re suggestions on audio relays in article c r r id megatest com alung megatest com aaron lung writes in article c qsbf iek ms uky edu billq ms uky edu billy quinn writes i built a little project using the radio shack vdc relays to switch audio i got pretty bad clicks when the thing switched i was doing most of the common things one is supposed to do when using relays and nothing seemed to get rid of the clicks my question is is there a good relay relay circuit that i can use for switching audio so that there will be no noise of any kind on the audio lines i will appreciate any advice or references to advice also exact part numbers company names etc for the relays will help are you switching high level signals or low level signals like pre amp out level signals also are the clicks you mentioning the big clack that happens when it switches or are you refering to contact bounce how are you driving the relays ttl gate output switching transistor how are the relays connected to what you are driving need more specifics to answer your question as a general rule no relay will cleanly switch audio if you try to tranfer the circuit with the contacts the noise you hear is due to the momentary opening and closing of the path the noiseless way of transfering audio is to ground the circuit in high impedance audio circuits a resistive t is constructed close to characteristic impedance of the circuit grounding the imputs connected to the t transfers the audio in low impedance circuits transformers are usually used and the inputs are shorted out or grounded secondaries are paralleled at the characteristic impedance sometimes if it is necessary to actually switch audio a second contact is used to momentarily short the circuit output for the duration of the switching time telephone relays are handy because contacts can be adjusted to make before break and vica versa but i haven t seen any of these for years nowadys switching is done electronically with op amps etc a novel circuit i used to build was a primitive optical isolator it consists of a resistive photocell and a lamp all packaged in a tube when the lamp is off the cell is high resistance turn the lamp on and the resistance lowers passing the audio once again this device in a t switches the audio varying the lamp resistance give a remote volume control use variable resisters and you have a mixer lots of luck tom tom wagner audio visual technician malaspina college nanaimo british columbia loc fax callsign ve gda weapon kentucky rifle snail mail to site q c rr nanaimo british columbia canada v r x i do not recyle i keep everything all standard disclaimers apply
