Hello all,

I am working on an audio project and am having a hard time finding any ideas on schematics. I am trying to build a simple circuit that will fade in music upon a switch closure. When the switch is open there is no audio. When the switch is closed the audio fades in from nothing to a preset limit. This fade in period needs to take about 1 minute.

 

You need something like a voltage controlled amplifier - http://www.analog.com/en/amplifiers...lifiers-op-amps/ssm2018/products/product.html

The control voltage can be a simple RC circuit.

 

Might be able to use analog opto-coupler as volume control. Need to then provide a variable 0 to 20 mA drive to input LED.

 

After thought: Not tried or simulated but might work. Q1 is darlington transistor to give high impedance load on C1. Vary R2 & or C1 to give desired slope. LED & R4 is analog opto-coupler or home built. R3 to suit LED-around 470Ω for IR LED.

 

You need something like a voltage controlled amplifier - http://www.analog.com/en/amplifiers...lifiers-op-amps/ssm2018/products/product.html

The control voltage can be a simple RC circuit.

+1, and here's another example
http://www.brainmapping.org/Steel/VCA.html

I'm not saying the opto-coupler won't work. Looks interesting.

 

Hello,

The site from "music from outer space" has a couple of VCA's.
Here is one of them:
http://www.musicfromouterspace.com/analogsynth/newdualvca.html

Bertus

 

Thanks for the reply guys...a Digikey order has been made and looks like I will be bread-boarding until I figure this out.

 

Hello all,

I am working on an audio project and am having a hard time finding any ideas on schematics. I am trying to build a simple circuit that will fade in music upon a switch closure. When the switch is open there is no audio. When the switch is closed the audio fades in from nothing to a preset limit. This fade in period needs to take about 1 minute.

One technique that could prove effective would be to design your audio amp and then on the input use a digital potentiometer in the volume control circuit. That way you could use a 555 oscillator and a bit of additional circuitry to increment or decrement your digital potentiometer. The rate of increase or decrease in volume would be determined by the frequency of the clock generated by the 555.

hgmjr