In article <1993Apr20.102756.1709@mala.bc.ca>, wagner@mala.bc.ca (TOM WAGNER, Wizzard of old Audio/Visual Equipment........Nanaimo Campus) writes: > In article <C5r60r.4ID@megatest.com>, alung@megatest.com (Aaron Lung) writes: >> In article <C5qsBF.IEK@ms.uky.edu> billq@ms.uky.edu (Billy Quinn) writes: >>>I built a little project using the radio shack 5vdc 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 2 variable resisters and > you have a mixer! >  > Lots of luck! > --  > 73, Tom > ================================================================================ > Tom Wagner, Audio Visual Technician.  Malaspina College Nanaimo British Columbia > (604)753-3245, Loc 2230  Fax:755-8742  Callsign:VE7GDA Weapon:.45 Kentucky Rifle > Snail mail to:  Site Q4, C2.   RR#4, Nanaimo, British Columbia, Canada, V9R 5X9   >  > I do not recyle.....   I keep everything!       (All standard disclaimers apply) > ================================================================================ --  73, Tom ================================================================================ Tom Wagner, Audio Visual Technician.  Malaspina College Nanaimo British Columbia (604)753-3245, Loc 2230  Fax:755-8742  Callsign:VE7GDA Weapon:.45 Kentucky Rifle Snail mail to:  Site Q4, C2.   RR#4, Nanaimo, British Columbia, Canada, V9R 5X9