Andy's Blog

Good Design/Bad Design #1

Andy W — Fri, 05 Sep 2008 20:53:00 GMT

I'm a sucker for a well though out, well executed design. My brother-in-law and I are both engineers, and we like talking about good and bad designs. Usually we lean toward criticizing the bad ones. Apparently other people do too, as there are web sites devoted to it. I don't have a web site, but I have a blog, so here's my first good design/bad design blog.

Topic: ice cubes

Good Design: I love the Arby's "duck turd" ice. [(c)AHW 2008, all rights reserved] An informal poll at the lunch table revealed that others too love the duck turd ice. If you don't know what I mean you'll just have to get some yourself and see what I mean. The ice gets your drink real cold real fast, and as a bonus it's easily crunchable (I like to eat ice, I know, it's bad for my teeth, yadda, yadda...)

Bad Design: The ice that comes out of about every home ice maker. Who designed these things? Did they ever actually try to use the ice that comes out of them? The shape of the ice is a round bottom with a flat top, kind of like a crescent moon shape.

The problem with this ice, and I'm sure you'll all agree, is that the radius of the bottom curve of the ice closely matches the inside radius of common beverage containers (cups, mugs, glasses, tumblers, etc.). When a beverage is consumed the ice invariably turns itself perpendicular to the flow of the beverage. Thus the ice creates a small dam of sorts to the intended imbibing of the desired refreshment. If he cares to drink more than a trickle, this requires that the intended recipient of said liquid refreshment tilt the glass ever higher in an attempt to obtain the optimal flow.

The attempt to obtain an adequate swig then results in the ice dam being overtopped, with an overabundance of beverage gushing uncontrollably toward the intended recipient's face, along with the unintentional social embarrasment and the attendant quips and comments about having a "drinking problem."

The Ultimate Driving Experience

Andy W — Sat, 16 Aug 2008 13:44:00 GMT

No, this isn't a blog about a BMW, although my brother-in-law used to own a 535i 5-speed, and I thoroughly enjoyed driving it. This blog is about the "Klipsch: The Ultimate Sound Experience" license plate and the 1999 Jeep Cherokee attached to it.

Klipsch more than likely ripped off the tag line from BMW, not a stretch considering several people at Klipsch drive them.

Some years ago, all the employees got said license plates, and I proudly attached mine to the front bumper of my Jeep. Since the Jeep is also black it matched perfectly. Also if you look closely at my avitar you can see that I am a member of JP Frog Offroaders, www.jpfrog.org, dedicated to the mangling of sheetmetal and the snapping of axle shafts. My aspirations don't quite extend that far, but a few months ago, after the loan was paid and after a few years of neglect, the Cherokee got a much needed supension lift, tow hooks, and 31" tires. Not large by any means, but adequate for semi-serious excursions off the beaten path. The "normal" Jeep in my club rides on 35"-37" tires, and about half of them have axles swapped in from full-size trucks. A couple more own Wranlger Rubicons which come from the factory with Dana 44 axles, locking differentials (I'll get to that later) and a 4:1 transfer case. A week ago we went to the Wilstem Ranch between Paoli and Frenck Lick, Indiana. One guy even brought out his brand new 4-door Rubicon, with only 1,000 miles on the ticker.

Needless to say, while most of the rest of the group were climbing of two-and-a-half foot rock ledges, I was taking the bypass.

I took the girls along for the 'wheeling/camping trip, partly because I had taken the boys out earlier this year, a partly because of the tightwad factor (children under six are free, and Allison is 4).

A few times I had to make a second or third run up the trail to get through or unstuck, but my Jeep was no match for one partiular ravine. It had a couple large flat rocks, which when wet were a slick as ice. When I tried to drive across, I slid sideways further down the ravine. At the low end my right rear tire slid into hole filled with loose rock and sand. On the other corner, the tire was lifted about six inches off the ground, and hence no power at the front axle. Without any traction at either corner, forward and reverse travel came to a halt. After a few tries it was ovious that I would only succeed in digging a deeper hole under the right rear and out came the winch cable.

A "locker" http://en.wikipedia.org/wiki/Locking_differential would have made the difference, since I still had adequate traction at the other two wheels. 'Wheeling the Cherokee is an interim step, as I'm in the middle of a very long build up of a 1984 Jeep CJ-8 http://en.wikipedia.org/wiki/Jeep_CJ#CJ-8. The current plan is fiberglass body, 4" lift, 33" tires, front and rear lockers, 4.10:1 axle ratio, and a Ford truck T-18 transmission http://www.novak-adapt.com/knowledge/t18_t19.htm, which I have already rebuilt and adapted to the Jeep transfer case.

The Cherokee performed admirably, as well as the Scrambler in stock configuration on 31"s. Here are a few pictures of my "stuck." (Note the Klipsch license plate.)

The One Tank Trip

Andy W — Sun, 20 Jul 2008 13:20:00 GMT

I have always had pet peeve when travelling with the family, albeit a lighthearted one... it would save so much time if my wife's bladder were as big as the gas tank. But it's not just her, there are children involved too.

Some years ago we took a trip to Marco Island, Florida. We had a wonderful time. My wife had a thing, so she couldn't enjoy the long road trip with me and the boys, so she flew down the next day, holding the baby girl on her lap.

Travelling with the boys was a joy. We would pee, eat, and fill up the tank, then drive five hours, stop, pee, eat, and fill up the tank. Lather, rinse, repeat. If it weren't for the two hour traffic jam near the Georgia border we would have made it halfway through Florida before stopping for the night.

On the way home we didn't even make it out of Georgia before the girls had had enough, and we stopped for the night.

But now, even my bladder has been bested. You may remember that last year I bought a big Ford E-150 van. It replaced a Mazda MPV that got an "OK" 17mpg on the highway with the AC running. Well, yesterday we drove from Indianapolis to Lansing, Michigan and back for my family reunion.

I filled up at the local Marathon station and headed out. Last night I pulled into the same gas station, pulled up to the same pump, and once again filled the tank.

Here are the stats:

500.9 miles, 30.149 gallons, 70 mph with the AC on low, two gas stops (for the vehicles following us), one stop for Subway, and three rest area stops (including one for me).

I have a 35 gallon tank, so I could have gone another 80 miles. My wife gave me a dirty look for suggesting it though, as the gas needle was pointing straight at the red line.

The fraction gurus out there will see 5/3 and deduce that we got 16.6 miles to the gallon. Impressive for a big brick with a 5.4L V8.

Andy's tightwad Tips - #5

Andy W — Fri, 09 May 2008 21:02:00 GMT

Use it Up, Wear it Out, Make Do, or Do Without

An old mantra that could use a little dusting off. I was reminded of this tidbit after a conversation with a coworker today. I sometimes think about how different life was for our parents and grandparents. Money didn't grow on trees. Nowadays you can finance dinner and a movie for 30 years at 14.99%.

When my granparents moved into the nursing home their old wringer washer was still being used. I have no idea how old it was, but it was older than their house. These days our expectations of quality and reliability when it comes to certain consumer goods have really taken a nose dive. My mother still uses the pans she was given as a wedding gift. That was 49 years ago. I've been married almost 12 years and I'm on my third set.

Of course there are examples good quality... my 60GB Western Digital hard drive comes to mind. As of yesterday, it's now attached (by a USB cable) to it's third computer. Apparently people get miffed when their hard drive dies.

In less that a year, through no fault of its own, my TV will go dark... well OK, it'll go staticky. I've been married 12 years and I have yet to pay for a TV. (Yes my tightwadedness goes way back!) The current one is so old/cheap that it doesn't have even a composite video input. Just a F-connector for the antenna. To watch DVDs I had to get a modulator. It didn't have a remote when a friend of mine got rid of it, but I discovered that my VCR remote (same brand) would perform the major functions. The remote doesn't work anymore... or the kids lost it, I don't know which... but when you have 5 children there's always someone around to change the channel.

I don't know of anyone getting rid of a flat panel TV with a digital tuner, so when the last analog TV transmitter is turned off I will probably just do without for a time.

Andy's Tightwad Tips - #4

Andy W — Tue, 29 Apr 2008 21:33:00 GMT

Aldi

I shop for groceries at Aldi. Not all of them, and not every week. Buying crap usually costs more than buying quality in the long run, but with food, there's not much of a long run, so you just have to go on taste.

The things at Aldi that I like, in no particular order, and that are very good quality:

orange juice (much better than Minute Maid... really.), frozen juices, bread, milk, cheese, butter, tortillas, bottles juice (1/2 gal), breakfast cereal, pancake mix, chocolate chips, solid white tuna (as good as the name brands), peanut butter (better than most), chili packets, taco packets.

Our Aldi just started a meat cooler... so far so good.

The things that are good enough:

canned veggies, canned fruits, ketchup, mustard, salad dressing (think Miracle Whip), most of the canned soups, refried beans, chips (although all the varieties are too salty), pancake syrup (used to be in the very good catergory, but now is full of fillers), hot sauce, salt, flour, sugar, pickles, napkins, trash bags, and more that I just can't remember right now.

Things that didn't make the cut... there are a couple of the salad dressing flavors that I didn't enjoy.

My wife just called, she's picking me up after work, and we're headed to Aldi, and we're doing a summer stock up... probably to the tune of $200... and that's about 3 grocery carts full.

Andy's Tightwad Tips - #3

Andy W — Fri, 18 Apr 2008 13:23:00 GMT

Orange Juice

So you have a growing family and a can of frozen orange juice for breakfast. A quick glance on the side of the can reveals the mixing instructions: Add 3 cans of cold water. Stir.

For all you Kentuckians out there, you have to empty the contents of the can into a pitcher first, you won't be able to add 3 cans of water to an already full can. Same goes for Kool-Aid. Two quarts of water won't fit in that itty bitty packet.

