Hi Thomas Why not use an Intersil analogue IC They are about $1 Mike ----- Original Message ----- From: "Thomas N" To: Sent: Thursday, July 11, 2002 7:49 AM Subject: [EE]: Analog switch using 2N3904 Hello everyone, I have two audio channels feeding the one audio amplifier. I want to add an analog switch between the signal and the amplifier so I can turn the switch on when I want the audio from a channel to go to the amplifier. I came up with a circuit, but it has some problem. My circuit is like this: The input signal is AC-couple by a 100n capacitor. The other end of this capacitor is connected to the Collector of the 2N3904. There is also a voltage divider (two 10k ohms) at the Collector of the transistor to bias the Collector voltage at 1/2 VCC. The Emiter is the output of the switch and it has 10k to Ground. The base of the transistor is connected to a 10k resistor. This is the control signal to turn on the switch. The switch work great, but with one bad thing; when the switch is turned on, the DC bias at the output of the switch is at about 1/2 VCC. When the switch is turned off, this bias goes down to ground. Due to the bias voltage change, there is a glitch on a input of the amplifier and cause a "click" sound. My problem is right here. How to keep this bias so there is no "click" sound. Do you have any idea how I can improve the circuit so my output bias voltage remains at 1/2 VCC when the trasistor is turned on or off? Do you have any similar analog switch using a transistor? Anything would be helpful. Thank you in advance! Thomas -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads