hum help!

[sliderule3_14]

Help!

This is my setup:

rega p3-24
ortofon quintet black mc
ortofon st-7 SUT
audioquest big sur cables
rogue audio rp-5 with 40db gain, 47kOhm input impedence phono input
cardas cables
NAD C275BEE amp
KEF LS-50

in a previous setup, I had the rega plugged directly into the rogue with the gain set to 60db and 30ohm load and it was dead silent when the needle hadn't dropped.

my motivation is to use a separate phono preamp than the one built into the rp-5, so I've added a SUT--eventually, I will bypass the internal phono preamp and use a regular line-in on the rp-5.

I've checked continuity on all the RCA outer sheath conductors to ground and there seems to be less than .5 ohm resistance. I checked that all my ground are connected--I have a grounding bar that connects all grounds together, with each ground connected to the bus bar with it's own wire.

but with the addition of the sut, which is also connected to the same ground, there is a hum, even at low volumes (gets worse at higher volumes). when I touch the tonearm, the tone of the hum gets deeper but the amplitude goes up (gets louder).

additionally, with the SUT added and the hum, I can hear the volume knob clicks as I turn up the volume!

Any suggestions?

Thanks!


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[jostber]

It might be a ground loop between the SUT and the turntable. Can you try to connect the ground cable from the SUT to the Rouge audio preamp instead?

[sliderule3_14]

It might be a ground loop between the SUT and the turntable. Can you try to connect the ground cable from the SUT to the Rouge audio preamp instead?

Jostber, i can give that a try when I get home. it seems like it would be equivalent to my current set up, though. the ground on the sut goes to a bus bar and the ground on the rogue goes to the same busbar. but I’ll try it anyways and see what i can see, or hear, that is.


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[sliderule3_14]

It might be a ground loop between the SUT and the turntable. Can you try to connect the ground cable from the SUT to the Rouge audio preamp instead?

jostber, no dice. the hum is still there. i’m probing with my multimeter. perhaps i’ll find something.


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[Blackdog]

Does your tonearm have the extra ground wire or is it wired like a typical Rega with ground connected to the RCA shell?

[sliderule3_14]

Does your tonearm have the extra ground wire or is it wired like a typical Rega with ground connected to the RCA shell?

it’s the typical rega “integrated” rca ground


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[Blackdog]

it’s the typical rega “integrated” rca ground
And that may be where the problem lies. It isn't a ground loop, it is a lack of ground, or more precisely lack of shielding ground.
A couple of clues. Touching the arm changes the tone and amplitude, and it is volume dependent. I don't know exactly how the Ortofon is wired , but I suspect the ground to the RCA input jack is isolated from the output and from earth ground. With that ground missing, the tonearm is picking up all kinds of noise.
Try this - With all the ground wires in place (I assume one from the transformer to the Rogue), take another piece of wire and attach it to the ground post and touch the ground on the RCA jacks (probably input jacks). Does the hum change or even disappear?

[Primalsea]

I find that a couple of lengths of wire with crocodile clips at each end are useful when trying to find a grounding problem. You can makes various ground connections between outer rings of rca plugs, binding posts, tonearms etc. Worth checking voltages differences with a meter first before making a connection as if there is a fault you might have quite a a voltage difference and you might get a bit of a loud pop.

[RothwellAudio]

Yes, I suspect the Rega's odd scheme for for earthing the tonearm is the root of the problem. The usual way (which is most problem-free) is for the L/R cartridge -ve pins to each have their own wires (connected to the RCA plugs -ve side) and no connection between them. Then a separate earth wire comes from the tonearm and the rest of the turntable's metalwork to the earth terminal on the phonostage or preamp. The earth wire should not connect to the cartridge's L/R earths except at the earth terminal on the phonostage or preamp. It should be possible to get hum-free performance with the system wired that way.
However, re-wiring the tonearm would be a fiddly and/or costly job, and it must be possible to get hum-free performance with Rega-style wiring, as you have proved with your original setup (with cartridge straight into the preamp).

This is what you need to check first: with nothing connected to the Ortofon transformer, check if there's continuity between the earth post on the transformer and the earth sides of the RCA sockets. It would be best if there isn't, but check that and then get back to me with your findings.

[hifi_dave]

Selling Rega turntables and arms for over 40 years, I can state that I have never experienced 'hum' caused by Rega's earthing arrangement. The screens and metalwork is earthed via the right channel plug and screen. For confirmation of the effectiveness in this case, the OP states that it was "dead silent" before the SUT was added.

