Spider27 Posted October 6, 2019 Posted October 6, 2019 Topic: Does impedance mismatch cause hum/noise? I am not familiar how to match impedance but did not have an issue so far with most of modern amplifiers but vintage amp that I am trying is picky in terms of signal input. What is strange is that amp does not have any background noise when Computer > DAC > Amp but when CD player directly connected to amp causing some low level background humming which is quite annoying between tracks. Even if CD player is standby mode and Amp selected different input other than CD, it still exhibit the hum. Only way to eliminate the hum is unplug RCA interconnect from CD to Amplifier completely then it is dead quiet again. My guess is that impedance is not matched correctly but I can be wrong. Can anyone point out amp and CDP are impedance mismatching? Here is brief spec between amp and CD player. Amp Input impedance: 10k ohms, 150mV sensitivity. CD Player 0dBFS signal output : 2.3V RMS Output Terminals : Gold plated Phono/RCA unbalanced and gold plated XLR balanced Frequency response : Less than +/- 0.1 dB deviation 20Hz-20kHz Phase response : Less than 2 degrees deviation 20Hz-20kHz Signal-to-noise ratio : More than 105dB Crosstalk : Less than -100dB Distortion : Less than 0.002% Intermodulation : Less than 0.002% (19kHz + 20kHz) Thank you very much...
Guest Muon N' Posted October 6, 2019 Posted October 6, 2019 (edited) Input impedance: 10k ohms (Edit: @Spider27 generally you want an output impedance that is at least one tenth of the input impedance of the next component, a greater difference is better, more than one tenth) That's a low input impedance, is it a power amp? There is no output impedance listed for the CD player, but regardless I would guess that the hum is likely a ground issue, or RF or EM Interference. On the impedance relationships can you please list the brands and models. Before the introduction of the CD Player amps generally expected a lower input level, but this is different to impedance matching. Edited October 6, 2019 by Muon N'
Spider27 Posted October 6, 2019 Author Posted October 6, 2019 (edited) 2 minutes ago, Muon N' said: Input impedance: 10k ohms That's a low input impedance, is it a power amp? There is no output impedance listed for the CD player, but regardless I would guess that the hum is likely a ground issue, or RF or EM Interference. On the impedance relationships can you please list the brands and models. Before the introduction of the CD Player amps generally expected a lower input level, but this is different to impedance matching. Hello, Thank you for the info. Amp; Exposure XV amplifier CDP: Consonance CD 120 Balanced (http://opera-consonance.com/products/digital/CD120.html) Edited October 6, 2019 by Spider27
Guest Muon N' Posted October 6, 2019 Posted October 6, 2019 (edited) I can't find the output impedance of the CD Player, but it shouldn't be too high. Try moving signal leads well away from power sources, and try moving the Player way from power sources also, try shielded interconnects (I imagine they are if being XLR) Edited October 6, 2019 by Muon N'
Guest Muon N' Posted October 6, 2019 Posted October 6, 2019 Does impedance mismatch cause hum/noise? For your original question, no....not as I understand things, but invite correction if I'm mistaken. I forgot to address this directly.
Spider27 Posted October 6, 2019 Author Posted October 6, 2019 9 minutes ago, Muon N' said: I can't find the output impedance of the CD Player, but it shouldn't be too high. Try moving signal leads well away from power sources, and try moving the Player way from power sources also, try shielded interconnects (I imagine they are if being XLR) Noted well. Thank you. Amp does not take XLR cable so using RCA interconnects . Tried two different RCA interconnect. Shorter cable generate a bit more hum than longer cable.
Guest Muon N' Posted October 6, 2019 Posted October 6, 2019 I thought it was balanced for some reason. Are thy shielded? If not try a shielded pair of IC's, but check on those other aspects in case there is electromagnetic interference from a power source. Beyond this you might need someone better than I to post here.
Spider27 Posted October 6, 2019 Author Posted October 6, 2019 7 hours ago, Muon N' said: I thought it was balanced for some reason. Are thy shielded? If not try a shielded pair of IC's, but check on those other aspects in case there is electromagnetic interference from a power source. Beyond this you might need someone better than I to post here. Thanks u. I am getting anther pair of IC and will try them when I get them. Re: power source, do you mean wall socket or power board? Wall socket is 2m away from audio rack and powerboard is abt 0.8m apart from the CDP and Amp.
