Donovan

well, it's entirely clean as far as i can tell. I'm using a tech 21 blonde pedal as an amp simulator (its not great, but it works). wow, you took off work to work on an led project? sorry i just find the irony funny for some reason now, i tried to add a post-gain volume control, and keep my gain stage at a fixed gain, but here's what happens: even though i have a log pot, as i adjust it, the volume is at zero, then at some point in the sweep it jumps up to max volume. I've wired the pot up several different ways, and I can't get this problem to go away. I assume it has something to do with the opamp's low output impedance and the fact that i'm using a 100K pot. But i tried it with a 10K trim pot, and i have the same problem. any solutions? That does sound kind of bad, doesn't it. Well, I originally took off because I was dead tired. My wife works 12 hour shifts on Sundays and Mondays, leaving me as a babysitter as well as 2-way transportation... doesn't make for a good Monday, especially when you add a doctor's appt to that. The LED project is just something I brought myself to do during the early morning hours as I've been excited about it and working on the concept and drawing for about a week, but today ended horribly after a crapload of trials, no sucess because the op amps can not give me enough gain to drive more than one LED. I am going to have to add a crapload more components. If I do get it going, it's going to be an RGB spectrum analyzer with color shifting to pitch, mounted in a strat pickguard, between the pickups. I use 100K pots as well. If the problem was the pot value, I think going higher would be better than lower. I haven't run into your exact problem, but I have run into something similar very similar where the last bit on the high end seems to jump up a bit suddenly,but I always though it was because I was not using log pots. Something else to try... maybe a longshot, but move your gain pot to outside the loop, where the resistor to ground goes and vary it there, then use a 100K fixed resistor inside the loop instead. That's how I've seen it most, though I did not think the way you have it should cause a problem. Can you draw how/where you've got it hooked up? I connect the volumes like this. This drawing also has the noise-reducing caps we talked about.

Well, what's the performance like now anyway? I'm assuming the sound you got is entirely clean or does it have some dirt to it as well? The quote character...ugh. I must have typed it 2000 timed in the past 3 pages. well sorry if you misunderstood, it was only a joke. Thanks, but not necessary... I think I came off as uber-persistent. hm, i'm not so sure about that. maybe if youve got a wall supply, where "ground" is actually connected to the ground (is it, actually, in a wall wart???), then the 0v would be more constant than the 4.5v. But with a battery, if the voltage all of a sudden jumps from 9v to 8v, i think the best way to describe what happens would be: the "9v" node jumps down by .5v, the "ground" node jumps up by .5v, and the 4.5v node stays where it is. This is because the "ground" is not actually anchored to anything big, like the actual ground. And it is best understood how the 9v battery reacts by viewing it as 2 separate 4.5v batteries, as is shown in one of my "sarcasm" drawings. This seems like more of a philosophical discussion of relativity than an application discussion, though. Some, but not all adapters. Obviously, none of the 2-prong deals are. I believe some of the 3-prong deals have the Gnd tapping the transformer. We can agree to disagree. I am going to back off on this Gnd discussion as my knowledge level is at its bounds and if you're happy with what you have, then I feel satisfied. If you're going to use an AC adapter, maybe look into rechargeables and a charging circuit, then you can be mobile when it's inconvenient to plug in. I'm off to enter my own frustration with an LED project I'm working on. I've been trying to do something similar to your project, but trying to get enough gain to rectify it and re-amplify the DC enough to drive LED's brightness. I took the day of from work and have been at this for about 8 hours already, unsuccessful and very annoyed... time to unplug. My 3 year old is playing my strat that is sitting on the living floor with about 7,000 resistors all over the place. Time to intervene.

