Parasound JC 3+ Phono Preamp Hum
Hum is definitely a system-wide issue and can be caused by a number of things, as well discussed already in this thread. Try to remove everything you can, start all over, adding in one piece at a time. http://www.hagtech.com/pdf/eliminatingnoise.pdf |
Eric, I haven’t read through this entire string, so maybe this was covered above, but will say that I’ve moved to a new home (new to me) and I’ve been chasing a grounding hum in my system for about a month now. I finally figured out the Parasound was the source of the hum. Gear and History: GoldenEar Triton 2+ with AQ Rocket 33 cables, Synergistic Research PCs Line Magnetic LM-518ia acting as a power amp, PC=AQ HC Hurricane Pass Labs HPA-1 acting as a 2 channel pre-amp and headphone amp, PC=Kimber PK10 Ch1: Parasound JC3+, PC=stock/Linn Sondek LP12 w/Lingo Ch2: Auralic Vega DAC/NAD M50.2 media player, both using Shunyata Delta NR Power: Wall Outlet: AQ NRG Edison, Conditioner: Shunyata PS8 with Delta NR to wall I had a fixed ground hum regardless of whether I was using the JC or the Digital media. If I ran the LM as an integrated amp and bypassed the Pass Labs the hum would be modest and I could live with it but didn’t like it. I tried putting a cheater on or unplugging a number of different things in my listening room and could not find the root cause of the problem. When I ran sources to the Pass and ran the pass pre-amp out to the LM pre-in the hum was boosted to a level that made it intolerable. Randomly, while not playing any music and hearing the hum I unplugged the Parasound and the hum completely left the speakers. I then took the cheater plug and put it on the Parasound and plugged it back in. Nothing! I realize the problem is the power in my new residence but what I don’t understand is why the Parasound is the only component affected and is there anything I can do short of using a cheater to fix the problem. |
Eric, I posted earlier on and suggested trying another headshell and/or running a long extension cord to another outlet in the house. As I stated earlier for whatever reason one of my hums had to do with the pins on the head shell on my 1200gr tone arm not connecting - just try it, you don’t have much to lose. Also for whatever reason when I ran a power cable from the phono pre to another outlet across the house the problem went away in another hum situation, this is at least worth trying since its relatively easy as well. |
@invictus505 OK, I tried a few other combinations: 1. When the JC3+ switch is changed from MC to MM, the hum is reduced, barely noticeable at 1:00. 2. When I connected the PS Audio GCPH with the same shorting plug setup to the Cayin, no hum except with the gain dial on the GCPH at full open and the Cayin at full open. During normal use the gain dial it is set at about 1:00. I walked the GCPH within a few inches of the Cayin, still no hum. 3. I then pulled out an old Sherwood receiver that i use in my garage system. Connected it to the JC3+, hum audible at 1/4 volume. 4. I then connected the GCPH to the Sherwood receiver, no hum. The tubes on the Cayin are not stock and have low hours. I realize it’s a Chinese amp, but counterfeit parts? Prima Luna too? It seems the JC3+ may be the problem. |
@ericsch Due to the fact that your other phono preamp also had a hum (at 50% volume instead of 25%), the JC3+’s previous owner did not have any issues, as well as many other pieces of evidence from the tests you just performed... My conclusion is that the Cayin is at fault. Cayin is either causing a ground loop due to improper grounding scheme, i.e. RCA jacks not properly isolated, signal/power/Earth all mixed together, etc. Or one or more of the components is failing, such as tubes, electrolytic capacitors, etc. Please note, most, if not every single part in the Cayin is a counterfeit. The next test would be to try another integrated, or receiver. |
Getting closer. Short both inputs on the JC3+ again. Pull the JC3+ out and place it somewhere in front of the Cayin, or hold it in your hands if you have too. Use a spare RCA cable (not the pair that runs parallel to AC cords) and connect the JC3+’s outputs to Cayin’s inputs. Turn everything on, hum still there?
@ invictus I did the above and pulled the JC3+ about 8 feet away from the rest of the system. The hum is still present, although not quite as loud as when the turntable is connected. I can hear it at 1/4 volume. What do you think? |
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@ericsch Getting closer. Short both inputs on the JC3+ again. Pull the JC3+ out and place it somewhere in front of the Cayin, or hold it in your hands if you have too. Use a spare RCA cable (not the pair that runs parallel to AC cords) and connect the JC3+’s outputs to Cayin’s inputs. Turn everything on, hum still there? |
Invictus said: "Do me these two tests. 1.) Disconnect the turntable from the JC3+, but leave everything else connected. Short both RCA inputs (center hole to outer sleeve) on the JC3+. Now turn the volume up and report back if the hum is still present." @invictus505 I did the above, shorted both inputs, the hum is still present, actually louder than before. |
Eric, It seem you have serval possible problems that you want to address. I have separated each problem with a reason and approach below. I believe that I have a ground loop. In a power supply there is +V, -V, Ground or 0V, and earth ground. A ground loop can form in a system when there is more than one path to earth ground. Earth Ground comes from the third outlet prong, through the power cord, into device 1, to device 1 signal Ground or 0v, passes through the signal interconnect cable, into device 2 signal Ground or 0v, into device 2 earth ground, through device 2 power cord, and back to the AC outlet third prong.
