NP-100v12: DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier

Posted on Feb 4, 2014

The NP-100v12 is a simple headphone amplifier that allows an entry level builder to experience assembling and listening to their own creation. I use the term builder as electronic experience combined with innovation which allows the creation of a device, rather than simple board stuffing. This amplifier can take on many shapes and sizes; I especia

NP-100v12: DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier
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lly like when builders reuse older devices as cases and even recycle some components from various discarded power supplies. I try to keep price at a minimum because this amplifier is very basic and allows the builder to seek out theory, and actually "listen" to their music, and grow to build more complex projects in the future. There are plenty of wonderful websites out there that can explain tube theory, I learned from the US Navy NEETS module 6. I will not go to in depth into the theory, but will introduce you to the 12AU7 (known in Europe as ECC82). The 12AU7 (ECC82) is a Twin Triode vacuum tube, it is very popular in the audio world because it is rather rugged and can be operated at lower voltages. You will find these tubes in vintage amplifiers and organs. They are even used in older vacuum tube volt meters and their life span can reach into decades. The 12AU7 has an amplification factor ( µ) of about 17, this is moderate as compared to its cousin the 12AX7 that comes in at 100. For purpose of the NP-100v12 the 12AU7 tube will be used in a common cathode configuration, and the incoming signal will be amplified by approximately 10dB. The 12AU7 is usually operated at plate voltages of over 120 volts, but fortunately it can be operated at lower voltages with decent results. As you see in the load lone graph below, we will operate in the 6 volt region. 6 volts allows enough "swing" for the signal to reach 12 volts and down...

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