A problem with AC Power you may not have considered.

My posting is not about a stereo system but it is related to AC Power, from which all stereos draw power. Read on, I am sure you will find this interesting. I certainly did and it caused me to rethink and replan AC Power to my stereo.

At my real job as an electrical engineer, I manage a cross-disciplinary engineering team for a large energy company.   We make large, residential green energy management systems, a size that borders between most large homes and utility companies. A few months back, we released a new product to the 230VAC single-phase market (Australia, Europe, etc.) and recently introduced the same product to the 240VAC split phase market (USA, Canada, etc.).   In addition to a slew of UL, IEC, IEEE, CSA, TUV, and other safety codes, we also had to meet FCC Class B emissions (which all your digital audio equipment must also meet) and also meet FCC Susceptibility requirements (which digital audio does not have to meet, unfortunately).  

Since the two products are almost identical, I thought we could leverage what we learned for the 230VAC unit onto the 240VAC unit.   Well, this is where the impact of grid power to our stereos comes into our interest.  

The emissions requirement is of two parts, of which you may be familiar. One is radiated emission, which is the noise the product broadcasts into the air. The second part is conducted emissions, which is the noise the product injects onto the power lines and runs throughout your house and probably into your neighbors as well.  

The 230VAC unit passed emissions, which I expected as we did a lot of design work to make it pass.   The conducted part was a concern, since that injected noise is from the equipment our vendor produces, not something we designed in house. Well, when the certified testing house tested conducted emissions, it failed.   A couple of weeks of debug later, at 2K$ per day, the problem was solved when I suggested they test with the grid connection running through 8 feet of steel conduit, since all installations have at least 8 feet of conduit.

Fast-forward six months to the 240VAC testing, which took place here in the USA. Surprisingly, the unit failed conducted emissions, even though we used the same 8 feet of steel conduit.   Another week of debug, again at 2K$ per day, we stopped testing since it was clear a new design is needed to fix it. I designed a 50 Ampere Balanced LEMP Filter that had over 50-dBm isolation in the affected frequency range.   Problem solved.   So, why did 8 feet of conduit fix the problem one time and not the next? A good question.  

I took the same 8 AWG THHN wire we used to connect the unit to the grid, ran it through the same 8 feet of 1 ½ inch steel conduit, and rented some high frequency test equipment. In the conduit we had two 8 AWG wires for Line 1 and Line 2, one 8 AWG wire for Neutral, and another 8 AWG for Earth ground.   I ran a bandwidth test from Line 1 to Neutral and tied the conduit and Earth wire to earth, while the other Line wire floated. The test started at 60 Hz, which I referenced as 0 dBm and I ran the test all the way to 30 MHz.   The generator produced 10Vrms, the level I checked at each step, and fed a 50-Ohm load.   To my great surprise, I had a 2-dBm rise at 10 MHz where it began to roll off and was only 2 dBm down at 30 MHz, the limit of the test generator.   In other words, that length of pipe and THHN wire had a bandwidth of +/- 1 dBm from 60 Hz to 30 MHz!   Whoa! We are allowing a ton of injected noise into our systems!

To prove that, I grabbed the power supply from an analog stereo amplifier and fed the test signal through the cord, fuse, transformer, and measured the bandwidth on the secondary.   In spite of a UL/CSA approved transformer, it was surprisingly transparent to the test signal.   Throughout the test spectrum, it was never more than 6 dBm down and it peaked in a couple of areas, too.  

Our homes usually don’t have grounded conduit, what most homes have is Romex wire.   That stuff is transparent to radiated emissions and we live in a world of radiated emissions. Think cell phones, FM and AM radio, TV broadcasts, all the communication frequencies, plus who knows what we have for the dirty noise injected by electric motors. Think your fridge, your AC unit, your furnace, ceiling fans, light dimmers, electric vehicles (that is the reason they don’t usually come with an AM radio these days!), the list can go on for a long time.

For my stereo system here at the house, I built a smaller version of the LEMP filter, added additional suppression, along with 20,000 Amps of surge protection. I am also installing a dedicated earth ground as well.   However, you don’t have to home brew – you can purchase equipment that meets the local safety codes and is LAB certified to meet multiple suppression standards. These units have strong filters in them to clean up line power. There are replacement AC line cords on the market that contain RF suppression.   I don’t suggest you get a new mortgage just to buy AC noise suppression equipment or new line cords, but I do suggest you do something to kill those RF demons.  

Look for equipment that has at least 30 dB of suppression from 100 KHz to 15 or 20 MHz. Thirty to forty dB is the range where most emission problems fade away, so that is a good starting point.   Some equipment has lightening suppression as well; look for an IEEE spec stated in joules of energy, the more the better with a test pulse of 8/20 microseconds.   Don’t be afraid to stack some of the equipment in series.  

The lighting in your listening room can also matter a great deal. Stick with plain, old school incandescent bulbs; avoid the CFL’s, LED’s, neon’s, light dimmers, and other lights that require power supplies to run.   Incandescent bulbs are very quiet, which is why they appear regularly in emission anechoic chambers.   Although digital equipment is less sensitive than analog equipment, it is not immune to susceptibility.   Vacuum tube equipment usually has an edge over solid state, too.  

I hope what I wrote is of help to you in your quest for improved sound.  

