Lowering the noise floor of the Crack

[tiller]

Hi all,

I have had my Crack for a couple of days now, and it really sounds fantastic. I am not sure what it is, but I am noticing all sorts of details in the music I hadn't noticed before, especially ambiences and room tones in recordings. Loving it!

That said, I'd like to lower the noise floor of the thing. At about halfway on the volume knob, there is quite a noticeable hum/buzz thing going on, ground-ish in nature. It is in both channels. I will reflow all the solder joints in the PSU section of the Crack as soon as possible. Beyond this, where else can I look to lower the noise floor?

Cheers,
Adam

[tiller]

UPDATE:

Once again, after posting a potential issue on this forum, I've managed to figure it out on my own, haha. Sorry for cluttering the board. Maybe there's some consolation in someone else finding my thought process useful.

Anyway, using shorting plugs on the input, the Crack is pretty much dead silent. Or at least silent enough to satisfy me. Tracing my rig back, it seemed as if the noise was coming from my Seduction. However, using shorting plugs on the input of the Seduction yields it pretty much silent as well!

I guess that means that the problem is with my turntable. I would think the grounding on my turntable, specifically. What is fascinating is that the problem exists whether or not the turntable is plugged in, and whether or not it is turned on. One would think lifting the ground (unplugging) the turntable would solve the noise issue, no? My electronics knowledge is not that great, and I cannot think of a reason why the turntable should create such a noise issue on the inputs of the Seduction regardless of whether it is plugged in or not, and whether it is powered on or not. Could it be a loading issue of some kind?

FYI, the turntable is a Rega P3-24. It has no dedicated ground wire on it's outputs. The chassis ground is tied to one of the signal grounds in the output phono leads. Everything is plugged into the same power outlet.

Thanks in advance,

Adam

[Grainger49]

Adam,

If the Seduction is silent with shorting plugs you might try the dance of moving the table and dressing the cabling from the table to the Seduction.  It is easy to try grounding the Rega.  First try a wire from any metal piece on the arm to the Seduction.  I think Rega grounds the arm through one of the audio cable shields.  This first try will make no difference if the ground is integral to the audio cables.  Then try a wire from any metal on the chassis of the Rega to the Seduction.

This needs not be pretty to try it.  Just cut a 6' piece of wire, strip both ends and touch to the metal while one end is screwed to the ground post on the Seduction.  It is quick and conclusive.

After these two things start moving the cabling to see if it is picking up noise.  If the cable is the culprit you can try another quick and dirty method of shielding it.  Wrap it in aluminum foil grounded to the Seduction.

Good luck, let us know what you find.

[tiller]

Thanks for the prompt reply Grainger, much appreciated.

I think I've made some headway with this issue through experimenting with things this evening. I will spare you all the details as I have tried A LOT of different combinations of interconnects and grounding, etc. Touching the ground wire which I attached to the Seduction seemed to do absolutely nothing in most cases. In certain cases (such as touching the end stub on the Rega's tonearm) it made things worse. I would think this is because it is in fact creating a ground loop, since the Rega is already grounded through the phono lead.

Anyway, I decided to try and isolate the system. I moved the Rega, Seduction, and Crack to another place in the room and hooked them up together. Again, with shorting plugs installed both the Crack and Seduction were satisfactorily quiet. Only when adding the Rega to the equation did I get a ton of noise. Unfortunately, as mentioned above, no alternate grounding scheme seemed to help reduce the hum. Moving the phono leads, or any cables for that matter, did not result in any change.

For the hell of it, I popped open the lid on the Rega and moved the tonearm. And wouldn't you believe it-- the hum changed. Even disappeared at one point! I thought, maybe the cartridge was picking up interference from the Seduction. Moving the Seduction around (as opposed to the Rega) did nothing. Moving the Crack around did nothing as well. I tried moving the extension cord it was all plugged into. No change.

