Rb301 Ground Wire Mod

[Fatmangolf]

I hot-wired my RB301 arm (that pdf is an excellent resource) but realised afterwards that my separate earth cable created a loop as most of my cartidges have one of their grounds connected to the cartridge body. This then connects to the arm via the fitting screws. So try disconnecting the arm earth/5th wire if you have one, see which option gives the least hum/buzz.

Another idea is to earth the brass bearing housing and sub-platter spindle. Just use a jubilee clip (is this the same name in the US?) to clamp the stripped end of the earth cable, run the cable through the Rega cable clamp and connect to ground at the preamp end. Same test applies as above.

Hope that helps.

[tiller]

Thanks fatman,

Regarding the tonearm ground... removing the jumper between the tonearm ground and the left channel ground while adding a dedicated run for the tonearm ground proved to be the best option so far. Sadly only a very very small improvement however.

Good call on grounding the spindle via the underside of the table. I'll give that a try and see if it makes any difference.

Cheers!

[Jim Leach]

Based on your extensive research to find the hum, I'd be very inclined to say it is a switching power supply on one of the circuits you are using.

These are popular with PCs as well as cell phone chargers. Basically any power supply that can take "100-240 VAC" in and get always the same voltage out. Microwave ovens are terrible in this regard as well.

And, YOU went to great lengths; however in an apartment situation, you can't control your neighbors! Maybe the guy next door has his cell phone charger in an outlet that shares power with you- and that may be on a "separate circuit" however if the 'dirty' power line is above yours in the panel, your power can be affected.

I have gone to great lengths to clean up my power, but I'm in a house. I have a new service panel and the top breaker is dedicated for the stereo rig, thereby avoiding a lot of line noise pollution.

It seems that the cartridge is a big problem based on your testing, but if you can clean up your power somehow, it will likely pay big dividends..

[tiller]

Yeah, very good points Jim. The interference is coming from somewhere, but unfortunately not from anything I have control over.

I am fairly certain it isn't noise on the mains though, and more likely some EMI floating around in the air. The reason I believe this is because the turntable picks up the hum regardless of whether or not it is plugged in and turned on. It is more likely to be the cartridge picking up the interference.

Oh, and not to mention the noise is greatly diminished when I put a different cartridge on the deck.

Thanks for the input!

[Jim Leach]

Often these type threads die off about now...

Please post when/if you find anything to resolve this. That is the bit often missing from the old posts and it prompts new posts which follow the same path.

[tiller]

Will do!

I am working on getting a new cartridge to see if that puts an end to the problem. Hopefully that fixes it!

Stay tuned...

[tiller]

So, for an update... I thought I'd post my latest findings on this issue in the event someone else stumbles across this thread in the future.

Thanks to the fantastic service from Robert at Audio Eden I was able to procure a brand new Rega Exact under warranty -- hooray for that! Unfortunately however, it made no difference in the amount of hum I have in my system. The fact remains though that when I put an old Shure M91ed on the deck, the hum is practically gone. I thought maybe the output of the Shure was so much less than the Exact that it is just giving the illusion of less hum. Checking the specs shows the Shure is rated at 5mV and the Exact at 7mV. I don't feel this is a big enough difference to make the hum disappear.

I think it's safe to say that the cartridge was not faulty. However, I think it's also safe to say that the shielding in these Rega carts, regardless of how good it is, is not good enough to block out the amount of ambient EMI in my apartment.

My next step is to try and find someone around town with an Ortofon 2M or Dynavector cart who will let me wire it up temporarily to check for hum. If these cartridges block out the EMI in my apartment I'd be tempted to sell the Exact and get a completely different cartridge.

That said, any Montreal-ers feeling particularly generous? Half-case of beer is yours if you want to drop by with one of the cartridges mentioned above, hehe.

I'll keep updating this thread as new info comes in. I don't imagine it will happen in a short amount of time though.

Cheers,
Adam

[Jim Leach]

Good info.

I'm curious to see how it shakes out.

On a side note, some people like the sound of the Rega cartridges, others not. I wonder if there is any relationship between that (personal preference) and the RFI that might be picked up at various locations... Just thinking out loud, but maybe there is something behind that...

[brianmch]

I don't have any hum using a Dynavector 10x5 on a RB301 with no additional grounding. (Since you asked if someone would bring a dyna over, thought this may be useful).

B

[Fatmangolf]

Do you own or can you borrow a multimeter?