Given my penchant for numbers and my kids penchant for fairness, reveals a disturbing problem.

The can of orange juice is 12 ounces. Adding three cans of cold water makes 48 ounces. A serving size is 8 ounces. There are only six servings of orange juice. Seven servings are needed.

Solution: add a fourth can of water. A little more quick math confirms that 60 ounces will fit in a half-gallon pitcher. The taste is hardly altered.

Bonus: 25% fewer calories per serving.

The other obvious solution is to use smaller cups. Yup, I do that too. And in following with my previous tightwad theme of reusing containers, from time to time Welch's grape jelly comes in fun kid-size character cups. I think the Pooh cups have all been broken, and we've got a some of Curious George cups and some Dragon Tails cups.

In my further quest for maximum tightwadedness, I noticed the frozen "grape juice drink" is only 20-30% juice... OK, what's the rest of it? Corn syrup. Then comparing prices and thinking about the orange juice lesson, I hit on an idea... if I buy 100% grape juice and thin it out, the kids will actually be getting more "juice" than if I buy the "drink." And thinned out with water, the cost is actually less than the "drink" mixed according to the instructions.

I've detemined that adding TWO extra cans of water makes only a noticeable difference in the flavor of the grape juice, but adds thee servings. It's now 66% juice, which is twice as much "juice" as the "drink".

Futher investigation shows the kids actually like the flavor of V8 Splash better when mixed half and half with water, and moves it toward the realm of affordability. Sunny Delight actually becomes a palatable drink when watered down in the same ratio.

And just for tuning in to my blog, here's a couple freebees: Do your ever find yourself chasing frozen chunks of orange juice around the pitcher trying to get it stirred? Try a potato masher. Also try this: a minute in the microwave on high with the top lid off. The metal on the bottom lid doesn't create any problems, but does get a little warm. Then add one can of water and stir (or mash) and then add the rest of the water. With less water it's easier to chase the chucks around. If you don't like the idea of the microwave, just use the potato masher before adding any water.

Andy's Tightwad Tips - #1 and #2

Andy W — Wed, 09 Apr 2008 18:24:00 GMT

So you'd like to be a tightwad, but you just don't know how to start...

I've been absent from the blog scene, having had very little time at work to think about blogging, but some comments in the lunch room have prompted a new blog series - Andy's Tightwad Tips!

Today you get a twofer...

Tightwad Tip #1 - Pack your lunch. This has multiple benefits, the most unexpected one was weight loss. I actually lost 15 pounds last year when I started packing my lunch. We had a very strict food budget last year (2007) and so paying $4-$8 a day for lunch was out of the question. The savings was immediate - about $100 a month or more, $1200 a year, it's like getting a Bush tax rebate, just not all at once.

The key to packing lunch is to take a serving of each item and put it in a food container as dinner is served. Viola! Lunch! But you say, "Yeah, but you have to pay for the food even if they're leftovers right?" Wrong. I stopped having second helpings at the dinner table, so lunch is essentially free. And the savings go futher than your wallet... if you're eating a healthy dinner you're saving the calories you would have eaten as a second helping... and you're saving the calories you would have eaten at the all-you-can-eat lunch buffet at Pizza Hut or the Biggie Fries and Frosty.

Tightwad Tip #2 - Reusable food containers. Amy and all my engineer pals like to see what I (or my wife, as the case may be) packed for lunch every day, but they get a real kick out of my containers.

"Is that a frosting cup?" Greg asked.

"Yup, check out the lid; it's the kind with the sprinkles!" I said.

Zip lock baggies cost money after all; three zip-locks a day, times 23 days in a month, comes to 69 zip lock baggies a month. And nothing ends up in the landfill. OK, sure, I do use some zip lock bags... but maybe only three a week

There are all sorts places to find great reusable containers... frosting, margarine, sour cream, cottage cheese, chip dip, deli meat, etc. Most of them do fine in the microwave, and have no problem in the diswasher.

And besides, if they get ruined, so what, it was trash anyway.

Hum and Buzz – Part V

Andy W — Mon, 21 Jan 2008 14:03:00 GMT

Balanced Connections.

In pro audio balanced connections are used almost exclusively, and with good reason. Using balanced connections is very effective in reducing and eliminating pickup and ground loops in the audio.

The most common balanced connections are in the form of XLR cables and ¼” TRS (tip-ring-sleeve) cables, and spade lugs are sometimes used.

Let’s take a look what a balanced connection is and at the physics behind why it works so well. (Balanced cables are used in other areas besides audio, so it applies equally to those situations too.).

A balanced connection will have two signal cables, an audio ground, and a shield. The shield in an XLR cable does not carry any audio information. The shield is connected at each end to the equipment or chassis ground (which is generally connected to the earth ground; many studios, especially ones in a building structure have a special grounding system, and other building codes to follow, but that is beyond our scope here).

