Auto wah/envelope filter schematic for a 6 string bass?

[fjdenigris]

Hey all! I would like to put together an envelope filter for a 6 string bass. Are there any schematics out there for this? I was not lucky in my search for one.

How about converting schematics for guitar to bass, any tips or suggestions?

Thanks in advance!!

[niftydog]

I would think that a moded guitar effect would do the trick. Although, the question is where to put the low frequency cutoff point! You'd definately want a blend control to maintain the bottom end, and you may have to look at the input stage to make sure you don't overload it.

If it works for regular bass, there's no reason it wouldn't work for 6's.

I'd probably start with a bassballs.

[fjdenigris]

Thanks niftydog, I really don't know how much difference a low B bass string makes.. Yeah I'm a newbie!

[Mark Hammer]

There are essentially 3 aspects to consider from your vantage point:

1) Is the device appropriately sensitive?  Will I have too hard a time getting it to sweep?  Will I have too hard a time getting it to sweep just a little?

2) Will the nature of the sweep be suitable for what I want to do?  Too fast, too slow, too upward, too downward, etc.

3) Where are the filters going to be situated, relative to the critical frequencies that need to be filtered?

In your case, many of the ECFs out there may not begin their sweep low enough for filtering to be evident on the lower strings.  Alternatively, if they are bandpass filters, you may not even hear the lower strings because the "starting point" for the filter may be higher up than your instrument needs, either because it is based ona guitar range, or simply a "normal" bass range.

In general, for basses, three scenarios are desirable:

a) one where multiple staggered bandpass filters are used to achieve a thicker sound
b) a lowpass filter in which low end is retained, and all "movement" of the filter consists of how much high end is let through or accentuated
c) a blend of clean signal (for bass) and some swept filter, whether bandpass, or other.

The E-H Baseballs can be suitable for your needs but the filters should be tuned downward.  The trimpots CAN tune the filters downward, but likely not far enough, so I'd recommend doubling the values of the filter caps.  They are currently .022uf and .0047uf.  Consider using .047uf and .012uf, and see if you like that.

On mine, I have an option to split the upper and lower filters.  You may want to consider doing something similar so that you can mix the level of each filter.  That might nail you a better sound.

[fjdenigris]

Woah Mark! Thanks!!!

[Mark Hammer]

You're welcome.

If you want to start simple, just to get an idea of what does and doesn't work for you, consider building either a "Nurse Quacky" ( http://www.generalguitargadgets.com/pdf/ggg_nurse_quacky.pdf ) or a "Dr. Quack" ( http://www.muzique.com/schem/quack.gif ).  These are both esentially modded versions of the old E-H Dr. Q.  The Nurse dispenses with one of the filter modes (happily, the one which is absolute useless for bass), while the Quack adds on a buffer for better frequency response, and both use Jack Orman's trick for making a broader range of dual op-amps usable for the pedal (more than simply a taste in sonic quality, the original was pretty much restricted to using the 1458 in order to even work properly).  Not exactly the bees knees of ECFs but both are easily built, and perf-able/tweakable in an evening.  Either will let you experiment easily and identify what you need, what's missing, etc.

Again, like the Baseballs, the filter range they come with is optimized for guitar and is determined by a pair of equal value caps (.0047uf in this case, since .005 is pretty much impossible to find) which set the range too high to be of use to a bass, most especially a bass with extend low range.  Dropping the range by two octaves (which means increasing the caps x4) is advisable.  Try a pair of .022uf caps for starters, and see if you like that.

For my money, I'd say a Dr. Quack with the one filter mode is probably best suited to your needs.  The filter mode you want is the one where the signal "enters" the filter via the .01uf/470k combo and the 47k resistor is tied to ground.  I'm also gonna take a wild stab and suggest you use a 47R resistor in place of the 100R value shown at the bottom of the schematic.  We can discuss why later on.