Turntable Hum, Can't Solve It

bar72

bar72

Active Member
Hi all.

Rega P3 Turntable with RB300 Arm (rewired with separate earth lead)
Parks Audio Budgie Phono Pre Amp
Cambridge Audio Topaz SR10 (6 month Old)

Just got the arm back from the guy who rewired it 2 years ago. He's checked the arm out and states that all wiring (including separate earth wire is fine).

So, I hook it up with Cambridge Audio interconnects (interconnects tested OK with multi meter for short / open connection) through the Budgie phono Pre to the Aux / CD and every other Line Input input on amp. I get Hum through speakers.

If I bypass amp and hookup leads from Budgie Phono Pre directly to my Tascam US122 USB soundcard, No Hum.

All plugs for TT, Phono Pre, Tape Deck & Amp into 4 gang extension then into wall socket.

If I select each input on amp, with nothing connected to CD, Line In, DVD or Phono RCA's, only speakers connected, I get zero hum until I select the Phono Stage on the Amp (Cambridge Audio Topaz SR10). This is with nothing connected to any of the RCA Inputs???

I could just set my TT up directly to my Tascam Sound Card and run back to the Cambridge Amp with another interconnect but that means I need computer on to listen to the TT. Not ideal as I'd prefer the TT Phono Pre into Cambridge Amp then run interconnects from line out to Tascam. That way I can run any input source into Cambridge to Tascam Card, without having to swap out interconnects every time I want to change from TT, Cassette, Radio, etc.

Is this a faulty Phono Stage on the Cambridge Amplifier that's causing my hum issues?

Any ideas greatly appreciated as this is driving my nuts trying to eliminate it.
 
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I have no idea about directional? They are Cambridge Audio Pacific (Yellow) Interconnects. Tried earthing TT to Cambridge Amp, still humming whether connected to earth on Phono Pre or Cambridge Amp?

edit: also tried running wire from phono pre earth lug to amp earth lug, no difference?
 
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This is just a shot in the dark, but you may have a ground loop in your phono stage. Try a cheater plug on your preamp and amp and see what happens. My guess is that it will not fix it, but it's cheap to try and if it does, you know what the problem is.
 
Thanks for the suggestions guys, worked perfect before then it just appeared overnight. that's why I initially thought it was the RB300 Arm playing up. Gonna swap out 4 gang extension lead, then swap out amp as I got an old Denon lying in cupboard. See what happens then.
 
bar72 said:
I have no idea about directional? They are Cambridge Audio Pacific (Yellow) Interconnects. Tried earthing TT to Cambridge Amp, still humming whether connected to earth on Phono Pre or Cambridge Amp?
Click to expand...

Some cables are made with a twisted pair and a telescoping ground shield connected at the source end - these usually have arrows printed on them to show signal direction. What I'm hearing you say is your SR10 has a hum even if nothing is connected to any inputs when you select Phono. Ground loop or not, this shouldn't be happening unless something with a strong field is near your SR10 and the high gain of the phono stage is coupling this to its input. Also, you say when you connect your external phono preamp to any input on the SR10, you get hum. It still sounds like you have something being coupled in via a high gain stage. Can you move just the receiver - no speakers or anything else to a different room, plug it in and listen for hum through headphones? Maybe that will yield some different results to go on.
 
Thanks Sam, yes, no interconnects near any RCA Input on Amp. Select DVD / Aux / CD, all quiet. Select Phono, starts humming with nothing connected. I have TV connected to wall socket on it's own, currently switched off at wall and the Amp, Phono Pre, Cassette Deck and TT into 4 gang extension into it's own wall socket.

20170811_135040.jpg


Nothing I can think that would be causing a problem but I shall move amp and post back.
 
Well let establish a few things and get info.

I'v seen no mention of a cartridge, some of them have a hum, like Grado

Level of hum?
all phono stages have hum, if your cranking up the volume while nothing is playing as your test, well it's normal to hear hum.
Is the hum loud or bad even with the volume set at normal levels?
do you hear the hum while a record is playing?
Does it hum when touching the tonearm?

Turntable, Tonearm and System ground wires:
They are not mandatory to use, and in a lot of cases cause more problems than they fix.

Disconnect all ground wires you have hooked up factory and of your own making.
Tone arm and if the TT has a factory ground move away from any other wiring neatly to test.

Hook up tonearm ground only to test.


Interconnects:

Need to be good quality
need to be routed neatly and not all tied together

Disconnect every other input to your system so as the table is the only source that your working with in all these test. It's a process of elimination.

In the wire routing of an external phono stage, never cross the input/output Interconnects, they can loop noise and hum, another reason for quality here.
 
Looking at your photo that is not in anyway neat routing of interconnects and AC wires.

20170811_135040.jpg

I see your phono stage output crossing over the stage it's self, remember wire is an antenna that can attract interference.
 
