Khodabear Posted March 12, 2012 Share Posted March 12, 2012 This is regarding a Switchcraft 640 Studio Control Center but the problem is pretty generic. I now have a Switchcraft 640 switch box that will allow me to interconnect multiple sources to any one of multiple amps and then out to any one pair of up to 12 pair of speakers. Swell.But AFAIK that would leave the idling amps without a load. I don't have any documentation for this unit, but there's a sticker on the bottom that advises the use of a "Phantom Load" - see the instructions.I could only power up the amp I want to hear, but that defeats the purpose doesn't it? Anybody have an idea how to wire this up? Anybody have one and a copy of the documentation? Thanks! __________________ Quote Link to comment Share on other sites More sharing options...
T.H.E. Droid Posted March 12, 2012 Share Posted March 12, 2012 As long as you can make concurrent connections (switchboard style) put a dummy resistive load on one speaker output set and switch that into the idling amp circuit. Although I'm not sure why an idling amp with no output needs a load. Effectively leaving it without a discrete load is the same as giving it an infinite load. Use high wattage sand or wirewound 8 ohm resistors. Quote Link to comment Share on other sites More sharing options...
Marvel Posted March 12, 2012 Share Posted March 12, 2012 Although I'm not sure why an idling amp with no output needs a load. This wouldn't be a problem with SS amps. Tube amps are another story. Quote Link to comment Share on other sites More sharing options...
Khodabear Posted March 12, 2012 Author Share Posted March 12, 2012 Tubes - are the issue. I'd sure like to find an instruction manual for it - or at least a schematic. As far as I can tell when you have an amp in as the active unit it's outputs are routed to whatever speakers you've selected. If you switch to amp 2 , amp 1's outputs are left hanging open. I guess I need to take it apart and see if the amp inputs , which are the amps speaker outputs, drop to another set of connections if not engaged. I kinda doubt it since there's no "Dummy Load" connection which you'd think there would be if that were the case. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted March 13, 2012 Share Posted March 13, 2012 simple....on all the amps outputs you connect to the box, your phantom load could be a 16 ohm 10 or 20 watt resistor if you are ok with a 3.2 load or a 32 ohm resistor if you are OK with a 3.5 ohm load....assuming your speakers are 4 ohms. Quote Link to comment Share on other sites More sharing options...
Khodabear Posted March 13, 2012 Author Share Posted March 13, 2012 Ok... My speakers are 8 ohm. From what you say I should calculate the resistance needed to achieve 8 ohms, but I'm not perceptivre enough to understand where in the circuit the would be placed. The box simply has 1/4" phone jacks in from the amp's speaker output and out to the speakers. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted March 13, 2012 Share Posted March 13, 2012 ok, lets make sure we are clear. you have a switchbox that recommends using phantom loads. so lets say you have 2 amps and 1 pair of speakers. if we assume your speakers are 8 ohms and assume both of your amps can drive a 4 ohm load, then if you put a 16 ohm resister across your amp terminals you would have a 16 ohm load when your switch box switches the speakers off the amp and a 5.3 ohm load when your switch box connects your amp to your speakers. the resister should be at least 10 to 20 watts. More watts for the resister is better. If you use a 32ohm resister the new load would be 32 with no speakers switched to the amp and 6.4 ohms when the box switches the speakers to the amp. Quote Link to comment Share on other sites More sharing options...
Khodabear Posted March 13, 2012 Author Share Posted March 13, 2012 Ok - getting the idea. Won't this have a negative impact on my output? Quote Link to comment Share on other sites More sharing options...
Guest " " Posted March 13, 2012 Share Posted March 13, 2012 Ok - getting the idea. Won't this have a negative impact on my output? sure...the resistors will soak power....about 1/3 power if you go with 16 ohm resisters. Quote Link to comment Share on other sites More sharing options...
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