Tube PHONO preamp interference - RFI, EMI, bad grounding?

Ok, solved it by now. (The selector for balanced or unbalanced in the back of the RCM is for the input, not the output.)

Works fine with both RCA or XLR. Great phono stage.

The new owner seems to have no issues with the EAR 834p. The interference still remains a mystery :)

Thanks everyone for your help! 

The chain is TT - RCA / single ended, shielded with separate ground wire -> RCM phono -> XLR out -> preamp

Could the problem be in the TT grounding?

The whole system is plugged into one wall outlet. 

Power amp plugged directly into the wall and the rest is on a unfiltered power strip.

Dover, You wrote, directed at me, "There is 230 volts floating around - you should be more careful if you are going to give advice on this forum."  Your advice directed at me is good advice for all of us.  However, I don't see where I advised any action on the part of the OP; I was merely trying to make sense of the written and pictured information, and I wrote here what I thought was true based on that information only. 

Filip, I just read a few reviews of your new phono stage.  It is interesting to me that it claims to be balanced but offers only SE inputs (the claim is you can feed the RCA jacks in balanced mode or in SE mode), although it does have both SE and balanced outputs. Before consulting us usual suspects, why not ask your dealer or better yet the maker of the product? One question: Are you feeding the stage in balanced mode using SE cables?

Hello again,

I have sold the EAR phono preamp few weeks ago. It was replaced with RCM sensor 2 phono stage (solid state).

It's a different story when it comes to the sound, there quite typical differences as in other tube vs. solid state comparisons. I'm very happy with the sound overall. 

Anyways, the phono works well when plugged into unbalanced mode.

I have just brought XLR cables to try the balanced mode and I get a ground loop.

The volume of the loop depends on the RCA cables used between TT and the phono stage. 

I have tried XLR cables with shortning plugs and the interesting thing is I get a loop only from the left channel. 

When I remove the plugs and leave the input without any connection, the loop is still there - not as loud though. It gets a little louder when I remove the TT ground cable. 

Any suggestion what to do? I'd like to use the balanced output of the phono, even with the loop I can tell it sounds better. 

@filipm

Would you suggest trying to move resistor between the audio and the ground plug? While chassis > IEC would be connected directly.

Yes I was going to suggest that. Run a wire from IEC earth to ground post, and then 33 ohm resistor from ground post to board.

Then just measure resistance between chassis and IEC earth pin - hopefully should read 0.

If it still measures 33 ohms between chassis and IEC earth pin that would mean that the chassis is connected to the board somewhere else other than the ground post.

Glad you are still with us - its worth getting the grounding sorted.

Good luck.

Would you suggest trying to move resistor between the audio and the ground plug? While chassis > IEC would be connected directly.

I’ll have to buy a new one. Will this work? - MBB02070C3329FCT00 (serial number of the resistor) - It was a Vishay dale, 33.2 ohm.

The resistor says "33R2F RN60P 9322J DALE"

I think the noise is air borne. Everything I have tried suggests it is, and yes, the chassis definitely acts as an antenna.

It simply cannot be in the AC because we have powered the EAR with a battery. The noise stayed the same.

Thank you

Or I could leave the resistor where it is and try to ground it through the ground plug on the chassis. What would be the most effective way to do it? Connecting a ground wire to a line stage chassis doesn’t work at all.

If the proper grounding won’t help I’ll sell the unit. It worked everywhere else. I’d be looking for an ARC PH5 which should be better anyways.

@lewm 

Indeed, if the 33 ohm resistor was in series between the IEC and the ground lug, on the one hand, and the PCB ground, 

 

Wrong.

With the EAR the ground lug is connected to the chassis.

The 33 ohm resistor must go directly to the board. - not the ground lug.

The ground lug/chassis should be connected directly to the ground pin with NO 33 ohm resistor in the path.

There is 230 volts floating around - you should be more careful if you are going to give advice on this forum.

@lewm This has to be corrected though. As I pointed out earlier, if the chassis isn't directly grounded it will act as an antenna rather than a shield.

Back in the 70's and 80's in South Dakota where TV stations were rare, farmers used to park an old tractor on a hill near their house and then point their TV antenna at that rather than in the direction of the TV station. They were using the tractor to collect RF energy which is then re-radiated.

We don't yet know if this sound is air borne, but if it is it will be important for the chassis to be grounded. Its also important for electrical shock hazard safety.

Indeed, if the 33 ohm resistor was in series between the IEC and the ground lug, on the one hand, and the PCB ground, leaving everything but the PCB containing the audio circuit at earth ground, that would be OK. But I still don't think we've hit upon the primary cause of the noise that the OP recorded and included in his initial post. (I realize Dover said all this before me.)

The EAR has rave reviews, and it just seems improbable that Tim de Paravicini with his reputation would make this kind of mistake.

Tim passed away (RIP) about 2 years ago. The simple explanation is this unit was built incorrectly.

@lewm - I have followed and appreciated your investigation and effort to make sense of the evidence, and I agree this is strange. The EAR has rave reviews, and it just seems improbable that Tim de Paravicini with his reputation would make this kind of mistake. Perhaps in the repairs to this EAR the OP talked about something wasn't put back together correctly - or it is a manufacturing defect and they got it backwards in production and put the resistor in the wrong place.

My Creek Integrated is wired up like atmasphere and dover were saying is the correct way, and my other phono stages are either battery powered or do not have an IEC third prong (powered by wall wart) - so I have own nothing personally to verify with - but you mentioned the Manley Steelhead -  which in its current iteration has three ground connectors, and they do make a distinction between circuit and chassis ground, with separate ground lugs, and allow the user to make their own choice about the grounding scheme; though I strongly suspect they would not leave the chassis floating in any of them. So I think there is definitely something to what you were talking about at least for some phono stages. 

Ok. My idea that floating the ground lug above ground along with the audio circuit is unconventional at best, based on what Atma wrote and my own measurements of two phono stages at my house. So I expect the ground lug on the EAR is in contact with the chassis. The ground lug is at chassis potential. Therefore I assume the IEC ground must not be directly connected to the chassis. (If it is, the 33 ohm resistor does nothing.) So, the 33 ohm resistor floats the whole device, chassis included, with respect to the IEC. That IS strange.

@lewm 

So that 33 ohm resistor we see in the photo, which is in series between the threaded screw and the 3rd pin of the IEC, according to the OP, is either doing nothing or the chassis is floated by the 33 ohm resistor which I certainly agree is not the best idea. The OP has dropped out so we may never know. 

We knew this days ago when the OP confirmed the chassis is 33ohms above ground. He measured it. 

@atmasphere and I have been trying over the past few days to guide him in the right direction - ground the chassis and ground lug to 0 and leave the circuit ( board ) floating at 33 ohms.

So that 33 ohm resistor we see in the photo, which is in series between the threaded screw and the 3rd pin of the IEC, according to the OP, is either doing nothing or the chassis is floated by the 33 ohm resistor which I certainly agree is not the best idea. The OP has dropped out so we may never know. I am going to get my meter to see what’s up with the ground lug on my Steelhead. It looks to be isolated from the chassis.

By my way of thinking, that actually makes the most sense if you are going to float the audio grounds; you want the upstream gear to be grounded at the same potential as that of the on board audio circuit. It seems that you want the ground lug to be at AC or earth ground, which is certainly not "wrong" either.

@lewm You want the ground post at chassis potential, not the audio ground. The grounding system is supposed to be ignored by the audio.

So the ground post is simply bolted to the chassis, along with the center pin of the IEC connector. The 33 Ohm resistor is then placed from the audio circuit ground to the chassis.

This sounds like an easy fix! It may not fix the RFi, but it won't hurt and it will make the unit safe and in compliance with EU directives.

It’s possible that we are arguing because our two countries have different codes re grounding. Everything I have written is based on how things are done here in the US. The 3rd prong of the IEC is earth or AC ground. Correct? We see here that there is a 33 ohm resistance between the 3rd prong or earth ground and a screw that we agree is a ground lug. I take it to be the back side of a typical grounding scheme to be found on many phono stages which is to be used to ground the turntable or tonearm. There is no significant current or voltage on the ground wire coming from a turntable chassis or a tonearm, so there is no danger of blowing that 33 ohm resistor and making the chassis dangerously "hot". This is why EAR could get away with what appears to be a 1/4 Watt resistor or 1/2 Watt at most. By my way of thinking, that 33 ohm resistor is to float the AUDIO ground with respect to earth ground. We also see that the screw is directly connected to the PCB, and I assume it is soldered to the ground plane. This is not dangerous and is a ploy to reduce noise. For me to be correct, I would need to know that (1) the screw we see is NOT touching the chassis, and conversely (2) the 3rd prong on the IEC connector is directly connected to the chassis. (That would mitigate your legitimate fear that the chassis is floated.) So, the lug and the audio circuit are both floated by 33 ohms over the AC or earth ground and the chassis. That is OK in the US, where the AC receptacle is connected to a solid earth ground in every home that is up to code, by the 3rd wire.

I am not an EE, so I would welcome correction if I am off base. I don’t want to be giving advice that may lead to a dangerous situation.

@lewm 

The ground lug is used for shielding, not signal. Thats why you normally would tie it to mains earth.

The suggested layout is not new - my old 1980's Theta tube gear uses it. The suggested grounding is to EU code.

Having the EAR chassis floating above ground at 33 ohms means that if something goes wrong and the 33 ohms resistor fails, there is a possibility that the chassis could go live and fry your beloved. Not a good idea. I am actually shocked the unit is not to code.

I see now that there is a difference between your thinking and mine. I perceive the ground lug, which is meant to be used to ground the turntable or tonearm or both to the phono stage, ought to be or can be floated along with the audio circuit with respect to earth ground. By my way of thinking, that actually makes the most sense if you are going to float the audio grounds; you want the upstream gear to be grounded at the same potential as that of the on board audio circuit. It seems that you want the ground lug to be at AC or earth ground, which is certainly not "wrong" either. In my way of thinking (float the ground lug), the photo shows exactly what you’d want; the ground lug for external upstream equipment is floated above earth or AC ground by the 33 ohm resistor shown in the photo and which we are told is attached to the 3rd prong on the IEC. Likewise, the ground lug is therefore at the same potential as the on board audio circuit by virtue of the other green/yellow wire which attaches the ground lug presumably to the ground plane on the PCB of the audio circuit. I see nothing wrong there. For all of the above to hold water, we also need to know that (1) the ground lug is not in electrical contact with the chassis, where it passes through the chassis wall, and (2) the 3rd prong of the IEC is directly in contact with the chassis, keeping the chassis at AC or earth ground. The OP can easily verify those two points by his ohmmeter; there is no need to de-solder anything, if the meter verifies that the IEC is in contact with the chassis and the ground lug is 33 ohms away from the chassis.

From what I have been able to read, this practice of floating the audio ground is "new", in the sense of the past 20-30 years and is not required but only makes for quieter audio. I checked two of the many phono stages I have lying around here or in use. My original Quicksilver has a ground lug that is not floated. It’s about 25-30 years old and sounds excellent when I use it. My Steelhead has two ground lugs, both appear to be isolated from the chassis.

I have a Beveridge system in my basement. Its direct drive amplifiers are about 40 years old, like the speakers. In the original design, everything in the audio circuit was grounded to the chassis, and the chassis was not at all grounded to the AC, because the amplifiers were originally supplied with a hard-wired 2-prong cord. I assume grounding was originally supposed to be handled at the Beveridge preamplifier, designed by Roger Modjeski for Harold Beveridge. This is a bit scary since the amplifiers develop 3200V in the output stage. When I got the speakers up and running, there was a low level buzz that I found very annoying. After some consultation and reading, I cured it by (1) installing a 3-prong IEC connector for AC and (2) connecting its 3rd prong to a pair of back to back high current SS diodes that in turn connect to the chassis. This "yin/yang" topology *(not my term but coined by others who thought of the idea) isolates the AC ground from the chassis and from the audio circuit in a safe way and seems to work to completely eliminate the buzz.

Finally, this EAR unit works fine in other locations. And Tim de Paravicini, the designer of the EAR products was no dummy. For those two reasons, I tend to think this whole brouhaha over the ground scheme is a red herring. The OP has some external source for RFI entering his apartment, IMO.

What I see in the photo is that IF the 3rd prong on the IEC is directly connected to the chassis, somewhere not visible in the photo, 

@lewm 

And thats precisely why I suggested he check the chassis for grounding after unsoldering the ground lug ( but keeping the link to the board through the 33 ohm resistor ).- there could be an unknown connection to the chassis from somewhere else - my fear is there might be another connection between the board somewhere other than the grounding post and if he grounds the chassis ahead of the 33 ohm resistor he will end up will multiple earth paths.

So in a nutshell bypass the ground lug, check the chassis is now ungrounded completely ( not 0 not 33ohms ), then he can earth the chassis and ground post directly to the mains input earth lug ahead of the 33 ohm resistor.

cc @filipm 

Believe me, I got it. I have a lot of DIY experience, as Atma-sphere will attest.

I just am not sure that all the reported information, by verbal communication and by photo, is internally consistent. That’s what I wrote. I was not contradicting you, but your approach seems to be dependent upon the verbal description only. What I see in the photo is that IF the 3rd prong on the IEC is directly connected to the chassis, somewhere not visible in the photo, and if the ground lug shown in the photo is isolated from the chassis where it perforates the chassis wall, then there may be no problem at all with the ground scheme. You and I are not in disagreement. I am only questioning the information we’ve received.

@lewm

Without de-soldering anything, just put one probe on the 3rd prong of the IEC, which is earth ground or AC ground, and the other anywhere on the chassis where there is bare metal. You ought to see continuity.

It’s very simple - from @filipm tests - both the chassis and board are floated at 33 ohms above ground. That is a problem as @atmasphere has pointed out.

If you look at the IEC earth pin there is only 1 33 ohm resistor attached from the earth pin to the board and ground post.- nothing else.

So the suggested fix is to isolate the chassis from the board and ground it to the IEC earth pin directly bypassing the 33 ohm resistor as suggested by @atmasphere and according to EU regulations.

In order to achieve this @filipm needs to be sure that there are no other ground connections between the board the the chassis, otherwise he will end up with other issues.

The ground lug should be disconnected from the board and earthed to the chassis.

If you go back and read my posts you will get it.

I think I am losing my mind here. The photo showing the two green/yellow wires both soldered to what is said to be a ground lug may not be consistent with your earlier verbal description of what you measured, namely a 33 ohm resistance between "ground and chassis". First, and most important, that ground lug you show in the photo I take to be part of a screw clamp lug on the outside of the chassis, which is meant for connecting the turntable and/or tonearm ground to the EAR. If that is so, then that lug MUST be isolated from the chassis, i.e., your meter should show an "OL" or very high resistance between that lug and chassis if you were to disconnect both of the green/yellow wires from it. In the current state, it should show a 33 ohm resistance between that (audio ground) lug and the third prong on the IEC where you plug a 3-conductor AC cord, because we see the 33 ohm resistor in series with that pathway. There should be very low or near zero resistance between the ground lug (that threaded screw) and audio ground because we see that one of the two yellow/green wires is soldered to the PCB directly, presumably to its ground plane. There needs to be another wire or contact connection between the third (ground prong) on the IEC and the chassis. If so, then this is is all good. Not the problem. Without de-soldering anything, just put one probe on the 3rd prong of the IEC, which is earth ground or AC ground, and the other anywhere on the chassis where there is bare metal. You ought to see continuity.

@filipm

I think if I unsoldered the green wires from the pin and soldered them together, I’d just ground the board while the cage would be left absolutely unshielded.

Yes, but I’m not suggesting you leave it like this.

We want to get to a place where the chassis is grounded (no 33ohm resistor ) but leave the board floating with the 33ohm resistor. This I believe is the optimum solution.

If you can prove the chassis ground can be detached from the board ( by unsoldering the ground post earth and checking that there is no continuity between chassis and circuit board ground ) then you can safely ground the chassis and ground post to the mains ground pin ahead of the 33 ohm resistor with an additional wire. In other words ground the chassis and grounding post without the 33ohm resistor but still run the 33ohm resistor to the circuit board.

You could do as you suggest and just eliminate the 33 ohm resistor and leave everything grounded at 0. Only downside is it may be suboptimal for the circuit itself in terms of noise floor.

