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

@filipm - my calculations might be incorrect, but the EAR  amplifies a those low frequency signals (the mechanical transformer hum is a pretty low frequency I believe) something like 2500 times depending on how low the frequency. First an equalization of 20db for the bass region of RIAA, then another 48 dB for its phono amplification according to the EARs specs. I wonder if lightly touching the tubes with a pencil eraser (thus absorbing some of that mechanical energy) affects it.

This may be caused by the DC voltage on the AC power that I mentioned earlier - easy to check, and you can filter it with device that goes in serial with the power, like the Van Alstine Humdinger or I think iFi has one too. Good test to take it elsewhere to see if you still hear the mechanical hum. Supposedly toroidal transformers are more susceptible. 

@ejb14 I have recorded the transformer hums.

I level of noise is not audible in the room of course but it's audible when you get closer to the device. The EAR is the loudest, the ALLO linear supply for my streamer and DAC is almost not audible at all. 

I placed my iphone microphone on the chassis when recording each of them.

I'd say it's normal but maybe I'm wrong. 

@filipm I think you have already determined that the ground pin of the IEC connector is tied to chassis. Is there an impedance between the chassis and the ground of the input signal? It may be that a component in the grounding scheme of the phono section has failed. This could cause noise to be injected into the phono section.

Regarding the power transformer noise in the rest of your equipment, some of that might be reduced by using a DC Blocker, provided the transformers in question are toroidal.

Its a common mistake to assume that physical transformer noise is getting amplified when you have problems like this. IME that is extremely rare; IMO you have two different problems.

@ejb14 you have mentioned to check for DC presence on the line. Three days ago I have finally received an IEC19 connector for the ARC REF150 power cord and plugged it into the wall (instead of into a power conditioner that restricts the dynamics).

The power amp started to buzz after about 30 minutes of warm-up. I have also uploaded the buzz on the soundcloud page. (One recording is with the closed chassis, the other one is the opened chassis, moving the mic around). The buzz comes from the transformer, not the speakers, nor the tubes.

I called the ARC dealer in the Czech Republic and they said it could be presence of the DC. When they heard the recording, they said it would actually sound differently. What do you think it might be? Can the presence of DC actually damage components?

I have found a thread about the same thing with a REF150 on this forum, the OP had to replace the power transformer but also reffered to a bad tube on the input stage.

Maybe it has something to do with the EAR preamp problem, because both of these units were working fine when I was buying the power amp and listening both of them together in Berlin. 

(It has started with plugging the amp into the wall, worked fine with the power conditioner - technically. the sound is much better when plugged into the wall of course. From that moment it buzzez even when plugged back into the power conditioner)

My experience with tubes is starting to drive me crazy :)

I’ll have the results about the DC on Monday I hope.

If it’s the presence of DC, can any power plant fix this? Of course PS Audio will claim it can but our ARC dealer says it will restrict the dynamics no matter what power plant I choose.

@filipm - I understand you are probably super frustrated by now - yes, you could go solid state, but the fact that the tubed units work fine elsewhere suggests the problem is not with your gear.

I suggest that if testing the power for DC shows that it is present, getting a Humdinger from Audio by Van Alstine. You can return it if it does not help. Just realize that atmasphere, who I am reasonably sure knows a lot more than me about this (I am just a hobbyist), is correct - transformer hum should not show itself in the audio signal, though he does say "extremely rare". Perhaps your situation is one of the more rare ones. As for damage, not sure -  I think I read somewhere that the power company will fix it if very bad "for safety reasons". 

I would also do what atmasphere suggested right away with your DMM - It would be a good idea to check the REF150 grounds as well, and like he said check for impedance between the ground and the chassis to ensure you do not have a grounding issue in the units. I would have thought that would present itself in all locations, but maybe it's worse at your place.

@ejb14 I am :)

I guess I’d have to get two of these Humdinger units - one for the power amp and one for the rest. Also, the question is how it restricts the dynamics of a power amp.

I have measured the impedance between the ground plug on the inlet and the grounding pin of the chassis (or any screw) - it’s 33.2 ohms.