The shield is effective against electric fields (and I won’t go very deep into any of these explanations, the physics involved can be found with Google), since the electric field inside the shield is zero (or approaches zero). The shield is made of a foil or braided wire or both.

Sometimes inexpensive cables will have a shield that is not braided, but only a layer of wire wrapped around the core. This can lead to an opening in the shield, especially at a bending point. The result is generally not severe for short runs, but on long runs, well, sometimes you get what you pay for, and at the very least you pay for the amount of copper in your cables.

Another thing to watch out for is a balanced cable with a drain wire running under a foil shield. The drain wire reduces the cable resistance somewhat, but since it will tend to be closer to one of the signal wires, it can cause an unbalanced pickup on the cable, which spoils the magic of the balanced cable.

So there, I said it… Sometimes there is a real, tangible, scientifically valid reason to choose one cable over another… Now back to the magic… er, physics of balanced cables.

The two signal cables are also twisted together. This is a common noise reduction technique called a “twisted pair.” Cables can pick up currents from outside electric and magnetic fields, and field strength is reduced as distance from the source is increased. If one wire is closer to the source than another wire, then the closer wire will be affected more. A twisted pair causes each wire to “take turns” as to which is closer to the source. In the end it tends to average out and both wires will pick up the same current/voltage. It is a physical fact that wires will pick up noise, and so we use this to our advantage as you will see…

The two signal cables in an XLR connection carry the same signal, but 180° out of phase. There are a few ways that the source equipment can do this but that is not important right now… what is important is what happens on the other end of the cable, at the receiving end. For simplicity, let’s say that the voltage one of the signal wires is 1Vrms and the other signal wire is -1Vrms (same magnitude, opposite direction, compared to the signal ground).

The equipment at the receiving end will have a differential amplifier (isolation transformers work too). For simplicity let’s say that it is a unity gain differential amplifier. That means it multiplies the difference of the incoming signal by one. So, (1Vrms - (-1Vrms)) * 1 = 2Vrms.

Now any interference that gets injected into the signal wires, as we saw a few paragraphs back, will be the same on both wires, both in magnitude and direction. Engineers have a fancy term for this. We call it “common mode” noise. Let’s say that each wire picked up 1Vrms of random noise on it way. Now watch what happens when we put it into our differential amplifier. (1Vrms – 1Vrms)*1 = 0V. The noise is gone!

Now if we mix signal and noise on the same cable let’s see what happens. ((1Vsignal + 1Vnoise) – (-1Vsignal + 1Vnoise)) * 1= 2Vsignal. In the real world the difference may not be exactly zero but a noise reduction of 40-60dB is not uncommon, so if the noise floor was halfway decent to begin with in the unbalanced case, the pickup with a balanced system will be vanishingly low.

Side note: instead of getting 1Vrms from an unbalanced signal, there is a 2Vrms signal at the receiving end, an apparent 6dB “gain” without the noise penalty. Some equipment employs this method some does not.

The other part of the magic of an XLR connection is this… separate signal ground and cable shield. Any currents due to pickup or ground loops are routed harmlessly in the shield, and stay out of the audio signal ground! Not so in a balanced ¼” TRS.

Now look at the ground loop HACDBJ in this sketch with a balanced XLR connection. Any currents that are picked up in the loop have no part at all in the audio signal. And any noise injected into the twisted pair cable is cancelled at the differential amplifier in DUT 2. Additionally, if (or when, as is generally the case) the amplifier stages in DUT 1 have power supply noise injected (as in an op amp… assuming that the two amplifiers are part of the same package and injected equally) there’s a good chance that it will be common mode as well, or nearly common mode, and therefore rejected at DUT 2 (at least to the level of CMRR at the receiving end).

What is CMRR? It is the Common Mode Rejection Ratio, expressed in dB, and for a good audio quality op amp can be 100dB, which is probably better than the cable, and that’s the point. How much rejection do you need? Well that depends on how much noise is picked by the cable. In a professional installation when you’re running hundreds of feet of mic cable or line level signals, you need all you can get.

Hum and Buzz – Part IV

Andy W — Fri, 14 Dec 2007 19:28:00 GMT

Antenna/Cable TV Ground loops.

OK so you’ve narrowed your ground loop issue down to your cable connection or your rooftop antenna. You’re not alone; this is one of the more common ground loop issues, but I don’t necessarily want to want to get into the gory details, so here are a few links.

http://www.epanorama.net/documents/groundloop/antenna_isolator_building.html

http://ecmweb.com/nec/electric_article_radio_television/

http://www.hdtvprimer.com/ANTENNAS/basics.html

Look in this link above and scroll down to the “Grounding Outdoor Antennas” section and you can see why it’s so easy to have a ground loop here.

Ground isolation is really one of the only answers here due to the grounding requirements of aerial antennas and cable systems. Isolation transformers or capacitors are commonly used. Both types will break the ground loop and provide isolation.