@dover I think If I wanted achieve the best shielding possible I'd have to leave the two green wires as they are but to cut out the 33ohm resistor. Then everything (the board, the chassis) would be grounded through the IEC with no resistance. I may be wrong, please take in account I'm a noob at this and I'm often missing what for others is common knowledge. So maybe if I cut out the resistor, it will lead to a ground loop.
I think if I unsoldered the green wires from the pin and soldered them together, I'd just ground the board while the cage would be left absolutely unshielded. 

@filipm 

If I desolder the 2 wires it only means the chassis would be completely lifted

Thats likely correct - but it would be prudent to verify that. I say  this because most of the time ground posts are insulated from the chassis, and there may be a different path we cant see.

If proven to be correct, and the chassis is now floating, then you would be able to earth the chassis to the incoming mains earth pin before the 33ohm resistor and achieve much better shielding - as per @atmasphere suggestion in his earlier post.

@dover the chassis and the board are connected by those green wires. 

board > right green wire > binding post < left green wire - 33ohm resistor - ground pin of the IEC. (which means the left and right wire are meeting in the binding post)

also, there are screws holding the board but they are not touching the circuit of course. 

There is a possibility that the joint of the board ground (where the circuit board and the grounding wire meet) needs to be resoldered. 

If I desolder the 2 wires it only means the chassis would be completely lifted from the ground. The chassis and these wires wouldn't be even electrically connected. 

What's your suggestion?

Let's not forget the error may not be in the preamp. It's working fine anywhere else but my place. Maybe it just needs better grounding from the binding post. But where to attach it if not the socket ground pin? I have no idea. 

(It's possible the grounding problem leads further - maybe the sockets are poorly grounded. Maybe there's a problem in the main switch. We still haven't measured that, if it's even possible. I'm waiting for the electrician to show up.)

@filipm 

Yeah so I can see that both the ground post and circuit board are all earthed through the 33ohm resistor. If the chassis and earth post measures 0 ohms then the chassis is lifted above ground ( not what you want ).

The chassis could be connected to the circuit board ground anywhere - it could be the binding post;  ?you would need to look around - are there any wires to the chassis ? It could be through circuit board legs ?

I would do the following test -

If you desolder the 2 green and yellow wires from the grounding post but leave them soldered together - then the circuit board would is still grounded through the 33 ohm resistor ( assuming you have reattached it ).

Now measure from the green wires to the chassis. If that measures open circuit then you would know that the chassis is earthed through the ground post mount.

Double check by measuring the chassis to mains earth tag - should be either 33ohms or open circuit. If it is 33 ohms the chassis must be earthed via the board somewhere else. If it is open circuit then we now know the chassis is earthed through the ground post mount only.

Depending on your test results I could suggest a very easy fix for you to the earthing issue. This may or may not fix your noise issue though, but in my view would be worth trying.

@dover It’s the other way around on the EAR I guess.

Here is a picture of the ground binding post. The wire on the right is connected to the circuit board. The one on the left leads to the IEC through the 33 ohm resistor.

That means the chassis relies on the grounding pin and not so much on the ground to the IEC, correct? Nevertheless, I have tried grounding the chassis using this pin and separate wire leading to the socket ground pin, a heater, chassis of the ARC preamp.. none of these made a difference. Maybe I was just using a poor wire (the was almost no resistance on that wire).

I guess things could change if this 33 ohm resistor was moved to the wire on the right - between the grounding pin of the chassis and the circuit board ground. Then the ground of the RCA connectors would be closer to the ground of the inlet and not the circuit board.

@filipm 

IF the first statement is correct and about the EAR (and succeeding posts suggest this is so) THEN the EAR is incorrectly grounded.

So we need to double check:

The ground pin of the IEC connection should tie directly to the chassis of the EAR. To not do so puts the unit at odds with EU directives for voltage safety.

The 33 Ohm resistance would then occur between the chassis (or ground pin of the IEC connection since they are the same) and the ground of the RCA connectors. 

So here's another measurement to take. What is the resistance between the RCA connectors and the chassis? If zero Ohms or very nearly so, I think we found the problem despite remonstrations from EAR.

