mj_gant Posted November 7, 2004 Report Share Posted November 7, 2004 Is there a way to attenuate a pickups output before it goes to the pot? I know most want more output, but I have a case of trying to match pickups with different outputs in a guit. Capacitor? Resistor? Quote Link to comment Share on other sites More sharing options...
Drak Posted November 7, 2004 Report Share Posted November 7, 2004 Try screwing the pkp itself down in it's mounting bracket or pickguard, that is the easiest way to attenuate a pkps output. Or screw the other one up, nearer the strings, or a combination of both, lowering one while raising the other. Quote Link to comment Share on other sites More sharing options...
mj_gant Posted November 7, 2004 Author Report Share Posted November 7, 2004 Try screwing the pkp itself down in it's mounting bracket or pickguard, that is the easiest way to attenuate a pkps output. That was the first thing I tried, not enough though. Thanks anyway. Isn't there a cap or resistor to lower volume? values? Quote Link to comment Share on other sites More sharing options...
frank falbo Posted November 7, 2004 Report Share Posted November 7, 2004 It's near impossible not to have the sound quality suffer when attenuating the output. Perhaps the best solution is a dual preamp like the ones from Bartolini. I know you're probably not interested in spending the cost of another pickup just to match them. But once you preamp a pickup's signal, it becomes "attenuatable" without any signal loss. Then you can locate the pickups wherever you want for the best attack and tonal response, and still be able to balance them. Quote Link to comment Share on other sites More sharing options...
Kyle Cavanaugh Posted November 8, 2004 Report Share Posted November 8, 2004 (edited) If each pickup has their own volume, you could try a lower pot value. It will be slightly softer and a little warmer. Half resistance= about an 8 on a Strat knob, for instance. Oh yeah, and you can make your own preamps real easily if you have some basic knowledge, and a stereo output jack. Maybe try this for each pickup and use a voltage divider (or a trim pot for adjustability) after it to attentuate the volume. But, at the same time, it will be clearer sounding, so if you're pleased with your sound already, you might also want to add a cap in parallel with it. Trust me, you can make this for less than $10 bucks or less. I've made them (actually more complex ones...) for close to nothing by desoldering the parts out of dead circuit boards and putting the circuit on a small, cutoff piece of perfboard. Edited November 8, 2004 by Kyle Cavanaugh Quote Link to comment Share on other sites More sharing options...
lovekraft Posted November 8, 2004 Report Share Posted November 8, 2004 (edited) Here's a problem-solver I've used in the past - it's a simple minimal parts count source follower buffer with an attenuator, so you can turn it down without losing high end. Use 16 volt caps and 1/4 watt resistors - click on the pic for a larger view. Most small-signal JFETs seem to work OK, so you can use that Radio Shack MPF102 if it's all you've got access to. Don't use this with a bass or with active pickups. <EDIT> Looks like great minds think alike - since we both posted a source follower. Edited November 8, 2004 by lovekraft Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted November 8, 2004 Report Share Posted November 8, 2004 I like this little preamp. I have it installed in one of my guitars and I am going to add one to my project guitar that I am currently working on. Quote Link to comment Share on other sites More sharing options...
Devon Headen Posted November 8, 2004 Report Share Posted November 8, 2004 Bizarre. I saw that link on the MIMF last night. I guess I should just experiment, but I'm trying to get a good preamp the bring down the impedance on a piezo before it leaves the guitar. Do you know if either of those is better for my scenario? Thanks, Devon Quote Link to comment Share on other sites More sharing options...
lovekraft Posted November 8, 2004 Report Share Posted November 8, 2004 If you're looking for a preamp, use the Don Tillman circuit that Paul mentioned - it's simple, quiet and fairly transparent. I'm sure that in addition to lowering the impedance, you're also going to want to boost the signal a bit. You can replace R4 with a 50K audio pot, and you've got a volume control. Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted November 8, 2004 Report Share Posted November 8, 2004 Oh, duh. We're talking buffers, aren't we?! That little buffer schematic that lovecraft posted looks a lot like the schematic I linked to, except that Tillman circuit is set up for service as a preamp more than a buffer. I like that Tillman circuit, because while it is a preamp, it's not amplifying the signal that much. It's maybe 3dB or so. It's really made to compensate for cable losses, etc., so in my mind it's something between a buffer and a preamp. Isn't a buffer supposed to be a guard against impedance mismatches and tone sucking due to cables and stuff? To me, they are close to being the same thing. Anyhow, the one guitar that I put it in really sounds better to me than before. It has also has the side effect of making a hot output humbucker even hotter. That's why in my current project, I am going to have the option to switch the preamp on/off. YMMV. Quote Link to comment Share on other sites More sharing options...
