This is an excellent 50mW Hi-Fi PLL FM Stereo Transmitter that features BH1417 chip. ROHM's new Japan has BH1417 is one of the most simple and practical integrated circuits, which combines phase-locked loop circuit, stereo encoder circuit, transmitter circuit, as well as other additions. Pre-emphasis circuit, limiter circuit and low pass filter can significantly improve the sound quality. The total harmonic distortion up 0.3%, stereo separation to 40dB, RF output level is 100dB. BH1417F is an excellent new IC chip, this circuit improves signal to noise ratio (S / N) of pre-emphasis circuit to prevent signal over emphasized limiting circuit, the control input signal frequency low-pass filter circuit (LPF), generate stereo stereo composite signal modulation circuit, FM transmitter phase-locked loop circuit (PLL) component. BH1417F excellent frequency characteristics, it can achieve 40dB of isolation, transmitted sound quality is similar to local FM radio stations.

5W PLL Stereo FM Transmitter features PLL synthesized drift free operation with high quality BH1415 chip. 5W RF output power is achieved with 2SC1971 6W transistor in the output stage. Front panel digital control comes with LED display and case is made high quality aluminum. The board features EMI filtering on audio and power inputs and comes with Microphone and Audio inputs. Once transmitter is turned on it starts broadcasting with previously selected frequency. Overall this 5W PLL Stereo FM Transmitter provides professional broadcast audio quality and rivals commercial broadcasts.

This is an article about my new PCB design for HiFI headphone amplifier using audiophile OPA2132 OP-AMP chip. Main feature is that the new PCB fits exactly to the classic Altoids tin-can. This new headphone amplifier incorporates moreover bass-boost circuit and constant current charger for 9V battery.

This device is fully functional sound card for PC. The main advantage of using PCM2704 against PCM2702 is much easier construction. As you can see on the block diagram it has built-in 5V and 3.3 voltage regulator, HID interface (MUTE, VOL+, VOL-), S/PDIF output. The circuit can be powered directly from USB port. Next advantage is that the output DAC is able to drive directly 32ohms headphones, but the output power is only 12mW. For all details please refer to the PCM2704 datasheet.

This Phone FM transmitter connects in series to your telephone line and transmits the telephone conversation over the FM band when you pick up the telephone handset. Transmitted signal can be tuned by any FM receiver. The circuit includes an "On Air" LED indicator and also provides a switch which can be used to turn off the transmitter. A unique feature of the circuit is that no battery is needed to operate the circuit since power is taken from the telephone line. The transmitter uses only a short piece of wire aerial about 4" / 10 cm long to transmit the signal and some of the RF signal is also radiated through the telephone line itself. The circuit might be used to share or record conversations, but is not intended for illegal use.

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