Not a ground loop hum???

I thought I had a ground loop hum, given that with my pre, cdp and amp all on, without any music playing, there is a hum emanating from my speakers. Following the advice seen here and elsewhere, I went out and got some cheater plugs to try and hunt down this annoying and, at times, distracting hum.

My system comprises: Anthem CD-1 (with DH-Labs power cord), Blue Circle BC21.1 tube pre (with BC62 pc), BC22 amp (Zu Cable BoK pc), Rune loudspeakers by Zu Cable (hooked up with Zu Cable Libtec speaker cable), Blue Circle MR1200 balanced power line conditioner/distributor (Zu Cable BoK pc), and van den Hul D102 MKIII interconnents.

Well, with the three components' power cord fitted with a cheater plug and all plugged into the power conditioner, the hum was still present, same intensity, volume, etc. Removing the cheater plugs one by one starting with the cdp, then pre, then amp, there was no reduction in the hum. In fact, I think I may have heard it get worse at one point.

Any ideas out there as to the cause of the hum? Maybe the tubes in the system are the culprit. There is a pair of Siemens CCa (6922 type) with Pearl tube coolers installed in the pre, and the tube in the cdp is a Telefunken CCa with a tube cooler.
Have you looked at your IC's - I've had a hum from time to time from the IC's passing too near a transformer (in my case, the amps). One way to check this out is starting at the amps disconnect and reconnect IC's going back to the source, one at a time (be sure to turn the amp off each time). You will be able to at least figure out which component is causing the hum and then you can check the IC's. Good luck.......
If you have a video cable line or satelite cable, disconnect it, see if the hum goes away. I went through a similar situation a year or so ago. I tried cheater plugs, floating grounds, etc, etc. It wound up the ground loop hum was coming from my cable line. Radio Shack sells ground loop isolators if this is the case. I'm using a MIT Iso-LinQ, no more hum.

Have you ever verified that your equipment and AC outlets are properly oriented in terms of polarity? Some components are HIGHLY sensitive to AC polarity. Having one component that is not oriented properly connected to others that are oriented properly can introduce a hum into the system.

Out of curiosity, how loud is the hum and at what distance from the speakers is it audible? Is the hum a constant level or does it vary with the gain of the preamp? Have you ever tried connecting the amp to the speakers by itself to see if it hums? If not, try that and see what happens. If no hum, hook up the preamp to the amp and then give that a shot. If nothing, then hook up the CD to the pre and see what happens. If you get a hum with all three hooked up, then try the CD directly into the amp ( NO discs in the unit unless you can vary the output of the CD player ). As usual, it is all just a matter of step by step diagnostics and trouble-shooting. Sean
All good suggestions above...

I had an interconnect hum once because the solder on a RCA plug was cracked, probably from being moved around too much over the years...

Resoldering did the trick...
You really need to start by unplugging everything in that circuit, not just in that outlet. Then, plug in only 1 piece at a time to find the hum.
Keep in mind that electricians can do weird things (1 outlet in my basement is tied into a kitchen outlet).
Thanks very much for the responses!!!

The IC's in the system: the pair from cdp to pre and the pair from the pre to amp are both essentially outside the equipment rack and neither of them comes very close to a component's chassis. The IC from tuner to pre rests mostly on the top shelf of my rack. I've tried to ensure that IC's are spaced apart from one another and from the PC's.

The system in question is strictly audio, but I'll look into the ground loop isolator idea if all else fails.

Sean, I was hoping you might comment/advise. I checked the outlet into which the power conditioner is plugged with a 3-prong outlet-checker (I've forgottent the proper name) to ensure its wired properly and it indicates the outlet is OK. As for the outlets on the power conditioner, I did not check those but will do so this evening. Although the cheater plugs I found/purchased don't have the ground blade, they are not reversible as one of the two blades is wider.