right, there is no voltage bias after the output cap. UNTIL you plug in a pair of headphones. Then youve got 37 ohms (DC resistance of my headphones) connecting the sleeve and tip, biasing the output side of the output cap so that the signal swings above and below whatever the sleeve is. Thus, it does not matter what the charge of the sleeve is relative to some arbitrary point such as the negative terminal of the battery. It matters what the charge of the sleeve is relative to the output tip connector. And this voltage will be 0V, regardless of where the sleeve is in relation to that arbitrary point. idk how the sleeve and tip measured 4.5v with the sleeve attatched to ground, but it did. and i repeated the experiment, and the results were the same. (as far as this little experiment, i'm puzzled) yes, and btw, i hope you dont take my stance as me trying to be difficult, or trying to disrespect you; i'm just trying to learn what i can about circuitry, and at this point i do firmly believe that the constant voltage between sleeve and the battery's negative terminal has no effect on the DC voltage b/t tip and sleeve I admit I felt some negativity in that last post when i saw the filenames, but I am to blame as well as my own frustration of trying to explain things which are approaching the limit of my technical jargon, but OK, today is a new day and now we're on a better track. 1) No, I can not tell you with surety what R6 does, but it appears to be a standard thing to do frommany resources. I have copied it (in your case I scaled it with the rest of your values). It does appear in the MXR Distortion + that I provided previously, as well as the DOD 250, and the active mixer schematics on this page: http://www.harpamps.com/schematics/. In the case of mixers, I found an explanation saying "The resistors further the isolation between inputs, i.e. serve to limit the back-feeding of input signals." 2) I omitted the cap from the 9V to Gnd as you said you already tried it and it had no effect. I do put that on all my circuits. I test all my 9V circuits with a 9V AC adapter. Those supplies are much noisier than a battery and I find I can discern a huge difference with that cap in that mode, which BTW they call a "supply bypass" cap, so I've included it in everything since as a default. I should also mention there are 3 varieties of this. The first one is, for me, usually a 100uF and goes directly across the battery + and -. The 2nd is smaller, usually a 1uF, directly across the + and - power inputs on any op amp or other IC in the circuit. The 3rd is the one going from "M" to ground. They all do the same thing. The one on the battery is the main one. The op amp power one and the "M" one both serve to cut any noise that was picked up in the line between the battery and the location of interest because these lines can pick up noise in even those short distances. Even though you could not hear a difference when you tried them, if you try it with an AC adapter, you may be pleasantly surprised at the difference and decide to go the mojo rooute as I have. If this is what you meant 2 posts ago, OK, that is what I would expect... a 4.5VDC swing with ouput connected and with an input signal running through it. With it just powered on and quiescent there should be 0VDC, only the residual AC quiescent noise. With it connected and running the 4.5VDC swing should only be with it cranking some music. It does matter. It is just good general practice to use one Gnd wherever possible. If you can use one massive Gnd, it will be a more effective Gnd. Everything else will be in reference to it and when there is an errort-type spikes/dips due to imperfections in the supply or components heating up, etc., they will be more efficiently sunked, for lack of a better term, and there will be less of a divergence or more of a convergence. Using "M" as a Gnd in those extra places, though you may not hear it, is less than ideal because "M" is not really static as a 0V Gnd is. "M" is an ever-moving (however slight) product of the current formed within a voltage divider and has its own noise associated with the fact that there are wires, resistors, and a current. Does that make sense? If you do insist on using "M", it would be a step up to use a zener diode regulator or a voltage regulator to form the midpoint as they have their own error-correction by nature. Also, there is a tradeoff relationship in the resistors you choose to form the "M". Lower value resistors have as a potive that they create less noise than higher value resistors. They have as a negative that they will consume your batery faster. The converse is true for higher value resistors used there. The same scenario goes for within your feedback loop. I am limited in being able to explain any of that better as I don't have any formal education on design. What I have is limited to what I learn from the resident nerds at my workplace, what I research online, and what I tinker with. So, I can only try to explain these things in the contexts they were explaonied to me or how I preceived them. The more I try to explain this Gnd stuff, the more dangerous it feels, so I'll stop here, but will be on standby if there's anything more I can help you with. One other thing Paul M mentioned a page or two ago... the TL072 is basically the same as the TL082 but lower noise. You can't get it at your local RS, but it, as well as many newer op amps designed specifically for audio, may serve you well. The LM741 and TL082 are general purpose op amps with specs that aren't so hot. You may see a large difference in perceived noise just by upgrading the op amp, though if you do go that route, no point in stopping at the 072, might as well talk to a specialist at Philips, Fairchild, or LT and get something really new and pretty. I feel the need to mention how much I am beginning to hate the SHIFT " typing sequence.

