unclej Posted December 10, 2004 Report Share Posted December 10, 2004 does manipulating the gain of an op amp by changing the ratio between the input and feedback resistors in an effects circuit make an appreciable difference in the sound comming out of the amp if all of the components past the output of the op amp remain the same? by the way, a couple of you suggested that i stay away from the 741. can you tell me why and give me a specific replacment or two? Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted December 10, 2004 Report Share Posted December 10, 2004 does manipulating the gain of an op amp by changing the ratio between the input and feedback resistors in an effects circuit make an appreciable difference in the sound comming out of the amp if all of the components past the output of the op amp remain the same? Yes. The feedback resistor is pretty much what controls the gain. The input resistor has a much smaller affect, although making it the wrong size can wreak havoc. Too big, and you start to lose the highs. by the way, a couple of you suggested that i stay away from the 741. can you tell me why and give me a specific replacment or two? The LM741 is a very noisy opamp for an audio circuit. I would use a TL071, NE5534 or an OPA134A. There are others as well, but those are probably the most popular ones. I have, however, used a 741 in some circuits, and it wasn't really a problem. Quote Link to comment Share on other sites More sharing options...
unclej Posted December 10, 2004 Author Report Share Posted December 10, 2004 thanks paul. i appreciate the info. and you know what's scary? i actually understood what i was asking this time. Quote Link to comment Share on other sites More sharing options...
JohnnyG Posted December 10, 2004 Report Share Posted December 10, 2004 the gain formula for inverting opamps is simply the feedback resistor (resistor from output to negative input) divided by the input resistor. for non invertin opamps its equal to 1+ (feedback resistor divided by resistor from positive input to ground) i could give you alot more info on how to tell which is which but you'll be able tofind it in 10 seconds on google and im feeling lazy atm sorry lol Quote Link to comment Share on other sites More sharing options...
unclej Posted December 10, 2004 Author Report Share Posted December 10, 2004 thanks jg..actually i found the formulas and that's what prompted the question. i'm building a mxr distortion + as a learning excercise and i plan to experiment with different diodes and diode configurations and now the different resister values. if i find anything that's gonna set the music world on it's ear i'll let you know Quote Link to comment Share on other sites More sharing options...
JohnnyG Posted December 10, 2004 Report Share Posted December 10, 2004 if you're playing about with that then you may want ot have a look around for the guide to different diode sounds in dostortion pedals. i cant find it atm but it'll tell you all about how LEDs/signal diodes and Germanium diodes will go in stomp boxes and gives rough guides as to how they sound. have a look for it. ithink its at muzique.com somewhere Quote Link to comment Share on other sites More sharing options...
unclej Posted December 10, 2004 Author Report Share Posted December 10, 2004 great, i'll look for that. the schematic that i found for the mxr distortion + offered three different options. using 1n4148's would make it more buzzy, 1n34's more fuzzy and a different array of 1n34's more crunchy. it also said use LED's for more crunch but i don't know what those are...yet Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted December 10, 2004 Report Share Posted December 10, 2004 (edited) Oh, duh. I was thinking about the input resistor of the circuit. Here I go posting while I'm working again. Sometimes I do dumb things that way... LED stands for "Light Emitting Diode" Here's an example of an LED: Sorry for the lo fi picture. I like the way LEDs sound in the feedback loop of an opamp distortion circuit. I seem to like Ge diodes the least... Edited December 10, 2004 by Paul Marossy Quote Link to comment Share on other sites More sharing options...
unclej Posted December 10, 2004 Author Report Share Posted December 10, 2004 whoah back there bubba...so you're saying that if i replace the two diodes in the feedback circuit with LED's that they work the same as..DOH..the term is light emitting DIODE isn't it? guess i'd better try a couple of those too. thanks Quote Link to comment Share on other sites More sharing options...
JohnnyG Posted December 10, 2004 Report Share Posted December 10, 2004 lol you learn amazingthingsevery day dont you i find that LEDs give a really good crunchy overdrive sound and they're the shiznit for everything from easy blues to ballsy rock Quote Link to comment Share on other sites More sharing options...
Paul Marossy Posted December 10, 2004 Report Share Posted December 10, 2004 so you're saying that if i replace the two diodes in the feedback circuit with LED's that they work the same as..DOH..the term is light emitting DIODE isn't it? Yep. They generally do impart a crunchy sound to a circuit when used for clipping. Different colors seem to have slight differences in the sound, too. I generally use red or green. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted December 10, 2004 Report Share Posted December 10, 2004 Back to the subject of the 741, I 've found that using them in high gain circuits such as distortion boxes often leads to intolerable noise levels, but then I've been told that I have a very low tolerance for noise. Any circuit that compresses the signal, whether by gain control or by clipping, is going to raise the noise floor in the process, so I'll usually use either a TL071/081 or a NE5534 over a 741 (or a "magical" 4558, for that matter) as a matter of course, for the same reasons I use metal film resistors and film caps almost without exception. YMMV. It's all about what you like, and what you can put up with. I've also had really good luck with the Burr-Brown chips, and the TI JFET input opamps work great for certain applications, but they're harder for me to get, so I usually stick to my perennial favorites unless I need some special characteristic. Quote Link to comment Share on other sites More sharing options...
unclej Posted December 10, 2004 Author Report Share Posted December 10, 2004 thanks all..i'll file those numbers away for future use. i've already purchased the 741's and guess i'd better use them. i don't know about that different color different sound thing paul..sounds more like santa syndrome to me. and my christmas just got a lot better today. i sold one of my customs to a local musician that i've been trying to get on board for a couple of years now. he's starting to make a name for himself in the austin music circles and that's gotta be good advertising for old unclej. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted December 11, 2004 Report Share Posted December 11, 2004 i don't know about that different color different sound thing paul..sounds more like santa syndrome to me. Actually, that one makes sense - the different colors all have different forward voltage drops, so they would have different sounds in the same circuit. Congrats on the sale! I hope it's a lead-in to that market for you! Quote Link to comment Share on other sites More sharing options...
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