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Vintage threads from the first ten years

Bass Effects

11/21/1999 10:48 PM
Padelis	Bass Effects Hi, one friend of mine asks me to build him a booster/fuzz effect for his bass.I don't have any bass effects schematics and i was wondering if I could use any of the schematics we use to build guitar effects.Can i and What modifications can I do to these schematics in order to work with a Bass??? Thanx in advance.

11/21/1999 11:05 PM
Bob Predaina	i think that the only differences with bass fuzzboxes is that they use a different value of resistor/capacitor for the tone shaping controls in order to move the filter frequency down an octave. but then, i may be all wrong here. . bob

11/21/1999 11:21 PM
Stan Bailey	Hello, Probably a little more involved than what uou had in mind, but I've heard "good players" talk about the fuzz in this pre-amp: http://www.lynx.bc.ca/~jc/pedals.html Stan

11/22/1999 3:05 PM
GFR	"good players" include Jaco Pastorius and Billy Sheenhan

11/22/1999 2:27 PM
Mark Hammer	Many guitar-oriented effects use capacitor values for low end rolloff that are suitable for guitar but perhaps introduce a rolloff too high for bass. They also tend to have a high end rolloff which is higher than what is necessary for bass. The first one you should fix by increasing the value of some of the capacitors in the signal path (or connected between ground and the inverting pin of an op-amp). I say "some" because it may not be a problem. If the calculated low-end rolloff is at 100hz or something like that, then it will be a problem. The second one is your choice. If the effect is a noisy one, then taking away unnecessary treble also improves the noise level. If the effect is a quiet one, then leave the treble in to make it suitable for guitar OR bass. Another consideration is that bass pickups can produce a fairly high level signal. Since distortion units are designed in anticipation of a particular signal level, you may want to play with the diodes in any diode-based clipping circuit to adjust the clipping threshold. So, if the device uses a back-to-back pair of 1N914's, you may want to stick another pair of back-to-back diodes in series with the first pair to raise the clipping threshold, or simply measure the voltage drop of the first pair and replace them with something that produces a higher threshold. For example, many germanium diodes might clip at 200mv, whereas others might clip at 300mv, silicon ones can range between 420mv and 700mv, LED's seem to have a higher threshold. Another way you can compensate for the extra output of bass pickups is in terms of the drive/gain control. You may find that the first 10 degrees of rotation of the drive control give you all the fuzz variation you are going to get. If this is the case, you can stick a small fixed resistor (say 20% of the pot's value) in series with the drive pot (if it is wired as a voltage divider - AKA volume pot wiring). Alternatively, if the pot is wired as a simple variable resistor, you can substitute a smaller value pot (e.g., 50k for 100k), or solder a fixed resistor between lugs to adjust the taper of the pot. See the technical articles on pot tapering at AMZ or GEO for this. If you need to turn the drive down to get the tone you want, you may also find that the overall output isn'y high enough, in which case you may need to add a small booster pre-amp to the output. Finally, tone controls are based on the character of the instrument. You may find that the tone-control cap is high enough that it has little effect on the sound; largely because it is turning down harmonics that the instrument isn't producing. You can imporve this by doubling the value of any tone-control caps. E.g., the Rat uses a 3300pf cap for its tone control. For bass, a 5600-6800pf cap would probably improve the control.

11/22/1999 2:27 PM

Mark Hammer

Many guitar-oriented effects use capacitor values for low end rolloff that are suitable for guitar but perhaps introduce a rolloff too high for bass. They also tend to have a high end rolloff which is higher than what is necessary for bass. The first one you *should* fix by increasing the value of some of the capacitors in the signal path (or connected between ground and the inverting pin of an op-amp). I say "some" because it may not be a problem. If the calculated low-end rolloff is at 100hz or something like that, then it will be a problem.

The second one is your choice. If the effect is a noisy one, then taking away unnecessary treble also improves the noise level. If the effect is a quiet one, then leave the treble in to make it suitable for guitar OR bass.

