KOETSU hum only on playback

When my tonearm is lifted off the record there is absolutely no noise or hum, however, when I start playback
there is a midrange hum on both speakers. I cleaned, polished and oiled the cartridge contact pins to no avail.
I guess, a ground cable inside might have come loose and is touching something. Sound is absolutely brillant in spite of the low hum on silent tracks.

 

Sounds like it could be picking up vibration from your turntable's motor?

Edit: Well scratch that I've just read what your turntable is so that is unlikely.

... but if this only happens the moment the stylus touches the record surface then it's gotta be some some of vibration no?
Does the humming change tone with platter speed?

 

The VPI Avenger is a belt drive and that is certainly where the vibrations can be coming from. The belt will transmit vibrations to the plater (hence to the record).

I would investigate the mounting of the motor. Perhaps mounting screws are too tight (or too loose), belt issues. Could even be the motor itself, slapping to each pole as it turns.

I have personally been thru this very problem with one of my home brew TTs.

 

Oil the cartridge pins- could you explain this please Sir?

 

I'd tend to think it's cartridge related, but you could try a couple of pd things:

1) does it hum if you drop the cart onto a record without the motor running? This could indicate something in the cart.
2) As Vinnn said, does the hum sound different at different speeds? This might point more towards a motor issue.
3) Try to isolate the motor base from the surface it sits on. Use something like a closed cell foam, maybe 1/2" thick and put the motor base on it, then re-test. This will move the belt up the platter, but with that platter I don't think it's going to matter. If the hum lessens, it points to a motor / vibration issue. If the hum stays as is, points to the cart.
Have you checked your bearing oil lately? Could also be a bearing vibration being picked up via the cart.

 

Product is called Progold, made by CAIG. Works wonders.

 

YEP. Just lubed.

From what you point out in 1. I think its the cartridge. I have another arm on the unit and it does not hum at all. I switched arm positions and hum continues on the suspected cartridge.

 

It does sound like the cart. Just for fun, what does it do if you disconnect 1 ch, then the other when playing? The other possibility is the arm itself or cable, wouldn't discount either. Is the cable a din connector or hard wired? If it was my Koetsu, I'd be hoping for it to be anything else

 

What happens if you move the arm into playing position and lower it to the record without the turntable actually playing? What if you do this with the belt removed so that the motor is on, but, again the platter is not spinning? This will tell you if it is a vibration issue or an electrical issue. Sometimes a problem with the internal wiring of the tonearm is position dependent (e.g., the ground wire is broken, but when the arm is at its rest position, the broken sections are temporarily touching). It could also be the cartridge picking up an electric field only when it is in a particular position. This may provide additional diagnostic help.

 

Great advise will give it a go this evening.

 

Does the hum occur when someone else is in the room?

 

No but when my cat walks in Boom! its more like a purr purr thing.

 

Well I am grinning from ear to ear. I put the cart on the records endless grooves and let it spin. I then lifted the motor off the marble base and hum is gone.
So, I found a square piece of Sorbothane rubber and put it under the motor. Now no more hum. It's gratifying to know my Onyx cartridge is not to blame.
I'm wondering if I need to service the motor....hummm.
p.s. got rid of the cat too

 

Ha, yes I guessed that before I saw this. But if things are a little too slippery, perhaps a loose connection?

 

Glad you found it. If the hum just started recently, then you might want to consider service. Is anything in the chain a recent change?

 

Actually quite a few things. I just add a new arm and base and a better and very revealing phono amp. Since I added another arm the arm with the suspect cartridge moved closer to the
drive motor and thus was more vulnerable to vibrations.

 

You just give it a very thin coat and no change in connection grip unless connector y loose from the start.

 

It is nice to hear that you have found the source of your problem and acure (at least temporarily). The issue is whether the vibration ftom the motor is excessive and whether it will get worse. Problems with bad motors have been reported for VPI tables in the past.

 

I use the spray and Q Tips. Couple of baths every year on all connectors.

 

Interesting. I'm going to be adding a second arm to my Clearaudio Innovation soon - and it will be closer to the motor - will have to keep an eye (or ear) open when I do.

 

Currently addressing a turntable hum: Dyna 20xl2l>VPI Classic 3>Lehmann BCSE=hum. Same front end but Nova Phenom ll=no hum. Never had that problem before with the BCSE. Moved it to a second Rega system and no hum. Cart just got back from a rebuild so I ruled that out.