By the time you go through all that is necessary, it won't be any cheaper than finding a leftover VG or a used one. I hear they're getting rid of leftovers for around $999. What's a Variax go for? It could be done 100% DIY. All you need is a PHD in electronic engineering, a purple heart, and the key to the city.

I connected the voltmeter so that 1 lead was on the sleeve of the output jack and the other lead was on the tip connector of the output jack. The way my schematic is now, with sleeve connected to "m", it read about -50mV. When the sleeve was connected to ground, it read 4.5V! Then I even connected BOTH sleeves to ground, and it still read 4.5V. If you don't believe me you can breadboard one yourself. Nice filenames on those drawings. Neither of those drawings is correct. This one is. I should have just drawn it that 1st day to avoid the decline in mood. Notice all negatives and Gnds are common, with VCC/2 (your "M") connected to only 1 place... not 2, 3, or 4, just the 1. 4.5VDC can not make it past the output cap. That defies the nature of the capacitor. It is not theoretically possible for you to have moved both sleeves to Gnd and measure 4.5V from signal to Gnd after the output cap. Before the output cap, yes, after it, no... unless, you have VCC/2 applied to Gnd somewhere else (which you do, the end of the feedback loop is another error) or your output cap is faulty. Any measure of 4.5VDC should be confined to within the op amp circuit (the input/output caps) with both sleeves connected to system Gnd. Instead of me building it your way, I suggest you build it my way. I've got over a dozen of these types of circuits built and need not prove the theory to myself. Please don't take any of this as badgering. I am only trying to help and would not want to feel like I am letting you go with misinformation, so if I can steer you right, I am going to, as painful as it may get for either of us. If this last part is correct the way I describe, I bet all of your detectable noise will be gone and wouldn't that be excellent? If not, and I'm wrong, well then at least you have something that works in a way you are satisfied, right?

Centered around 0v? are you sure about this? When I passed the signal through the input coupling cap, all the DC was removed. There was only AC. And I was required to put the 100K resistor to "m" to tell the signal what constant voltage to swing above and below. It doesn't just know what DC voltage to use. So why would the signal after the output coupling cap "know" what DC voltage to use? It doesnt. You assume that the AC signal would choose ground by default, but it doesnt. It'll use whatever you give it. Here I gave it "m" via the sleeve, so it swings above and below "m", which is perfect, because the sleeve is at voltage "m". It works exactly the same as if i connected the sleeve to ground. If you don't believe me, look at that underlined sentence and try substituting "ground" everywhere you see "m". It holds exactly the same truth value! remember, voltages are relative. They are not values of charges but instead they are differences between charges. If an AC signal is riding on 4.5v, the 4.5vDC is irrelevant as long as the place to which the AC is flowing is also at 4.5v. Note that the entire post-output-cap circuitry is not even connected to ground(except by the 100K power supply resistors which can be ignored). So the current isn't flowing from 4.5v to 0v, it is in fact flowing from 4.5v to 4.5 v. So there is 0 DC current. As close to 0V as theoretically possible. You are making my point by making the assumption that "M" is the ground you should be using on the ouput side. You took out the DC with the output cap and are then putting it back in. That is bad for reasons I've explained 3X now. You should be using system ground everywhere except 1 place and the only reason to use it in that place is input biasing. Everything else should be a 0V Gnd. If you don't believe me, get a volt meter. You will see 4.5 V on your output. This is not good. I am only trying to help, but unfortunately,don't know how else to convince you. Good luck.

