"Grunge"

stellavox said:

I want to comment on the aspect of “grunge” (alternatively called RFI or EMI or ...) creeping into a playback system from the outside. I’ve experienced it directly at home, at a friend’s, and have read of many anecdotal problems. Don’t know if this is the proper forum but from a cursory inspection of other forum threads it hasn’t been mentioned anywhere else – so here goes…..

From just its impact on audio reproduction we live in a VERY polluted environment. “Grunge” can be borne into or generated within your home and conducted through the power wiring - acting as an “antenna”. Or it can just flow in through the walls in the form of electric and/or magnetic waves (transmitted).

The effects range from severe to “unknown”. A few years back, a friend was trying to assemble a system on the second floor of his house and try as we might we couldn’t get an objectionable level of “hum” out of his phono hookup – it worked fine downstairs however. On my current system, if I put my tape pre on max gain and turn the volume all the way up I can (sometimes) faintly hear a local radio station. One of my customers had the same problem but much more severe. A potential customer was experiencing an objectionable background “buzz” from the combination of my preamp / his deck. I added the word “unknown” in the first sentence as you may be experiencing a problem and not even know it – yet “something” is or feels wrong.

I want to separate out conducted from transmitted “grunge” for the purposes of how it can get into your system. It gets "conducted" through the power cords; it gets “received” (opposite of transmitted) "through the air" by potentially ANY system component – even your speakers.

The electric power system is supposed to generate and “conduct” current alternating at the rate of 60 hz. Fluorescent lights and (the many) switching power supplies in your home, not to mention the variable speed drives of your “next door” machine tool company generate higher frequency harmonics that can make it into your home and be conducted right into your system components. Commercial radio and television installations (which are pretty easy to spot) and cell phone installations (which are not) produce electromagnetic radiation.

How can this “grunge” get into a component and what effect can it have? Even with some kind of power line filtering on the input of a component, conducted high frequency components could make it into / through? the power supply and perhaps “modulate” the downstream supply voltages. Received electromagnetic waves are insidious. They can get in through any “antenna” which includes input or output cabling – or even a ventilation hole!. Once inside, although the frequencies of these waves are typically many orders of magnitude higher than what our ears can perceive, they can be “demodulated” or “rectified” down to a perceivable level by various internal parts or interconnections.

I realize that all kinds of ink has been spilled on this subject. There are MANY references to specific kinds of interference and its mitigation. There are a number of products designed to “sniff out” conducted problems – detecting electromagnetic problems are another matter. My own feeling is that if you live in a metropolitan environment, because of the high probability of “dirty neighbors” your system may very well be “swamped”. How is it responding? Let’s discuss this – what problems and solutions have you experienced?

One final thing I want to mention is the actual impact of “tweaky” accessories on grunge. Certain esoteric accessories, especially metallic ones, seem to produce improvements in certain listening environments. Manufacturer’s claims or questionable explanations aside - their effectiveness could be due to their configuration and specific placement in a room. They could actually be “shunting” very high frequency electromagnetic waves away from one or more susceptible components - in effect acting like a low pass filter. A case in point; my friend whom I earlier mentioned had “hum problems upstairs” (which we did trace to a line-of-site radio station tower) found that some current tweak, a little length of ‘wire-type” product that you hang from your speaker terminal, seemed to sound better. Another correspondent who tried them realized no improvement. Maybe the accessory actually mitigated waves in one room that didn’t exist in the other.

Charles

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mep said:

Since this forum has so many resident geniuses, I would like to see someone write an article on a really good grounding scheme for our systems. Copper ground rod outside with copper ground line run into the listening room attached to a copper ground bus bar to attach all of the components to? Something that is practical, doesn't look heinous, and that will work to knock out hum nasties.

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stellavox said:

mep: Thanks for your comment. It raises a good point that perhaps I should have mentioned.

There is no one "cure-all" because there are different problems. APART from grounding and ground loop-related problems - problems which may be caused by and only exist WITHIN your system, there are other problems related to "grunge" coming in from the outside world (WITHOUT).

Attention to good grounding practices, like Doc alluded to in his recent tape head posting, should be able to solve the "within" problem - perhaps someone has another "favorite" reference they can pass on. With regards to transmitted or radiated grunge, one sufferer I know was only able to eliminate / significantly reduce the effect of a nearby radio tower by creating what I believe is referred to as a Faraday Cage - effectively creating a shielded box (grounded in some manner) within his equipment rack to house sensitive equipment. Regarding reducing conducted grunge - dedicated branch circuit from the breaker panel / line filtering / AC regeneration / balanced power / battery power - are all methods which have worked for various individuals.

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FrantzM said:

One could listen in a Faraday Cage the problem of EMI/RFI coming from the power lines remains whole.. Some power supplies deal with it very well most don't ... Another problem are indeed as the OP mentioned, EMI that are generated inside your istening room.. Dimmers for one are serious offenders but also many digital components..
more later ...