I don't have a metre to measure the volume of the hum (I would guess that it's about as loud as a really big bumble bee; can't think of another comparison right now), but it is at a constant level regardless of the position of the attenuator. I can hear it from up to 12 feet away, and when I listen at low volume at night (so as not to disturb my better-half or the littl'uns) I can hear the hum between tracks and during soft passages. My pre has the Shallco stepped attenuator and by low volume I mean it's at the third to fifth step.

I had tried several weeks ago hunting down the source of the hum in the sequence that you suggest, but will have to check again as I can't remember the results.

Sugarbrie, if memory serves, the van den Hul's are not soldered, probably because of the carbon fibre layer, and they are barely a year old. But I'll check this as well. I'd hate to think that one of the BC components could be to blame, but the hum is drivin' me nuts.

On a separate noise issue, my MR1200 makes quite a bit of noise that comes and goes. I wrote to Blue Circle and they suggested the AC to my house may be particularly dirty, so the noise is indicative of the transformer/filtering working hard. I don't know, I mean why pay for conditioning/filtering to keep noise out of the audio components only to have it show up in the conditioner/filter. BC also indicated that it may be due to the on/off cycling of the furnace at this time of year, but the two don't seem to coincide. They'll retrofit the MR1200 or the BC62 PC with a quiet device, but I'm waiting until we move to our new place in a couple of weeks before spending anymore on power conditioning/filtering.
Mghcanuck: I just realized that, going by your moniker, you are probably Canadian. If that is the case, i can no longer help you. Sorry 'bout dat.

Bwahahaha. I had to do that just for the sake of Pbb always spouting off about Canada and the superiority of things Canadian. I hope that he and other Canadians can laugh after they get over the initial shock value. What good is "hanging out" if you can't have some fun at one of someone else's expense : )

Getting back to the point, just because a device uses a three prong or polarized two prong power cord doesn't mean it can't be wired with reverse polarity internally. On top of that, one can have correct polarity, but if there is a difference in ground potential from one component to another ( due to leaky cap's, resistive connections, etc...), you can also run into a hum. You'll need to disconnect ALL of your interconnects to check thi AND have access to an inexpensive multimeter too.

When checking components individually, you have to disconnect interconnects between them, not just turn them off. This is both for checking component polarity AND finding out what specific component or combination of components is causing the hum.

As far as the power line conditioner making noise, it may be something as simple as loose nuts & bolts holding down a transformer or a lack of internal damping. I agree that buying a product to solve a problem and then creating another demonstrates a lack of product engineering. Then again, it might be a great product and simply slipped through the cracks of "Quality Assurance".

Having said that, you might want to check into a device that Kevin Deal of Upscale Audio sells. It is supposed to suppress DC offset problems in the AC line, which can cause some of the problems that you are experiencing. From what i've gathered, i think that he sells it with some type of return policy, so find out the specifics before shelling out the cash.

As a side note, a quantity of DC on the AC mains will cause your transformers to run much hotter than normal. Then again, some high bias amps will "warm" the transformer quite noticeably, so this can be a hit or miss trick when dealing with amps. Sean

Your realisation is correct, eh?! But I appreciate the humour, so no harm done. Pbb may indeed be quite ardent at times, but it probably has more to do with a feeling of inferiority due to living next to such a big and powerful and awe-inspiring and free and great and did I say powerful nation like the US, well I guess there is no "like the US" since it really is the only super-power, and that's just super IMHO, but now I'm rambling and so I'll stop. :-)

Aha, I have a multimeter! What am I measuring for? Sorry, but my electrical knowledge is, shall we say, pretty limited. I gather that the first step is to disconnect all IC's and only have one component plugged in at a time. I seem to remember you may have covered this in another thread where you had a kit that would be shipped from one A'goner to the next so they could check for polarity and difference in ground potential. Could you provide the link to that thread or instructions/advice? Thanks very much.

I am going straight to the Upscale Audio web site to look for the device you mentioned.

