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Old 25th June 2012, 06:38 PM   #21
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The gain of the op-amp is linear, regardless of the supply voltage. So, if you have a lower voltage supply you will push the op-amp into clipping sooner than you would with a higher voltage. In other words, the lower supply voltage will decrease the op-amp's clean headroom.

For example, if you have an op-amp set to a gain of 50, give it power supply of +/-4.5V (9V), and give it an input signal of +/-100mV, you should get an output signal of 100mV * 50 = 5V. However, since you only have 4.5V on the rail, the output will be clipped. Now if you have a second stage but this time you're putting +/-4.5V signal to the input, loads of clipping. Two stages with a gain of 50 each would be a total gain of 2500, which is pretty crazy. Go for it!
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Old 25th June 2012, 06:47 PM   #22
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MXR Distortion Plus uses a non-inverting amp, but this shows how you can use the DC offset idea. Notice the voltage divider made with 1M resistors at the top, feeding the + input. I made several designs based on this one back in high school. This is actually a very good, very simple design to start from.

Click the image to open in full size.
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Old 25th June 2012, 07:53 PM   #23
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GOING FOR IT RIGHT NOW. the picture does not show up though. i would just tie a 4.5 line directly on the fedback input line? while the 9v is on the op pin? can you send a link to the schematic
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Old 25th June 2012, 08:37 PM   #24
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Just do a google search for "MXR Distortion plus schematic" and you'll find it.

All you want to do is create a 4.5V DC offset for your input signal. So a 50% voltage divider using 100k or higher from the 9V rail, attach it at your op-amp signal input. Doesn't matter if you're using inverting or non-inverting, just offset the one that your input signal goes into. Don't forget about the DC blocking capacitors on input and output.
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Old 26th June 2012, 12:25 AM   #25
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Generally speaking the first stage of a guitar preamp/pedal should be a "Non-inverting " stage ......
In a inverting curcuit (post 13) the input impedance (R in) is part of the gain equation so you will get varying gain depending on what guitar you are useing which isn"t desireable and forces you to use high value resistors in the feedback loop to get a lot of gain which introduces resistor noise .....

The first stage should allways be a high impedance non-inverting stage , after that you can use inverting stages because the output impedance of the first stage is constant and low , I find it best to keep the output the same phaze as the input.......

There are different ways to get different distortions sounds useing diodes , You can use different diodes and in different configurations in the feedback loop or on the output of the opamp , you can even use Mosfets as diodes and even tubes as diodes for distorion .....
Remember that the diodes will clip the voltage at a different voltage depending on the type of diode which can limit your output volume especially if useing germanium diodes ......

Generally speaking every guitar curcuit should use a Fet input opamp as opposed to a BJT opamp , fet opamps have a high input impedance which is needed for guitar ......

just trowing out random related info .....

Cheers
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Old 26th June 2012, 12:34 AM   #26
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in what order would be best. ex. buffer high/low pass filter stage 1 gain EQ stage 2 gain high/low pass filter? anything im missing ?
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Old 26th June 2012, 04:53 AM   #27
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voltage divider bypass tonestack? EQ the clean sound?
mainly all the types of circuits i missed and best order ?
how can i add BASS boost. contour so forth,. ? what is the best way to introduce a relay into the input?? and connecting it to a female plug????? sound to plug relay.??
is a tuner a simple circuit to incorporate? tap tempo????

Last edited by freeminimika; 26th June 2012 at 04:59 AM. Reason: ideas
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Old 26th June 2012, 12:37 PM   #28
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Wow, that's some serious scope creep. haha...

You have enough questions that I think it might be best for you to browse some examples. Check out Schematic Heaven to get ideas from other effect pedals.
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Old 26th June 2012, 03:24 PM   #29
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I used too used the MXR+ distortion circuit with one gain stage after it.
then after that I used precision full wave rectifier with a mix control.
I used 1n34 germanium diode cilpping diodes on the first two stages.
Other versions I used 1N914 's and led's, But I liked the 1n34's the best.
I don't know were my final schematic is at the moment otherwise I would post it.
Using a TL074 I also used one stage to drive a 4013 CMOS Dual D Flip Flop as an octave divider.
It was a killer little unit as it covered four octaves and it did a excellent job of not mis-triggering.
I first built it on a protoboard and plugged and played the coupling and feed back capacitors until I got the sound I was looking for.
it was very fussy with a rich tone and had a lot of gain.
Using the TL074 it was the opamp to use of the day and was nice and quiet compared to the more common LM324 as it had almost no hiss at all for the amount of gain that it had.
It had a good tone and I rarely used it through any eq.

jer

Last edited by geraldfryjr; 26th June 2012 at 03:34 PM.
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Old 26th June 2012, 06:12 PM   #30
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ya i kinda hit you with too many at one time; im in ITT and they dont explain how it works like you do. You should think about a lesson channel on youtube. the opamp is doing almost all the work in mxr. is that how the analog pedal industry .. opamps.
Is it smart to run a JFET into a op amp? what does this do ?
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