@atmasphere is correct.

Chassis should be at ground.

In my Music Reference RM4 mc head amp the chassis is grounded ( no resistor ) to the mains input ground.

There is a 12ohm resistor from the "ground" on the circuit board to the chassis.

In other words the circuitry is floated above ground. This is not uncommon.

When you measure the resistance between the -ve RCA and chassis you get 12ohms.

The binding post is connected to chassis earth ( measures 0 to ground pin of mains inlet..

By contrast the EAR appears to float everything, chassis and circuitry, above ground. Bizarre and dangerous as @atmasphere has pointed out in an earlier post.

One thing you need to be aware of is the grounding post on the EAR - sometimes they are insulated from the chassis and sometimes not. It appears that the EAR binding post is connected to the circuit board "ground" (after the 33 ohm resistor ) not the chassis.

In my view you should get a tech to ground the chassis directly to the ground pin on the inlet, but leave the board floated above ground., The tech will need to find how the chassis is currently earthed to the board and remove that connection to ensure the circuitry is still floating above ground, the chassis is at 0  and there are no earth loops.

If you are not comfortable with this get rid of it.

@lewm Yes, I didn't realize the resistor might be there. I was told that sometimes it's intentional to avoid ground loops. But at the cost of poor grounding? 

I'll buy a new one but I'll also try to solder the ground wire without the resistor. 

@ejb14 communication with EAR isn't like ARC customer service (super fast), unfortunatelly. They responded only twice and it took them a week or two. 

​​​​​​

@ejb14 they sell them here, about 20 cents a piece. they have two options, 33ohm 1W or 33ohm 3W. but nice guess - vishay dale :)

I have already taken pictures of the preamp. I think I'll sell it. I'm always reading how wonderful it sounds, how upgradable it is but I'll try to find an ARC PH5. 

@filipm  - I think lewm is referring to R16 in the CRC filter in the schematic, which you said had to be replaced (he circled it in one of the images). 

The linked images I posted and dpop sent show the additional resistor you found connected to the IEC inlet. Given that it appears in the other EAR pics we have found out there, with the same yellow heat shrink suggests that EAR built them this way. Might be a good question to ask EAR.

No, the 33 ohm resistor in the filament supply filter should not be causing your problem. I was just wondering whether you had inadvertently measured resistance across it in your earlier report.

@lewm so removing that 33ohm resistor wouldn't be a good idea if I understand it correctly. 

The resistor is right behind the ground plug of the inlet so it's basically anywhere if I place one probe on that plug. 

@filipm Looking at that above linked picture, I can now see (rather clearly) what the little silver screw on the back does. As you mentioned Filip, it supports a shield - a shield that isolates the audio portion of the EAR, from the power supply portion.

If you examine the schematic that someone else posted above, you can see there is a 33 ohm resistor shown in the schematic as a series element in a CRC filter for the filament supplies. I don’t know how you could have been measuring the resistance across that resistor, given your description of where you placed your probes, but if your probe was touching something that you could not see that was on one side of that resistor and the other probe was on the other side of that resistor, then you could have measured it inadvertently. Maybe you should retest that resistance between the two probes that you’ve earlier reported and which atmosphere remarked upon. That’s the only 33 ohm resistance that I cansee in the schematic, but of course you might be measuring the parallel sum of two or more other resistances.

It sure looks like the resistor is in place on *this* particular unit:

picture of resistor

I live near a major Air Force Base and occasionally get interference (although mostly on FM) from one of the radars on the base.  The periodicity of the noise to me is a giveaway that it is something causing a "sweep".  What that might be you are better to guess than me.

@filipm thanks for posting those pics. Very interesting..yes, if you want to put it back together the way it was you may need a new 33 ohm resistor, but those are cheap enough. That one looks like a Vishay-Dale metal film, which are often found in audio because of how quiet they are.

I searched the web for images of the EAR 834p to see if I could find some that did not have the resistor, but of the ones that I found were a good enough pic to see the wiring in this spot of the EAR - all had the resistor there. So it seems intentional.

This one appears to have the same resistor as yours..(you may have to click the plus sign cursor once to increase its size)

This one does as well.