Breaking the ground loop can either be done on the coax side of the TV tuner/cable box or on the audio side between TV tuner/cable box and the audio preamp/receiver. When breaking the loop between the TV tuner/Cable box and the audio preamplifier, a wideband audio transformer for the line level signal is probably my best recommendation.

BEWARE… many of the inexpensive audio isolation transformers are based on telephone transformers and don’t have the bandwidth required for hi-fi audio. Perhaps this made little difference in the past, but many shows are now broadcast with much better audio quality than before. Read the specs… if the audio bandwidth is not specified keep looking.

Also keep in mind that the ground loop can be connected to your system on the video cables if your receiver is doing the video switching. In addition, DC level is important in video signals so whatever you do may have an impact on video quality as well.

Ground loops on the video side of things can also cause “hum bars” to appear on your video screen (horizontal stripes that move slowly across the screen).

New cable standards, including HDTV and digital cable, along with widespread use of cable modems for high speed internet access have placed serious constraints on the use of ground isolation equipment if you choose to isolate your ground on the coax side of the cable box. So again if this affects you, read the specs and make sure the unit you are purchasing will not prevent you from using your cable or internet access the way you plan to.

My best recommendation, if your equipment has it, is to use the optical audio output on your cable box or HDTV receiver to connect to your audio equipment. Maybe our readers will have some more recommendations.

Other than this I can’t make a specific recommendation since I don’t have cable… you know, that whole tightwad thing… J

Fun with Anagrams

Andy W — Tue, 11 Dec 2007 16:36:00 GMT

AKA how to tick off Melissa after she puts out her Christmas decorations.

I suppose Amy will want an update every day (yes, I have a big long list), but I don't have that kind of time.

BTW, one of the Anagrams for Amy Unger is Angry Emu. LoLz

Hum and Buzz – Part III

Andy W — Fri, 30 Nov 2007 22:17:00 GMT

Ground Loops 101

Let’s start our discussion of ground loops with two pieces of chassis grounded equipment. Class II equipment can exhibit hum and buzz too, but the mechanism is a little different, but we’ll talk about that in another installment. We’ll also start with an “unbalanced” signal connection since it is more prevalent in commercial equipment (RCA-type connections and stereo mini-plug connections are examples of unbalance signal connections).

In the first example below a ground loop is created when the two pieces of equipment are plugged in and connected. DUT 1 might be a CD player and DUT 2 might be a Receiver. The signal from DUT 1 is passed through a signal cable to DUT 2. The “signal ground” connection is made between points “C” and “D”. Generally points “C” and “D” are also connected to the metal chassis. The “chassis ground” connection is made where the “earth ground” wire attached to the chassis. This happens at points “A” and “B”. The bare wire connection at points “H” and “J” on the AC outlets are earth grounded by the wire running back to the breaker panel.

The ground loop is formed, starting at point “H” to “A” to “C” to “D” to “B” to “J” and back to “H”. For simplicity we’ll just say “HACDBJ”. Any magnetic flux that passes through the loop will cause an electric current to flow in the loop. Any time current flows in a wire there will be a voltage impressed on that wire. Any voltage on the signal ground connection “CD” will become part of the audio signal and will be amplified. By virtue of the fact that your whole house is wired with AC wiring with currents flowing every which way, the ground loop will be bathed in magnetic flux. (Cable shielding is only effective for electric fields.)

Also any current on the earth ground between points “H” and “J”, regardless of where it comes from (like a light dimmer on the same circuit) will create a voltage in proportion to the current on “HJ”. Since the connection “HACDBJ” is in parallel with “HJ” part of the current will flow in “HACDBJ” and part of the current will flow in “HJ”. In electronics terms a parallel path is known as a “current divider”. The current flowing in “CD” will have an associated voltage, and this will be added to the signal from DUT 1.

The second example above is essentially the same as the first. The difference is that the two pieces of audio equipment are powered by two different circuits on the breaker panel. DUT 3 sends a signal to DUT 4 along an unbalanced cable with a signal ground “CD”. The chassis are grounded at “A” and “B” and the outlets are grounded at “H” and “J” just like before. The big difference here is that now the ground loop goes all the way back to the breaker panel. The loop is now a very large loop and can have even greater potential to pick up hum from magnetic fields. Also, now you have ground and neutral currents on the neutral bus bar coming into play. Ground current and neutral current from all the other circuits in the house can now put voltage on your signal ground “CD”.

So what can be done?

1. Make a block drawing of the components in your system, showing the signal connections (a single connection is fine for stereo connections) and the power cables. Also show in your sketch which power cables have an earth ground. Identify the house circuits that you are using, and show any other equipment that is sharing the same circuit (light dimmers, motors – like appliances, things with switch mode power supplies – computers and such, and things that might draw a lot of current or be injecting noise on the ground).

2. Study the diagram to see where your trouble might be coming from. Then try some trouble shooting and make notes of what happens. Only make one change at a time; do and undo the change so that you can have an A/B comparison.

