|Max dB with Doug Blackburn
Back Issue Article
How Stuff Works
Knowing how something works isnt everything, but it can remove some of the mystery. Lets see whats going on inside your audio components.
To amplify an audio signal.... Simple? You may find its not what you thought!
We all know generally what audio components are doing -- or do we? How about an amplifier? It receives a line-level signal from the preamp and makes the preamps signal a lot bigger, so that it can drive loudspeakers, right? Seems simple enough. But that is not what an amplifier actually does. An amplifier makes a brand-new audio signal. It does not make the preamp signal "bigger." In fact, inside the amplifier, the signal from the preamplifier is used as a template for the new larger signal and then discarded, dissipated as heat through resistance and/or sent to ground. The raw material for the brand-new big signal leaving the amplifier is the AC power from your wall. Let me say this again in slightly different words: The amplifier creates a giant clone of the original preamp signal and the original preamp signal disappears forever after it is cloned. Hmmm, is this splitting hairs or something important to understand? Well, it helps put things in perspective. Youve probably received a document that was a copy of a copy of a copy, so you know that you lose a little bit of quality every time you make a copy of something. The same thing happens inside your audio system.
"What about the preamp?" Same deal. If you have an active preamp, it throws away the original source signal after using it as a template to make a bigger version of the source signal. And again, the power coming from your wall is the raw material for the new preamp signal that is created.
"The CD player?" Now you are at a source component. The AC power from the wall is converted to laser light to read the CD, another bit of electricity from your wall becomes a digital signal, and a final bit of AC becomes the analog audio signal that goes to the preamp.
"How about a phono cartridge?" This one is a little different. A phono cartridge is the only source component that creates the audio signal from scratch (wink-wink, nudge-nudge). Just get that LP rotating and the phono cartridge will make an audio signal without outside power.
"Oh my God. That means that before I hear music, the signal has been created and cloned at least twice and probably three or four times if Im playing CDs!" Well its even worse than that actually. You see, each gain stage in any component does the same thing -- uses a smaller signal as a model for a new, larger one. Your CD player might create and discard an audio signal two times internally before shipping it off to the preamp. Preamps usually have one to three gain stages, so there are that many more birth/clone/death cycles in the preamp. Amplifiers also have gain stages, at least two, perhaps three or four of them, so there are even more birth/clone/death cycles.
Think of these gain stages as steps in a staircase. Trying to get from the ground floor to the 2nd floor with only one big step is a real problem, so we add steps (gain stages) to go up (amplify) a manageable bit at a time. Each time you put an audio signal through a gain stage, a little something is lost. So one path to better sound is to minimize the number of gain stages in the path from the CD or LP to the sound waves emanating from the speakers. Of course there are practical limits and eternal arguments about whether an amplifier can be made to sound better with two or three or four gain stages. Today theres no universal answer to the question about the number of gain stages. Sure, fewer gain stages are theoretically better, but it is harder to build good-sounding gain stages with huge amounts of gain. Designers and manufacturers argue for their way as being the best when in reality there may be several different "best ways" depending on the total circuit design.
I talked about power several times already. The raw material to create the signal that comes from your CD player, from your preamp, and from your amp comes from your wall outlet. From the wall outlet, it goes to the transformer in the component, through a bridge rectifier that converts AC to DC, is filtered with capacitors, then regulated (usually). Those are the components in the power supply in each component in your system. Power supplies are very important indeed, much more important than they are given credit for. Its a fact of life -- equipment being designed and built to a price point wont have the best possible power-supply components. Even in terms of high-end components, the lower-cost equipment will have simpler, lower-cost, lower-performance power supplies, but they are still leagues better than the power supplies in non-high-end brands. One of the reasons people can make money selling modification kits or installing modifications of cost-effective components is because there is almost always room to improve on the performance of the power supply in a cost-constrained piece of equipment.
Now lets jump one step further back in the sound chain, to the AC power at your wall outlet. By now you ought to have some new appreciation for just how critical the power you provide to your components really is. Feeding the components clean, unlimited power gives better sound -- period. Lower-cost components are going to sound significantly better with appropriate power conditioning. Even if you have fairly expensive components, anything you do to improve the quality of power is going to be audible. I guess I dont have to tell you that I consider power-line conditioning a requirement for a high-end system, not just something that would be nice to have some time in the future.
What goes into a power conditioner? Well, there are only a handful of different items to choose from. Inductors, isolation transformers, capacitors, surge-suppression devices, lightning arrestors, ferrites, wire, electrical outlets, chokes -- thats about it. No matter what kind of fancy name or fancy price gets put on the box, it has some combination of the above inside. All the formulas and configurations for power filtering are available in electronic reference books written 50 or more years ago. You dont see much of anything new in power filtering/conditioning after what was known in the 1940s.