That is what should happen with that power bypass cap when you disconnect the batttery the way you did. This is why devices incorporate power switches. The cap is discharging once you remove the battery. What it does is charge up and keeps a better DC level than the battery can, tregardless of whether it is audible. In the even of momentary spike or dip in the batery voltage (that's what you're simulating by disconnecting that battery), the cap makes up the difference by feeding what is necessary from its store. In a configuration with this cap, the power switch is usually put in place to cut either the positive or negative rail at the point it connects to the cap. That kills power and disconnects the cap at the same time, so the behavior you mentioned is not there. You are wrong about this and seem to be confused or misled on Gnds in general. I've already explained why "M" should not be connected to the sleeves, but try a different way. Even if you can get sound that you think is OK in this configuration, I don't think it is a good idea to move forward with these wrong ideas, but do what you will. Let's start with just the guitar, no circuit. Your guitar's output connector has a tip and a sleeve. The sleeve is the Gnd at 0V. The tip can sway plus or minus about the sleeve. The guitar's untouched signal does sway positive and negative. It is true AC. So, picture this as a sine wave centered around zero volts. Nothing the op amp does can go negative, ever, unless 2 batteries are used, because one battery can only be 0 to 9V, all it can do is be somewhere between zero and 9V... varying degrees of positive. When you add "M" to the raw guitar signal,you're biasing it to 4.5V, so instead of having true AC centered around zero, you have 4.5VDC that has an AC riding on it. The AC is shifted up by 4.5V. There are times when you do want this and times when you don't. You don't want this on the sleeves ever. Let's pretend though that you did want it on the input sleeve. So now instead of a pure AC, our signal at the tip is now centered around 4.5V. Once you pass the 0.1uF capacitor on the input, you remove the 4.5V. Remember, the cap blocks it, so then we're back to a true AC! Let me ask you then, what was the point of adding "M" to begin with? There isn't one. Not only is it useless on the ring, but adding an imperfect variable in and then using an imperfect method to remove it has to add noise. "M" is added after the input capacitor. Doing it there does not allow it to bleed backward into the guitar signal because of the input cap. This is where we DO want "M", to move that signal from being centered around zero to centered around 4.5V. This accomodates the 9V battery and this is the only reason to do this. On the output side, before the signal passes the 220uF cap, it has the DC offset of 4.5V on it. The purpose of the output capacitor is to remove that 4.5V and bring the signal back down to a true AC, centered around 0V. So like I asked before about the input side... on the output side, why would we remove the DC with a capacitor only to add it again at the ring? Removing it with the output cap is correct. Adding it back in at the sleeve is not. Incidentally, both the input and output sleeves should be connected to the systerm Gnd. Again, here's how it should be: Unless your guitar is all opened up, the closes thing you have to Gnd is the guitar's output connector sleeve. The op amp negative power input should be connected to the output connector's sleeve should connect there too, as well as the end of the line in your feedback loop. "M" should not go to any of those. As a last piece of evidence for this, study the MXR schematic again. Find their "M" made by 1M resistors and a 1uF cap. How many places do they add that signal to? Only one, on the signal AFTER the input cap. All other places are system Gnd at a theoretical 0V. What I think you've done is make one mistake, then make a 2nd, so you have a case of 2 wrongs that actually do make a right. Yes, you're wrong about the treble bleed mod. It is not something to apply to the gain pot. It would be something to apply to a volume on the circuit's output, after the circuit's ouput capacitor. The treble bleed mod allows a certain amount of highs to forgo being sent to ground as you roll off the volume, preserving a lot of what gets lost in turning down a traditional volume knob.

