Members Speeddemon Posted March 28, 2006 Members Share Posted March 28, 2006 I received a DOD FX-17 Wah/Volume pedal today, and I tried it out immediately. The volume function works normally, as does the wah, but the upper-half of the wah's sweep sounds very thin, while the lower half sounds super-smooth. Like it switches between 2 timbre's of wah. Now there are 2 holes on the front side, with small trimpots behind them. Does anyone know what these do? Link to comment Share on other sites More sharing options...
Members jonny guitar Posted March 28, 2006 Members Share Posted March 28, 2006 top and bottom sweep for wah Link to comment Share on other sites More sharing options...
Members bbrunskill Posted March 28, 2006 Members Share Posted March 28, 2006 I though on was wah sweep and the other was output volume . . . Try googling it.Cool pedal though, whacked out wah tone! Link to comment Share on other sites More sharing options...
Members jonny guitar Posted March 28, 2006 Members Share Posted March 28, 2006 Originally posted by bbrunskill I though on was wah sweep and the other was output volume . . . Try googling it. Cool pedal though, whacked out wah tone! That would explain why I could never get mine set up right as a wah. Link to comment Share on other sites More sharing options...
Members hoerni Posted March 28, 2006 Members Share Posted March 28, 2006 Here's the best page I've found lots of pics and links The trim pots in question are shown and explained near the bottom. There's links for mods and other stuff at the bottom. I picked up one of these a couple of weeks ago. It was broken and didn't sweep at all. After looking through the schematic I figured out the basics and started debugging. Turned out to be a broken solder joint on the transistor that connects to the fixed plate of the variable capacitor. Now, it seems to work fine. The sweep is very synthy but I don't think it was too thin on top. I did mess with the pots but don't remember where they are. Link to comment Share on other sites More sharing options...
Members Speeddemon Posted March 29, 2006 Author Members Share Posted March 29, 2006 Output volume trim for the wah, the volume pedal-function or both? Link to comment Share on other sites More sharing options...
Members hoerni Posted March 29, 2006 Members Share Posted March 29, 2006 Originally posted by Speeddemon Output volume trim for the wah, the volume pedal-function or both? I think the volume. to be fair though I didn't test it in wah mode... Actually looking at the schematic, they both appear to be in the control voltage generating circuit. I don't think they directly affect the wah or the volume, but rather the sweep range / contour. I'd need to check it out again with the pedal in front of me to say more. Link to comment Share on other sites More sharing options...
Members hoerni Posted March 29, 2006 Members Share Posted March 29, 2006 Okay, spent a few minutes with it in the lab, and I've determined that it isn't easy to describe what these pots do. If you look at the schematic Technical Explanation (you can skip this) There are a few sections of the schematic that can be grouped by functionality. First we have the Controller section. This is comprised of the 4007 chip, the variable capacitor (created by the foot pedal) and the MPS4124 transistor. The next section is what I'll call the controller drive section. This is built around the LM358 op amp. Then you have the 2 parallel audio effects, the volume circuit based on the 3080 op amp and the wah circuit based on the 13600 chips. From my rough understanding of the circuit, it looks like the 4007 is running as a ring oscillator (at about 1MHz). I think that the variable cap is changing the cutoff frequency of the filter at the input to the MPS transistor. Then the transistor and associated components act as an integrator to create a DC voltage in the 3.8 to 3.3 volt region (heel down to toe down) Here's what the trim pots do As I mentioned in the last post, the trim pots are in the controller and controller drive section, so they will affect both the wah and volume functions. As well as the 0 - 5 volt output - which is actually a good way to measure what you are doing with the pots. First we'll look at P1 (the right hand trimpot if looking at the front of the unit). With the trimpot in the center, you get full sweep on the voltage output from 0 to 4.75 (measured with a relatively new Duracell ). You will see 0 volts with the heel down and 4.75 with the toe down. As you increase P1 clockwise from the middle, the maximum voltage (with the toe down) will decrease from 4.75 to 0 (while leaving the minimum unaffected). If you then bring the pot back the the center and rotate it clockwise from there, you will raise the minimum voltage (with the heel down) from 0 to 4.75. (while leaving the max relatively unaffected) This has the effect of changing the min or max frequency the wah is swept too or changing the min or max volume for the volume control. The other pot P2 will narrow the range by increasing the minimum. With the pot all the way counterclockwise, the minimum is 0 volts (and the maximum is slightly lowered). As you increase the pot (rotating clockwise), the minimum voltage (heel down) will increase to about 1 volt. (when P1 is in the center). The fun thing is this pot works in conjunciont with P1 so you can lower your max freq with P1 and then reduce the range with P2. Some quick numbers (using a Fluke 37 volt meter and an old HP 3562A Dynamic Signal Analyzer) Voltage -> peak freq 0 volts -> 237Hz (3dB BW = 56Hz Q~=4) 0.5 volts -> 459 Hz 1 volt -> 750Hz 1.5 volts -> 1.05 kHz 2 volts -> 1.33kHz 3 volts -> 1.88 kHz 4 volts -> 2.5 kHz 4.58 volts -> 2.90kHz (battery must be dying - this should be 4.75 volts) To answer the original question I think you want to check out P1 and see where it is set. Turn it more clockwise to reduce the maximum voltage and hopefully reduce that thin upper end sound. If that doesn't work, try the mods. Damn! This pedal is a lot cooler than you're average wah (from a geek perspective ) Link to comment Share on other sites More sharing options...