This one is a great pic, with what appears to be a "standard" (cheaper) metal film resistor between the ground post inlet and the IEC ground, and appears to be connected to the PCB ground plane directly (which would then match your EAR if I read things correctly).

Look at the first one again though at the RCA input jacks - there is some component they have bypassing signal to ground - a capacitor perhaps for noise filtering? Showing my inexperience here, I have not seen a capacitor that looks like that, perhaps one of the more expert folks on the thread can tell us what it is. Likely a custom mod (especially considering the Hovland MusiCap capacitors in there that I am reasonably sure are not stock given their cost).

That photo showing a 33 ohm resistor partially encased in yellow shrink wrap looks like very amateurish work. Could be the ill advised work of a previous owner. Also, is that resistor connected at its other end? If not, it’s not doing a blessed thing.

You never mentioned whether tightening the transformer laminations, etc, had a beneficial effect on noise emanating from the chassis (not the noise that we started out talking about which contaminates your audio signal).

At this point you’re  receiving a lot of advice of questionable merit, apart from posts by Atma-sphere. If you don’t have or can’t access local expert help, I suggest you pay attention to Atma.

@filipm Unfortunately, I don't have the engineering and design knowledge that's required to explain why that's in the circuit. Looking at the resistor, at this point in time, if you wanted to re-insert it back into the circuit, it's going to be impossible to do that, with the lead now clipped right at the resistor. I'm not sure I would have removed it, as you say the EAR plays fine anywhere else you use it, besides when used with *your* system. That means you have a problem that's exclusive to *just your* setup.  

There's a 33ohm resistor on the grounding cable between the chassis and the inlet.

@filipm Thanks for the reply Filip. Looking at the pictures you have provided so far proves to me that the chasis is *not* floating (from earth ground), as I can see the green earth ground wire is soldered directly to the rear panel banana standoff/TT ground connection screw thread. That was one thing I was questioning. I still *highly recommend* purchasing this isolation transformer from Amazon. 

XtremPro Hi-end Ground Loop Noise Isolator/Filter 

It's pretty cheap, and it's always nice to have one of these in anyone's bag of tricks, when hooking up audio pieces of equipment. Again, if you do purchase this, it gets inserted between the TT preamp output, and the preamp input the TT preamp is feeding. 

@atmasphere It is pretty simple - the resistance occurs here. It's either in the wire or in the joint. But the resistance between the grounding pin of the chassis (not the inlet) and the solder joint is 0.01. 

I'll try to resolder the chassis ground wire to the ground pin of the inlet. 

@ejb14 We have tried both MM and MC settings, worked just fine. There's nothing touching the board. 

@dpop That silver screw is holding a plate between the transformer side and the tube side. 

@dpop I'm still here. Just working late last few days and haven't got the time to reply properly. 

I'm not sure if things are resolved but what @atmasphere mentioned sounds like the answer. I haven't got a reply from the EAR factory what are their thoughts on that 33 ohm resistance on the grounding. I'll have to find what causes that resistance and fix it. Or someone else will have to fix it for me. 

I'll have time to take more measurements tomorrow night. 

Thank you!

I thought of that while I was writing my response, but surely this is it, right? [Famous last words.] I hope @filipm has it resolved, or another preamp, at least. He sure has hung in there where lesser men would have thrown in the towel by now.

@oldrooney ...but has the problem really been resolved? We haven't heard from @filipm for a few days now. 

I’ve spent considerable time reading this thread, but it has been worthwhile. @atmasphere got the ball rolling on a solution, @budlite22 confirmed it, and @ejb14 moved things along, while @dpop chimed in too. It really was a drama proving that solutions grow quickly and surely when one starts by asking the right questions and answering them by proven tools and methods. Reminds me of a Sir Arthur Conan Doyle mystery, “Facts, Watson, we must have facts and reason shall lead us to a solution. What can we deduce from the facts before us?” Well done, all. I’m nearly as grateful as I’ sure @filipm is to finally have solved the mystery. And all I can say to @ahal1 is wow! I’ve got to get me one of those! (Where were you earlier?)

Had a similar problem and surprisingly 

a power line conditioner solved it - 

this is the model i have.