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  • Connecting speaker signals to line level inputs

    Sometimes it is necessary to connect a device which has only speaker outputs to external amplifier’s line level inputs. Because speaker levels are much higher than line level signals, the direct connection does not usually give satisfactory results. That’s the reason why I developed this signal level attenuator for connecting speaker signals to line level […]

  • Line level signal to microphone input adapter

    Sometimes there is need to convert line level signals to such signal that it can be connected to microphone input. Because the line level signals are typically in range of 0.5..2V and the microphone signals are in millivolt range, quite much attenuation is needed to match the signal levels. This means that typically you will […]

  • Powering microphones

    Copyright Tomi Engdahl 1997-2010 This document is a collection of information and circuits for powering electret microphone capsules. This document is written for people who understand the basics of microhone circuits. VN:F [1.6.9_936]please wait…Rating: 4.8/10 (232 votes cast)VN:F [1.6.9_936]Rating: -1 (from 61 votes)

  • Dynamic microphone to electret microphone input

    Design and copyright Tomi Engdahl 1999 Summary of circuit features: Circuit which works as an preamplifier which allows you to replace an electret microphone with a dynamic microphone. Circuit protection: No special protection circuits used Circuit complexity: Very simple one transistor circuit Circuit performance: Worked well, although distortion and noise performance is not very good […]

  • Audio line isolation transformer

    Copyright Tomi Engdahl 1996-2010 If you want to do the ground loop elimination in audio path, you have to cut the galvanic connection but pass the whole audio range. The simplest and most common way to do the isolation is use audio transformer which is ment for audio use. Transformers for audio use have some […]

  • Audio amplifier output relay delay

    Design and copyright by Tomi Engdahl 1998 This is a simple circuit which I built to one of my audio amplifier projects to control the speaker output relay. The purpose of this circuit is to control the relay which turns on the speaker output relay in the audio amplifier. The idea of the circuit is […]

  • 8-watt audio power amplifier

    The LM383 is an affordable, high-performance amplifier suitable for automotive applications. High current carrying capacity (3.5a) enables the device to low impedance loads with low drive power Distortion. The LM383 is current limited and thermally protected.<cut> High voltage protection is available (LM383A), the Way, the amplifier to withstand 40V transients on its offer. The LM383 […]

  • 5.8 W Audio Power Amplifier

    This circuit use TA7222AP to speaker audio. The price of only $ 0.99 and 5.8 watts, can supply with muting Control.<cut>Power provide for the use of 8-12Vdc, it is a good idea for car audio power amplifiers, coin-op machine game, safety Use system, etc. Fig 1. TA7222AP pin out Pin Name Description 1 Vcc Supply […]


    This circuit is the audio amp section for a complete optical transmitter. The increased circuit and filters the voice audio signals from an electret microphone. The circuit is described in detail in Section receiver Dave Johnson’s Handbook of Optical Communications Through the air. <cut> Click on Drawing Below to view PDF version of Schematic </cut> […]


    For some RFID systems, which is at 125KHz, a very low distortion signal source is required. The circuit on this page results in a 10-volt peak-peak signal into a 50 ohm load, with a distortion of only 0.01%. <cut>Click on Drawing Below to view PDF version of Schematic </cut> VN:F [1.6.9_936]please wait…Rating: 0.0/10 (0 votes […]