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Mike Lavigne said:

great subject.

twice recently in my system i was able to observe the before and after of 'Grunge'. in retrospect; it's clear (pun intended) that you don't really appreciate what 'Grunge' is until you hear the effect of it's absense.

last fall Rich Brown brought the King/Cello repro unit over to my place for the first time. Ki Choi had wired in a switch on my Studer heads so we were able to A/B the system easily thru the stock Studer electronics and then the King/Cello. most noticable with the King/Cello was the absense of this cloud of grey 'grunge' veiling the sound. i was only able to identify this characteristic when presented with it's absense.

at that point there was still work to do with the King/Cello before it was ready for prime time in my particular system; but it was easy to see we were going in the right direction. the 'grunge' in this case was likely both 'recieved' and 'transmitted' from the 'active environment' of inside the A-820. the isolated power supply and gain stages of the King/Cello removed much of the crud.

a couple of weeks ago i installed the Equi=tech isolation transformer. it has a stout double ground rod and is balanced for common mode noise rejection. big difference in noise i've already described in another recent thread. as i work my way thru my music collection i continue to be reminded of the effect of less grunge.

i live out in the boonies so my environment is likely not as noise polluted as some others; but i know there is plenty of grunge to avoid.

sometimes grunge is reduced just by cleaning the contacts of your power cords or interconnects.

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Mark (Basspig) Weiss said:

I've decided to weigh in on this, only because of the fact that I actually worked as Chief Engineer for numerous AM & FM radio stations in the Northeast over the years, as well as because I have RF design experience and was in the process of producing my own line of broadcast equipment. So here's some of what I know that applies here:

RF pollution comes in many forms. The nastiest is UHF TV, because of the super power levels (up to five megawatts) and short wavelengths' ability to get into smaller spaces within equipment, vent holes, etc. as well as the fact that it carries both audio and a rather complex and (audibly) nasty visual amplitude modulated carrier at the higher power level.

A simple RF carrier gets into power supplies and becomes audible in the linear power supply when the rectifiers are just coming into or going out of their conduction cycle at points just before and after 90° and 270° on the AC power waveform. When RF is riding on this current pulse, the eddy currents become able to travel throughout the chassis/PCB traces far more easily, since the RF acts like a carrier, only the audio this time is the 120 cycle switching of the fullwave rectifier. This manifests itself as a 120 cycle hum in the audio system. I see this a lot in radio studios that are co-located with the transmitter.

Modulation on RF carriers just changes the intensity and type of noise we hear. It can be the 60 buzz of the vertical interval blanking signal on a television carrier, or audio program material on an AM or FM station.

Mitigation of these types of pollution involves:

Stopping it from getting into the power supply
Stopping it from getting into the chassis and interconnects through free air

One of the cheap and dirty tricks I use to mitigate neighbors' complaints when a station receives a telephoned or written complaint from a nearby resident, is coiling the AC line cord nearest the entry to the equipent into 4-5 turns about 3" diameter as a coil, and ty-wrapping it to stay put. This forms a VHF trap and is the cheapest form of relief.
Sets with plastic cases can be mitigated with aluminum foil, though it is important to make certain no ventilation slots are blocked and that no electrical terminals will come into contact with the foil. Grounding the foil will sometimes help.

Ultimately, the better solution is to RF toughen the equipment. This involves modification to the power supply. I like to use ferrite transformers in series with the AC line, using the cross coupling to shunt the HF noise, while the windings in series pass the 60Hz unimpeded. This, followed by common mode and differential capacitor banks to shunt off more noise. On the rectifiers, I add snubber capacitors. In severe cases, I even add inductors/chokes in series with the rectifiers, forming a choke input filter. Finally, relocating the ground return from the transformer as far as possible from the load ground within the unit results in reduction of rectifier switching eddy currents. The common mode stuff is the hardest to remedy.
The next thing to deal with is the inputs. In severe RF environments, I put 47uH chokes in series with all inputs and outputs, with 47pF shunt capacitors after the chokes on the amplifier circuit side. This attenuates the RF coming into the equipment through audio interconnects.
The use of quality, shielded cables for interconnects will be most noticed in an RF polluted environment. Many cheaper cables have spaces between the braid weave. Better cables like the Monoprice stuff I use, have denser braids that leave little open space for noise to leak through. This will benefit both the RF shielding and increase immunity to 60Hz hum from nearby line cords and other sources of EMI.
Lastly, orientation of equipment can make a difference. Broadcast RF is a coherent wave. As such, it behaves like standing waves in a room, due to multipath (reflections and bouncing) of RF energy from an FM or TV signal. Thus, moving a piece of gear 6' (about half a wavelength for an FM broadcast) can make a big change in interference.

I have a lot of experience with this as I live in the center of the aperture of a 50,000-watt FM/AM combo station, and cellular site. They have two bays of ERI rototiller at 499' HAG, and the field intensity at my property is enough to lock up digital personal electronics like PDAs and video cameras. To mitigate this, I shielded the house during construction, and grounded the shields to earth every 6' through straps at the foundation. The house is a Faraday cage, essentially. I have zero RF pollution in the house.. of course no cell service either, which is a slight inconvenience.. but my audio gear is clean and free of 'grunge' from electrical noise, having taken these measures over the past 38 years.

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MylesBAstor said:

And I'll weigh in and say that in a system that doesn't suffer from RFI, chokes and coiling wires degrades the sound. Been there, done that. If it was that easy, everyone would do it.

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FrantzM said:

And why would that be? What about the very huge inductance to which YOUR power lineis connected, the power transformer outside your house? Have you performed a controlled in which it was clear and conclusive that it was so ?

You clean up tour AC your system will sound better.. Of course there are ways to do so.. Just dropping ANY isolation transistor in a system is not a guarantee of great results.. properly sized and designed they enhance performance. That is all there is to it ...

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