To test for possible ground loops. 1 Turn off each device 2 Use an ohm meter to measure the conductivity between the signal connector ground, the outside of a RCA connector, and the third prong on the device AC power inlet. If the reading is then < 5 ohm, the signal ground is connected to earth ground.
To remove ground loops 1 Pick one device and make it the conductor of earth ground, typically the largest power draw or the amplifier. 2 Put all other devices connected by signal interconnects, that are not fiber optic, on a 3 to 2 prong adapter. This will allow earth ground to still provide protection against electrical shock, via the signal interconnects, while only providing 1 path to ground. 3 Power up only 2 devices at a time, CD player and amp for example, and see if a difference is made in the hum. If not then power down and remove the 3 to 2 prong adapter. Continue with all devices till the hum is minimized.
I believe my turntable phono ground is not correct. Phonos are by nature high gain devices and therefore will amplify any electrical interference or ground loops. In general connect your grounds as follows. 1 The tone arm cable and tone arm ground should be connected to the phono ground binding post. The phono can be on a 3-2 prong adapter and get its earth ground via the preamp or amp provided that is third prong is connected to its RCA or balanced connector ground. The tone arm and tone arm cable MUST be shielded for best performance with a low output cartridge. 2 The table or motor ground connector should connect to the ground from the turntable power supply which is connected to earth ground. This assumes that the table or motor ground is not connected to the tone arm / cable / phono ground.
I believe the hum is coming from my phono or other device Hum generated internally is caused by internal ground loops or poor power supply noise rejection, PSSR < 80dB for phonos and < 65dB for amps. To test a device for hum. 1 Turn off all devices 2 Disconnect the input cable to the device in question, for example the tone arm cable from the phono. 3 Use shorting RCA plugs to short the signal inputs, in the in this case phono. This will ground the input signal into the device thereby ensuring the noise is not from the outside of the unit. You can also test the device without shorting plugs but that assumes the device was designed properly with “pull down resistors” to ground or in a phono your loading. 4 Turn on the phono, preamp, and amplifer 5 If there is hum then it is the phono or preamp or amp 6 To test the whole system, start by shorting the inputs to the amp and then add one device at a time until you have tested all devices with their inputs shorted 7 For step up transformers you may need to ground both sides of the transformer designated as ground. A phono cable by nature does not have a ground as no part of the phono cartridge is connected by ground. It only gets grounded when connected to the phono preamp
I believe my device placement is incorrect. Good phono setup is as follows: 1 Phono is located within 6 inches of the tone arm 2 The turnable power supply and motor are as far as possible from the phono preamp, 2 to 3 feet for the power supply. The motor is what it is. 3 There are no other devices or power cords within 1 foot of the phono preamp either on the sides, above, or below. This includes wireless phones, networks, computers, and blue tooth 4 The cables into the phono preamp are shielded as well as the tonearm 5 The cable from the phono preamp runs unimpeded to the preamp / amplifier with no crossing of AC power lines. 6 Ideally the tone arm cable and the phono preamp to amplifier / preamp are only 3 feet in length. This provides the best cable capacitance per foot. 7 Twisted cables perform better then solid core in that they provide a bit of natural noise rejection.
I believe I am getting noise from my power cables Power cables can radiate noise and this noise has the most affect on low level signals such as a tone arm / phono cable. If this is the case, then use a shielded power cable from Mouser, part number 686-17742,or Digikey. This will require that the third prong is connected to earth ground, to 3 to 2 adapter. These cable differ from other power cords in that there is a shield to keep the AC noise in. Other cords rely only on the twisting of the cable.