The pot in the feedback loop is a gain control, not a volume control. If you put a pot on the output, that is a volume control. There is a difference, in that gain is a multiplier of the original signal and can never be less than one, unless the circuit is setup as an attenuation circuit, but yours is not. Volume is what allows a reduction of the total (post gain), all the way down to zero. If you can get zero, it probably is not a true zero, but if it functions to your liking, it is not a waste either. The cap config for "M" that you mention, I have not seen that one, but do not think it makes much of a difference, other than series capacitors half the capacitance, so it doesn't sound like a good thing, since higher capacitance is better there (lower corner frequency for the low pass filter) but I could be wrong there on why they did what you saw. The active "M" allows you to bring "M" to other parts of the circuit (like another signal entirely) without worrying about the crosstalk so much,for example if you were building a mixer out of many op amps. Right now, if you connect "M" to other signals, they may bleed into one another, but with the active "M", there's more push-to-"M" power for lack of a better description. Yes, jumpering the tip and the ring will give mono in both sides, but will reduce the output as well. To get around this, you can use 1/2 of the TL082 as a right and 1/2 as a left, then you won't lose volume and you'll have 2X the output you currently have. Very importantly, in looking at your latest schematic, I do not believe you should have the sleeve of the input or output connectors going to "M". I think those should go directly to system Gnd, 0V... not the 4.5V "M". That is VERY likely to be the cause of the rest of your hiss. What is happening is you are adding a 4.5V bias to the input before you are even into your circuit, then removing it with the 0.1uF cap on the input (undoing what you've done by connecting "M" in the firstplace). Then, at the output, the 220uF cap removes DC bias (the "M"), but after that you're adding it back again. That is going to add noise and reduce the life of your speakers... they don't want a DC bias. They want to be in their natural resting position... having "M" connected to the output is liking putting an offset to the speaker cone and reduces headroom.

Yeah, it would be nice if RS stocked them.

OK, I just noticed a rather large design issue. I did not realize before you have a volume on the input! This is not the best way to go for signal-to-noise-ratio reasons. This is part of your noise problem, in my opinion. I would lose that altogether, so you are allowing the full guitar signal in and adjusting gain (and output volume) as necessary. Put a 100K pot in where you have the 100K resistor in the feedback loop. Where you want a volume control is on the output (after the output capacitor). Yes, your tone will be more trebly when volume is up and it will lose highs as you go down. This will happen with any value standard pot. Not that it is a good thing, but is normal. This is just like what happens with a standard guitar volume. You can do a treble bleed mode, like show on this page... read whole page: http://www.projectguitar.com/tut/potm.htm ...or, if you want it to be less trebly, then adjust the value of the cap in parallel with the 100K resistor in the feedback loop. A larger cap should yield less treble, but make small adjustments there! Yes, the TL082 lacks those pins because it is internally compensated and does not need offset nulling. No, DO NOT remove the cap between "M" and virtual Gnd. It is serving the same function as the 9V bypass cap, but in a different spot. Removing it would reduce performance and increase noise. As far as you rpoposition of: ...can you draw that? I'm not quite following you there. However, since the TL082 is a dual op amp, what some designs have is one half of the TL082 doing a different version of an active "M" that can serve as a "virtual Gnd" for many other op amps, whereas your passive "M" can not do so without affecting the rest of the circuit. Then, they use the other half for the gain section.

First off, congratulations on getting where you are. You should be proud. This stuff frustrated me for a LONG time. Paul is correct. The LM741 is a "general purpose" op amp, not specifically intended for audio. You are probably always going to have some noise unless you modify your choice of chip. However, I do think we can do 2 more things to drastically reduce the noise you have now. I have not mentioned them previously because we were already throwing a ton of info at you and may have been overwhelming and I considered it much more important that you actually get sound and gain first. The best news of all here is that if the following 2 things don't do the trick, then most of the other 8-pin DIP package op amps share the same pin configuration, sort of a standard, so switching from the LM741 is a simple pop-out-old, pop-in-new. 1.Condition the battery power going into pin 7 of the LM741. To do this, add a 100uF (or larger) cap from pin 7 (V+) to Gnd. This forms yet another low pass filter, sending a great deal of the AC spikes/dips from the battery to Gnd and allowing just the bulk of DC to get to the op amp's power input. Not doing this makes a pretty big difference in my experience. The connection to pin 7 should be as close to the body of the component as possible, NOT at the end of a long lead, to avoid any other induced currents long the way to the pin. 2. Balance the inputs. The LM741 (and all differential op amps) are subject to minute variations in the manufacturing process that makes them "less then idea". This means they have some error in the inputs, referred to as input offset current. When you apply gain to a signal, the error is amplified along with the signal. To get around this, the manufacturer provides pins for measuring and "nulling" the offset, sort of like a calibration procedure which restores the op amp to a more perfect balance, thus reducing any imbalance, reducing error, and reducing noise on circuits with gain. Look at this page and go about 3/4 down, check out Fig. 11 and the procedure there. Unfortunately, you need a multimeter to do this. http://www.uoguelph.ca/~antoon/gadgets/741/741.html I think you are right about the one other resistor. I could not find any documentation to support this, buyt I seem to remember that there should be a resistor somewhere in the circuit that is the parallel sum of your R1/R2 gain resistors. I have never bothered with these as I never had a static gain setting, I always use a potentiometer for variable gain, so that resistor value would need to change every time I moved the pot... not practical. If you've been going to Radio Shack for your components... try the TL082 op amp. It is better quality and provides 2 op amps in one 8-pin chip, so you could do stereo and get the benefits of pre-balanced inputs and JFET inputs, which are better than the bipolar transistors the LM741 utilizes.