3. Make loops smaller. Smaller loops have less magnetic flux inside them. Try running the AC cables right next to each other; use twist ties to hold them together temporarily. Shorten signal cables and twist tie them up.

4. Does your AC cable or signal cable hang in a “half turn” around a power transformer. (If this needs a sketch please let me know.) The cable will become part of the transformer. If your equipment cables hang in loops; tie them up. Reroute cables to eliminate or shorten loops.

5. Move or reroute cables away from cables that carry large currents or are known to have currents with high harmonic distortion (almost every appliance/piece of equipment that is not resistive will have varying levels of high harmonics on the AC power line/cord). Distance is your friend in these cases. Try a different cable orientation or a stack your components in a different order. The sensitive part of a PCB in one component may be right on top of a noisy transformer or rectifier in another. Maybe it sounds crazy but a sheet of steel between components can help, and in extreme cases it may be necessary to wrap a steel sheet around the offending transformer (a magnetic “short” circuit). I have measured hum reduction on the order of 25-30dB by doing this. But it’s better and easier just to move the noisy transformer away from the sensitive equipment.

6. Reduce the ground voltage between components. Plug all your components into the same AC outlet. Use a power strip if you have to. If there is a noisy light dimmer on the same circuit and you plug the system into a single outlet you can reduce the ground voltage difference (the voltage on “HJ”) to zero or nearly zero. Make sure your power strip is rated for 15-20 Amps.

7. Plug the offending equipment into a different circuit outlet, so that the noisy ground will not be on the same line as your audio equipment. Or if there is a permanent fixture/appliance (e.g. a ceiling light on a dimmer), plug your audio equipment into a different circuit.

8. If you are building a house, it can’t hurt to run a dedicated AC line to your equipment. This will generally cost $200-$300. If you can talk them into it, run a 20A circuit with 12AWG with a corresponding breaker and outlet instead of a 15A circuit. Keep the run as short as possible and don’t run it parallel with any other runs. And for a truly esoteric touch (I’m not claiming this will help, but it might) run the line in flexible steel conduit. If you are in an existing construction, it is not impossible to run a dedicated line, and sometimes there are creative solutions to getting an AC line where you want it, using an existing line that is more noise free.

9. Transformer coupling. Sometimes there is no other way… perhaps that can be its own installment.

10. The “pin 1 problem” (this is in reference to pro or “prosumer” products using balanced connections). This may require internal modifications... the manufacturer may already know about if if they have a product with this issue... but that's for balanced connections, and that's another discussion for another time.

Hum and Buzz - Part II

Andy W — Fri, 16 Nov 2007 18:57:00 GMT

Electrical equipment is grounded for safety reasons. Grounding can also help prevent RF interference

First… let’s get some agreement on nomenclature… since I’m writing, I get to pick. [:neener:] There are many different ways to refer to “ground” and much depends on the context. As with everything else we measure, we need a reference point, and in electronics we call the reference point either “common” or “ground.”

A) Earth Ground: this refers to the fact that your house wiring is grounded by the Earth (the planet we live on) and we use and we use the terms “earth” and “ground” interchangeably. Your house wiring is grounded by attaching a large gauge wire from the Neutral wire at your breaker panel to a buried water pipe or a long stake driven into the ground. If your house were not grounded the voltage on the neutral conductor of your house could be very high compared to the piece of ground you are standing on. Fortunately with transformers, the primary side of the transformer doesn’t necessarily care what “ground” is on the secondary side.

As shown in last weeks sketch, the neutral coming into your house is earth grounded, this “earth” is distributed around your house along with the “line” and “neutral” to the outlets around your house.

“So if the neutral is grounded at the breaker panel, why do I need another ground wire?” you ask. A very good question indeed.

Let’s take the chandelier above your dining room table. You have three wires that come to that round hole in your ceiling: L, N, and E (Line, Neutral, and Earth). In the US the Line is BLACK, the Neutral is WHITE and the Earth Ground is bare wire. Now you attach those three wires to corresponding wires in the chandelier. There is a two wire cable that passes through a metal tube or decorative chain that goes to the light bulbs. The ground wire is connected to the metal parts or can pass through the tube or chain of the fixture. (In the sketch I showed the Line and Neutral running along side the chain for clarity.)

Now let’s say the person that connected the light decided not to attach the ground wire, everything works and nobody knows any different. Now imagine that after time the insulator on the LINE connection wears through or has a small cut and is now in contact with the metal parts of the chandelier. If only the LINE connection is cut, then the light will still work, but the metal parts of the light are now “hot” (energized). Now if you touch the light fixture you can get zapped.

If the ground wire had been connected correctly, and the insulation on the LINE connection failed, the current would go through the ground wire back to the breaker panel and the circuit breaker would simply open, removing the voltage from that circuit, and no one would be shocked.