Devon Headen Posted November 9, 2004 Report Share Posted November 9, 2004 Where can I get a schematic for a preamp with a little more boost than that? Is this (the 50K pot) useable? I've never seen a "double pot" before. Is it like a blend pot? http://www.cascadesurplus.com/catalog/inde.../sort/2a/page/2 Quote Link to comment Share on other sites More sharing options...
lovekraft Posted November 9, 2004 Report Share Posted November 9, 2004 (edited) To get massive gain from the Tillman circuit, simply get another 10µF electrolytic cap and wire it in parallel with R2, positive side towards the JFET source and negative to ground. As shown, the circuit will give you a gain of 6 or 7dB, or slightly more than double the input. With the extra cap installed, the gain jumps to almost 20dB, or 10 times the input voltage, but be aware that distortion will increase as the circuit is driven closer to it's headroom - a hot pickup can easily overdrive it and clip the output signal, although it's unlikely that piezo pickups will. If you want to be able to preset the gain, you could change R2 to a trimmer and bypass only a portion of it - PM or email me if you don't follow any of this, I don't always explain things really well. The pot you linked to will work great - it's just a waste of the other half of it, but at that price it's not really a big deal. <EDIT> Just noticed that both Don Tillman and Paul mention getting only about 3dB of gain from this circuit - my experience is a bit different, the one I built (using a 2N5457) more than doubles the input signal, according to my multimeter, without any audible distortion so long as the input is below 100mV. This could simply be the product of the variation in JFETs, or some inaccuracies in my test equipment, so please take these gain figures with a large grain of salt. Lets just say for accuracy's sake that there is a clearly evident audible boost qwith the stock preamp - with R2 bypassed, it turns into a nice little overdrive that breaks up real sweet wth hot humbuckers. Edited November 9, 2004 by lovekraft Quote Link to comment Share on other sites More sharing options...
mj_gant Posted November 9, 2004 Author Report Share Posted November 9, 2004 Guys, thanks for all of your suggestions. I am not interested in a preamp. What would happen if i took a 200k mini pot (flat type) and put it inline before it hit my main 500k pot? I could then attenuate inside the cavity and leave it set. Any thoughts? M Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted November 9, 2004 Report Share Posted November 9, 2004 Check out this page: http://www.muzique.com/lab/buffers.htm Maybe it will help you decide what you want. Tillman's circuit is basically a buffer/preamp circuit. You could put a trimpot at the output and essentially you have the same thing as the other circuits mentioned. I think that these little circuits would work fine, IMO. Quote Link to comment Share on other sites More sharing options...
daveq Posted November 9, 2004 Report Share Posted November 9, 2004 Lovekraft - C1 is drawn as an electrolytic and is in the path of the guitars signal. Since it is being used as a coupling cap, does it really need to be electrolytic? Does the FET require that an electrolytic be used for some reason? The reason I'm asking is that I have read many times that we should avoid using them in the signals path due to their poor audio qualities. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted November 9, 2004 Report Share Posted November 9, 2004 I'm sure that using an electrolytic (or tantalum) cap as a coupling cap is something of a compromise in this case, but considering the size and expense of a 4.7µF poly cap, it's a compromise that I can easily live with. You might use a ceramic cap there, but I personally avoid them like the plague - for size, price and quailty, a tantalum is probably the most optimal choice, but that's merely my opinion (and I'm no purist!), since this choice is aways going to be subjective, based on which your ears prefer. HTH. Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted November 9, 2004 Report Share Posted November 9, 2004 I would take the electrolytic cap rather than a ceramic, unless it was rated for 1KV... Quote Link to comment Share on other sites More sharing options...
lvs Posted November 9, 2004 Report Share Posted November 9, 2004 What would happen if i took a 200k mini pot (flat type) and put it inline before it hit my main 500k pot? An attenuation of around 4dB with the mini pot at maximum. But it will kill brightness and even have the effect of a lowpass tone control. Bridging the inserted resistance with a cap of around 680picoF will restore resonance though; it may even restore too much brightness, and ask for an extra resistor in series with the cap itself. A sideeffect of the cap will also be a slighty different tone when the two pickups work together in parallel. Maybe you could do a simple test with a cap and 220K trimpot first, and if you think it has potential, insert a 20K trimpot in series with the cap for fine tweaking if needed. Finally, it would be best to replace the trims with fixed resistors. A few caps between 470-680p together with a trimpot (or two) don't cost much money. Quote Link to comment Share on other sites More sharing options...
Devon Headen Posted November 10, 2004 Report Share Posted November 10, 2004 Is it alright to use a 25V 4.7 uf cap for c1 instead of the 16V lovekraft recommended? Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted November 10, 2004 Report Share Posted November 10, 2004 Is it alright to use a 25V 4.7 uf cap for c1 instead of the 16V lovekraft recommended? Absolutely! Its always OK to go higher, but you never want to go lower than your power supply. In low voltage circuits like these, people generally use 16V caps. A fresh 9V battery puts out about 9.5V, so a 10V cap, which is next voltage range lower than 16V, is really pushin' it. Quote Link to comment Share on other sites More sharing options...
Devon Headen Posted November 11, 2004 Report Share Posted November 11, 2004 I figured that was the case, so I went ahead and ordered it. Thanks . Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted November 11, 2004 Report Share Posted November 11, 2004 Glad to be of help. Quote Link to comment Share on other sites More sharing options...
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