I didn't know audacity could do that... where is that?

Col- What this thread DOES need is organization. Why not have one post that you repeatedly edit with the most up to date, clostest thing to success that each of you have. When you make progress, simply come back and edit it. Make it all inclusive, so that all you have to do is point us less technically adept folks to it and let us sink or swim. IMO, PSW should have done that at post #1, but why not start now and help cut down on the chapters of needless reading you mentioned? If it's well-written and coherent and speaks to the intended audience (those of us without a PHD in quantum mechanics), it would be very well received. Write it and they will come.

It's a code, not a straight value. The implied unit is pF, but the last didgit is a multiplier. http://www.kpsec.freeuk.com/components/capac.htm

The cap in parallel with 200K forms a low pass filter, rolling off the highs... the right value attenuates frequencies above the audible range (20kHz). I am holding that that other cap does need to be connected to ground. Study the MXR schematic a bit more. Notice after that cap (a .047uF), they have some more resistance (a 4.7k followed by a 1M potentiometer). That is KEY! ...not the exact values, but the premise. You're blocking DC going to ground, and allowing AC to go to ground. This is what tells the op amp that it needs to boost AC and not boost DC. Op amps amplify difference between the inputs. Also notice that in the MXR schematic, their "M", formed in the top half of the drawing, uses 1M resistors to form the 4.5V, then yet another 1M resistor in seried before connecting it to the + op amp input. You might try that. In any case, using higher values there than your 15K's will save battery life AND reduce noise because higher values will allow less curent through and bring the low pass filter's F to a lower number, providing a cleaner "M" reference voltage. At this point, I am convinced your cap values are your biggest problem. I do not think you need to worry about impedance matching. Op amp inputs are high impedance, so they won't mess with your guitar in a backward manner. The outputs are low impedance, so they should be able to match high and low impedance on the next stage without a problem. What might be an issue is that the op amp's output current is not all that high, so it might have trouble driving headphones, I'm not sure as I've not tried it. I used the LM741 to drive as a preamp, not an actual amp, and it works excellent. You might want to try hooking up the output to alligator clips and clip them onto another guitar cable going into your normal amp in order to test easier, at least for sound quality and to see if you are getting any working gain. Get some potentiometers when you go to RS. Yes, their prices are about 100X higher than buying online, but nothing beats them for the sheer convenience of it... mine is a 20 minute drive, which equals no wait for delivery and no minimum orders like you may find online. Anyway, I think you're on the right track. This can be a long and frustrating road your first time, but once it clicks, imagination is the only limit to the kinds of projects you can embark on.

I want to remove the rosewood board from my guinea pig guitar to do some wiring from its underside. What's the safest way to get the fretboard off the neck? Can I heat it up to make it easier?

