Guitar Essentials: What You Need to Know About Point-to-Point Wired Amps

February 27, 2008

PHOTO: Mataresephotos

Before dissecting the subject more thoroughly, let’s establish a few definitions. A “printed circuit board” is a glass-epoxy or phenolic-resin board with a thin plate of copper on one side (sometimes both sides), onto which circuit components are soldered. Electrical connections between components on such a board are created by “etching” away certain portions of the copper plating to leave copper traces—which look like narrow tracks—in patterns that determine the signal, power, and grounding paths around the circuit.

Manufacturers moved over to PCBs for amplifier construction for a number of reasons. If you plan to make a lot of the same design of amp, etching PCBs to a precise and carefully laid-out pattern will often provide more consistent and reliable results than wiring up each circuit individually, where slight variations in wire positions and lengths occur according to which worker on the line assembled the unit. Also, PCBs can often have components loaded onto them by machine, and have their solder connections made all at once in a process called  “dipping.” In short, PCBs are used because an amp manufacturer may consider them the best option for consistency and reliability, as well as because they are a more cost-effective means of building an amplifier.

In common parlance, a point-to-point circuit is one in which all connections between components and the trace-less (non-etched) circuit board are hand wired. To be strictly accurate, a genuine PTP circuit is one that uses no circuit board at all, but makes all of its circuit connections directly between components, using the leads of those components themselves, and very little wire—a resistor connects the input jack to the preamp tube socket, a capacitor connects the output from that preamp tube to the volume control, and so on.

In truth, this kind of circuit is extremely rare. It is most commonly seen today in amps made by Matchless, Bad Cat, and Star, and in some vintage amps from Gibson, Valco, and very early Fender models. Most of the earliest guitar amps used PTP construction, in fact, because they were generally simple enough not to require the imposed logic of a circuit board. In the genuine PTP amp, the signal path is usually as short as possible—which, when done right, can help minimize interference and noise in the circuit—and the circuit flows logically from input to output. The circuit itself, therefore, tends to look very much like the schematic diagram from which it is built. Fans of PTP manufacturing say the logical signal flow and short wire runs make for a bolder, richer tone.

Alongside the pluses, there are potential downsides to PTP circuits. If done poorly, they can often be prone to a lot of noise and electrical interference, because an inexperienced builder might not adhere to critical considerations—such as keeping signal wires and power supply wires from running close or parallel to each other, and so forth. Also, even in high-quality PTP amps, components can sometimes be more difficult to access and disconnect because of the somewhat rat’s nest-like intertwining of components and connections. Physical factors—such as the heat from tube sockets, or the movement that occurs in a tube socket terminal when a tube is wiggled loose for replacement—might impact directly on components in the PTP circuit, rather than on the flexible wires that make connections in other types of hand-wired circuits. Of course, the labor-intensiveness of PTP circuits is directly related to the high cost of these amplifiers.

Very often, when guitarists discuss so-called PTP amps, however, they mean amps that are made with eyelet boards (as most commonly seen in vintage Fenders and Ampegs), or tag or terminal boards (as seen in vintage Marshalls, Voxes, Hiwatts, Traynors, and plenty of others). All of these are some form of insulated, non-conductive fiberboard into which metal eyelets (or posts or terminals) are mounted. Signal-shaping components in the circuit—primarily resistors and capacitors—are soldered between these terminals. Also soldered to them are the wire connections going from points in the circuit to other components within the amp: jacks, switches, potentiometers, tube sockets, and transformers. It’s these direct wire connections that lead many people to mistakenly refer to such amps as “point to point”—a slight misnomer that’s easily forgiven.

When built right, and laid out logically with an economical signal flow, these designs still yield extremely toneful amps—even if they might involve a few more inches of wire through the course of the circuit (a minimal, and possibly inconsequential consideration). Good examples of this kind of construction have the advantages of being easy to repair, because almost any component can be changed by desoldering two easily accessible joints, and lifting out the part. They are also extremely rugged, as the circuit board offers the components some insulation against heat and vibration. In fact, any of these methods, done right, have few significant down sides—other than that they are rather labor intensive, due to all the hand-soldered joints and hand-wired connections. Makers that use this type of circuitry today generally fall into what we call the “boutique” realm, which includes brands such as Victoria, Dr Z, TopHat, Cornford, Mojave, Clark, 65 Amps, Bruno, and Reeves/Hiwatt. The category also includes up-market models from major makers, such as Marshall’s Hand-Wired series, many of Fender’s Custom Shop amps, and Vox’s new AC15H models.