REF150 - the impedance between the ground on the inlet and any screw on the chassis - 0.01 ohms (0.00-0.02)

Could there be a grounding issue on the AC line? It can, right? And it’s probably quite hard to solve I guess. There’s a dedicated line for the living (listening) room with about 5 sockets around the room. Maybe a lot easier than looking for a ground issue there could be to run another dedicated line that would power the audio stage only. (That would only exclude a router and few lights that don’t really affect anything - I have had them unplugged of course)

Just to be clear - the noise in the REF150 is happening inside the unit - on the transformer and does not affect the sound. Maybe the music gets lean and thin when the buzz gets stronger but that I’m not 100% sure of. Still, it could be another problem, not really related to the noise of the phono stage. The REF150 was a second hand purchase and even tho we listened to it for about an hour and it was fine, something could have gone wrong when plugged directly into the wall.

The noise of the phono stage comes out through the speakers.

Also - one thing I wanted to be sure of - with the use of shorting plugs I should eliminate any signal coming from the air, right? BUT when the chassis is not properly grounded the signal still comes through and gets picked up by the phono stage tubes, is that correct?

If the transformer itself is humming, try tightening down on the screws that hold it to the chassis, and on the screws that hold the laminations together. Sometimes the case of the transformer can be a little bit loose and this can allow the laminations to vibrate and produce a hum. Transformers by their nature do not transmit DC, but DC can cause the transformer to be noisy. Make sure the transformer laminations are tight and that the transformer itself is firmly affixed to the chassis, and then report back whether that did any good as regards this latest problem. Of course I do not expect this to cure your problem with RFI. 

This is definitely a fascinating post (at least for me), with so much detail explored. The greatest thing that was accomplished right off the bat was the fact that the OP (filipm) was able to record and post the noise or interference that he is experiencing and hearing. When trying to troubleshoot noise and interference, *that* is worth gold all by itself. With so many suggestions already being offered and tried, I'm not sure I have anything left in my arsenal to propose. I'm going to go back over all of the tips and suggestions, and see if I can offer anything. This is definitely one of the worst cases of noise (RFI & EMI) that I've ever heard. So far, it looks like finding a fix for this particular setup is quite the challenge. I completely understand your frustration filipm, but admire your tenacity.  

>>>very late at night or very early morning, do you still have this noise? If not, then I’d suspect someone in your building is the culprit.<<<

I was just wondering if this question was ever answered? Is the noise consistent at all times of day or night?

Do you have any other phono cartridge (already mounted in a headshell) besides your Nagaoka MP200? If you do, does the noise change (in any way) when using a different phono cartridge?

As an A-B test, is there any noise difference when completely bypassing the EAR (pretending for a moment it doesn't even exist), and feeding the turntable (TT) directly into the ARC LS16 mk1 TT input (I realize the Bryston B60 does not have a TT input)? If the noise still exists, does it still exist when trying a different set of RCA cables (feeding the ARC LS16 mk1) ? I apologize if these questions/suggestions have already been put forth.

@lewm I have done that. A quarter of a turn for each transformer to be fully tied up. I could probably do a little more but I'd have to push it hard. I'm already ok with spending something extra for a service, I just hope they won't suggest anything crazy like changing all the tubes and a transformer. They also said how important it is to have matched pairs and that you won't really find them on regular online tube stores. I have found a very similiar thread also with a REF150 (non SE version), contacted the OP and I think there will be more to it than the screws. I also talked to a guy who builds tube amps and he told me I should have replaced all the tubes right a way as a prevention. Well, I think it will get resolved sooner the EAR preamp issue anyways. 

@dpop Well, I used to have an Onkyo A7 integrated with a decent phono stage, Tesla ARS840 speakers and Tesla NC450 turntable (all for about $700). Good times, no problems (just horrible acoustics) and lots of listening time with friends. :) 

Now I have built some amazing acoustic panels and clouds, hanged curtains and I'm left with a streamer, chord qutest dac and a solid state power amp. Thanks god the LS16 is working!

I have tried: different power cords, RCA interconnects, powering the EAR from a battery, pairing it with different components, changing its physical location within the room, placing it into a baking pot, shorting plugs (I think that proves it's not the turntable or cartridge issue), running a ground wire into a socket ground pin, ground wire to a apartment heating unit., lifting the ground on the EAR's power cord, turning off everything in the apartment except the audio stage. I even had my neighbors wifi routers unplugged for half a day, different times - late night, early morning.. nothing changed.

what worked: taking the EAR somewhere else, friends' places etc. (sounds lovely), covering the unit along with all the interconnects into a baking pot placed on the floor (as pictured before), holding the output interconnects with both hands (grouding it).

what I would like to try: few floors lower - same building, plugging it in in a friend's aparment in the next building, a power plant, different set of 12ax7 tubes, some kind of a filter, tube shields.