B) Chassis Ground: chassis ground plays the same role as the ground wire in the chandelier in the above example. A grounded chassis will have the Earth wire entering the chassis and then securely attached to the metal of the chassis. In case of insulation failure or component failure inside the chassis, the voltage on the chassis will not change; it will remain firmly “grounded.” If insulation failure occurs inside the chassis, the fault current will be routed to earth ground, and either a fuse or circuit breaker inside the chassis will open, or in extreme cases, the breaker at the house panel will open, eliminating the risk of electric shock.

WARNING: If you are thinking about using a “cheater” plug on your audio equipment to eliminate a ground loop, re-read the above paragraph, and then don’t do it, or fault current could be routed through YOU.

The chassis ground wire according to UL, CSA, and EU standards must be able to carry the full fault current without fusing (melting the wire). This is required since if the chassis ground wire fuses before the internal fuse or panel breaker opens, the chassis will remain “hot” and you can still be shocked.

Electrical equipment that does not utilize a three-prong AC cord does not have an earth grounded chassis. In this case UL, CSA, and EU standards require that hazardous live voltages must have double or reinforced insulation (two layers of adequate insulation). This is also referred to as Class II insulation. Transformers of Class II products also have to meet the insulation requirements. Parts that are not insulated must meet specific “creepage and clearance” requirements (which is to say there must be adequate space between conductive parts and hazardous live voltages – the air is the insulation).

Some equipment will also have a polarized (wide blade) AC plug. This ensures that the fuse or switch inside the equipment is always on the “hot” side of the AC line. If you defeat the polarized plug by replacing it or cutting it, it is possible to flip the plug over and you are putting the fuse on the neutral. Now if you have an insulation failure the chassis could still be “hot” even if the fuse blows!

WARNING: If you can’t plug in a polarized AC plug, get an electrician to change your obsolete AC outlet. Defeating the polarized plug can be very dangerous.

C) Signal Ground: This is the reference voltage for the audio (or video) signal in your system. Each component in your audio rack will have a signal ground. The signal ground connection must be “clean,” in other words, any voltage on this ground will be treated just like any other voltage on the signal line; it will be amplified and become part of the sound coming out of your speakers, or if in the video, can cause a noisy picture. Sometimes this is called “common” as in a “common emitter” amplifier.

D) Digital Ground: This is the ground reference for digital signals. As with analog signals, poor ground on digital signals will have an equally degrading effect. One common problem is “ground bounce” this occurs when there is noise on the digital ground and the digital circuit misbehaves because the voltage of the digital bits is no longer valid. Ground bounce can also cause many digital circuits to reset without explanation, as it would if there were a power loss or a “brownout” (a partial loss of voltage).

E) Power ground: The power supply in your audio equipment needs a return path too. We call this the “power ground,” and sometimes this is also called “common.” Electrical current needed to power the circuit components returns to the power source on the power ground.

Next Week: Ground Loops 101

Hum and Buzz – Part I

Andy W — Fri, 09 Nov 2007 21:12:00 GMT

It is a fact of life. Ground current happens. And where it flows makes all the difference.

In a perfect world there would be no ground current on the AC power line. AC would enter on the LINE, and return on the NEUTRAL, and the earth ground would just sit there. In the real world there is inductive and capacitive coupling that creates ground current. Ground current can also be created by various electrical and electronic equipment, or it can be created by the pick up RF energy, especially when the ground forms loops (loops can increase the amount of RF energy that is picked up).

Before we get too deep into ground current let’s take a look at how a typical house is wired.

Power comes from an electric substation to the pole outside your house. The distribution voltage is approximately 13kV, but higher voltages are used. The power then goes to a transformer which takes the high voltage AC and steps it down to 120V for your house. Usually a few neighbors share a transformer. The center tapped secondary of the transformer gives you two “hot” wires, each with 120V, and a neutral wire. The voltage between the two “hot” wires is 240V which is the sum of 120V+120V, which are 180° out of phase. Even though there are two “hot” leads entering your house, and they are 180° out of phase, technically this is still a single phase system.

SIDEBAR: 13,000 Volts eh? Yes, so don’t be tempted to touch it, not even with a 10 foot pole. The moisture in a wooden broom handle will conduct enough current to light a 100W light bulb (meaning it could kill you). Linesmen use fiberglass poles.

Victims of electrocution at this level will have a burn where they contacted the power line and their feet are blown off (or whatever part of their body was touching the ground at the time). Not cool.

Really super cool: These are linesmen working on LIVE high tension wires (100kV-500kV). Yes those are electrically conductive suits. Talk about a “bird on a wire!” http://www.chopperworx.co.za/powerline.html A helicopter drops them off and picks them up. http://infao5501.ag5.mpi-sb.mpg.de:8080/topx/archive?link=Wikipedia-Lip6-2/1536956.xml&style#3 for more info on live line work.

