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Old 11th May 2013, 06:13 PM   #1
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Default preamp for guitar

im looking to build a good clean preamp to install in my guitar to use for a lead boost! Any ideas or info would be great ! I need it to have a vlm contr and by pass swtch to turn it off and on ! Like i said im going to use it for a lead bost so doesnt have to be bunch more then normal but would want it adjustable ! Thanks !! Oh yea im not liking the lm386 much works ok but not real clean i find!
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Old 11th May 2013, 06:43 PM   #2
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This one is really great!

Discrete FET Guitar Preamp

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Old 11th May 2013, 07:10 PM   #3
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will the mpf102 work for this
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Old 11th May 2013, 07:40 PM   #4
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Yes the MPF102 should, you will find information on this site.
FET Preamplifier, Part 1

Here is another more complete diagram (drawing of the circuit is downloadable).
Onboard JFET Preamp

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Old 11th May 2013, 09:47 PM   #5
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Questions:- when the preamp is installed, do you want the same sound on your guitar, just louder (in which case you wire it in after the present Volume/tone controls, and switching it in and out of circuit is a doddle) or the extra clarity and attack you can get by running a pickup into a genuine high impedance (which involves a certain amount of rethinking to make the instrument controls function at all)? I tend towards the former for guitars, and the latter for basses, but it's a question of taste.

Silly question; how long a guitar lead do you use? With a passive guitar the capacitance of the lead interacts with the inductance of the pickups for a rather odd frequency response, if the cable's long enough for the effects to be in the audible. With an active, most of these effects are eliminated; and since this is effectively a low pass filter (slightly resonant) there's a tendency for the brightness to go up as well as the gain when you switch to lead, which might take a touch of body out of the sound.

I like that first circuit, even if I tend to put a pnp transistor in the output (I'm generally hitting for enough current to be able to drive straight into a desk, not just a guitar amp). The second? Why the two inputs and mixer? Two pickups? And 250k is too low an impedance.

How are you intending to switch on and off the battery? If you put power on the circuit with the same switch that you use to put it into operation I'm betting heavily on a pop when you change from passive to overdrive. If you want it to turn on when you plug a jack in, you'll be changing the guitar jack; the convention is to use a three pole jack socket and assume the jack shaft will connect the ring to the sleeve, which it does, most of the time, but it means your ground's got DC flowing through it. A switch on the finger board you're likely to touch while you're playing, and one round the back of the guitar is going to get forgotten, probably at an impotant gig, bu Murphy's law.

My preferred solution was to put an XLR on the edge of the guitar (when the guitarist could be persuaded this was a good idea) and use balanced mic cables to bring signal and power from a box by the amp. Not as well screened as a good guitar cord, but with the lower impedance output of the preamp there's less interference being picked up anyway. Not sure the argument holds for your "switch to passive" specification, though (although mine did have a relay inside the guitar so that if power failed they reverted to passive).

Trust there's some useful information in there.
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Old 11th May 2013, 10:07 PM   #6
tinitus is offline tinitus  Europe
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sounds more like you could use a volume/expression pedal
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Old 11th May 2013, 10:40 PM   #7
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i have one but this is more of a idea i have for a friend that will let him step it up a little without using feet

im not wanting to change the sound just boost it a little louder for a lead
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Old 12th May 2013, 03:41 AM   #8
JMFahey is offline JMFahey  Argentina
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This one is very goo, not only for Strats , of course, and has a lot of resources to help you.
Stratoblaster Booster
They offer a PCB if you wish, or Thermal Transfer for DIY PCB or perfboard layout.
And although they suggest building it into a pedal-like form, it's actually meant to be built-in the guitar.
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Old 12th May 2013, 03:54 AM   #9
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thanks jmfahey this looks like it ! Of course i will build it from scratch and change a few things but great start for what im looking to do
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