My electrician says it could be some kind of a server station near by, or a bitcoin mine. He's coming back soon to measure the grounding properly along with the DC presence. 

But really, if it was coming from the AC line, the battery would have solved it. But if it's coming from the air, how come the shorting plugs didn't work? (The result with the battery was the same noise + strong ground loop. The shorting plugs just acted as antennas, just like a regular RCA cable. And yes, I have made them properly and tested them with a DMM.)

I'm not sure you answered my question though; in your current living space, with the problems you're now encountering with the EAR turntable preamp, what happens to turntable noise when you plug your turntable directly into the AR preamp's turntable inputs? Is there any difference comparing that wiring connecting setup, to the noise encountered with the turntable plugged into the EAR (and then routed to the AR preamp)? I understand that with the RCA cables in the baking pot, noise has been reduced. I'm also wondering if shielding (design, or lack there of) on the Nagaoka MP200 is part of the problem here, along with RCA cable shielding. I completely understand that you want to continue using the EAR, but I'd still be interested in knowing if noise is reduced (and by how much) when going directly into the AR with the turntable. Just curious.      

@dpop I have tried these chains:

TT - EAR - Bryston B60

TT - EAR - Classe CP60 + CA200

TT - EAR - ARC LS16 + CA200 or REF150

TT - CP60 + CA200 (as the CP60 has a solid state phono stage) 

(the LS16 doesn't have a phono stage even tho it says "phono" on one of the lines, only SP preamps have phono stages)

the noise gets picked up only by the EAR, solid stages (I had 3, they were ok)

At first I thought the EAR was the problem but the seller told me he never experiences anything like this. So I took the EAR to my friend's place. Horrible wiring, cheap components - absolutely quiet and great sounding. 

Right now I have covered the input cables (TT>EAR) with a metallic sheath, there's a little improvement but I can tell it gets picked up by anything, the input, output, the grounding cable, maybe the power cord too. Maybe it's really a grounding problem as I measured 33 ohms between the grounding pin on the chassis and the grounding pin of the inlet. but I had it opened several times, the groundind pins are well soldered, I even had few capacitors changed. 

Sorry, I didn't realize that the LS16 didn't have an internal TT preamp. Is there any TT noise when going into the CP60's TT input (using the existing RCA cables that you're using with the EAR setup)?

I just noticed this:

>>>solid stages (I had 3, they were ok)<<<

So to be 100% sure, in your current high RFI/EMI environment, using a SS phono stage (the CP60) produces no noise? Is that correct?

So to be 100% sure, in your current high RFI/EMI environment, using a SS phono stage (the CP60) produces no noise? Is that correct?

...when using the exact RCA cables you were using when hooking up the EAR?

>>>I measured 33 ohms between the grounding pin on the chassis and the grounding pin of the inlet.<<<

If the piece of equipment you're referring to is the EAR, that figure should be much closer to zero ohms. If you were measuring the resistance of a wire that was maybe 100 feet in length, sure, maybe *that* figure could be 33 ohms, but it shouldn't be when measuring a connection the distance of inches, especially a ground connection.    

You have a very unique setup, where you're mixing balanced (XLR type) and unbalanced (RCA type) pieces of equipment together, and in a situation like that, they don't always want to play nicely. This is when ground loops can take place. 

Are you familiar with a ground lifter plug? I know we have them in the US, but I don't know if you have them there. I'd be interested in hearing what the EAR would sound like, if you lifted the AC ground to it, while still keeping the TT ground connected to the EAR. 

It also sounds like you purchased the EAR used, and I'm wondering if anyone has made some internal modifications along the way. 

>>>So I took the EAR to my friend's place. Horrible wiring, cheap components - absolutely quiet and great sounding.<<<

I'd be curious in knowing if his system has the same meshing of XLR and RCA equipment as yours does, or is his exclusively RCA unbalanced connected equipment?

@filipm the EARs transformer is pretty noisy mechanically at your place; suggesting a power issue. The battery test was interesting and you would think would rule out dirty power, but that may have also just demonstrated the same power issue - have you tried the battery test elsewhere (like at the friends place where the EAR sounds fine)? I suspect the same results. 

I listened to the noise again - the noise is a pulsing sound over what looks and sounds like a ground buzz. This may be a stretch, but perhaps your EAR's power supply is near end of life and when combined with the transformer issues at your place, is sagging and recovering rapidly, like a motorboat noise. It may not occur elsewhere because the wall power is just better enough there to allow the EAR's power supply to keep up. This would cause the tube circuit to generate the noise in the output regardless of input (search tube motorboating on youtube). 

