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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 inputs without signal level problems. Continue Reading »

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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 need 40-50 dB of attenuation.

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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. Continue Reading »

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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 (but usable for many non-hifi applications)<cut>
  • Availability of components: Uses common and easily available components
  • Design testing: I have built this circuit and it worked well with Sound Blaster 16 sound card
  • Power supply: 3-9V current limited power from electret microphone input (same as normally supplied to two wire electret capsule)
  • Estimated component cost: Electronics components cost less than $10 including connectors
  • Safety considerations: No special electrical safety considerations. Continue Reading »
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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 problems like distorted bass response and attenuating in high-frequency response. Basically a transformer slows down upper frequencies and allow the low frequencies to pass first, creating what we perceive as a “fat/warm” tone. Inadequate frequency response on the low end (rolloff at like 20Hz), causes low frequencies to be “slowed”, allowing the upper frequencies to be heard first, this is perceived as “barky/ brittle”. High-quality audio transformers cover whole audio band with good response, but those are quite expensive. Continue Reading »

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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 wait around 5 seconds ofter the power up until the spakers are switched to the amplfier output to avoid annoying “thump” sound from the speakers. Another feeature of this circuit is that is disconnects the speaker immdiatly when the power in the amplifier is cut off, so avoinding sometimes nasty sounds when you turn the equipments off. Continue Reading »

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3-state sound generator with LM556

LM556 is a dual timer that can be operated as two LM555. Continue Reading »

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Dark Detector with LM555

This is a dark detector circuit. This circuit will generate sound if no light source and silence when light falling on CdS. Continue Reading »

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Light Detector with NE555

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Mini organ NE555

This is a mini organ circuit. The 555 timer circuit will generate tone like organ when presss S1 to S5. VR1 use to adjust frequency interval. Continue Reading »

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