I would suggest you look at the earthing arrangement and siting of the SUT. If the SUT is anywhere near anything with mains on, it might well pick up 'hum'.

[RothwellAudio]

I would suggest you look at the earthing arrangement and siting of the SUT. If the SUT is anywhere near anything with mains on, it might well pick up 'hum'.
That's a good point which I forgot to mention. Nearby mains transformers can induce hum into the SUT, though moving the SUT only a few inches (any maybe turning it through a few degrees) can reduce the hum dramatically.

Over the years I've had lots of people contact me regarding step-up transformers which hum, and they nearly always start by saying they have "an earth loop" causing hum. Sometimes that's the case but often it isn't. The other two most common causes of hum are:
1) placing the SUT too close to a mains transformer, and
2) using unshielded interconnects between the SUT and phonostage.

[sliderule3_14]

This is what you need to check first: with nothing connected to the Ortofon transformer, check if there's continuity between the earth post on the transformer and the earth sides of the RCA sockets. It would be best if there isn't, but check that and then get back to me with your findings.

Hi, there seems to be continuity between the grounding post and all the RCA earths. Is that bad?

[sliderule3_14]

I also performed the following checks:

with a banana plug on the SUT ground (using the free end to touch) and the SUT ground wired to the preamp ground:

I touched the green wire and the buzz on the right channel increased dramatically
I touched the blue wire and the buzz on the left channel increased dramatically
I touched the right channel of the rega rca earth and the right channel buzz increased dramatically
I touched the left channel of the rega rca earth and the left channel buzz increased dramatically
I touched the SUT right output rca earch and no increase in buzz (which is weird since I thought I had continuity with all the ground post on all the SUT rca earths)
I touched the SUT left output rca earch and no increase in buzz (see above aside)
I touched the tonearm bare metal and the buzz in both channels increased notably

I also moved the SUT away from my setup with no change in buzz

additionally, I swapped the SUT output interconnects (which are audioquest big sur cables) with Schiit Pyst cables with no change in hum.

Not sure what I'm dealing with here as I'm not an electrical engineer

Thanks all for your feedback!

[struth]

I had a hum appear on my setup the other day. Only thing I'd done lately was changed CD players to the oppo. It was the tonearm plug very slightly loose

[RothwellAudio]

Hi, there seems to be continuity between the grounding post and all the RCA earths. Is that bad?
Possibly, in this case it is bad. Those RCA sockets have nylon washers to isolate them from the metalwork, so it should be possible to break the connection between the RCA earths and the earth post.
Try this if you're confident with a bit of rewiring:
Keep the earth post connected to the metalwork, but break the links between the negative terminals of the RCA sockets and the earth post. The earths of the right channel input and right channel output should link to each other and to the right channel transformer. The earths of the left channel input and left channel output should link to each other and to the left channel transformer. There should be no connection between the left channel earth and right channel earth.
Use a ground wire to link the earth post on the SUT to the earth post on the preamp. Try it with/without the ground wire to see which is quieter.

[sliderule3_14]

I looked up some SUT schematics and several did have the grounds tied together. However, upon opening the case, I did see that only the output grounds where tied together explicitly. There where insulating washers for the input grounds, but somehow there was continuity with all the grounds, but I couldn't tell how. Am I missing something?

[RothwellAudio]

I don't know. Maybe I'm missing something. I told you how to wire the SUT. You can choose to wire it like I said or choose to wire it some other way.

[DSJR]

Rega arms are earthed in a way to suit Rega! Most of the time when these arms are used on other decks it causes no issues at all, but I have known hum problems to arise occasionally and just sometimes, the phono stage used doesn't help either. I assume the hum is there all the time and with stylus lifted off the record?

Induced hum is a different thing and can be due to magnetic fields from nearby transformers all adding up, so if a Rega or Grado mm cartridge is to be used, or especially a low output mc type, careful siting is essential if a Rega deck is used although in this case it may be just an earthing arrangement.

In this particular case and bearing in mind the deck is a Rega complete, it may be a good idea to try or borrow a different mc stage, such as a Rega Fono MC, purely to keep it all in the family and to check the arm wiring hasn't gone awry if nothing else...

[sq225917]

Rega use the signal gnd wire on one channel as the gnd. Which is fine in single ended phonostages which throwaway signal - on both channels by grounding them to the phonostage chassis.

But step up transformers don't do that, they use the full voltage swing between signal minus and plus on each channel. They retain the fully balanced signal that comes from the cartridge. Rega assumption that they can do what the hell they like with one signal - from the cart is the root of the issue.

