Limberpine Posted December 3, 2020 Author Share Posted December 3, 2020 5 hours ago, billybob said: After you answer the last 2 posts above, using the same extension cord from another location, plug into it with the 2 prong DAC only. What happens? Now plug the amp in by itself. What happens? If all good after the 2 tests, plug both into extension. Thanks! Okay, so the dac is a 2 prong only plug. So you want me to plug that into the extension cord then do dac to preamp via rca and then preamp to power amp via RCA. Then see what that sounds like and compare it to amp only via extension cord? Quote Link to comment Share on other sites More sharing options...
henry4841 Posted December 3, 2020 Share Posted December 3, 2020 Shorting the inputs means taking a jumper wire with alligator clips and hooking one end to the center pin and the other end to the outside ring. One can take an old RCA cable, cut it and tie the 2 wires of the cut end together and plug in the connector to the amplifier. They make special plugs for this function as well of which I have. https://www.amazon.com/Viborg-Stopper-Plated-Copper-Protector/dp/B017DH76VS/ref=sr_1_2?dchild=1&keywords=RCA+SHORTING+CAPS&qid=1607026936&sr=8-2 Cutting an old RCA cable and doing like I said serves the same purpose for testing. The plugs are put on RCA inputs of a Preamplifier, especially phono stages, to prevent noise. Common on professional equipment as well. 1 Quote Link to comment Share on other sites More sharing options...
billybob Posted December 3, 2020 Share Posted December 3, 2020 17 minutes ago, Limberpine said: Okay, so the dac is a 2 prong only plug. So you want me to plug that into the extension cord then do dac to preamp via rca and then preamp to power amp via RCA. Then see what that sounds like and compare it to amp only via extension cord? Looks like you have already done extension cord to amp with no change. No need to do other components. If you can , reach another room with extension cord just to amp and speakers. Quote Link to comment Share on other sites More sharing options...
billybob Posted December 3, 2020 Share Posted December 3, 2020 Just now, billybob said: Looks like you have already done extension cord to amp with no change. No need to do other components. If you can , reach another room with extension cord just to amp and speakers. If you still have noise, guess your amp is the culprit as was the thinking of Jimjimbo, I think. Quote Link to comment Share on other sites More sharing options...
babadono Posted December 3, 2020 Share Posted December 3, 2020 On 12/1/2020 at 9:46 PM, Limberpine said: So I did ground the RCA to itself and hum in both speakers. I also took the RCAs off altogether, just speaker wire to amp and there is still a hum. Like this...How did you do this before? Quote Link to comment Share on other sites More sharing options...
babadono Posted December 3, 2020 Share Posted December 3, 2020 11 minutes ago, henry4841 said: Shorting the inputs means taking a jumper wire with alligator clips and hooking one end to the center pin and the other end to the outside ring. One can take an old RCA cable, cut it and tie the 2 wires of the cut end together and plug in the connector to the amplifier. They make special plugs for this function as well of which I have. https://www.amazon.com/Viborg-Stopper-Plated-Copper-Protector/dp/B017DH76VS/ref=sr_1_2?dchild=1&keywords=RCA+SHORTING+CAPS&qid=1607026936&sr=8-2 Cutting an old RCA cable and doing like I said serves the same purpose for testing. The plugs are put on RCA inputs of a Preamplifier, especially phono stages, to prevent noise. Common on professional equipment as well. The most versatile is a "dummy plug". It will help troubleshoot equipment and interconnecting cables. https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf For quickness start about page 100. 1 Quote Link to comment Share on other sites More sharing options...
billybob Posted December 3, 2020 Share Posted December 3, 2020 29 minutes ago, henry4841 said: Shorting the inputs means taking a jumper wire with alligator clips and hooking one end to the center pin and the other end to the outside ring. One can take an old RCA cable, cut it and tie the 2 wires of the cut end together and plug in the connector to the amplifier. They make special plugs for this function as well of which I have. https://www.amazon.com/Viborg-Stopper-Plated-Copper-Protector/dp/B017DH76VS/ref=sr_1_2?dchild=1&keywords=RCA+SHORTING+CAPS&qid=1607026936&sr=8-2 Cutting an old RCA cable and doing like I said serves the same purpose for testing. The plugs are put on RCA inputs of a Preamplifier, especially phono stages, to prevent noise. Common on professional equipment as well. Do it Limberpine... Quote Link to comment Share on other sites More sharing options...
babadono Posted December 3, 2020 Share Posted December 3, 2020 50 minutes ago, Limberpine said: Totally appreciate your help! I just don't know ow what you mean by shorting the inputs. Would that mean, I connect either amp to the speakers with and RCA running out of said amp and then use a screw driver to connect the male end to the shield of the the White RCA plug? Sorry, I mean short both inputs. Their center pin to its shield. You can make your own "shorting plugs" with spare RCA connectors or sacrifice an old pair of cables like @henry4841 suggested. Or use alligator clips. Just something that makes good connection. 1 Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted December 3, 2020 Share Posted December 3, 2020 1 hour ago, Limberpine said: I used an extension cord and an outlet across the room. No change in noise. I put my multimeter on the ACV 200 setting and the put the red on red and black on black terminals on the speaker and it just read 00.0 A 200V range is too high. Does the meter have a 2v range? Maynard Quote Link to comment Share on other sites More sharing options...
