Hi everyone,
Been a while! Start-up has led to little time for DIY projects over the past four years!
Anyway, got a quick question on my TT set-up: Just changed the arm on my TT and experimenting with alternative grounding options. Original set up had the arm ground connected to the TT ground as well as provided an external grounding wire, to connect to the chassis ground of the phono pre-amp.
I am now trying to decide if I should replicate that or instead just ground the arm to the signal ground and nothing else. Does anyone have any wise words as to the advantages and disadvantages of either option?
Intuitively, it doesn't sound right to add anything to the signal ground, in case this results in interference messing up the voltage differential between signal live and ground. Equally, the idea of keeping the tone-arm completely disconnected from the motor of the TT sounds appealing.
I tried the option of connecting the tonearm ground to the phono pre chassis but not the TT motor ground, but this resulted in motorboating.
Look forward to ppl's thoughts!
Been a while! Start-up has led to little time for DIY projects over the past four years!
Anyway, got a quick question on my TT set-up: Just changed the arm on my TT and experimenting with alternative grounding options. Original set up had the arm ground connected to the TT ground as well as provided an external grounding wire, to connect to the chassis ground of the phono pre-amp.
I am now trying to decide if I should replicate that or instead just ground the arm to the signal ground and nothing else. Does anyone have any wise words as to the advantages and disadvantages of either option?
Intuitively, it doesn't sound right to add anything to the signal ground, in case this results in interference messing up the voltage differential between signal live and ground. Equally, the idea of keeping the tone-arm completely disconnected from the motor of the TT sounds appealing.
I tried the option of connecting the tonearm ground to the phono pre chassis but not the TT motor ground, but this resulted in motorboating.
Look forward to ppl's thoughts!
Does the signal ground figure in this anywhere? Is that set up giving any problems?
What turntable and what arm?
FWIW my SME arm has 3 ground wires. signal is screened twisted pair, so each shield has a cable, then a 3rd from the arm itself.
Grounding the tonearm to the phono chassis should not cause an issue unless there is another ground path causing a loop.
FWIW my SME arm has 3 ground wires. signal is screened twisted pair, so each shield has a cable, then a 3rd from the arm itself.
Grounding the tonearm to the phono chassis should not cause an issue unless there is another ground path causing a loop.
No major issues with that set up - there was a very minor hum but only audible when pre-amp was cranked up all the way and no record was on.
Signal ground not connected with chassis ground in this set up, no.
I've separated the signal ground from chassis ground (case) on my disco mixer, by putting o-rings under the RCA jack rings.
Minimum hum occurs when grounding the turntable green wire to the case. Same results on my dynaco PAS2 preamp,turntable green wire to the case screw minimizes hum.
The dynaco PAS2 case is definitely not connected to anything, a two wire power cord. The two wire power disco mixer, I've tried grounding the case to the 3rd pin of the outlet strip with a separate plug. No effect on hum, which is inaudible.
Not sure the wall plug receptacle 3rd pin actually has a green wire to the breaker box, or just connected via the white wire. This house was built in 1936, rewired 1985 with pvc romex, a couple of outlets have real safety grounds but not many.
None of the setups have the turntable shell connected to signal ground. Haven't tried it since I got to inaudible hum without that.
Minimum hum occurs when grounding the turntable green wire to the case. Same results on my dynaco PAS2 preamp,turntable green wire to the case screw minimizes hum.
The dynaco PAS2 case is definitely not connected to anything, a two wire power cord. The two wire power disco mixer, I've tried grounding the case to the 3rd pin of the outlet strip with a separate plug. No effect on hum, which is inaudible.
Not sure the wall plug receptacle 3rd pin actually has a green wire to the breaker box, or just connected via the white wire. This house was built in 1936, rewired 1985 with pvc romex, a couple of outlets have real safety grounds but not many.
None of the setups have the turntable shell connected to signal ground. Haven't tried it since I got to inaudible hum without that.
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TT is Technics SL1210 MKII, arm Jelco 750D. Same set up as SME - 3 ground wires, two for the cart ground and one for the arm itself.
So you think that even if I am only grounding the tonearm to the phono chassis but not the TT chassis I should not be getting a buzz? Any ideas on what ground path could be causing the issue? It wasn't buzzing when I had the old tonearm on, which was connected both to phono and TT chassis...
Turntable chassis back to mains earth, which the 1210 should internally. Depending on your phonostage , arm gnd to phonostage chassis, which will be signal gnd common, or add a ddrc, back to back diodes, 10r resistor and a couple of uF film cap, and then to chassis gnd.
