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Amplifier Classes & Hand-Wiring

One man's journey through the technical details of amplifier design and construction.
Editor's Note: This article is adapted from a detailed explanation of ampifier classes and wiring, originally posted in FretBuzz

I work with a lot of engineers, and a number of these guys are audiophiles, meaning they are hard core audio (stereo) dudes. (Bose is a four letter word to these guys, and if you've ever heard one of their systems, you would know why).

I had them explain it to me, and here is my non-engineering explaination of what they said. It is a little long, but you ought to see what they drew on the board, so this is as far down as I could condense it, given my limited technical knowledge.

Despite my initial impressions that Class A refered to the level of quality (like Grade A), it refers instead to the type of circuit design. There are actually various classes of design from A through D, and even a few others, if I understand correctly.

"what is interesting here is that the Class C is actually, in pure terms, a better device."
Class A refers to a type of circuitry where a single tube or transistor can handle the full voltage range of a sine wave. In other words, if the total voltage "drop" from 0 to the peak of the wave is 15 on the plus side and minus 15 on the negative side, it can handle the entire voltage range (absolute value of 30) by itself.

In a Class C unit, which is the other most common type, the amp will have a series of transistors or tubes of lesser value (say, two of them) that will be wired in series which the signal passes. Therefore, using our 15 volt example, you would have 8 2-volt transistors on the negative side, then a lead to ground, and 8 2-volt transistors on the positive side.

OK, now what all this stuff means in the world outside the circuit is this:

The Class A unit passes the signal through fewer devices or gates. Therefore, the original tonal quality of the signal remains truer to the origin than in a Class C device, where the signal is passed through numerous gates.

Net result: The amplified signal is closer to what you play on your guitar in a Class A unit than a Class C.

Now what is interesting here is that the Class C is actually, in pure terms, a better device. It is more powerful, as more transistors or tubes equates to more power. It also has more punch, especially in the bass end. Now before you jump in and shout about the great bass end in that Mesa/Boogie you own, keep in mind that the bass end on the guitar (60-80 Hertz or cycles/sec, I am estimating) is significantly higher than the bass end of human hearing (20 Hz). So, since these guys focus on the ability of an amp and speakers to manage this extremely low frequency, which Class A just can't do, we as guitarists still get a very nice bass end in our range with a Class A.

In short, the Class C is a far more efficient and powerful device than a Class A. One of my audiophile engineer friends went so far as to say that he wouldn't own a Class A device for his stereo. However, he also once worked at Mesilla Valley Music Center in Las Cruces, NM, while he was going the New Mexico State University (BSCS). He used to set up sound for concerts, and repaired amps. He has a real respect for the folks at Mesa/Boogie, and the products they build, even though they are Class A devices.

About Handwiring
When you opt for solid state versus tubes, what you are mainly see are IC (Integrated Circuit) Boards. IC Boards have a unique problem known as cross-talk. Cross-talk is a type of electronic noise in which the signal from one circuit is bleeding over into an adjacent circuit. Look at some IC Boards and note how close the solder runs are on the circuits.

Therein lies the problem.

What handwiring does is allow for separation of the wires (assuming it's performed correctly) from each other. Another good thing about wiring is that it will run a wire over a shorter distance, and if there is a parallel wire nearby, a good manufacturer will run a 90 degree turn in an elbow, not a sharp right angle, and cross the one wire over the other. This removes the possiblility of crosstalk, since crosstalk depends on long, parallel runs. But as both my audiophile friends pointed out, wiring is the least of your problems if the components and design are mediocre or even poor. A million dollar studio is really junk if you are passing the signals through 75 cent resistors, cheap capacitors, or crummy transistors (which they do, by the way).

I asked my friend if handwiring meant that someone took the time to give the circuit their individual and custom attention, resulting in a superior product. He said, "yes, however...". If you program robotics correctly, you could get a quality product. It's analagous to how luthiers today are using CNC to perform the repetitive tasks that require precise cutting, and that are virtually impossible for a human to replicate. Of course, in the end, all the precision manufacturered stuff has to be assembled, and that is where a human touch can make the final difference.

Although I am not sure exactly what point to point wiring is, I bet it deals with short runs from one specific point to another, and not some roundabout, cost-cutting solution.

One other thing to keep in mind - soldering is critical. I learned from my father-in-law (another retired GE engineer) that a good solder connection is always shiny. If solder is not applied properly (and it takes skill and experience to learn how to do this correctly), you will end up with what is a known as a cold solder. You can spot these, either by coming over to my place and seeing what a terrible job of soldering I do, or easier still, look for soldered connection that are hazy or dull-looking. This occurs when the solder is not properly heated and/or the surface is not properly prepared. The net result is the connection does not allow the unhindered flow of current, resulting in resistance to current low at the point of the solder connection. This is similar to when your garden hose gets a kink in it. Current is still getting through, but it is less than the total signal (read as "tone is weak").

So there you have it. Straight from the engineers' den to technical detail.

If you don't have a friend that is a hardcore audiophile, get to know one. They will open you mind up to the world of sound, not just music. My one friend took me up to Santa Fe to the home office of Audiophile Magazine (which doesn't accept advertising. Note that my friend is always complaining that guitar magazines are compromised in their product reviews because they depend on advertising money from the same people that produce the products they review: spelled conflict of interest). Anyway, it was amazing!!! The recordings that really flip these guys' switches tend to be live to two-track, no mixers, processors, etc. (Listen to Sheffield Labs recordings if you can get one, on a good system). And I'll tell you, when you hear most recordings today on one of these systems, it will make you cry. It is bad - real bad, in most cases. Then, when you listen to some of this two-track stuff on the same system, it's like liquid sound: totally unbelieveable! But that is another topic for another day....

When not listening to Phil Keaggy, Mark Nemier pays particularly close attention to the sage words of his audiophile friends.