Guest Muon N' Posted October 6, 2019 Posted October 6, 2019 (edited) 4 minutes ago, Spider27 said: Thanks u. I am getting anther pair of IC and will try them when I get them. Re: power source, do you mean wall socket or power board? Wall socket is 2m away from audio rack and powerboard is abt 0.8m apart from the CDP and Amp. I would have looked at borrowing a pair of shielded IC's but only if the ones in use now are not shielded. I don't want to be sending you down a spending path unless it solves the problem, so the problem needs to be found first Power cables also, and the transformers in each piece of gear can radiate EM Waves, electromagnetic interference, so signal cables away from power cables, and components spaced apart ect'. Can you try the CD Player in another system to see if that replicates the hum issue? speakers would need to be as sensitive as in this system now. The other possibility is maybe it is a ground loop, then it gets more complicated. Can you try pluging into different wall sockets, like not everything plugged into a single power board and wall socket. https://hackaday.com/2017/03/09/wtf-are-ground-loops/ https://web.mit.edu/jhawk/tmp/p/EST016_Ground_Loops_handout.pdf Edited October 6, 2019 by Muon N'
Decky Posted October 7, 2019 Posted October 7, 2019 (edited) No. Grounding can cause hum. Impedance mismatch will cause signal loss and deterioration of S/N ratio. If you are mixing SE and balanced connectivity you should isolate signal ground from the chassis (i.e. mains ground) which is a bit tricky if you are not sure how different equipment is grounded. My guess is that the CD player has the signal ground shorted to the mains ground and that is creating a ground loop through the amp. Ideally there should be a capacitor between the signal and mains grounds or more complicated solution with cap, resistor diode networks. Also, check the offending cable for breaks of weak contacts. Edited October 7, 2019 by Decky 2
Spider27 Posted October 7, 2019 Author Posted October 7, 2019 Here are a few extra findings after trying based on suggestions. + Tried 2 other amps (Rotel & Denon) that I have and CDP does not cause any hum with the other two amps. + Tried same RCA interconnect to other sources and does not cause hum. + When CDP Digital Out to DAC then to Amp then no hum. + CDP analog output level seem stronger than Computer or Streamer via DAC Analog out so I turn the volume knob a bit down when CDP is directly connected to Amp. I am using nothing fancy but stock power cable for all of sources and components and did not have any issue.. One strange thing is that I can hear CD loading mechanism spinning CD for initialisation not from CDP itself but via speaker. It is only 1~2 sec before starting music and tiny sound but could not hear spinning sound out of speaker when other amps used at all but XV amp does reveal the CD spinning sound during initialisation via speaker out. My suspicion is that XV amp input sensitivity is higher and possibly amplify the signal more than other modern amps? Could be wrong. Actually this is not a major issue. Once music started, sounds wonderful and I can hook CDP to DAC if slight hum bothers me badly but my DAC inputs are all engaged so I have to unplug either computer or Streamer if I connect CDP to DAC which is a bit cumbersome.
aussievintage Posted October 7, 2019 Posted October 7, 2019 2 minutes ago, Spider27 said: One strange thing is that I can hear CD loading mechanism spinning CD for initialisation not from CDP itself but via speaker. If you have a ground/hum loop, then it will pick up electrical noise from anything emitting it, like the CD loading motor. A test is to lift the ground on the CD player power, so the only ground connection is via the interconnects. Note: this is temporary , and a safety issue, so you should only do so understanding the risk. But it will tell you if that is the problem. 1
Guest Muon N' Posted October 7, 2019 Posted October 7, 2019 (edited) Are the other two amps 3 pin power cords or 2 pin? is the Exposure 3 pin or 2? Edit: player 2 pin or 3 pin? Edited October 7, 2019 by Muon N'
Spider27 Posted October 7, 2019 Author Posted October 7, 2019 6 minutes ago, Muon N' said: Are the other two amps 3 pin power cords or 2 pin? is the Exposure 3 pin or 2? All amps are 3 pin and CDP is also 3Pin power cords.
Guest Muon N' Posted October 7, 2019 Posted October 7, 2019 8 minutes ago, Spider27 said: All amps are 3 pin and CDP is also 3Pin power cords. Yeah, I better leave this for the other guys, they are better at the tech's side
Lloyd Posted October 7, 2019 Posted October 7, 2019 This whole grounding issue makes my head hurt. I have read so much advice from people who reckon they should know. And guess what? No two people provide a consistent and definitive answer. If it isn't a simple and elegant explanation then it is wrong.
aussievintage Posted October 7, 2019 Posted October 7, 2019 13 minutes ago, Lloyd said: This whole grounding issue makes my head hurt. I have read so much advice from people who reckon they should know. But many don't know. Common internet problem. 13 minutes ago, Lloyd said: And guess what? No two people provide a consistent and definitive answer. Partly because the number of ways it can manifest itself can be quite complicated, and diagnosing the problem, especially when the person reporting the problem, due to lack of knowledge, leaves out important information, can be near impossible. All people can suggest is a list of things to try. 15 minutes ago, Lloyd said: If it isn't a simple and elegant explanation then it is wrong. Dead wrong. There are no laws of physics that say fixing it has to be easy or straightforward. It's a simple in principal only.