Having checked the cables that you can get for the Jelco arm ground is seperate from cartridge ground, so there must be a ground loop. If you have a metal armboard for the Jelco that would explain it. I've not taken a 1210 apart, but I suspect that is the problem. You need to either isolate the arm fully from the deck and the gnd to preamp case or connect the arm ground to a suitable point on the TT.
Are you able to plug the preamp and the deck into adjacent power sockets. That can reduce issues with ground loops.
Are you able to plug the preamp and the deck into adjacent power sockets. That can reduce issues with ground loops.
> interesting if you tried a number of different options
And if fingers are nimble, a lot faster than taking a popularity-poll in a forum.
Clip-leads are often the fast-path to THE answer:
And if fingers are nimble, a lot faster than taking a popularity-poll in a forum.
Clip-leads are often the fast-path to THE answer:
An externally hosted image should be here but it was not working when we last tested it.
You are right - the arm board is aluminium and it follows that this means the tonearm ground does have a connection with the TT chassis. Would you mind explaining why this would create a ground loop though?
BTW, all my audio equipment (TTs, mixer and amplifier) is connected to the same socket, through an extension. Prior to doing that I had a nasty loop going on between the pre-amp/mixer and the amp.
Actually I did try a couple of things: What gave the best result was connecting the tone-arm ground to the signal ground - total silence was achieved. I also know that another solution that works is connecting the tone-arm ground to both internal TT grounding point and pre-amp chassis ground - this was the original set up and the stock tonearm of the 1210 is similar to the Jelco, in the sense that both have separate arm ground to cartridge/signal.
More than anything I wanted to get people's feedback and thoughts to understand what is causing all this. Have always struggled to properly understand what causes ground loops and by implication I have always struggled with "best practices" for grounding, so would really appreciate any explanation based on this practical example.
The differential would remain the same so long as it was connected by a loop free low impedance path
This proves it
I didn't have to do this because the green wire from my player connects to the metal tone arm only. The rest of it is plastic except for the motor. Being double insulated, it was sold with a two wire power cord, in 1979. So the safety ground was not involved with the turntable, only with the case of the mixer. I got to dead quiet "hum" by attaching the green wire to the mixer case, which was isolated from the RCA rings which were analog "ground". The mixer did hum with the RCA rings touching case, as the mixer was designed & sold. Polarity of player power cord doesn't matter, no hum either way. It is belt drive so no connection motor to platter (plastic) or to LP either.
Also my "obsolete" 1970 amp has no safety ground connection either , so no ground loop there either. Don't try this ground loop extermination method at home fans, you might shock your grand-child on an amp case. I don't have any, toddlers are kept out with a entryway lock. Too many choke hazards in here for toddlers, too.
Ground loops are common in bands, where the instrument analog ground is connected to the mixer ground, which is safety grounded, and the power amp is safety grounded, so instrument cable to wall plug through wall wiring to mixer to instrument shield is a big area ground loop. With all that beer being slung around, and performers touching analog ground on the mikes with their faces, safety grounding is important. Bands have to use transformer or differential op amp "DI" units to separate the instrument cables from the wall wiring, to break the ground loop.
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My experience with setting up many turntables is that there is no all-situation right answer. Sometimes no ground connection is quietest, other times a ground wire from the chassis is best, sometimes tonearm wiring, sometimes both.
I would suggest if at all possible to have both available and see which one works best by experimentation. Almost always one method is superior to the other options, so it's easy to figure out.
You can use almost any wire you have hanging around to use as a ground wire from the 'table to a preamp, and for your tonearm ground you can connect it to a metal part of the chassis, or a non-metal part if you decide it's best unused.
If you choose a metal part of the chassis, you can then run the chassis ground from that same point to your phono preamp (for both) or from a non-metal part, again from that same point to your phono preamp for tonearm only.
The final option would be tonearm to metal chassis, but no ground to the preamp.
Sometimes the signal cable you use provides the ground path (especially with shielded cables).
I would suggest if at all possible to have both available and see which one works best by experimentation. Almost always one method is superior to the other options, so it's easy to figure out.
You can use almost any wire you have hanging around to use as a ground wire from the 'table to a preamp, and for your tonearm ground you can connect it to a metal part of the chassis, or a non-metal part if you decide it's best unused.
If you choose a metal part of the chassis, you can then run the chassis ground from that same point to your phono preamp (for both) or from a non-metal part, again from that same point to your phono preamp for tonearm only.
The final option would be tonearm to metal chassis, but no ground to the preamp.
Sometimes the signal cable you use provides the ground path (especially with shielded cables).
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Yes. Especially in situations where the cartridge case with it's connection to one of the two channels' ground pins is not galvanically isolated from the headshell/tone arm/chassis a separate ground lead most certainly will produce a ground loop.
Best regards!
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