I think you need to do a few things. 1) Where you have your feedback loop connecting to "M", I believe that needs to go to ground, meaning the same place the battery negative goes. Also, there really needs to be a resistor where you removed that one. That, along with your 200K resistor are what sets the gain. In your current configuration, there is no gain loop, at least in the conventional sense. I think you are getting "open loop" gain, or something close to it, which is the op amp going wide open. What most setups have instead of an actual resistor (where you removed yours) is a potentiometer. Gain in your configuration is G = R1/R2 + 1, where R1 is your 200K and R2 is the one you removed. A 200K pot in the spot you removed that resistor from yesterday would let you vary gain from 2X to whatever the open loop gain of the op amp data sheet says it is, within the bounds of the power supply. 2) If you can, try changing the cap values. They play a really big role in what gets amplified and what gets attenuated. I think your values are too large, with the exception of your output cap. Since the cutoff frequency is F = 1/(2*pi*R*C), you can see that F becomes smaller as R or C becomes larger, so what this means is that for a low pass filter (formed in the feedback loop), the bigger the cap, the lower the cutoff frequency, and the more that highs will suffer. a) Try a 0.1 uF in place of your 1 uF input cap. Try a 0.01 uF in place of the cap that's in parallel with your 200K resistor. c) Try a 0.047 uF in place of your cap that goes directly to "M", but again, that should not go to "M", but rather to ground, ground being same as batery negative. Lastly, in answer to your question, none of these caps ned to be electrolytics. In fact, you will have a hard time finding electrolytics in the values you most need. You need smaller values, probably a good idea to get a cheapo $5 kit from Radio Shack . You need values from .001 uF up to 1uF to experiment. Look at this circuit, I believe I got this from DIY stompboxes.com. It has the same general setup that you need to accomplish with regard to ground, "M", and the gain feedback loop. I built this and it works kicka$$

15K resistors will eat battery quicker,but should work. Everything that was connected to GND should still be connected to ground, with the exception that MAYBE the 1K resistor could go to "M", but I don't think so. Try it going to GND first. Make sure the op amp negative power input goes to GND, not to "M". The 10K and 100K resistors... not sure about the 10K, but the 100K and the 1uF cap make a high-pass filter. The 10K may be noise-minimizing or impedence-related. Both of those resistors should be able to be removed without killing function. Lastly, I THINK that another thing they are not telling you is that for your gain to work,you'll need another cap. In your drawing, insert a cap directly to the right of the 1K resistor. I believe this is th eonly way to get gain working in the config you have. Do a search for "MXR Distortion Plus Schematic" and check out how the opamp is set up. It is as bit more complex, but shows how a good gain is set up. What op amp are you using?

Bill- I remember your Ace Frehley top. That came out really nicely. I'd like to see some closeup pics of some of your fretboard stuff. Your pics that I could find are all very small, too small to make out any detail. How do you route the wires? Are they inside the neck? What kind of surgery does that require or is there some spare room inside a guitar neck? (I've never disassembled one). I don't think I could bring myself to going the route of cutting channels along the outside for aesthetics sake. I agree, you're right, you can run a series string off one resistor. That's not a problem at all. Drivers come in when you want functionality or power conditioning that you don't get from a battery. This thread has me inspired and kicking around a unique LED idea myself. I started laying out a rough prototype tonight on a breadboard and so far so good, the simplified version works, but I don't want to give away the details until it's done as I don't think it's been done yet and I'm excited to be the first. The downside is it is going to require a lot of routed wood for all the components on the circuit board to fit. The project will have only about 15 LED's, but will take about 30 other through-hole components on a proto PCB to run in different "intelligent" modes.

Theoretically, it could have influence based on interference. If it is electrically conductive and magnetic, then it can act as an antenna and can affect the flux of the pickup to some degree when in close enough proximity through inductance. In the practical world, it may or may not have a perceivable effect, but I'd guess not. Further, I've not read anything suggesting others ghave had a similar issue, but I guess that does not carry much weight. I believe the frequency range it picks up on is calculable based on the rod's length, but this is a precision, low tolerance measurement, meaning the likelihood of you picking op on some AM or FM is low, but this kind of theory gets very complex very quickly, and is beyond me as you'd probably have to also consider the other properties within the rest of the system. To demonstrate, a friend and I attempted optimizing the length of the antenna on an iPod vehicle interface. We varied the length by a few hundredths of an inch and failed miserably. The signal was decreased greatly... again, precision, low tolerance measurement. About the minimum distance, the relationship of magnetically induced signal to distance is inversely and exponentiall proportional, sort of like gravity, so each increase in distance has the effect of exponentionally decreasing the items ability to induce a current.

