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Old 17th January 2011, 05:23 AM   #1
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Default electric violin - headphones amplifier

I have an electric violin with piezoelectric pickup.

Does someone have a simple plan for an "headphones amplifier" ?

I'm looking for something small and simple for me to build.

I prefer something based on 2N3904

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Old 17th January 2011, 06:51 AM   #2
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Most of the headphone amps schematics that you are likely to find are expecting a pretty high signal from a CD player or the output from a DAC, iPod, or computer sound card. Most of those are in the 1-2 volt range.
Your piezo pickup doesn't put out anything like that, so you will need an amp design with higher gain, I think.
In this case, non-diy might be cheaper....
You might want to consider something from the guitar world - there are headphone amps aplenty for electric guitar, or you could opt for something like a Pandora which would give you straight amplification plus a whole bunch of effects, which could be fun.
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Old 17th January 2011, 06:56 AM   #3
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You won't get simpler than a single opamp and 9 volt battery.

To use 2N3904's would be far more complex to bring a piezo level signal up to a low impedance output to drive phones.
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Old 17th January 2011, 06:58 AM   #4
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If it is a piezo pickup, it will need a high impedance load (a bit like the old ceramic phono cartridges used to need). A simple opamp design running on a 9V battery is easy enough to make. If you use a FET-input op-amp, it will give you a high enough input impedance. Are you sure your pickup is piezo? My electric violin uses an electret mic as the pickup. I guess you want to output of the amp to be able to drive headphones for practice playing?
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Old 17th January 2011, 11:06 AM   #5
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ok.. so ignore of the 2n3904..

I need something small and simple to amplify my electric violin..

I tried to build the circuit below, but it was not very good (i get very weak signal in the headphones)
Click the image to open in full size.

and I find this preamp based on FET
Discrete FET Guitar Preamp

but I'cant find the j201 or 2N5457 in radioshack.. maybe someone can help me to find something with components from radioshack..

Ouroboros - yes is piezo pickup..

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Old 20th January 2011, 11:52 AM   #6
Mooly is offline Mooly  United Kingdom
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Hi Amber... you must still be under moderation as you are not triggering the thread notifier.

The input impedance of your circuit is to low for a piezo to work into. That's the first problem. The second is that (if this is what you are doing) it won't drive headphones at all. You would need another stage to do that. The circuit in your link overcomes problem 1, the input impedance is determined by R1, 3 megohm. It still would not drive h/phones.

Can you get a 2N3819 fet ?
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Old 20th January 2011, 01:14 PM   #7
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After some research I once considered building the attached circuit for a piezoelectric pickup of an acoustic base guitar.

I bought the J201 via Farnell, but you can find it dirt cheap on ebay.

The simplest headphone amp may be a CMoy amp, just google it.

I recently built me a NP-100v12: DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier and I'm still very pleased with it.
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File Type: pdf FETPreamp.pdf (94.4 KB, 64 views)
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