Are the filter capacitors in the EAR's power supply original? They are probably over 20 years old at this point if so. I'd take those out and test them or just replace 'em.

@ejb14 

These had to be replaced. R16 died, the others were replaced along with it. 

It stopped working for a while as I was experimenting with it. 

I'm thinking of sending it to the factory, at least I will write them again with a suggestion.

@dpop I have also tried RCA only interconnects with two of these chains. For example Bryston B60 doesn't have XLR inputs. Now I'm only using XLR between a preamp and a power amp. 

33 ohms were measured on the EAR's phono ground pin or any screw (chassis) and the ground pin on the inlet. All the other solid state phono stages worked fine. Maybe except a Primare R15, there was a pretty loud surface noise, kind of like white noise. 

I always thought it was a subjective point of view, my girlfriend keeps telling me I only keep analyzing the system (of course when I'm not happy with the sound). Nevertheless I always had a feeling there's not enough juice in it, specially with the Bryston B60, it wasn't stable, sounded weak or lean sometimes. I was always surprised when I took the amp elsewhere. 

What else can we measure on the AC line when an electrician comes over? 

There's a simple voltmeter on the power conditioner I'm using for the sources. It shows some drops time to time, it's usually around 228-229V but it goes down to 225. If we find out the AC line is horribly dirty and unstable, is a power plant good idea? Something like PS Audio PP12 (I'm just a bit confused now, I have seen some measurement that suggest it's an overpriced piece of crap and I'm being told to stay away from power conditioning)

So to be 100% sure Filip, while in your apartment, using a SS phono stage (for example, the CP60), and the turntable connected *to the* CP60, the noise goes completely away? Is that correct?  

if so, I kind of agree with audphile1: At this point, the cure is worse than the disease. Dump this phono pre-amp and get one that’s properly designed to not be susceptible to this type of interference, at least within your setup (or simply use the CP60's TT preamp, if that is quiet). Seriously. You’re going to drive yourself nucking futs.

It's almost guaranteed that spending lots of money on parts (different RCA cables, ferrite cores, heavily shielded AC cables, new tubes, tube shields, etc.) is not going to fix this EAR issue. It's either a grounding problem (which I can't seem to diagnose via this thread), or it's an EAR design issue (the EAR can't filter and repel the high amount of interference in your apartment). You also mention that some components have already been replaced in the EAR. I'm wondering why they failed in the first place? That's not typical of (and very rare IMO), of audio gear, and in a way, sends up an immediate red flag for me.  

@filipm R16 could have been sacrificed due to a bad tube - which can happen in any tube gear - if that was the case be happy that was the only thing that died.

But - dpop and audiophile1 are correct - this is more of a puzzle than searching for that best sound. The EAR has quite the reputation, but if you just want fantastic sound and not this hassle, you might want to consider an alternate route.

For me, it’s both as I love a good puzzle and great sound. I will add that is seems to be similar for a lot of the folks over at audiokarma dot org - they have quite a few posts on building EAR clones over there, and so far us audiogoner’s here have not been able to solve this. They helped me through a number of puzzles in the past.

Back to your problem. It’s possible you have a combination of a power issue in your place and the EAR is not dealing well with it, potentially due to near failing components. If power is the issue the power company must fix it. But if they cannot, I’ve no personal experience on what you need to do. I would research double-conversion power units - (AC to DC to AC) with a complete separation from the AC power; I believe there some out there are running their audio completely on these things, but I think it has to be complete - no component can be plugged into the wall or your risk a ground loop issue again - so big and expensive. Make sure you can return it if it does not work for you.

On the EAR, given that you had to replace some parts already, best to replace all those electrolytic capacitors as well. I think the EAR came out in the late 90’s, and if this is an original unit, those electrolytic’s in the power supply especially may be near end of life. They are cheap and easy to replace. Just make sure to find units with the same capacitance with same voltage rating or higher and similar dimensions. Nichicon, United Chemicon 105+C caps would be good for the power supply. I would also while you are there reflow all the solder joints on the boards. Takes less time than you think, and that way you are assured there are no bad joints.

When you replaced those film capacitors, did you use new ones of the same capacitance and voltage? The voltage could be higher, but I believe the capacitance value needs to be exact or near exact or it could negatively affect the circuit. For R16, - same - did you use the exact same resistance and wattage value? I think higher wattage would be ok though, especially if the old one burned out for an unknown reason.

