joint somewhere.
You haven't told whether the oscillation is high or low frequency. Knowing that would be a great help in troubleshooting and fixing the circuit.
Teemu K
Cat5 is ethernet/lan cable, from which ive used the wires (braided), its 24AWG and very weak, i have some some from the similar ethernet cable but its solid one, also 24AWG so i'll maybe redothe wiring with it to see if it will be stronger.
I changed the 10pF cap for a 1nF one coz it was the next lowest one that i had and most of the sound disturbance is gone.
I really can't tell whether the oscillation is high or low frequence.
I guess i'd need an oscilloscope for that?
I did try with a program called oscilloscope for windows which gave me about 550hz sweep on 0.5ms/div and 5550hz on 5ms/div but i dont really know what they mean🙂
I changed the 10pF cap for a 1nF one coz it was the next lowest one that i had and most of the sound disturbance is gone.
I really can't tell whether the oscillation is high or low frequence.
I guess i'd need an oscilloscope for that?
I did try with a program called oscilloscope for windows which gave me about 550hz sweep on 0.5ms/div and 5550hz on 5ms/div but i dont really know what they mean🙂
The problem with the humming/osc. whatever, appeared to be just my second cable (dist->amp) which was probably catching up some RFI.
Now i must just change that 10pF cap back as with 1nF its definitely filtering too much highs.
I'll post some link after that how the final version sounds, thanks for all the help
Now i must just change that 10pF cap back as with 1nF its definitely filtering too much highs.
I'll post some link after that how the final version sounds, thanks for all the help
Has anybody ever modded a Distortion+ in order to obtain cleaner sound?
Now the drive is very strong which i like but the sound is not even close to clean, its very muffy, sounds like its coming from a bass.
I can have some 3mb mp3 sample from it if anybody wants to hear.
If i cant make the sound cleaner, i guess i'll have to try a boss DS-1 clone.
Now the drive is very strong which i like but the sound is not even close to clean, its very muffy, sounds like its coming from a bass.
I can have some 3mb mp3 sample from it if anybody wants to hear.
If i cant make the sound cleaner, i guess i'll have to try a boss DS-1 clone.
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
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
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?
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?
DolbyR said:
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
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?
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?
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
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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