I wonder whether there is an earth loop in there somewhere. If you unplug the drop leads from the phono sockets on your preampand (carefully) remove the clips from the cartridge terminals, you could test for connections between the left and right shield and the arm/chassis earth. Then plug the ground connections back onto the cart pins and test again. You are looking for a connection between the different grounds/earths, if you find one try disconnecting that cart conenction. Then reconnect the preamp and increase the volume from zero, listen for the buzz.

When I use my Rega Exact, I haven't noticed a buzz. I quite like the Exact cartridge so it's worth persevering with IMO. But I like my Goldring 2500.

Other ideas:
*With things conencted up as now and moderate volume, lift the turntable up and away from the wall if the cable allow this and listen to see if the buzz is lower.
*Turn other electrical equipment like TV, aircon, etc off. Same comparison on level of buzz
*Use a cable/power detector to test for live power cables in the nearest wall to your TT. If there are any, try picking the TT up and moving it way from the wall. Same test as earlier, is the buzz lower?
* Try the move away from wall test in last point.

Hope this helps.

[tiller]

As I said before, I don't think the problem is isolated to the cartridge out of context / in isolation. Rather, there is a source of enormous EMI in my apartment somewhere and the cartridge is picking it up. The problem is the cartridge in my apartment, or perhaps other high EMI areas. Respectfully, it is irrelevant whether or not one's cartridge picks up hum in their own setup. It is my setup/apartment, in combination with the cartridge, that is the issue.

Fatman, earlier in this thread I outlined the steps I've taken to narrow it down to cartridge. Good idea on checking for continuity between the signal leads/grounds and the tonearm ground. I own a decent DMM and will try that later. It still stands that the Shure cartridge is MUCH quieter, which makes me believe the tonearm wiring is fine.

As for your other points:

Moving the turntable: I have tested various locations in my living room, and yes, they make a difference in the hum being picked up. I thought perhaps it was coming from some other gear. I have moved every piece of gear independent of the turntable, tried turning off all my appliances etc. None of them make any difference. The only difference is made when I move the turntable. Some locations are worse, some are better. This makes me believe it is ambient EMI in my apartment.

I am sure there are mains cables running through the wall next to my TT. It is a small apartment and all the kit is located next to an outlet. I fail to see why this would be a problem however. Surely other people have TTs in this area and aren't picking up hum?

Thanks for the input folks!

[tiller]

So, regarding the ground loop stuff. I really really don't think it is a ground loop because if it was the hum wouldn't react to physical placement of the turntable in the room.

Nevertheless, I just checked continuity of the leads coming off the turntable. They all check out fine. Both signal grounds go to their respective sleeves on the phono plugs. Both signals go to their respective tips. The tonearm ground I added remains independent. Nothing is tied together at any point until they are plugged into the phono pre, at which point the signal grounds and the tonearm ground are tied together on the ground plane of the phone pre -- expected behaviour.

I think this is more evidence of the cartridge picking up EMI.

This is driving me batty, so I am going to experiment with moving stuff around again tonight.

Thanks!

[wobbleu]

This might be a bit 'off the wall' but could you try shielding the cartridge body with foil to see if it has any affect - they have copper tape for sale on ebay which will cut easily with scissors.

I vaguely recall reading a post somewhere about mu metal being used as a shield around a cartridge...

Obviously great care would need to be taken to avoid cantilever etc

[tiller]

Interesting idea wobbleu... I have some copper tape around here somewhere I could try. Although I'd rather not modify the cartridge if at all possible.

I've managed to get the hum a little quieter by unplugging practically all of my other equipment. Honestly, I am amazed at how susceptible the cartridge is to other equipment as I figure my setup is no different than most.

Just some other tidbits of info that could maybe help out:

- The hum is much stronger on the left channel.
- The cartridge picks up a significant amount of interference from the motor when the TT is running. Do people have this problem with other carts?
- Disconnecting the cartridge and shorting the tonearm wires (L- to L+, R- to R+) results in practically no hum. Using an older cartridge (Shure M91ed) results in practically no hum.
- The only thing that truly makes a difference is physically moving the turntable. I hooked up a very long set of phono leads, cranked the volume, and walked around my room with the turntable. I managed to find a place where it was quietest, but unfortunately that place is not practical for setup purposes.

Anyway, I am moving in a couple of months so I am tempted to try and ignore the noise and hope that it won't be so bad in my new place.

Thanks for the input folks!

Adam