One other thing - I noticed the step-up transformers in your EAR - does pressing the MC/MM switch have any effect on the noise with the shorting plugs on? If so that may be your ground issue there - reflow the solder!

@filipm I didn't see that R16 was in the power supply before between the filter caps - should have looked more closely. Not sure what would cause that to fail, but I wouldn't be surprised if it was dirty power (in truth I don't know). In any event, I think that even more supports the thought that you should replace all the electrolytic capacitors in the power supply section and reflow all the solder there as who knows what else would have been affected before the resistor failed.  

@ejb14 We'll see what we can find on the AC line but I wouldn't be surprised. I am already looking at some power plants. Not sure if PS Audio is the way to go, I have been told by ARC that they recommend plugging their power amps directly to the wall otherwise I'll end up with limited dynamics. Other people say their system sounds better with a PP without any restrictions in the dynamics. Haven't tried any filter, nothing. 

I'll check what the capacitors say, a friend of mine has replaced them for me. I still have a picture of the old ones. 

The step-up transformer - yes, the noise level is different. the opposite I'd expect actually. I have a MM cartridge and the noise is stronger when the EAR is set on MM. There should be higher gain with MC settings but the noise is less audible, significantly. But it's still there for sure - and it would also be audible during playback.

I have talked to a guy who builds tube amps, a local. He's willing to take a look at the REF150 and I will take the EAR along. If he won't find a problem, I'll sell the EAR. It's gonna be a bit weird if someone comes to listen to it though :) 

@dpop 

The 33 ohm resistance can be there to avoid a ground loop, as I was told by people who build tube gear. 

You're right, I won't linger on it. I'll let one more person to see the preamp and if he says it's fine, I'll sell it. If not, we'll try to repair it.

I found the answer from the EAR factory - 

It's difficult to say but I suspect a broken earth connection to the screening of the input cable or possibly a broken earth connection on the 834P itself.

This would account for the lower noise level when touching the cable where the user's hand would give some grounding effect. 

Does the noise go if all input cables are disconnected from the 834P ? 

Be careful with adding additional earths as this may create an earth loop and introduce hum noise. The other possibility is a poor earth on the 834P metal top cover. This should be grounded via the four fixing screws. if this is not grounded it will pick up all sorts of external noise.. 

---

I'd like to try PH5 phono stage but it's a real hunt in Europe. All the ARC preamps are always gone really quickly. 

OP,

My condolences on your plight. In hearing your first recording, my reaction is that is digital… digital signals sound like that.

As for the ARC amp… I assume you tried plugging into the power conditioner. It doesn’t sound like a ground loop. But if all components are plugged into the same circuit, that is eliminated.

On the ARC amp. Can you use an insulator and push on it and stop the buzz?

Good luck. I would borrow components (even cheap ones) and swap them out… to identify to verify it is the EAR. Then just swap it out. Sorry to hear of your predicament.
 

@filipm ok - sounds like a plan. Good luck to you!

FYI - one last thing - that 33 ohm value you found between the phono shields and the chassis on the EAR does not sound right - all the phono stages I have have negligible values (0.1 ohms) like your REF150 between shields and chassis and ground. I looked up the schematic of the EAR and suspiciously R16 is a 33 ohm resistor, and more suspiciously R16 was recently replaced. I am not an expert, but in the schematic it doesn't look like it supposed to be attached to ground. I'd recheck that one.

That noise to me sounds like something is generating on the building AC power service line or on the apartment circuit. I would like to see what's else is on the same circuit. Sounds like a motor driven fan or compressor and even a celling fan or something turning. "Maybe even the buildings boiler room generator or vibrating power massage chair"!

The vibrating chair was only for humor but something is oscillating on this circuit...

Bill M

That noise to me sounds like something is generating on the building AC power service line or on the apartment circuit. I would like to see what's else is on the same circuit. Sounds like a motor driven fan or compressor and even a celling fan or something turning. "Maybe even the buildings boiler room generator or vibrating power massage chair"!

The vibrating chair was only for humor but something is oscillating on this circuit...

Bill M

I have measured the impedance between the ground plug on the inlet and the grounding pin of the chassis (or any screw) - it’s 33.2 ohms.

REF150 - the impedance between the ground on the inlet and any screw on the chassis - 0.01 ohms (0.00-0.02)

@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  yes, I was referring to the EAR.

I have measured the impedance between the ground of the RCA input/output and the chassis. You're right - it's 0.01 ohms.

Seems like there's a poor grounding on the inlet. I wrote to EAR if that's on purpose or not. 