A rugged and well-laid-out PCB can certainly present an efficient and low-noise signal flow—as can a well designed handwired circuit—and the use of a PCB in itself isn’t necessarily evidence of a lower-quality product. Randall Smith used PCBs in his Mesa/Boogie combos way back when he founded the company in the early 1970s, and he still does today. Certainly, the early Boogies can be considered among the forefathers of boutique amplifiers, and a lot of hand wiring still went into constructing these high-gain lead monsters. Other makers of high-end amps such as Soldano, Rivera, Koch, and Vero also use PCBs—as do the “standard” lines from Fender, Marshall, and Vox, and all contemporary amps from Traynor, Laney, Ampeg, Peavey, Crate, Krank, and Randall. But you will generally notice a difference between the PCBs in the highest priced tube amps that carry them, and those in the most affordable. A thick PCB with wide tracks, a fluid layout, and easily accessible parts can still make for a great-sounding and easily serviced amplifier. Not all PCBs are created in this way, though, and some are much harder to service than others.

In many cases, the quality demarcation is found not necessarily in the circuit board, but in other places—such as whether the tube sockets and/or pots, switches, and jacks are mounted directly to the circuit board, or to the chassis, with flying leads between sockets and board, rather than with direct solder connections to the board. In more economical production the sockets, switches, and pots are often soldered directly to either the main PCB or—in a slightly better option—to one or more secondary PCBs. When this is done, however, these boards can be prone to cracking with excessive vibration or movement—the kind that occurs when you wiggle a tube to remove it from the socket, flip a switch repeatedly, or just throw the amp in and out of the van. Boards can also be damaged over time from too much direct heat passed on from tubes.

If, however, you build an amp with a thick, rugged, well-designed PCB carrying high-quality components, and you mount the switches, jacks, potentiometers, and tube sockets to the chassis itself (which provides excellent heat dispersal and resistance to physical stress), then you’ve got a product that should run with many of the big boys of the handwired world.

In addition, the types of components used in the circuit—meaning the make and quality of the resistors and capacitors—often vary widely according to price and construction technique. PCBs that are machine loaded with these parts—and which have their terminals all soldered at once in a “solder dipping” process—usually don’t carry the higher-end components, which are often physically bigger, and less efficient to work with (as well as being more expensive). Instead, these designs use the smaller, more generic components that the rest of the consumer electronics industry uses, and which the loading and dipping machines are designed to work with. These also tend to be the amps that are harder and more time-consuming to service. Sometimes, in fact, as is so often the case with the PC or DVD player you send back to the factory for repair, a technician might simply pull the entire circuit board and replace it, rather than try to diagnose and repair the problem itself.

None of this is to say that you need to run out to buy a PTP or hand-wired guitar amplifier. Hand-crafted U.S. or European-made goods in any corner of the consumer market cost a lot more than mass-manufactured goods, and this article doesn’t intend to imply that the extra expense is justified for every player out there. Makers of quality tube amplifiers that use PCBs still employ a lot of hand assembly in the manufacturing process, and plenty of pro players record and tour with amps such as Fender Bassman Reissues, Vox AC30TBXs or Custom Classics, Marshall JCM800s or TSL100s, Mesa/Boogie Triple Rectifiers, Soldano SLOs, Peavey 6505s, and plenty of other righteous models that carry printed circuit boards.

That said, lots of pros and hobbyists alike derive massive pleasure—and righteous tones—from any of a number of handwired tube amps available. Whichever machine you turn to for your tone, at least now you can walk the walk, and talk the talk. More to the point, when it comes time to research, test, and, eventually, make your next major amp purchase, you can more intelligently asses the elements in the models you are drawn toward, and, hopefully, understand a little more about what makes them tick.

Warning!  Guitars amplifiers contain lethal voltages. Unless you are a qualified technician, do not remove the protective rear panel, or pull the chassis out of your amp’s cabinet. Tube amps can still contain dangerous—possibly lethal voltages—even when they have been unplugged for a long time. Filter capacitors within them store electrical charges that can easily zap a stray finger, resulting in serious injury and even death. So don’t go poking around inside those circuits. If you require repairs or modifications—or are just curious—consult a qualified professional technician.
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