As wiring colors and schemes vary greatly, it will be easier for someone to help if you can provide a drawing of some sort.

Well, where did you get that schematic? There appears to be a major flaw in that design or a portion left out of the schematic. I ran into this exact issue when first trying to utilize op amps for sound a few months back. This is because of a few things. One, there are A LOT of bad schematics on the web. Two, even the half decent ones do not specify how to setup the power supply properly. Op amps are made easiest to use with dual supplies, and they don't tell you this in most of the op amp primers. Googling "single supply op amp circuit" will explain in further detail what I am about to summarize, but here's a links to what I consider the holy grail of single supply op amp circuits for DIY'ers... Texas Instruments document The circuit as is, should work with dual (series) power supplies with "GND" connected to the tap between the two. That circuit, I do not believe can work with one 9V battery as is. This is because one of the inputs needs to be referenced to the midpoint of the power rails to be able to swing above and below something in creating a AC wave. Like it is, the op amp is probably slammed to either +9V or GND all the time, hence no sound. It would as is be more of an onn/off detector, telling the op amp to send full rail in one of two states, full on or full off. More or less, you are telling the op amp to do something it can not. Once you bias to 4.5V, then the signal has a workable reference point, from which it can swing above and below nicely. Do NOT confuse this idea with giving power at the op amps power inputs. I do realize we often leave the power inputs off the drawing as a matter of readability. However, these are 2 entirely different concepts. The power inputs just supply the op amp with power. Biasing the inverting or noninverting input to VCC/2 or virtual GND creates a "reference point". How to do this: Create a virtual GND or a VCC/2. This is usually a simple voltage divider, utilizing 2, series 100K resistors that are connected between +9V and GND. The midpoint of the resistors is 4.5V. That midpoint is your virtual GND or VCC/2. To cut noise, a cap in parallel with this midpoint and going to GND shunts unwated AC to GND by creating a low pass filter. Incidentally, you should do this low pass thing any place you add + voltage to a chip as well, meaning the op amps positive supply pin should have a low pass filter on it. Bias one of the inputs to virtual GND or VCC/2 (4.5 volts). In this picture, from the Texas Instruments document I linked earlier, the virtual GND gets attached to the line marked (VCC/2). In your drawing, I'd try adding the VCC/2 point right at the noniverting "+" input. This should get you SOME sound, whether or not your gain feedback loop is properly set up... that's another hurdle to figure out after you try what I've outlined above, but I suspect the design may also need other work-overs in that dept. Lastly, your circuit is going to need an output capacitor as well to ditch the DC bias coming out of the op amp. What the output will have as AC is actually 4.5V, plus or minus some swing. The swing is your AC wave. An output cap removes the DC bias, leaving only the AC portion. To do this, add a 1uF cap onto the output after your output resistor, and probably ditch the output resistor entirely. Not doing this will likely put your headphones out of ideal operating range, if not causing them to fail entirely. Edit: I just looked at the 2 links in th eprevious posts and confirmed that yes, those schematic assume you are eiyhrt using dual supplies (2 batteries with a center tap) or creating a virtual GND, using a VCC/2, so none of those circuits should work without doing this. Funny how they expect us to just know this!

I get over-excited sometimes... eyes will be waiting to see what you come up with.

Actually, Keegan, I think you are wrong about the frequencies... so I'm not AS dyslexic, but my math still sucks. Bass low E = 41 Hz http://en.wikipedia.org/wiki/Bass_guitar_tuning Guitar Low E = 82 Hz http://en.wikipedia.org/wiki/Guitar_tunings

Woh, I am dyslexic! I have no idea how I was of by that amount, and yes, I meant on guitar. Sorry, I thought that's what his project was... and I also thought 80 was the low E, so 160 would be 4th fret, 2nd string. 80 is a bass' low E???? I have been misinformed and am going to have to kick someone's a$$!