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Old 25th June 2012, 12:44 PM   #11
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I don't have any schematics handy, but they were very simple. Two stages, each with adjustable negative feedback loops. I used germanium diodes at the output of stage two for extra clipping.
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Old 25th June 2012, 12:52 PM   #12
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when u say negative you mean inverted or non inverted? also did u use a filter or buffer? or eq in what order ??
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Old 25th June 2012, 01:12 PM   #13
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Inverting, like this one:
Click the image to open in full size.

In place of Rf I put a pot to adjust the gain. For a dual stage I used a dual-gang pot that would adjust the gain of both stages at the same time. This allowed me to have a huge range of gain, anywhere from classic rock overdrive to full on shred metal. I made mine very simple, with just a passive tone control (cap and pot to ground after the final stage, right beside the clipping diodes), and relied on the amp for final EQ. On the input I just used a capacitor to block any DC offset from going out the input. I did have a later version that used a single transistor as a buffer before the first op-amp.
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Old 25th June 2012, 01:17 PM   #14
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What are the hardest clipping diodes/leds?
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Old 25th June 2012, 01:27 PM   #15
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Quote:
Originally Posted by freeminimika View Post
What are the hardest clipping diodes/leds?

Silicon diodes (1N914, 1N4148 etc) clip "harder" (= more harsh) than germanium.
If you choose your supply voltage carefully in your pedal, you could also try to clip against the rail voltages....

YMMV
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Old 25th June 2012, 01:28 PM   #16
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what do you mean by clip against the rail voltage?
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Old 25th June 2012, 01:28 PM   #17
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I only experimented with a few types, standard silicon (1n4001, etc) and some germanium diodes (don't have the part number handy). With dual stage you'll be getting a lot of your clipping from inside the op-amps, which is partly why the JFET based op-amps are better IMO. The tone of the overdrive and distortion is less harsh. For metal you may be thinking that harder clipping would be better but what I found is that smoother clipping gives a more consistent crunch and better tone. I would recommend that you build using DIP sockets for the op-amps so you can swap out different types and experiment with it until you find the balance of tone that works for you.
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Old 25th June 2012, 01:31 PM   #18
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Quote:
Originally Posted by fastfolkert View Post
Silicon diodes (1N914, 1N4148 etc) clip "harder" (= more harsh) than germanium.
If you choose your supply voltage carefully in your pedal, you could also try to clip against the rail voltages....

YMMV
Oh yeah, and speaking of power supplies, I always used 9V with a 4.5V DC offset at the op-amp input. This low voltage made it very easy to clip at the rails internal to the op-amps. Then of course you need the input and output caps to block the DC component.
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Old 25th June 2012, 04:15 PM   #19
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why is it easier to clip the 4.5?? your saying the 9v goes to the V and 4.5 into the input then feed it back into the inverted op ?? what does tieing a resistor to 4.5v before the + on the op amp do if my feed back is coming to the - ??
"This low voltage made it very easy to clip at the rails internal to the op-amps" WHAT do you mean by clip the internal rails?
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Old 25th June 2012, 04:18 PM   #20
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"With dual stage you'll be getting a lot of your clipping from inside the op-amps, which is partly why the JFET based op-amps are better IMO" can you clarify this a lil ? Imo? BTW thank you alot for the help its exACTLY THe the information im looking for. its hard to find answers so indepth.
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