I am getting a echo or bump when I set the tone arm down in the cradle. This would indicate that shock through the cartridge is large enough to be picked up and amplified. There are three possible causes: 1 The tone arm is being dropped into the cradle with too much force 2 The phono preamp has too much gain 3 The suspension in the phono cartridge is not sufficiently compliant |
Hum can indeed be difficult to isolate. hifiman5 has given some very good advice. I would suggest the following: 1) Use a quality multi-outlet strip to plug all of your components AC plugs into 2) That may eradicate your hum issue. If it does not then you should lift the grounds on your power amp with a "cheater adapter (not the pre-amp). 3) If the hum persists then get yourself a set of shielded interconnects for your photo stage. 4) At this point I would suspect that you will have a quiet system, if not then experiment with the TT ground connected/disconnected. You will solve this but only with all of your components plugged into a multi-outlet strip. |
I have a JC3+ and I have had him issues in the past but never from the unit. Get a long grounded extension cord. Like one you use for outside yard work. Plug it into another outlet in another room. For whatever reason this worked for me. If you had a hum in your previous phono pre it’s most likely not the pre. Also make sure your cart leads are tightly plugged in. And finally if you have a removable headshell it might not be making full contact on all 4 pins. This happened with my new Technics 1200 gr. Changed the shell and hum went away 100%. |
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@ericsch Do me these two tests. 1.) Disconnect the turntable from the JC3+, but leave everything else connected. Short both RCA inputs (center hole to outer sleeve) on the JC3+. Now turn the volume up and report back if the hum is still present. 2.) Do you have Comcast cable in that room? Disconnect the coax cable by unscrewing it from the box’s cable in. Is the hum still there? Unused balanced inputs will have no impact. |
Separate the AC cords from the ICs first, then we'll talk. If you could manage it even for experimental purposes, for example by bringing power via a long extension cord that would permit you to re-route your AC cords so they don't have to go through that hole together with the ICs, that might tell you something. |
@helomech I have another stock headshell with a Shure V15 V-mr and the hum remains. The Sillnote is designated as a phono cable. I'll try some of your other suggestions and possibly some cable swaps. @yogiboy I'll try the cheater plug. @invictus bpoletti was duly ignored. I've had a Halo 5 channel amp in my home theater system for many years. It has never failed me. |
Have you tried using a cheater plug? If not give it a shot! https://www.homedepot.com/p/GE-15-Amp-125-Volt-Polarized-Grounding-Plug-Adapter-Gray-2-Pack-543002/2... |
I own a Hana SL and JC3 Jr. I only get a very low level "hiss" above 50% on the volume knob -- far louder than I’d ever listen. Have you tried any other cables between the TT and preamp? Is the Sillnote Morpheus shielded and designed for low level phono signals? Cable spacing may be the issue, but in the past, I’ve run phono cables (even cheap ones) quite close to power cables with very low to zero noise. More often, the noise is a cartridge -- turntable interaction issue, (like Grados on a Rega), a loose connection, or a faulty cable. I’ve now owned three pairs of defective Audioquest cables, so even "good" cables can be the culprit. I had one of their tonearm cables that caused hum simply because the spade lug was poorly crimped to the ground wire. You might also open up the JC3 and check for any loose connections. You’ve tried bonding the turntable to the integrated but have you tried bonding the preamp to the integrated AND preamp to the turntable, using short bonding wires? That won’t likely solve your problem but it worked for me in a couple setups. Double check the quality of connection between the cartridge and headshell. If you’re using an aftermarket headshell, that’s another potential problem area. I’ve had an aftermarket headshell with a neck that was just barely to short to allow good contact between the mating pins. Lastly, make sure there’s a good distance between preamp and any components with large transformers (that would include the 1200G). |
Thanks for the suggestions thus far. @hifiman5 I will probably call Parasound if I can't solve the problem on my own. I am confident that the JC3+ is in good working condition. I purchased it from a gentleman who sadly had become ill and had to sell his equipment. @varyat I may try that, but it will be complicated due to room considerations. @lewm Not the answer I was looking for, but of course you are right. I have to start by fixing the cable routing issue. I have a custom built cherry vertical cabinet. In order to separate the cables as you suggested, I would have to remove all the components and widen the spaces at the back of each shelf to allow for more separation of the cables. Right now the cables are jammed through a small 5 inch opening at the back of each shelf. I had the cabinet built 10 years ago and obviously did not think it through completely. At that time, I had a Rega Fono, with no hum. |
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You had hum with both the old phono and the new JC3+. You say you can do nothing about the fact that power cables run in parallel with audio cables in your set-up. In my opinion, that's the first thing you must rectify before you assess any other causes. AC cords are surrounded by an electromagnetic field, and ICs, especially small signal phono ICs, will pick up the EMI when run in parallel. You have there a known cause of hum, and it probably has nothing whatever to do with the JC3+. At the very least, separate the AC cords from the ICs by at least 8-10 inches, and see if that ameliorates the problem. Other ideas: isolate the AC to your CDP and to your turntable from all the other AC feeding your other components. Both devices can feed EMI back on to the AC line and contaminate other equipment. |