Limberpine Posted December 3, 2020 Author Share Posted December 3, 2020 1 hour ago, babadono said: The most versatile is a "dummy plug". It will help troubleshoot equipment and interconnecting cables. https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf For quickness start about page 100. Does Parts express sell those? I really try not to order on Amazon. Don't hate! 😁 Quote Link to comment Share on other sites More sharing options...
Limberpine Posted December 3, 2020 Author Share Posted December 3, 2020 40 minutes ago, tube fanatic said: A 200V range is too high. Does the meter have a 2v range? Maynard Doesn't look like it. Pic attached. Quote Link to comment Share on other sites More sharing options...
billybob Posted December 3, 2020 Share Posted December 3, 2020 8 minutes ago, Limberpine said: Does Parts express sell those? I really try not to order on Amazon. Don't hate! 😁 So you do not have just 2 phono rca ends to plug into the phono section just to check? Quote Link to comment Share on other sites More sharing options...
babadono Posted December 3, 2020 Share Posted December 3, 2020 20 minutes ago, Limberpine said: Does Parts express sell those? I really try not to order on Amazon. Don't hate! 😁 Nope. Roll your own or buy from Jensen Transformer. They'll set you back like $10 maybe $15 by this day and age. Quote Link to comment Share on other sites More sharing options...
Limberpine Posted December 3, 2020 Author Share Posted December 3, 2020 1 hour ago, billybob said: So you do not have just 2 phono rca ends to plug into the phono section just to check? I have a set of RCA plugs attached to a cable and could sacrifice one of them for this, given that they're $6. But, once I cut the RCA ends off, do I just strip some of the wire and wrap it around the shield? Quote Link to comment Share on other sites More sharing options...
babadono Posted December 3, 2020 Share Posted December 3, 2020 10 minutes ago, Limberpine said: I have a set of RCA plugs attached to a cable and could sacrifice one of them for this, given that they're $6. But, once I cut the RCA ends off, do I just strip some of the wire and wrap it around the shield? Yes but soldering them would be more reliable. But wait for this test you just need to short the center pin to the shield and only temporarily. Do you have alligator clips or jumpers with alligator clips? Just plug the cable into the amp inputs and on the other end where the center pin and shield are accessible short them together with the alligator clip. 1 Quote Link to comment Share on other sites More sharing options...
henry4841 Posted December 4, 2020 Share Posted December 4, 2020 1 hour ago, Limberpine said: I have a set of RCA plugs attached to a cable and could sacrifice one of them for this, given that they're $6. But, once I cut the RCA ends off, do I just strip some of the wire and wrap it around the shield? Do not cut at the rca ends but leave 6 inches of wire. Strip insulation off, a 1/2" is fine, from both wires and tie them together. Just wrapping them together should be good enough to do this test. What it will tell is whether the hum is in the amp or in front of the amp, something else being wrong in cables or source. Shorting the inputs is something most builders of amplifiers do when testing a new amplifier. You have two wires in an RCA cable that terminate at the RCA connector. The shield part of the RCA cable is where one wire goes and the other wire goes to the plug in the center of the RCA connecter. What you want to do and will do if you follow my above advice is connect the two parts of the RCA connector together. That is what is called shorting the inputs together. I hope this make sense. 1 Quote Link to comment Share on other sites More sharing options...
Limberpine Posted December 4, 2020 Author Share Posted December 4, 2020 Set the SS up and there isn't any hum. Just had to listen to some tunes! Will make the RCA short here soon and post pictures to make sure its right and retest the tube amp. 1 Quote Link to comment Share on other sites More sharing options...
billybob Posted December 4, 2020 Share Posted December 4, 2020 13 hours ago, Limberpine said: Set the SS up and there isn't any hum. Just had to listen to some tunes! Will make the RCA short here soon and post pictures to make sure its right and retest the tube amp. Hope it works out. Forget now which speakers you have. Quote Link to comment Share on other sites More sharing options...
Limberpine Posted December 4, 2020 Author Share Posted December 4, 2020 1 hour ago, billybob said: Hope it works out. Forget now which speakers you have. I have a set of 1978 Cornwalls, and a set of 1978 LA Scalas. This tube system is running the LA Scalas. 1 Quote Link to comment Share on other sites More sharing options...
billybob Posted December 4, 2020 Share Posted December 4, 2020 Just now, Limberpine said: I have a set of 1978 Cornwalls, and a set of 1978 LA Scalas. This tube system is running the LA Scalas. That's right, remember now. Best of both worlds. Do you ever run the Dynaco amp with the Cornwall's? Quote Link to comment Share on other sites More sharing options...
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