"Good enough" synth pedal for bass

[egasimus]

I've been reading up on DIY analog guitar synths for a while, and what I've learned is that constructing one is nigh impossible. Of course, this doesn't help me much - I have a couple of songs that are written with a synth bass in mind, and I'd prefer to play them with my bass guitar instead of a keyboard. So, from your experience, can you recommend me a design to build? I'd prefer if it could produce a sawtooth-ish wave, and it has to have reliable enough tracking for the low notes. I'm looking for 80-s/90-s bass sounds, but a VCF making a 'bwow' sound isn't really mandatory. Of course, I could always add a frequency doubler in front, and/or play an octave or two above for better tracking then have the circuit drop its output a couple of octaves - that's mostly okay with me.

[newfish]

For the complexity of the build, the Behringer copy of the Boss thing is more than adequate.

A very good Bass Playing friend of mine recently ditched his EHX Bass Micro Synth in favour of the Behringer box - smaller footprint, and less 'valuable kit' to worry about on the road etc...

I guess a 'Synth Pedal' isn't like a compressor / Fuzz / whatever.  The times you use them are few and far between, so for 90% of the time, you're looking for a decent 'bypass' signal.

Sorry - I've just encouraged the purchase of a commercial product on a DIY Forum.

I feel all dirty - and I really like it.

[markeebee]

The Behringer thing is the best thirty-something quid I ever spent on a non-DIY effects box. It's a real laugh. Works best with a fuzz In front of it, and I've got it in a bypass loop.

[Keppy]

I really like the Synthbox. I'd give it a try if I were you, just because even if it's not what you're going for you might really like it anyway. It's a nice compact build, too (I put mine in a 125B).

[DavenPaget]

The Behringer thing is the best thirty-something quid I ever spent on a non-DIY effects box. It's a real laugh. Works best with a fuzz In front of it, and I've got it in a bypass loop.

Yep , behringer things are cheap but it's made from plastic , too bad beta aivin doesn't copy most .

[screechingowl]

Look for some building blocks here:
http://folkurban.com/Site/GuitarEffects-681.html
Especially these:
http://folkurban.com/Site/QDVCF-714.html
http://folkurban.com/Site/SimpleSquareWaveShaperMadeSimpler-712.html

I haven't used these personally, but they may get you close to what you want...

[nexekho]

I was reading up on these synths and had an idea, not sure if it's feasible; use a comparator pair/flip flop to generate a nice even square wave, run it through a 10x PLL (this is the bit I'm unsure on) and then clock a 4017 off that (use the divide 10 output of the 4017 as feedback?) through a bank of pots forming a wave shape with an envelope dropping the volume when the guitar fades out.  Would only be monophonic, but ULTIMATE WAVE SHAPING.    Also, by making the reaction speed of the PLL variable you could make nice slide-style pitch bends.

[egasimus]

The PLL part is the show-stopper It takes a good while for a PLL to settle to the correct frequency, especially for lower notes; and it seems that a PLL multiply-by-X (4046 with counter in feedback loop) needs X cycles of the note "up front", to get the counter going. That is, 250ms latency at 40Hz... Bummer. It would work for higher frequencies, though.

The absolute best wave shaper/frequency multiplier I know of is just a microcontroller counting the time between the last two zero crossings, and outputting a PWM signal with that length. That's t/2 latency (50 ms at 40Hz... much more manageable).

But first of all, I need good, solid tracking. Gotta get those ATmegas out of my breadboard (can't do anything useful with them, anyway) and maybe try something with, what was it, NE570/571 dual rectifier, and the adaptive schmitt trigger from the EHX Microsynth...

[Gurner]

The absolute best wave shaper/frequency multiplier I know of is just a microcontroller counting the time between the last two zero crossings, and outputting a PWM signal with that length. That's t/2 latency (50 ms at 40Hz... much more manageable).

This was something I'm actually about to try....but I'm expecting false frequency readings from the guitar signal's pesky 2nd harmonic which tends to zero cross too & screw things up!

What's the prescribed way of suppressing that dodgy zero cross?

[amptramp]

The absolute best wave shaper/frequency multiplier I know of is just a microcontroller counting the time between the last two zero crossings, and outputting a PWM signal with that length. That's t/2 latency (50 ms at 40Hz... much more manageable).

This was something I'm actually about to try....but I'm expecting false frequency readings from the guitar signal's pesky 2nd harmonic which tends to zero cross too & screw things up!
What's the prescribed way of suppressing that dodgy zero cross?

The bass guitar puts out a signal based on combined outputs from the four strings.  If you have separate outputs for each string, it may be a little easier to sort out.

But there is another way to do this - connect each fret to a synth input at the corresponding frequency.  When the string makes contact with the fret through the grounded bridge, this information can be used to operate a synth using the strength of the signal as the volume.  This also works better with separate outputs for each string.

[Gurner]

The bass guitar puts out a signal based on combined outputs from the four strings.  If you have separate outputs for each string, it may be a little easier to sort out.