Try this thread about Noise, hum and AC polarity. Sean

PS... I am by NO means a "super-patriot", but your humourous response tells me that you at least weren't offended by my crass sense of humour : )
not meaning to hijack this thread, but I have another question about hum. When I touch the volume dial on my pre, I get a pretty significant hum, but its not there when I am not touching it. Any ideas?
Swampwalker: Your preamp is poorly designed and lacks stability. Adding the conductivity of your body to the electrical characteristics of the preamp via chassis ground is enough to alter the performance of the circuit in what is an audible manner. If audio components were properly designed, their chassis wouldn't be connected to the active circuitry in any way, shape or form. Sean

Once again, you have proven to be 'da man! That's exactly the thread I had in mind. Looks like I've got some work to do. Thanks very much for your valuable input and advice.


PS... I'm not offended in the least. The US and Canada, despite recent disagreements, have one of the closest relationships between nations on Earth. Some humour in the relationship can help keep it healthy. To paraphrase: "A bit of foolishness now and then is cherished by the wisest of men." Not that I'm wise, far from it, but I think the message is pretty wise itself. All the best.
Just thought I'd provide an update. I checked the outlets on the MR1200 power conditioner with the polarity-checker-plug, which indicates the hot and neutral are reversed for all three duplexes. Arrrrgh! So, do I open up this $750US piece of equipment and try to properly wire the damn thing or do I return it to Blue Circle? Seeing as how I'm not technically/electrically qualified, I'm tempted by the latter option.

Max: Why don't you call up Blue Circle and let then know what is going on. If you don't have a local dealer that you purchased it from, BC should cover the bill on shipping both ways since this whole mess was due to their lack of quality control to begin with.

Other than that, i'm glad that you were able to figure out what was going on without losing too much hair or sleep : ) Sean
Max, I have one of those devices that you plug into outlets to diagnose several problems. When I plugged it into my Balanced Power Technology 3.5, it told me that there was a faulty ground. I called Chris Hoff. He said that balanced power confuses the device. He also said the most common results are reversed polarity and improper ground. So, your Blue Circle unit may be functioning properly.
Do you have dimmer switches anywhere in your home? If yes, try turning them off, and see if that makes a difference. That suggestion solved all of my problems last year.
Balanced power WILL play games with an AC polarity tester and is the sole exception to what we think of as "proper AC power". Anything else should have a very specific hot, neutral and ground ( as far as i know ). Sean
I had sent an e-mail to Blue Circle and the response was as Brooks1 and Sean have indicated. Balanced power outlets will indeed show reversed hot and neutral or other icorrect wiring, because there is 60V coming from the neutral and 60V coming from the hot in relation to ground.

Blue Circle insists that it is likely really dirty incoming AC causing mechanical noise in the transformers of the MR1200. I'm back to my question of why bother with this relatively expensive power conditioner to prevent noise in the stereo components only to have the conditioner make noise.

I've swtiched over to the $200 Monster HT1000 power bar that was lying around since I received the $750 MR1200. Guess what, no noise from the HT1000. This just ticks me off.

Next week we move into our new house, so I'm really eager to see what kind of results I will get from these two units plugged into the dedicated line I had installed. Will the MR1200 continue to hum? Will the Monster piece mash the Blue Circle again? Enquiring minds want to know! FWIW, I'll post my findings in a few days and continue to ponder Chris VenHaus' solution of wiring two 0.47uF 600V Auricaps in parallel in the dedicated outlet if the MR1200 is still noisy. Has anyone out there tried the latter yet?

Thanks again to all for your comments and ideas.

Max: The caps won't correct what is a design error or quality control problem with the Blue Circle PLC. If you want to use that and get good results, it needs to be replaced or repaired for proper operation. That is, if this unit doesn't take standard polarity AC and convert it to "balanced" power. I'm not familiar with this specific unit, so i'm adding that as a disclaimer. As mentioned, "balanced power" will play games with polarity sensing devices. As mentioned in another thread, "balanced power" can also undermine the design integrity on some well engineered gear. As such, adding such a "tweak" to your system may actually be detrimental to performance and / or the lifespan of the gear.

