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previous: Rob Hey guys, maybe someone can help me... -- 8/27/1999 12:24 AM View Thread

Re: what's a T-wah?

8/27/1999 2:03 AM
Mark HammerRe: what's a T-wah?
The T-Wah is an older BOSS unit that predates the Dynamic Filter. Same deal, though. Up/down sweep, bandpass/lowpass, sensitivity, and resonance controls, but no footpedal control.  
AMPAGE readers know of my obsession with envelope-controlled filters. For my money, asking what's a "good" ECF to build is a bit like asking "what's a good effects chain to buy?". Most ECF's have a pretty unique personality, since there are many parameters to filtering sound, many parameters to deriving an amplitude envelope and control-voltage, many combinations of each of the above, and lotsa room for component tolerances to add a lovely unpredictable spin to the whole shebang. Most of the time, what's "good" depends on what you like to play.  
That being said, many people find there is more than enough personality for them in the Mutron III, schematics for which abound at the various sites like Aron Nelson's, RG's, Justin Philpott's, and an ever-increasing array (not to mention the clone at Mike Burgundy's site). Most parts are easy to obtain, although the photocell/optoisolator can be problematic for some folks.  
Another contender is the EH Bassballs, whose schematic can be found at Mike Burgundy's site (scroll down on your left to almost bottom and you'll find a link to it). This is a pretty flexible unit that uses garden variety components, and has ample room for easy-to-do mods. It works exactly like the famous Dr. Q, which is another decent pedal (albeit a little one dimensional).  
My fave is the MXR Envelope Filter, because of the variable attack time (which I think allows for better matching of the effect to the song, in addition to some interesting special effects). I keep promising to verify the hand-drawn schematic I have of this one and send it out for posting, but I'm about 4 years behind on promises. As much as I like it, I wouldn't recommend novices attempting it because of the parts count, because it uses CMOS chips (static sensitive), and because one has to be particular about which version of the CMOS chips; in short, because too many things can go wrong. On the other hand, I've made two without much problem so they can't be that hard.  
I don't have the schematic in front of me so I may be wrong, but I think the 2k pot on the Dynacomp is a trimpot serving as a "distortion trim" control, something which is normally found on 3080-based devices, and compensates for the quirks and constraints of that chip, rather than any kind of spiffy control to inject more personality into one's sound. This is set for cleanest sound and left alone. It is a board-mounted component, not a pot on the chassis.

Rob thanks, markI've be... -- 8/27/1999 4:17 AM
R.G. Absolutely correct on the 2K Mark. ... -- 8/27/1999 2:39 PM