Introduction, HOW IT Works | Ramsey Electronics QAMP20 guide

INTRODUCTION

The Ramsey QAMP series of QRP power amplifiers are compact 10 to 20 watt RF amplifiers for QRP CW transmitters. These amplifiers are made to be driven by transmitters in the ½ to 2 watt range. Built-in to the power amplifier is a sensitive T-R relay which will switch the unit in and out of the antenna line. When in receive, the amplifier is bypassed and the antenna feeds directly to the input jack. When you go to transmit, the T-R circuit detects the transmit RF power and automatically switches the power amplifier into the circuit and amplifies the applied RF power. If you decide to run "barefoot", turning off the QAMP will disable the amplifier and your QRP transmitter will feed directly through the amplifier without any amplification. Power is supplied by any 12 to 15 volt DC source with a current draw of 1 to 3 amps depending upon RF power output. A 5 pole low pass filter using toroid cores keeps harmonics and spurious signals very low. The entire amplifier is very easy to construct, but does require you to wind a few coils and RF transformers - we'll lead you step-by-step through all steps!

HOW IT WORKS

The QRP amplifier is very simple with most of the "magic" being done by just a few parts, the pair of MOSFET transistors and the ferrite wideband transformers. Transformer T2 matches the 50 ohm amplifier input to the push-pull inputs of the FET transistors. The term push-pull means that one transistor amplifies the positive portion of the input signal while the other transistor amplifier the negative portion - put another way, one is pushing while the other is pulling! The center tapped transformer splits the input signal so each transistor will only amplify the correct part of the input signal. Incidentally, this push-pull technique has been used for years in both vacuum tube and solid-state gear.

The push-pull signal output from the FETs is combined and impedance matched to 50 ohms by ferrite transformer T1. To reduce any harmonic content, a 5 pole low pass filter consisting of L1,2,3 and C4,5,6,7 is used.

The FET transistors are biased "on" slightly for best gain and linearity. Zener diode D1 provides a constant voltage for the bias network R2,3,4. Bias pot R4 allows adjustment of bias voltage to the FET transistor gates. It is adjusted for a set amount of current through the transistors.

The T-R relay circuit uses a simple diode detector consisting of D2 and D3. The detector output is amplified by transistors Q3 and Q4 to drive relay K1.

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QAMP20 specifications

The Ramsey Electronics QAMP20 is a versatile high-fidelity audio amplifier designed to meet the needs of audio enthusiasts and professionals alike. This compact amplifier is characterized by its exceptional sound quality, robust construction, and user-friendly features, making it suitable for a wide range of applications, from home theater systems to professional audio setups.

One of the standout features of the QAMP20 is its power output. With a maximum output of 20 watts per channel, the amplifier delivers clear and powerful sound, capable of driving a variety of speaker types with ease. The QAMP20 is particularly well-suited for small to medium-sized speakers, providing ample power to enhance the listening experience without distortion, even at higher volumes.

The QAMP20 employs advanced technology to ensure the best possible audio performance. It features a class AB amplifier design, known for its excellent linearity and low distortion. This technology strikes a balance between performance and efficiency, ensuring that users receive high-quality sound while minimizing power consumption. Furthermore, the unit utilizes high-grade components, including capacitors and transistors, which contribute to its overall durability and reliability.

In addition to its impressive audio performance, the QAMP20 boasts a user-friendly interface, making it easy to integrate into any audio setup. It includes multiple input options, allowing users to connect various audio sources, including CD players, computers, and digital music players. The rear panel features standard RCA inputs, while the front includes a 3.5 mm auxiliary jack, providing flexibility and convenience.

Another noteworthy aspect of the QAMP20 is its compact design. The amplifier is lightweight and small enough to fit seamlessly into most setups without taking up much space. This portability makes it an excellent choice for both home and on-the-go applications, allowing users to enjoy high-quality audio wherever they are.

In conclusion, the Ramsey Electronics QAMP20 stands out in the crowded market of audio amplifiers due to its combination of power, advanced technology, and user-centric design. With its ability to deliver exceptional sound quality and its flexible connectivity options, it represents an excellent investment for anyone looking to enhance their audio experience, whether at home or in a professional setting.