If you're interested in some alternative points of view on tweaking your AC, try reading the tweaks found on David Magnan's website. As with anything else involving high voltage & current, be careful and use some common sense. It is NOT worth getting injured or killed no matter how much better you think your system will sound after doing something that could be considered "unsafe". Sean
Mghcanuck I feel your pain. I have been adding new power lines to my basement and picked up a hum. I rerouted cords. I put magnetic shields on cords. The hum did not subside. Finally, I put a Monster HT1000 on my video cable line which was also new and plugged the cd Player and tuner into it. The result no hum.

And do you know what where the worst hum was located? The TV speakers.

I'm even thinking of buying a second HT1000 for my main system. It also has Cable and a FM Tuner.
Sean, the MR1200 does indeed convert the AC from the wall into balanced power provided at its outlets. Are you saying that it should not hum regardless of how dirty the incoming AC may be? That was my assumption when I purchased the piece, given the filtering that it is supposed to perform and the positive reviews that BC has garnered for their balanced power line conditioners.

I've got the product designer/maker telling me that the noise is due to really dirty AC and that there's nothing to be done except have one of their power cords fitted with a quiet device that will resolve the noise issue in the MR1200. On the other hand there is the possibility of a QC issue with my unit.

I'm going to test the MR1200 in the new house next week and see what happens. If it's still noisy, perhaps I'll send it to BC for a check-up. Beyond that, I'm just not sure what to do.

Danny, I'm guessing the main difference is that the HT1000 does not have a transformer, or at least not one that converts the incoming AC of 120v in relation to ground into balanced AC of 60v from the hot and 60v from the neutral, so there is no possibility of transformer hum. The purported advantage of a balanced power line conditioner, such as the Blue Circle Music Rings among others, is that it offers even greater benefits in terms of lowered noise floor, etc. Not in my set-up though.

Thanks once more for the input. Much appreciated.

Check out the Granite Audio website for a product called Ground Zero. I bought one of these units after going through the same process you have with no luck and lots of frustration. Ground zero took about 20 minutes to connect to my system and it completely eliminated the humming altogether. What remains is the darkest background and lowest noise floor I've ever had in my system. Simply amazing! It was worth every dollar spent. Check it out!
Completely forgot to provide an update on the situation with my MR1200. Well, after trying it out in our new house and hearing the same level of noise, I sent the power conditioner back to Blue Circle, paid for shipping and about $60 for the filter add-on. They also checked it for mechanical and QC issues. Once I had it back home and inserted into the audio system, no more noise/hum from the unit!

Now I have two other noise isses to resolve. One is hum from the speakers, which increases in intensity as the volume is turned up. Could this be the inherent noise from the tubes in the preamp and or CD player? I've read in a couple of places about the noise from high gain preamps being audible through high-efficiency speakers? My speakers have a rated sensitivity of 101dB.

The other noise I recently discovered when I tapped the chassis of my preamp by accident. I gave the middle of the face plate a a light rap and heard distortion out of the left channel speaker. Any ideas?

Thanks again for any advice and suggestions.

Your hum could easily be residual hum from the tube pre-amp, although in my system it sounds more like tube rush/hiss. Do I assume correctly that this hum is well below the level of the sound of the music you are playing? Tapping the chassis, probably a microphonic tube in the left channel.
Hi Newbee,

Thanks for your response. That's correct, the hum is not audible when music is playing.

Damn that tube! I don't know a lot about tubes, but I should have thought about the possibility of it being microphonic. Time for a new pair I guess.


Mgh: Did you ever resolve the problem that you were having with the left channel? What about the hum in your speakers that was volume sensitive? Sean