Soooo, the Rega is picking up stray EMI from something. What it is I have no idea. I guess there's no real option when it comes to trying to fix the issue at the Rega, since the cartridge is what it is, no?

Is this possible? None of my other equipment has this issue. Before I go moving a ton of stuff around, should I worry about devices that are not active/powered up? I can't see how they could be causing interference. Maybe it's my old CRT television? I'm glad I think I've made some headway with this, but unfortunately I feel like a whole new can of worms has been opened!

Any advice is much appreciated

Adam

UPDATE: Moved pretty much everything in the room whilst listening for a change in the noise. Unfortunately nothing I moved made any difference. I'm worried that it could be mains wiring in the apartment doing this? I do notice funky things going on with some of my other gear (guitar amp for example) on occasion so I wouldn't be surprised if there's something funky in the wiring of this place...

[Grainger49]

Everything you did makes sense.  One last possibility, try removing the cartridge clips and shorting each channel together.  This takes the cartridge out of the equation.  If it reduces the noise it might possibly come from the cartridge.  Try another cartridge.  You don't have to mount the cartridge, just dangle it from the arm wires.  That way you don't mess up your present cartridge's setup.

[Paul Joppa]

Another long shot here - sorry  :^)  One thing that often causes hum is other devices in the house or on the same power system - fluorescent lights, light dimmers, refrigerators, cell phones, aquarium pumps, all kinds of stuff are potential sources. If your noise is steady, it's probably not a cell phone which will make intermittent noise - you can rule out some things. But a bit of time spent turning as many things off as possible might identify a culprit.

Since the noise appears whether or not the Rega is plugged in, it's not likely to be line noise - must be EMI pickup. Does moving the tonearm have the same effect with the Rega unplugged as it did when it was in a different location and plugged in? If so, you have to guess that in a certain position the turntable provides shielding for the tonearm wiring.

Oh - one other thing. I googled "Rega P3-24 grounding" and got 12,600 hits. I only looked at the first page, but almost all of them were this same problem, including a long (6 page) thread at Audio Karma.

[tiller]

Thanks very much for the replies, gentlemen. It is much appreciated. Especially considering we've determined there really is no problem with any of my Bottlehead gear!

Anyway, to answer your questions Paul. The Rega does in fact exhibit the noise regardless of whether or not it is plugged in, which obviously rules out something riding on the mains causing the hum. Or a ground loop for that matter.

Regarding moving the tonearm: the effect of moving the tonearm and the changing noise always exists, regardless of where the deck is, and whether or not it is plugged in. The effect is not always the same however. For example, on my coffee table there is a position where I can cancel the hum out completely. On my stereo rack however, this point does not exist. The hum modulates every time I move the arm though. I believe this would add further weight to the idea that it is picking up EMI from something. Could be my fridge for sure, as it's in the same room, but about 20ft away. I've unplugged practically everything else to no avail.

I have been pretty busy yesterday and today and haven't had much of an opportunity to experiment with this further. Hopefully I will have a chance tomorrow to short out the cartridge (as per Grainger's advice) to see whether or not it is guilty of picking up the EMI. I have a feeling it is the culprit. I too have found a lot of posts elsewhere regarding noise in these tables/carts. One guy even said he had a Rega cartridge similar to mine mounted to a wand to act as an EMI detector, haha!

Thanks again folks. I will report back!

Adam

[tiller]

So I took off from the studio a little early to experiment with the cartridge. The curiosity was killing me!

As I feared, shorting the tonearm wires (taking the cartridge out of the equation) reduced the hum very significantly. It didn't yield the deck completely silent, but I am willing to attribute that to the fact that I was simply holding the clips on the tonearm wires together in a pretty half-assed way.

After that I dug out an old Shure cartridge I had kicking around with the stylus sheared clean off the thing. Wired it up to the Rega, and sure enough, hardly any hum.

So the cartridge it is...