You need to rewire your tonearm. No amount of fiddling will otherwise fix this. As long as signal- in one channel is used as earth it'll always hum.

[hifi_dave]

Just done a dem using the Rega P6 with Ania cartridge. Now, of course, this uses Rega arm wiring, which I have never found to be a problem. We were trying various step up transformers and a Rothwell Headspace. There was no hum, buzz or any extraneous noises from the Rega set up - total silence and that's the way I have found it to be with numerous, various Rega turntables over the years. The Rega wiring is practical and not a problem.

[RothwellAudio]

Rega use the signal gnd wire on one channel as the gnd. Which is fine in single ended phonostages which throwaway signal - on both channels by grounding them to the phonostage chassis.
But step up transformers don't do that, they use the full voltage swing between signal minus and plus on each channel. They retain the fully balanced signal that comes from the cartridge.
There's the same voltage between the positive and negative terminals on a cartridge whether it is wired balanced or unbalanced - there's no difference between the two.
Also, a step-up transformer can be wired as balanced input with unbalanced output, or balanced at input and balanced output, or unbalanced input with balanced output, or unbalanced at both input and output. There's a multitude of options. The most common is unbalanced input and unbalanced output. In all cases the voltages are the same.

Just done a dem using the Rega P6 with Ania cartridge. Now, of course, this uses Rega arm wiring, which I have never found to be a problem. We were trying various step up transformers and a Rothwell Headspace. There was no hum, buzz or any extraneous noises from the Rega set up - total silence and that's the way I have found it to be with numerous, various Rega turntables over the years. The Rega wiring is practical and not a problem.
Yes, Rega's wiring shouldn't be a problem. I'm still trying to work out exactly what is wrong in the OP's setup but I'm confident it is that Rega's wiring uses just one signal negative as the ground for the arm but the SUT is linking both signal negatives together. Or maybe it isn't :scratch: It's a lot easier having the equipment in front of you than diagnosing problems via forum posts.

[sliderule3_14]

Guys, thanks for the feedback. I did another series of experiments:

1. I removed the cart and shorted the red-to-green and blue-to-white wires using alligator clip wires
2. To see if the tonearm continuity was missing, I checked between the tonearm and the SUT grounding lug, and it was there
3. I opened up my SUT and checked continuity on all the grounds, it exists, which means all grounds are connected, but I couldn't find a way to isolate the input ground from the output ground as it seems they're connected somehow in the transformer. there are only two wires coming from the input connection (ground and signal) see this picture: https://www.pinterest.com/pin/483292603746340417/

Could this be a component compatibility issue. I can't imagine ortofon selling something that is inherently poorly designed. Does anyone else have experience with this particular SUT?

Thanks all!

[RothwellAudio]

see this picture: https://www.pinterest.com/pin/483292603746340417/


Pinterest requires a sign-up to see the picture, and authorisation to access all kinds of personal data. I didn't do that.

[RothwellAudio]

Here's a simple test which will be useful:
disconnect the SUT from the preamp, but leave the interconnects which you had between SUT and preamp connected to the preamp's inputs. Insert a pair of shorting sockets into the free ends of the interconnect (where the SUT was). Is there any hum?
Now touch the earths of the two shorting sockets together. That will create an earth loop. Does it hum now? If so, it's because having the L/R earths connected at the far end of the interconnect has created an earth loop which the preamp has problems with. Some preamps don't hum when such a loop is created, some preamps do. The difference is due to the way the preamp's circuit is laid out on the circuit board.
If you get hum when you do the test you will also get hum when the SUT is in place because the SUT is also linking the L/R earths together. To cure it you need to break that link (like I said in a previous post).

[RothwellAudio]

... I couldn't find a way to isolate the input ground from the output ground as it seems they're connected somehow in the transformer.

Do not disconnect the input earths from the output earths. The L input earth should be connected to the L output earth. Same for the R channel. It's the L and R earths which should be isolated from each other. Read post #15 again.

[RothwellAudio]

...this uses Rega arm wiring, which I have never found to be a problem. We were trying various step up transformers and a Rothwell Headspace. There was no hum, buzz or any extraneous noises...
I hope the Headspace acquitted itself with honour :)

[hifi_dave]

It sure did. I have used it frequently for demos. It's one of those go-to items which I can take off the shelf and use without worrying about the performance or even if it will work.

[RothwellAudio]

It sure did. I have used it frequently for demos. It's one of those go-to items which I can take off the shelf and use without worrying about the performance or even if it will work.

Glad to hear it :thumbsup: