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Parasound JC 3+ Phono Preamp Hum

I know hum problems have been discussed ad nauseam on this board, but after trying a few different things, I have been unable to find a solution. I recently purchased a used JC3+ to replace a PS Audio GCPH with Underwood Mods. Although the GCPH had some hum, the volume had to be turned up to past 50% before it was audible.

With the JC3+ I get a low hum at 25% and loud hum at 50% volume. What I am describing is with everything on, no record playing.

The SL1200G TT is grounded to the JC3+. I’ve tried the following: 1. Added a ground wire from the TT to the integrated chassis, a Cayin A-88T Mk II. 2. Changed cables from TT to JC3+. 3. Changed cables from Integrated to JC3+. 4. Plugged JC3+ directly to wall outlet. 5. Changed to AC polarity on the JC3+ via the switch on the back from normal to invert. 6. I’ve tried using no ground wires.

Due to my cabinet configuration, power cables and audio cables run parallel and close to each other. There is no way I can arrange them to be perpendicular to each other.

If I lift the tonearm and let it fall back on the cradle, I can hear the echo or bump through the speakers.

My cartridge is a Hana SL.
Cables: TT to preamp, Silnote Morpheus
preamp to Integrated, Morrow MA4 (and tried AQ King Cobra)

Everything is plugged into a rather inexpensive, basic Belkin PF30 power strip.
I have been considering upgrading to a AQ Niagra 1000. Not sure if that would help with the hum.

The JC3+ is definitely a better sounding preamp than the GCPH . I can’t hear the hum when playing music, but I’m quite disappointed that the JC3+ hums louder than the GCPH.

Again, I know hums have been discussed to death, but any ideas or suggestions for my specific problem would be appreciated.
Eric

ericsch
invictus005
597 posts
 
@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.


atmasphere's avatar
atmasphere
11,841 posts
 
^^ +1
ericsch OP
753 posts
 
@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.

atmasphere's avatar
atmasphere
11,841 posts
 
That was the test that was needed. I agree also that it sounds like the Parasound is having a problem, perhaps a bad filter capacitor, since it seems to be affecting both channels.
invictus005
597 posts
 
With these further tests, it’s possible that an electrolytic capacitor is failing in JC3+’s power supply. My only concerns is that it usually happens in much older units and the hum is usually not a clean 60Hz tone, but rather a distorted buzz. 
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