In a thread on Audio Karma, someone pointed out that the cartridge shield is tied to the right signal ground, while the tonearm ground is tied to the left sig. ground, creating potential grounding problems. He suggested swapping the channels coming off the cartridge thus making the cart shield and the tonearm ground both tied to the left SG. I gave this a shot and, from what I can tell, the hum has reduced quite a bit. I can still hear it at 50% on the Crack, but it's an improvement.

The only solution to this issue now, at least that I can think of, is getting a new cartridge. Sadly, an expensive solution. Do you fine gentlemen have any other thoughts?

Maybe I could wrap the whole cartridge in aluminium foil and poke a little hole for the cantilever to stick out through, haha!

Cheers,
Adam

[Paul Joppa]

At this point, the technical approach would be to revamp the cartridge/tonearm/interconnect shielding design. That could be an impractical project though.

For purposes of documentation, here's how ti would be done - theoretically, of course. The idea is to shield the wiring all the way from the phono preamp to the cartridge body. Using twisted pairs for the cartridge (two pairs) with a good shield around them, all the way from the preamp to the cartridge. The tonearm ground is attached to the shield, and can act as a shield if the wires are inside. The cartridge shell (presumably metal, right?) is attached to the shield, but the signal wires are not. Making the shield continuous so the wires are never visible will take some creating mechanical engineering! At the preamp, the shield goes to the ground screw, and the tonearm wires to the RCA plugs. The "cold" side of the signal pair in connected to the shield inside the Seduction, and nowhere else.

That will give as good EMI protection as it is practical to get. Notice the single shield; that prevents the possibility of making a loop of the interconnect grounds which might pick up magnetic fields. An approximation is to keep the two cables close together (if they are not already glued together).

[Grainger49]

  .  .  .   The only solution to this issue now, at least that I can think of, is getting a new cartridge. Sadly, an expensive solution. Do you fine gentlemen have any other thoughts?

Maybe I could wrap the whole cartridge in aluminium foil and poke a little hole for the cantilever to stick out through, haha!

Cheers,
Adam

Stranger things have been done, but I haven't seen them.

[tiller]

Thanks once again Paul and Grainger!

At this point, I don't think I am willing to play around with the tonearm wiring myself. That could be a VERY expensive mistake, hehe. I will however probably break out the tonearm ground from the SG to a dedicated run to the Seduction eventually.

Until then (and until I saddle up for a new cartridge) I will just have to live with the hum. It's not too bad when music is playing thankfully.

Many thanks!

Adam

[deltaunit]

I had a similar problem with my Rega TT; I had mine placed on the shelf above an integrated amp and it's transformer created a low background hum. Moving the tonearm from it's rest position across the platter reduced the effect as it moved further away from the transformer below. I cured mine by moving everything further apart.

It sounds like you've moved everything around though but just incase you are moving everything around together in a stack it might be worth a try. That said, I'd expect a small amount of hum above background noise from my phonostage/tt when cranked up anyway.

Good luck.

[Grainger49]

  .  .  .    At this point  .  .  .   I will however probably break out the tonearm ground from the SG to a dedicated run to the Seduction eventually.  .  .  .

Adam,

I wish I had thought of that myeslf.  An excellent idea if you know where they are bonded (tied together).

[tiller]

Thanks for the tips deltaunit. I have moved everything around in my living room to no avail. The only thing that makes any difference is moving my turntable, therefore I know its none of my equipment that is emitting the EMI.

Some further developments: I decided to take the plunge and modify the tonearm to give it a dedicated ground line to the Seduction. So, no longer is the tonearm ground tied to the left channel's signal ground. Unfortunately, this made little, if any, difference. For the record (i.e., someone stumbling across this thread looking for information) the tonearm ground and signal ground are tied together in the end plug on the tonearm.

Anyway, I think it's official: the Rega cartridge is shielded poorly. Either that or I live inside a power substation. The next move is new cartridge, but that won't be happening for a while.

Thanks again for all the insight folks! Much appreciated!

Adam