I don't see how that can help...becuase even with individual hex pickups....you've got the same issue....was that an open e with a stong 2nd harmonic contained (therefore zero crossing too) or is it the e fretted at the 12th fret. etc .....in other words you've the same dilemna....even on a per string basis of how to  - electronically or logically - eliminate/differentiate the strong 2nd harmonic from the root.

But there is another way to do this - connect each fret to a synth input at the corresponding frequency.  When the string makes contact with the fret through the grounded bridge, this information can be used to operate a synth using the strength of the signal as the volume.  This also works better with separate outputs for each string.

Bang goes 2012! (the title was "good enough" which I interpret as not reworking your guitar's fretboard!!  )

[nexekho]

The absolute best wave shaper/frequency multiplier I know of is just a microcontroller counting the time between the last two zero crossings, and outputting a PWM signal with that length. That's t/2 latency (50 ms at 40Hz... much more manageable).

This was something I'm actually about to try....but I'm expecting false frequency readings from the guitar signal's pesky 2nd harmonic which tends to zero cross too & screw things up!

What's the prescribed way of suppressing that dodgy zero cross?

How about using a pair of thresholds, scaled by the volume?

[Gurner]

fine, except a guitar signal looks nothing like a sine wave with only a fundamental frequency contained therein. ....superimpose a 2nd harmonic on there (prevelant especially when the string is freshly plucked)...and alas it'll zero cross too, something like this ....



(the signal is just to illustrate the point - not be totally representative of a guitar signal....although it is more representative vs the drawing)

The resulting zero cross timings are going to be all skewiff.

[nexekho]

fine, except a guitar signal looks nothing like a sine wave with only a fundamental frequency contained therein. ....superimpose a 2nd harmonic on there (prevelant especially when the string is freshly plucked)...and alas it'll zero cross too, something like this ....

As long as your thresholds are setup properly I see no problem there with it catching those peaks only.  The zero line isn't even considered in the above.  If you zoom in you'll see some horizontal lines.  Using two thresholds and a flip flop, everything between those two lines would be irrelevant.

[nexekho]

To clarify:

As you'd be counting the time between the peaks on a microcontroller, the off duty cycle won't even matter.

[Gurner]

Ok, rather than zero detect (which is what we'd been discussing)....you want to go with 'peak' detect?  - but that will only work when playing at a (very) precise & consistent 'level' ....what happens when you play quietly? (your peaks aren't triggered)....or too stongly ( the second harmonic then triggers your peak it too)...at least with zero detect, you can be sure of the event happening.

[nexekho]

Ok, rather than zero detect which is what we'd been talking about ....you want to go with 'peak' detect?  - but that will only work when playing at a (very) precise & consistent 'level' ....what happens when you play quietly? (your peaks aren't triggered)....or too stongly ( the second harmonic then triggers your peak it too)

Which is why the thresholds are a percentage of the amplitude of the signal, scaling them down with the signal fade.

[Gurner]

Ok, rather than zero detect which is what we'd been talking about ....you want to go with 'peak' detect?  - but that will only work when playing at a (very) precise & consistent 'level' ....what happens when you play quietly? (your peaks aren't triggered)....or too stongly ( the second harmonic then triggers your peak it too)

Which is why the thresholds are a percentage of the amplitude of the signal, scaling them down with the signal fade.

but to measure percentage of amplitude, you have to track changes in amplitude - which takes time (no envelope detector is instant - also to have dependable results, you're gonna need to 'average'....even more time )...& during that time 'recalibrating', you're gonna miss or breach your existing thresholds(eg from playing quietly to loudly suddenly)

[nexekho]

Ok, rather than zero detect which is what we'd been talking about ....you want to go with 'peak' detect?  - but that will only work when playing at a (very) precise & consistent 'level' ....what happens when you play quietly? (your peaks aren't triggered)....or too stongly ( the second harmonic then triggers your peak it too)

Which is why the thresholds are a percentage of the amplitude of the signal, scaling them down with the signal fade.

but to measure percentage of amplitude, you have to track changes in amplitude - which takes time (no envelope detector is instant - also you're gonna need to average....even more time)...& during that time, you're gonna miss thresholds or breach thresholds (eg from playing quietly to loudly suddenly)

There is no perfect solution ;]

...not without going way overboard for a synth stompbox anyway.

[Jaicen_solo]

This is a bit of a pet subject of mine actually.
As far as synth bass sounds go, are you looking for aggressive analogue, smooth Moog or digital sounds?
For my money, a GR20 with a GK3b will get you most of what you're looking for, assuming that you can deal with the latency, which is not actually as bad as many people will tell you.
You do need to have a clean technique, and well set up gear but the rewards are there for those willing to put in the work.

A simpler approach is to build/Buy a Wooly Mammoth clone. That will give you most of the Muse synth bass sound (Time Is Running Out etc..). I've found I have very little use for filter sweeps when i'm using synth bass, so the Mammoth is a go-to.

I also have a GR33b, but that's another story.