Another consideration is that bass pickups can produce a fairly high level signal. Since distortion units are designed in anticipation of a particular signal level, you may want to play with the diodes in any diode-based clipping circuit to adjust the clipping threshold. So, if the device uses a back-to-back pair of 1N914's, you may want to stick another pair of back-to-back diodes in series with the first pair to raise the clipping threshold, or simply measure the voltage drop of the first pair and replace them with something that produces a higher threshold. For example, many germanium diodes might clip at 200mv, whereas others might clip at 300mv, silicon ones can range between 420mv and 700mv, LED's seem to have a higher threshold.

Another way you can compensate for the extra output of bass pickups is in terms of the drive/gain control. You may find that the first 10 degrees of rotation of the drive control give you all the fuzz variation you are going to get. If this is the case, you can stick a small fixed resistor (say 20% of the pot's value) in series with the drive pot (if it is wired as a voltage divider - AKA volume pot wiring). Alternatively, if the pot is wired as a simple variable resistor, you can substitute a smaller value pot (e.g., 50k for 100k), or solder a fixed resistor between lugs to adjust the taper of the pot. See the technical articles on pot tapering at AMZ or GEO for this.

If you need to turn the drive down to get the tone you want, you may also find that the overall output isn'y high enough, in which case you may need to add a small booster pre-amp to the output.

Finally, tone controls are based on the character of the instrument. You may find that the tone-control cap is high enough that it has little effect on the sound; largely because it is turning down harmonics that the instrument isn't producing. You can imporve this by doubling the value of any tone-control caps. E.g., the Rat uses a 3300pf cap for its tone control. For bass, a 5600-6800pf cap would probably improve the control.

11/22/1999 4:46 PM
Adrian	I never could use effects for my bass setup until I started doing DIY pedals. The suggestions for modifying guitar oriented pedals is really solid but for me distortion type pedals don't work well. If your bass player already can achieve a bit of distortion with the amp alone a booster might just be the thing. The Minibooster works very well for bass and has a natural and warm tone, great for pushing the front end of a tube bass amp. I have yet to try it on an SS amp though. The minibooster is on AMZ and Aron nelson's site ( a Jack Orman design). Also I use A clone of the Electro Harmomics Hogs foot bass bosster which can create some distortion when hit hard. One stetup I have toyed with is splitting the signal with a buffer and running one side to a distortion pedal and the other "dry" to preserve the fundamental - mix 'em back together at some ratio via a potentiometer. This would probably work well with a clean sounding amp.

11/22/1999 4:46 PM

Adrian

I never could use effects for my bass setup until I started doing DIY pedals. The suggestions for modifying guitar oriented pedals is really solid but for me distortion type pedals don't work well. If your bass player already can achieve a bit of distortion with the amp alone a booster might just be the thing. The Minibooster works very well for bass and has a natural and warm tone, great for pushing the front end of a tube bass amp. I have yet to try it on an SS amp though. The minibooster is on AMZ and Aron nelson's site ( a Jack Orman design). Also I use A clone of the Electro Harmomics Hogs foot bass bosster which can create some distortion when hit hard. One stetup I have toyed with is splitting the signal with a buffer and running one side to a distortion pedal and the other "dry" to preserve the fundamental - mix 'em back together at some ratio via a potentiometer. This would probably work well with a clean sounding amp.

11/22/1999 9:53 PM
Padelis	Hi, I want to thank all who replied and especially Mark Hammer who helped me a lot.Thanx Mark.I decided to build a DIY bass pedal.I modified the minibooster circuit for use with bass.Then I drew a fuzz with one opamp stage and diode clip distortion something like Dist+ and at the end I used a Fender tone control made for bass by me.Also I added a switch to bypass the fuzz unit.The effect is plug and play.I hope that it will work and sound great.Then I will publish the schematic. Padelis

11/22/1999 9:53 PM

Padelis

Hi,

I want to thank all who replied and especially Mark Hammer who helped me a lot.Thanx Mark.I decided to build a DIY bass pedal.I modified the minibooster circuit for use with bass.Then I drew a fuzz with one opamp stage and diode clip distortion something like Dist+ and at the end I used a Fender tone control made for bass by me.Also I added a switch to bypass the fuzz unit.The effect is plug and play.I hope that it will work and sound great.Then I will publish the schematic.

Padelis

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