Hi 4-2-7, OK, I have an Audio Technica AT150MLx Cartridge. tested with multimeter and all values in tolerance so I believe cart is good. Hum isn't over the music, I only hear and see it in Adobe Audition when everything sitting idle. When I say see it, I mean the level meters in Audition are fluctuating around -60dB on the level meters before dropping the needle. (Evrything else in my hardware chain is around 90dB - 108dB SNR ratio). Doesn't do this if I bypass the Amplifier and route Phono Box direct to Tascam USB Soundcard? Level Meters don't even register a hum if Phono Pre is directly connected into Tascam Sound Card.

TT Tonearm ground only, connected to Phono Pre or Amp = Hum

Interconnects are Cambridge Audio Pacific, not cheap but not from the 99p store either.
Interconnects tidy and not crossing near power cables, etc

Moving Interconnects around does nothing.

Nothing else bar speakers connected. Nothing else connected in house sockets (went and unplugged / switched off everything in the house, inc. Fridge).

Swapped out Amplifier for a Denon, same problem with the hum so I can eliminate the Cambridge Amp.

Budgie Phono Pre is Brand New with about 5hrs on it. As I say, no problem if I bypass either the Cambridge Amp or Denon Amp.
 
ALL phono stages make noise, they are not as quiet as all your other inputs....

bar72 said:
Hum isn't over the music, I only hear and see it in Adobe Audition when everything sitting idle. When I say see it, I mean the level meters in Audition are fluctuating around -60dB on the level meters before dropping the needle.
Click to expand...

bar72 said:
(Evrything else in my hardware chain is around 90dB - 108dB SNR ratio).
Click to expand...

Parks Audio Budgie Phono Pre Amp
Specifications

- Tubes: Two matched 6922 Electro-Harmonix tubes (included)

- Gain: 38dB (suitable for carts with at least 5mV output)

- Input Impedance: 47K, adjustable

- Output Impedance: 6K ohm

- RIAA Accuracy: +/-0.5dB from 20Hz to 20kHz

- Distortion: less than 0.1% at 1kHz with 30mVrms input

- SNR: typically 78dBA with 5mV input

- Overload: Minimum headroom of 200mVrms at 1kHz

- Warranty: Two years

- Power: 7W

- Input Voltage: 100 to 240VAC 50/60Hz external 12VDC supply

(EU-UK-OZ adapters free upon request)

- Weight: 20 oz (570g)

- Size: 7” x 5” x 4.5” (180 x 130 x 115 mm)
 
Thanks for the additional info 4-2-7. It's my 1st Valve driven amp, didn't realise that hum was the norm with phono stages.
 
DSC_0007.JPG Move your phono stages location. Doesn't take much. My wires are a birds nest and I have 3 different phono pre's on line. All quiet as a graveyard.
 
woofmytweets said:
are your interconnects directional? tried grounding the phono stage chassis to the amplifier chassis?
Click to expand...

What is a directional interconnect? The signal is AC. Alternating current. It has no "direction" per se - it has both back and forward :p


Or did you mean "shield connected on one side only?"
 
bar72 said:
Thanks for the suggestions guys, worked perfect before then it just appeared overnight. that's why I initially thought it was the RB300 Arm playing up. Gonna swap out 4 gang extension lead, then swap out amp as I got an old Denon lying in cupboard. See what happens then.
Click to expand...
It costs about 79 cents per cheater plug. It takes about 30 seconds to put them into the mix. To me, it's the quickest way to eliminate and determine is a ground loop is your problem. IMHO
 
RB300 had a full rewire due to failing. Seperate Earth lead was installed and ran everything ran fine through my old Pro-Ject Phono Box SE II. Started getting a problem with hum and thought it was the tonearm so I sent back to J at Audio Origami and he's returned arm with no fault found. Everything within tolerance. While the arm was away, I decided to upgrade to a Budgie Phono Pre Amp. Anyway, arm is back, runs through Van Damme Interconnects from tonearm to either Budgie or Cambridge Amplifiers Phono Stage. No matter what phono stage I try, both humming away that is noticeable when I turn up the volume. Tried moving Budgie to other side of room, different interconnects, still no difference. I'm going to shunt the lot to another property tomorrow and see if the issue is to do with the house wiring as I had a periodic electrical inspection from one of the landlord's electricians and unsure if it's a coincidence but everything was good when I used it prior to his visit.

I tried wiring an earth wire to the ground lug on the wall socket, from the Budgie and hum got worse? Same with the Cambridge Audio Amplifier, took a wire from the amps earth pole and wired to earth on wall socket, it also got worse?

Only other thing that I can think of is the sparky decided to move the kitchen light switch from the kitchen to the living room wall behind the original switch and did a "pull back" on the wires. I have noticed that the earth on the old & new socket has been left disconnected? would this cause a hum?

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20170811_183440.jpg


Cheater plug not an option, got young kids in the house. While unlikely, I'd rather have my kids than a Stereo System that has Earth Bypassed ;
 
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