The Bybee filters, however, are an exception. They are new to high-end power conditioning because theyre based on de-classified military technology, which implies that the original knowledge is probably 30 years old or more. These filters operate at the quantum mechanical level. This means they act on individual electrons, shunting "bad electrons" (presumably those physically misshapen with a charge that is either too high or too low) out of the AC line. Tunneling electron microscopes have given us the ability to learn that all electrons are not identical. From this information, it was learned that those electrons outside the ideal parameters cause noise and distortion in electronic circuits, which limits the resolution of sensitive equipment like military SONAR. Eliminate the non-ideal electrons from the power supplied to sensitive equipment and you improve the resolution capabilities. But the Bybee filters are about the only "new" idea in filtering/conditioning for high-end audio systems that have come along in a long, long time. Note that there is no guarantee that Bybee filters will work better in your system than conventional filters or conditioners. They are one more tool in the arsenal, not the proverbial silver bullet -- they dont remove other kinds of noise and distortion that older filter designs will.
"Does that mean all those $300, $500, $700, $1,500 and higher-priced power-line conditioners arent worth what is being charged for them?" Not at all. Some of the internal components can be pricey. It takes some care and attention to select the right kinds of filters. Tuning the filters for the correct response is not trivial. Packaging and combining the filtering devices takes time. Then theres selecting the correct wire and routing it. The materials used to hold things in place inside the box and selecting the best-sounding electrical outlets are more details that have to be right. All of those things and more have to be considered when designing a power-line conditioner for the high-end-audio market. You usually get what you pay for in a high-end power-line conditioner. But because there are so many possible combinations of materials and choices for values of capacitors and inductors and sizes of isolation transformers, PLCs all perform differently when you move them around from system to system. I am beginning to think that if you listened to a particular power conditioner in 100 different systems, 50% of the time it would sound about the same, 25% of the time it would sound a lot worse -- perhaps even worse than no power conditioner -- and 25% of the time it would sound even better than its "normal" sound. All these "changes" in sound come from how that particular PLC interacts with the power in the home and the components in the system.
You know about voltage, but do you know about current?
Even today on the few occasions when learned audio publications write about the workings of high-end audio components, they leave people with misconceptions about what is going on. Lets say, for example, that the Armageddon 300 amplifier draws 12 amps at its full rated power. You probably envision the current as being delivered at a steady 12 amps with no variations -- a flat line that drops to a lower level when output power demands are reduced (unless the amp is class A, in which case the current is high all the time). This is actually quite incorrect. Current actually cannot flow to the amplifier for substantial periods of time during each AC cycle (AC voltage changes from positive to negative 60 times every second; one cycle is 1/60th of a second or .0167 seconds or 16.7 milliseconds). When current can flow to the amp, it does so with a vengeance. One reference book shows the replenishment time as 3.3 milliseconds for each half of the AC cycle. This means that the "+" power supply has 3.3 milliseconds every 16.7 milliseconds to recharge completely. Ditto for the "-" power supply. It also means that for 10.1 milliseconds out of every 16.7 milliseconds, no current flows.
The 12-amps-at-full-rated-output figure is an averaged current measurement. If you look at current with an instantaneous-measurement device like an oscilloscope with a current probe, you see the truth: distinct periods where current flow is zero followed by very steep spikes which go around three times higher than the average current. Your nice, easy-sounding 12 amps is made up of 35+-amp peaks between valleys of zero current. This is one of the reasons using 20-amp or even 30-amp electrical circuits in your home can improve the sound of a high-end audio system. The higher ratings require higher-rated breakers in the distribution panel and larger wire from the distribution panel to the outlet. All of this makes it easier for those very high instantaneous current peaks to be supplied to the amplifier with absolutely no limiting of any kind.
Current spikes are what cause some power conditioners to make power amplifiers sound emasculated. Some power conditioners just cant pass the huge current spikes without limiting them. This is most likely to happen if you use a cheap power strip to get more electrical outlets to plug your stuff into. However, inductors and isolation transformers will limit current peaks to high-current amplifiers unless the inductors and isolation transformers are physically very large -- and they get very expensive when they get big. Remember, the possibility of current limiting applies mostly to amplifiers. Inductors and isolation transformers in power conditioners can be very effective for smaller components which have far lower current demands.
Thats it for this month. If theres something along these lines youd like to see in a future column, let me know.
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