aussievintage Posted October 7, 2019 Posted October 7, 2019 This was written for guitar amps but a lot of good general info here. http://valvewizard.co.uk/Grounding.pdf
Spider27 Posted October 7, 2019 Author Posted October 7, 2019 1 hour ago, aussievintage said: If you have a ground/hum loop, then it will pick up electrical noise from anything emitting it, like the CD loading motor. A test is to lift the ground on the CD player power, so the only ground connection is via the interconnects. Note: this is temporary , and a safety issue, so you should only do so understanding the risk. But it will tell you if that is the problem. Actually it worked. I have a spare stock IEC cable and I broke ground pin so leave 2 pins only and connected the cable to CDP and Power board and no CD loading noise or background hum.... Hence you & @Muon N' were correct that it is grounding issue. However, I am not sure if it is safe to use 2 pin power cable and if not, then what the ideal solution would be.
March Audio Posted October 7, 2019 Posted October 7, 2019 18 hours ago, Spider27 said: Topic: Does impedance mismatch cause hum/noise? I am not familiar how to match impedance but did not have an issue so far with most of modern amplifiers but vintage amp that I am trying is picky in terms of signal input. What is strange is that amp does not have any background noise when Computer > DAC > Amp but when CD player directly connected to amp causing some low level background humming which is quite annoying between tracks. Even if CD player is standby mode and Amp selected different input other than CD, it still exhibit the hum. Only way to eliminate the hum is unplug RCA interconnect from CD to Amplifier completely then it is dead quiet again. My guess is that impedance is not matched correctly but I can be wrong. Can anyone point out amp and CDP are impedance mismatching? Here is brief spec between amp and CD player. Amp Input impedance: 10k ohms, 150mV sensitivity. CD Player 0dBFS signal output : 2.3V RMS Output Terminals : Gold plated Phono/RCA unbalanced and gold plated XLR balanced Frequency response : Less than +/- 0.1 dB deviation 20Hz-20kHz Phase response : Less than 2 degrees deviation 20Hz-20kHz Signal-to-noise ratio : More than 105dB Crosstalk : Less than -100dB Distortion : Less than 0.002% Intermodulation : Less than 0.002% (19kHz + 20kHz) Thank you very much... Sounds like a ground loop. 1
March Audio Posted October 7, 2019 Posted October 7, 2019 (edited) 13 minutes ago, Spider27 said: Actually it worked. I have a spare stock IEC cable and I broke ground pin so leave 2 pins only and connected the cable to CDP and Power board and no CD loading noise or background hum.... Hence you & @Muon N' were correct that it is grounding issue. However, I am not sure if it is safe to use 2 pin power cable and if not, then what the ideal solution would be. Its is not safe. If the device is not class II double insulated ( has a double square symbol) you *MUST* have the ground connected. You can minimise it by using an interconnect with a very thick shield. Note this isnt about reducing interference or pick up, its about minimising the resistance so a smaller voltage is developed across the lead. Also plugging everything into the same mains board. Unfortunately this is an inherent flaw of single ended RCA connections. One of your signal wires (shield) is used to connect two bits of kit. If they are not at the same potential because one or more is connected to earth then a current will flow in the shield. This is what you hear. Edited October 7, 2019 by March Audio
Spider27 Posted October 7, 2019 Author Posted October 7, 2019 5 minutes ago, March Audio said: Its is not safe. If the device is not double insulated (it has a double square symbol you *MUST* have the ground connected. Noted. I took it out and replaced with 3Pin again. At least it was worth it to confirm that it is a ground issue.
aussievintage Posted October 7, 2019 Posted October 7, 2019 6 minutes ago, March Audio said: Its is not safe. If the device is not class II double insulated ( has a double square symbol) you *MUST* have the ground connected. Correct. There is one odd trick you can do. Lift the shield connections for each channel, at one end of the interconnect only. This breaks the ground loop. The signal path will use the safety ground. Not ideal, but will be much quieter than at the moment.
Spider27 Posted October 7, 2019 Author Posted October 7, 2019 1 minute ago, aussievintage said: Correct. There is one odd trick you can do. Lift the shield connections for each channel, at one end of the interconnect only. This breaks the ground loop. The signal path will use the safety ground. Not ideal, but will be much quieter than at the moment. Please excuse my dumbness. What is shield connection? Do you mean, desolder ground joint on RCA connector (#2 from the attached photo)?
aussievintage Posted October 7, 2019 Posted October 7, 2019 Just now, Spider27 said: Please excuse my dumbness. What is shield connection? Do you mean, desolder ground joint on RCA connector (#2 from the attached photo)? Yes, both channels, but only at one end. If the diagnosis of a ground loop is correct, and it appears to be, it means both amps signal grounds are connected to safety ground, and to each other via that path, so that connection (the one that the shield would normally make) is already made, and all you need is the centre wire. You only disconnect at one end, so that the shield itself remains grounded and does it's job of preventing noise pickup by the interconnect wires. 1
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