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Old 15th May 2013, 03:13 PM   #11
Zero D is offline Zero D  United Kingdom
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@ swissCHEESER

See my screenie for correcting the circuit you drew.

As you're using OpAmps now, try mine & see how it compares
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Last edited by Zero D; 15th May 2013 at 03:16 PM.
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Old 31st May 2013, 10:11 PM   #12
Zero D is offline Zero D  United Kingdom
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What's the outcome ?
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Old 1st June 2013, 09:18 AM   #13
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Default Outcome until now

Thank you for your post ZeroD. I suppose the outcome is more hair pulling, and failure. I have built the circuit Mooly suggested...it doesn`t really work..for me anyways....took a long long time to build as well. I`m sure I`ve made some design failures...but gosh -- this is darned frustrating. I`ve spent the greater part of what feels like a year on this thing and reckon I might never get it to work.

Do you have any suggestions?

I`ve posted my schematic. Any time and expertise you would contribute would be greatly appreciated.

presently, when i plug in a quarter inch jack to the input and touch my thumb to the tip of the cable -- one light will dim slightly and the other will get a bit brighter....the tip of the iceberg to what i want. if i plug the cable into the guitar - i get virtually nothing unless i play really aggressively on the higher pitches. Seems like 33x gain, followed by up to 50x gain, followed by 33x gain should be enough to amplify the guitar signal enough to function with the last part of the circuit. But honestly, i have no way to check it to see if it is working. My oscilloscope is on the fritz and by Job, I am not sure what to do next.

does this circuit make sense to you? should it work? what parts of the circuit are faulty with respect to the design? how can i modify the circuit and get what i want? i want the two LEDs at the end of the circuit to respond to the input of the guitar dynamically. one should be on when the guitar is not being played -- the other one off. when the guitar is played the one which was on should dim (more or less, based on the dynamics of the signal) and the other LED should light up (more or less, based on the dynamics of the signal)

any ideas?

swissCHEESER
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Old 1st June 2013, 02:24 PM   #14
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Default at ZeroD

that last resistor towards ground in the last opamp which isn`t marked is a 33k.
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Old 1st June 2013, 04:19 PM   #15
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Default ZeroD

ZeroD, all that jibberish at the end of my last post was an attempt to put in the blue bug-eyed smiley. results are par for the course. anyways, i wanted to chime in again to let you know that i tried the above schematic several times in circuit simulation before building. worked great of course. in the real world -- sure doesn`t...perhaps also par for the course. thanks for your help. -swissCHEESER
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Old 1st June 2013, 04:24 PM   #16
Mooly is offline Mooly  United Kingdom
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You say it works in simulation but not in the real world.

Is the feed from the guitar suitable for driving the input stage as it stands ? What program are you simulating it in ?

I've deleted that last post
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Old 1st June 2013, 04:31 PM   #17
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Default suitable input

Mooly, I`m not sure about the input of the guitar....what should it be to be classified as suitable to drive the input stage? As for the simulation -- I used the java applet found at this website. Circuit Simulator Applet if you are up for downloading that applet, i can post the text file which you can import and see it working on a computer. the exact same circuit -- doesn`t function the same in the real world. ho hum.
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Old 1st June 2013, 04:36 PM   #18
Mooly is offline Mooly  United Kingdom
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I wondered if it was LTspice you were using.

Isn't a guitar pickup high impedance ? That needs to work into a really high impedance.

Let me have a think and see what I come up with I'm not keen on those on line circuit simulator do dahs
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Old 1st June 2013, 04:49 PM   #19
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Default giutar pickup impedence

Mooly, thanks for putting some time and thought into it. Regarding the guitar...and the pickup output impedence....i measured the 1/4 cable when it was plugged into the guitar and get 3.8k ohms resistance....not sure if this equates directly to impedence. Anywho, online my preliminary research tells me it is normal to expect output impedence in the range of 6k to 10k from the normal passive pickup guitar. As for how that equates to the input impedence of the circuit....well...i have no idea.
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Old 1st June 2013, 04:55 PM   #20
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Default impedence

not even sure if i`m spelling that right...but if i wanted to raise the input impedence of my "amp" to allow for a better acceptance of the signal.... would it behoove me to swap out the 10k resistor on the input with a 100k..? and then swap out the 1nF cap on the input with a 100pF? hmmm....perplexing. not sure why that would make a difference....would it?
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