@erik_squires   Would series mode suppressors further complement my Equitech 2Q balanced power transformer? I do use Sound Application and MIT Cables power conditioning cables/units to excellent effect.  My experience has been that there’s always a benefit by maximizing elimination of ac noise. (I wish I could get technical details on these products.)
Working on reducing the AC noise floor with ByBee products, give me satisfaction.  I think they use some cristals in their devices, as you did in your last experiment,  isn' it Elisabeth ?
@ptss - I cannot tell you if you will hear a difference, but in my mind there’s very few technologies in audio power conditioning well documented:

  • Series mode surge suppression
  • Balanced power
  • Active power regeneration (PS Audio)
  • Power regulation
  • Active power cleaning(LiFT and PerfectPower)
You can find a Furman unit with most if not all of those available.

Everything else is just some form of shunt noise reduction, which is almost never documented.

The series mode protection is also licened by PS Audio if not others. I consider it the minimum due to:
  • Very low impedance
  • Best lightning supression
  • Audible frequency noise reduction

@mrmb, @soix - Here are some ideas for noise suppression. There are a number of quality noise suppression devices out there. Furman is a good brand, so is PS Audio and Tripplite, but do check out the specs. Here are the specs for a Furman M-8X2, a basic power distribution and noise suppression, and priced at $80.

· Standard Level AC Surge Protection: Merit Class (sacrificial)

  • Spike Protection Mode: Line to neutral
  • Energy Dissipation: 150 joules
  • Peak Impulse Current: 12,000 Amps
  • Let Through Voltage (@125 amps, 8/20μS waveform): 400 volts

· Noise Attenuation: Transverse mode: >23dB, 200 kHz to 10MHz

So let’s explain what this means. Sacrificial means when a lightening pulse hits the device will short the input power forcing a fuse or circuit breaker to blow and opening the circuit.

Essentially, the unit will have to be replaced; the philosophy is it’s better to replace something inexpensive than expensive stuff downstream. This is how I designed the LEMP filter, I had all the noise filtering up front and following by sacrificial electronics.   It is good of Furman to specify this, since you know what you are getting.   The other philosophy is non-sacrificial, that is a design that has aggressive filtering and stores the energy in a reactive space, thus dissipating the energy more slowly.   A good example of this is here: https://zerosurge.com/wp-content/uploads/2018/04/2R-Series-0418.pdf and here: https://zerosurge.com/

There is no reason you can’t combine the two philosophies. J Put the heavy filtering up front, followed by spike suppression.

Spike Protection Mode means the protection is from Line to Neutral and there is no protection from neutral to ground.   This is a reasonable concept since neutral is tied to ground at the main panel. There are other arguments against this, stating neutral should be spike protected to ground. However, the more protection one adds, the more the cost goes up.   At some point, has you have to evaluate bang for buck.   Personally, I put in neutral to ground protection, both as spike and as filtering but then I wasn’t trying to hit a price point.

Joules is the unit to measure energy, equals the work done when a current of one ampere passes through a resistance of one ohm for one second, which is one Watt. Joule units define the energy dissipated by the device; the more the better.   150 Joules here is not much, 3000 Joules is getting somewhere, 6000 Joules or more is healthy. Expect to pay a lot more as these numbers go up.  

Peak Impulse Current is the maximum spike current that the surge protection circuit can handle to protect downstream electronics.   Again, 12,000 Amps is a starting point, I put in 44,000 Amperes and there are bigger devices out there than what I used. That LEMP filter I designed for the energy system had 300,000 Amps of Peak Current.

The 8/20 microsecond waveform is a standard IEEE test waveform for lightening spikes where the maximum voltage is reached in 8 microseconds and decreases to 50% in 20 microseconds.   Therefore, the higher the voltage pulse the narrower the pulse becomes.   There are other IEEE standard pulses but this is the most commonly used one.  

Let Through Voltage is an important spec. It tells you the amount of voltage that the protection circuit will allow to pass through before the circuit begins to attenuate the spike. Here it is say it will allow a 400V pulse at 125 Amps.  Understand there is always a Let Through Voltage, keeping it tame is a tough call and an engineering compromise.   Reduce the Let Through Voltage and the pulse circuit works a lot more, heats up, and is in a weakened state when the big spike comes along. Relax the design and the pulse circuit is more able to handle a big pulse but allows more energy through when it does happen. The only good solution here is a good design.

Everything I wrote about so far is about spike suppression, which is lightening and spike noise from motors, air conditioners, etc.   This has nothing to do with EMI and RF noise, which is more problematic for sound quality.   The spec 200 KHz to 10 MHz is the bandwidth where the EMI filter works and produces at least 23 dB of suppression.   In my first posting, I stated look for something that has at least 30 dB of suppression from 100K to 20 MHz, so this unit is a bit on the shy side of what I suggested.   Forty dB is much better and it is unlikely you will find anything above 60 dB.

So, is this bad? It costs $80 and for that price, the protection is quite fair. If you have the budget, definitely look for more EMI suppression. If you live in areas where high winds are common, earthquakes, or massive storms, having a lot more spike suppression is a good idea.   It is not just lightening that produces massive electrical spikes.   A storm knocking out a power pole can do a real number on your system.

@elizabeth - You are just as crazy as I am.  Awesome!