Members Speeddemon Posted March 30, 2006 Author Members Share Posted March 30, 2006 I'll check your post later, because there's a nymfo gf moaning to me 2 meters from this PC, but I can tell you now that the trimpots DID affect the way the volume pedal functioned! When I had a half-decent wah sound, the volume pedal had only whole its sweep narrowed down in the last quart of the pedal's fysical travel! By turning both trimpots to around '11:30h', the sweep was full and normal again, but then the wah had the thin top-end. Link to comment Share on other sites More sharing options...
Members hoerni Posted March 30, 2006 Members Share Posted March 30, 2006 Originally posted by Speeddemon I'll check your post later, because there's a nymfo gf moaning to me 2 meters from this PC, but I can tell you now that the trimpots DID affect the way the volume pedal functioned! When I had a half-decent wah sound, the volume pedal had only whole its sweep narrowed down in the last quart of the pedal's fysical travel! By turning both trimpots to around '11:30h', the sweep was full and normal again, but then the wah had the thin top-end. There might be another way to modify the circuit in the volume or wah section so it can do a better job of both. It kinda makes sense that you can tweek it for one or the other, but not both. You could also find some fixed values you like for wah or volume and put it a switch to go between them. Link to comment Share on other sites More sharing options...
Members Roy Brooks Posted March 30, 2006 Members Share Posted March 30, 2006 I've got an FX17 on eBay right now. Link to comment Share on other sites More sharing options...
Members hoerni Posted March 30, 2006 Members Share Posted March 30, 2006 Originally posted by Roy Brooks I've got an FX17 on eBay right now. I'll be interested to see how it goes. Lately they've been in the $40 range, but a few months ago they were over $100. Your's looks pretty clean, so it's probably worth what you're asking. Hmmm, I might have to keep watching these to get a second for a fun project... Link to comment Share on other sites More sharing options...
Members Speeddemon Posted March 30, 2006 Author Members Share Posted March 30, 2006 Originally posted by hoerni I'll be interested to see how it goes. Lately they've been in the $40 range, but a few months ago they were over $100. Your's looks pretty clean, so it's probably worth what you're asking. Hmmm, I might have to keep watching these to get a second for a fun project... There went one in Germany a few days ago for a mere $20! with box and manual, but according to the description, I could gather a bit that it was somewhat defective. I've seen the one go for $146! All the others went for $30-50 usually. Mine was $36, with box, manual, warranty card:) And the battery door was there too. I'm considering picking up a 2nd one too... Because as a volume pedal, it works cool AFTER the distortion pedals, but BEFORE a delay (for ambient swell sounds), but BEFORE the distortion, it works as a sort of variable gain setting. My distortion comes from a Tubefactor, which is very responsive to input; less input=less drive. Link to comment Share on other sites More sharing options...
Members hoerni Posted March 30, 2006 Members Share Posted March 30, 2006 Originally posted by Speeddemon I'm considering picking up a 2nd one too...Because as a volume pedal, it works cool AFTER the distortion pedals, but BEFORE a delay (for ambient swell sounds), but BEFORE the distortion, it works as a sort of variable gain setting. My distortion comes from a Tubefactor, which is very responsive to input; less input=less drive. Well that makes sense. Attenuation is the opposite of gain (real gain, not what most people refer to as gain which is really gain + saturation). So a volume pedal in front of a distortion would reduce the voltage at the first gain stage of the dist. pedal. and make it sound less distorted. You should be able to do this with any volume pedal. Link to comment Share on other sites More sharing options...
Members sonaboy Posted March 30, 2006 Members Share Posted March 30, 2006 Originally posted by Speeddemon I received a DOD FX-17 Wah/Volume pedal today, and I tried it out immediately.The volume function works normally, as does the wah, but the upper-half of the wah's sweep sounds very thin, while the lower half sounds super-smooth. Like it switches between 2 timbre's of wah. Now there are 2 holes on the front side, with small trimpots behind them. Does anyone know what these do? one time back in college, someone from a band that played our house party left one there. i used it to prop open my bedroom window for years. the end. Link to comment Share on other sites More sharing options...
Members TrashFace Posted March 30, 2006 Members Share Posted March 30, 2006 the switch on mine is kinda messed. some one should buy it cheap and fix it. Link to comment Share on other sites More sharing options...
Members sonaboy Posted March 30, 2006 Members Share Posted March 30, 2006 Originally posted by TrashFace the switch on mine is kinda messed. some one should buy it cheap and fix it. i think ashley, who works for Zvex is always looking for wah casings to make her filter pedals, or something. i sold her an old crybaby casing. i imagine she'd still be able to get her effects guts in a box like the FX17 case. what's her username on here again? jadesky? Link to comment Share on other sites More sharing options...
Members hoerni Posted March 30, 2006 Members Share Posted March 30, 2006 Originally posted by sonaboy i think ashley, who works for Zvex is always looking for wah casings to make her filter pedals, or something. i sold her an old crybaby casing. i imagine she'd still be able to get her effects guts in a box like the FX17 case.what's her username on here again? jadesky? Not sure what she does exactly, but this is a very non-traditional wah shell. There is no rack and no pot. might be tough. Link to comment Share on other sites More sharing options...
Members hoerni Posted March 30, 2006 Members Share Posted March 30, 2006 Originally posted by TrashFace the switch on mine is kinda messed. some one should buy it cheap and fix it. How much do you want for it? (and why isn't it in you .sig) Link to comment Share on other sites More sharing options...
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