2. amps-preamps
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Halo P3 Phono Hum

Running a Parasound Halo P3 and PSAudio hca-2 with Kimber Hero XLR interconnects. Phono hum is discernable at 47 volume level on the P3 and gets louder as volume goes up. I can connect 2 RCA interconnects to the phono input jacks and not connect them to the turntable and I get the hum. Leave internconnects off altogether and hum is totally gone, even at max volume. I connect cables to turntable (Pro-ject RPM6) and hum is still there. Grounding cable attached or not to preamp makes no difference. Grounding to different ground than stereo makes no difference. Hum is not present on other inputs, even at max volume.

What is going on here? This preamp is under six months old. I'm considering buying an outboard phono stage to get rid of the hum, but am unsure if that's throwing good money after bad. Thoughts from the group would be appreciated.
rg500g
nsgarch's avatar
nsgarch
2,524 posts
 
It sounds to me like you may not have finished grounding your TA/TT to the preamp.

First of all, your cartridge ground(s), blue and green, should not connect to any EARTH ground, neither must the cartridge body be grounded (even if it was metal.)

So, the black ground wire comes out of the tonearm wand and screws to the tonearm base which is electrically connected to the TT ground lug, is that correct? If so, you then need to run a small insulated wire from the TT ground lug to the ground screw on the back of the preamp (near the phono inputs.)

Use the AQ cables, and don't lift/cheat the ground on the preamp. You might want to lift the ground on the amp, though it's probably not necessary since it's connected to the pre with XLRs which are hum cancelling anyway.
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kurt_tank
1,189 posts
 
I suggest you investigate the Grado as being the cause of the hum. (If you do a bit of searching, you will find that others have had hum difficulties with their Grado cartridges as well.)

Just a thought.
rg500g OP
17 posts
 
My ground wire comes out of the tonearm tube where it meets the headshell and attaches to a screw that is screwed into the aluminum tube. I verified continuity between that screw and the grounding lug at the TT base. Per original posting the ground wire is present between TT grounding lug and grounding post on preamp. Makes no difference whether its connected or not. Pwr amp and pre are on totally different grounds.

I'll do continuity check on blue and green wires to ensure no continuity with earth ground.

I've heard of the Grado hum and wobble, but any Google finds don't reference the hum without the needle in a groove and the record in motion. Any recommendations on a cartridge I can buy CHEAP just to check if 'Grado hum' is the culprit? I intend on tossing it or giving it away afterwards.
rg500g OP
17 posts
 
Got feedback from Parasound. Pretty Interesting...

When I stated that hum was not audible until I had dial at 47 out of 80 possible steps the technician stated that such was not outside of the product's acceptable limits. He stated that a high gain device such as a phono preamp was very susceptible to picking up hum, and that the wall wart plugs (I've got 4 on a surge suppressor/line conditioner strip on separate breaker from preamp) may induce the hum, the cartridge, the speaker being 3 feet from preamp/turntable/etc. all may be culprits and that there's no easy answer here.

GREAT... I'm going to buy a cheapo shure or some other cartridge and put it in to see if hum is lessened, otherwise I may hear some light hum in the quiet passages of some LPs I play loudly, like Firebird or some organ pieces.
rg500g OP
17 posts
 
SOLVED

The hca-2 amp was inducing the hum. I had to move it to the bottom of my rack, about 2' below its previous position, and put the preamp above it to lend its mass as an ad hoc shield. Hum absolutely GONE. Got hiss, but that's expected when the volume is maxxed.
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