Thanks! 

What can I do to find out what causes this 33 ohm resistance? 

@filipm I'm looking at one version of the schematic on line...

https://rockgrotto.proboards.com/thread/11529/ear-834p-phono-stage-mods

...and it looks like the earth ground (e) is actually part of the audio circuit. Wow, I've never seen anything like that before. I would think this design makes it super susceptible to picking up atmospheric electrical noise. I don't care how good it sounds, this is a piece of equipment I would personally (and maybe you should too Filip) not incorporate into my audio system. IMO, it's a very poor design, but, I can see you're more than determined to keep using it, and make it work in your electrically noisy environment, so, I'll give it another try...

To fix this would probably entail a complete do-over (let's eliminate that option right now). From looking at this schematic (if this on-line schematic is a true version of *your* model), it looks like anytime you plug this EAR into a grounded outlet, the entire ground system that it's plugged into becomes part of the audio circuit (I hate to think of what this thing would sound like in a high RFI radio station environment, which already has loads of RFI and EMI in the surrounding atmosphere). 

My first suggestion is to (however you can accomplish it) lift the "e" ground at the chasis iec connector (I hope you know how to solder). It has to be done there, and nowhere else. Now how does the unit sound (with the turntable ground connected to the EAR where it should be)? If that still produces noise, I would reconnect the "e" ground, and purchase an Isolation Transformer, like this one:

XtremPro Hi-end Ground Loop Noise Isolator

Connect the XtremPro (since it probably employs a transformer of some type in its design, I don't know how perfectly flat its frequency response is) between the output of the EAR, and your preamp input (while still connecting the TT ground at the ear). How does the EAR sound now? The XtremPro should (hopefully) break the ground loop that's taking place with the design of the EAR. If that works, if needed, you can always shop around for a higher quality RCA isolator. Good luck.  

@filipm wow - now we are getting somewhere - I think @atmasphere is right on track and @dpop has some great suggestions too. Why it sounded good elsewhere is still a mystery...I would have thought if this is the issue you would always hear this noise. Did you use the MC switch at your friends place and just not notice the what would be then lowered noise?

Also, one thing to get out the way, an easy one - are the leads from the R16 replacement touching the chassis under the board (or any of the other leads under the circuit board)?

@ejb14 Hmmm, you just made me think of something. It's possible the chasis is floating (no earth ground connection). Filip, do you see that little silver philips screw on the back panel with the bonding washer (washer with ridges which digs into the panel when screwed down) underneath it? Is there any wire connected to it inside the EAR? 

I have measured the impedance between the ground of the RCA input/output and the chassis. You’re right - it’s 0.01 ohms.

Seems like there’s a poor grounding on the inlet. I wrote to EAR if that’s on purpose or not.

Thanks!

What can I do to find out what causes this 33 ohm resistance?

@filipm Grounding in audio products is poorly understood, especially in the context of meeting safety requirements! In the US its a bit of the Wild West; some know what they are doing and others don’t, often using techniques from the 1950s that are no longer considered kosher in the age of grounded outlets.

That 33 Ohm resistance isn’t a bad thing- its just that its in the wrong place. How it should have worked is that the connection between the IEC and the chassis should have read zero Ohms and 33 Ohms between the RCA grounds and chassis. In this way the chassis is held at ground by the power cord- and noise collected by the chassis is grounded. The audio circuit is thus floating at ground potential owing to the 33 Ohm resistor but shielded from the outside world. In this way ground loops are avoided even though the power cord is grounded.

Right now the chassis is less effective as a shield it can act as a bit of an antenna instead. You don’t get ground loops though, because there is a 33 Ohm resistor between the AC power cord ground and the audio ground. But in practice, this approach is noisier insofar as RFI and the like are concerned.

IMO the preamp needs to be modified- ’fixed’ or whatever you want to call it, but not so much to fix the RFI issue as it is to fix the potential shock hazard should something go wrong. You really want that chassis grounded so if something like a power switch were shorted to the chassis (for example if the unit were dropped and then plugged in), the fuse would instantly blow, protecting the user. Right now what would happen in that scenario is the 33 Ohm resistor would likely fail, leaving the chassis live, causing damage to equipment downstream and also being a possibility of a lethal shock hazard.

This is of course based on what you’ve told me so far.

Had a similar problem and surprisingly 

a power line conditioner solved it - 

this is the model i have.

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?)

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

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.

@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!

@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. 

@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. 

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

@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.  

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 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).

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.

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

picture of resistor