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Point-to-Point Wiring
Myth VS. Reality

circbordIn the course of a recent interview, I was asked how the Trem-o-Verb gets its great vintage performance--without being wired point-to-point, and "would it be even better if it were?"

Perhaps this wasn't such a surprising question since the author had recently reviewed some pricey amplifiers whose manufacturers emphasized that their amps were indeed wired point-to-point, as if that mere fact would indicate (to those "in the know" at least) a product of precious distinction.

What Is It?

In point-to-point, the resistors and capacitors are joined with wires to solder points laid out on an insulating tag board. Wires from each solder joint then run off to the tube sockets, switches, and controls. One manufacturer has even rejected the tag board and uses phenolic terminal strips screwed to the chassis instead. This method deserves recognition for being the slowest, most labor-intensive and most error-prone wiring method of all. Point-to-point is probably about the oldest construction style and it's still appropriate for making a "one-off" piece of electronics. But does it produce a better sounding amp?

My job as designer has always been to focus on the "black magic" of amplification: first, how to get it and, second, how to get it consistently. And there, my friends, is the biggest disadvantage with point-to-point, consistency is very hard to maintain.

What We Do

From the first, Mesa/Boogies have used a combination of point-to-point and printed circuit board methods in order to ensure absolute consistent placement of critical parts and conductors. It is easy to demonstrate how moving some parts or lead wires as little as 1/4" can make a huge difference in the top end "transparency" of the sound--exactly where a lot of the magic lives--or dies.

Inside a typical point-to-point amplifier are signal wires leading from the component board to the preamp tube sockets. Because many of these can be quite critical, we always locate our tubes along the center line of a printed circuit board so the lengths of traces can be extremely short and perfectly consistent.

Great care and many scrutinized revisions result in a circuit board layout that avoids any unwanted "stray couplings" that can rob tone, or may even include a few nuances of intentional interaction (black magic) which cannot be reliably duplicated in the point-to-point style.

And Why We Do It

For example, the great top end of the Dual Rectifier has an aggressive bite but avoids the harshness by the way two very important traces are laid out on the board. One trace is on the top and the other runs right beneath it on the bottom side of the board. Thus the very small--but significant-amount of capacitance coupling these two together through the board performs a subtle filtering kind of negative feedback in a critical region where the harmonics can be made to line up just right. Obviously the alignment of the traces on both sides of the board must be precise and consistent for this to work.

Here's an illustration of the different wiring techniques. Think of printing books versus writing them out longhand. Once the type is properly set each printed page will be the same--no errors. Now go one step further and imagine trying to line up the letters on both the top and bottom sides of a sheet of paper--this time by writing longhand. It's all but impossible. Yet such precise alignment is critical to achieving the performance we're after--each and every time. With a printing press or a printed circuit board it's easy.

Where do we still wire point-to-point? Anywhere it makes a better amplifier is the brief answer. Many manufacturers try to put everything on printed circuitry, but we individually mount and point-to-point wire all jacks, switches, transformers and 8-pin power tubes. The reasons are increased reliability and total ease of replacement. If those parts are PC mounted, major disassembly is required to get at them. Even worse, they can cause the whole PC to fracture if they're bashed in hard enough, then the amp is practically non-repairable.

Our commitment is to provide a professional instrument which, with minimal maintenance, can last a lifetime or more. All our circuit boards are double-sided and "plated through" meaning that each and every hole has a platinum and copper sleeve formed inside of it which is integral with the copper traces on the top and bottom. This way each component lead is soldered three times: top, bottom and inside the hole.

Most manufacturers use singlesided boards where there is only one solder connection per part on thin foil glued to the boards surface. Moreover, these boards, once installed can't be hand-soldered for repair or replacement without totally dismantling the amplifier.

Let's Talk History

I must have repaired thousands of old Fenders--and I was the guy who could usually get rid of the stray noises--but not always. I finally found out why some of these noisy amps seemed incurable. The noise was originating in the point-to-point tag board itself! The board material can absorb moisture and become slightly conductive. The factory's recommendation was to bake the boards in a drying oven then dip them in melted wax to seal out the moisture!

Here's another: Tag boards warp, and the warpage increases the space between eyelets. Years ago, a guy phoned me, freaking out that his Fender had gone down before a big gig. I listened to his description of the problem, then advised him to pull out the chassis and look for the brown-black-brown-silver resistor running lengthwise across the board. "Give it a little tug and you'll probably find it's broken loose at the solder joint," I told him. He called back relieved and ecstatic--said that he'd never fixed anything before in his life. No sweat. I must have fixed a hundred black face Fenders where point-to-point board warpage had caused this problem. Don't get me wrong, I love Fenders. Without them, it's safe to say, none of us would be here!

Conclusion

So there you have it, four specific advantages of the printed circuit board: 1.Consistency of location, 2.Ability to use the board for intentional coupling, 3. Immunity to noise-causing moisture, and 4.It does not warp.

Now what about the way in which a conductor affects the sound? Is a round copper wire better than a flat copper trace on a circuit board? Not according to Randall Research (no relation to me!) who has studied audio conductors under all conditions, including at the molecular level under an electron microscope. His opinion is that if there is any advantage either way, it would be with the circuit board trace whose profile offers far greater surface area. It is well established that audio signals (especially the higher frequencies) tend to flow on the surface of the conductor, not through its core.

All this is not to say that there aren't great sounding point-to-point amplifiers-obviously there are. But having built lots of amplifiers both ways myself, the mere fact that an amplifier has been wired this way is, as far as I can see, a guarantee only that it will cost more. If there was an intrinsic sonic benefit to using point-to-point throughout, you can bet that we would do it!


 
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