OK, back to the blog… In your house the power goes to your breaker panel and to the “main breaker” (the main breaker is omitted in my sketch for clarity). The main breaker feeds the bus bars. Opening the main breaker disconnects the electricity to the entire house. Each bus bar carries one of the two “phases,” and where you install the individual circuit breakers determines which “phase” you get. Installing a 240V breaker connects to both “phases” (the breaker is a “double” wide). These circuits are used for HVAC, dryer, and range. There is also a neutral bus bar. The house earth ground is attached here also. (Notice the earth ground symbol is a capital “E” turned on its side) If you cut open an AC wire you will see three wires as shown. All of the neutral wires (WHITE insulation) from all of the house circuits are attached to the neutral bus bar, as are all of the circuit ground wires (BARE copper wire, can also be GREEN for 240V). The “hot” wires (BLACK for 120V, BLACK and RED for 240V) from each circuit are connected to the circuit breaker.

Did you notice in the diagram how both the “N” and the “G” go back to the same bus bar in the breaker panel? The electric current could care less whether it gets back to the bus bar on the “N” wire or the “G” wire. The insulation prevents the current from flowing on the “G” wire… of course it’s this ground current that we’ll focus on here.

More next week…

AES 2007 – DSP-Based RIAA Filters (Attn: Vinyl Fans) - Part II

Andy W — Fri, 02 Nov 2007 22:24:00 GMT

For those of you waiting with bated breath (LOL), here is part II, finally…

The author presents an argument that if instead of normalization after truncation (see part I of this blog for an example of truncation), the digital samples are processed by a digitally implemented inverse-RIAA filter, and then carefully matching the gain, the residual error is greatly reduced. In fact, he claims that the magnitude of error is only on the order a few LSBs out of 24 bits, and he claims that this proves to be over four bits less than expected 6 or 7 bit loss.

I have no way of knowing what filtering or algorithm is applied in DSP so I can’t comment on his findings, however today’s floating point DSPs have incredible amounts of processing power, and the accuracy of the computations involved in not in question.

The other argument presented was based on the review of perhaps thousands of available vinyl recording, his own and others. He selected around 40 recordings that were singled out based on the amount of high frequency content. His theory is that if a recording has a high level of high frequency or treble content, the resolution of the bass frequencies would be the most impaired.

This stems from the fact that when doing a digital recording (or an analog to digital conversion), you will eventually run out of headroom, and any transient that exceeds 0dBFS (full-scale) will be clipped.

When doing an inverse-RIAA filter digitally it is imperative that the maximum level on the recording is known, otherwise you will either 1) clip the signal on the peaks if the level is too high or, 2) underutilize the available resolution if the level is too low.

By sampling these specially chosen recordings, and using peak responding, peak-hold audio analyzer software, he discovered that the peaks were lower that what would be expected based on the RIAA curve alone (which would imply that you would have several of resolution for free).

That is not strictly the case however, since the analog gain level must be set based on the peak value of the coherently summed signal of bass, mids, and treble, not just the peak value at discreet frequencies across the spectrum. But remembering that the mids and especially the bass are de-emphasized, and by analysis of the program peak level on the selected recodings, validated the use of the peak responding, peak-hold analysis, and that with LP recordings this is unlikely to exceed 1 bit (6dB).

His argument continues that RIAA equalization in the analog domain followed by digital conversion would be a reduction in fidelity since 1) the program peak level would now be defined by the recording’s bass level, 2) there would now be less resolution available for the treble, so the treble will be truncated instead of the bass, 3) humans have better hearing in the treble range, 4) treble doesn’t benefit from the reconstruction effects of the filter.

So there you go… If there are errors in getting his point across they are probably mine.

The Last Yogurt

Andy W — Mon, 22 Oct 2007 16:30:00 GMT

Forgive me for my choice of title. This has really nothing to do with yogurt, but more about the connections that people make in this crazy world of ours.

My wife e-mailed me a tragic news story shortly after I arrived to work this morning.

http://www.wthr.com/Global/story.asp?S=7244095

For the past year my wife has been getting non-homogonized milk from an Amish farmer. My wife has met him, and as he has had some health problems recently, she has been quite concerned. I'm not much of a milk drinker, but the non-homogenized milk is easier on my kids stomachs, even my baby boy drinks it without any problems. All of my kids prior to this had been fed soy or rice milk until they got old enough to where the cow's milk didn't bother them anymore (bright red butts and a diarrhea). Not the best thing, since there is little or no fat in soy and rice milk.

One day the delivery man who brings the veggies and milk from the Amish farmers out in Rockville, Indiana said he brought some plain yogurt for us to try (several local families meet once a week to pick up the delivery), and since I like yogurt very much, and since I haven't been happy with store-bought yogurt for many years now my wife brought it home. Well we've been getting it ever since. He milks the cows, he makes the yogurt.

As you've probably already surmised, Melvin Fisher is the dairy farmer who was killed in yesterday's crash.

I just sat down to lunch, and opened the lunch box my wife packed for me this morning. And I just ate the last yogurt.

If you would, please say a prayer for a little girl who was air lifted to Riley Children's Hospital, who will be missing her parents and three brothers very much.