How a Demograf Audio amplifier is wired, and why

Look inside a hand-built tube amplifier and you may find no circuit board in the signal path at all: resistors and capacitors soldered to tube sockets, terminal strips and one another, with wires running between them. This is point-to-point wiring. This guide explains what the term means, how it compares with printed circuit boards and with turret or tag boards, what layout and grounding have to do with it, and what we document about how Demograf Audio amplifiers are built.

What is point-to-point wiring?

In point-to-point (PTP) wiring, components are connected directly to one another and to fixed anchor points in the chassis: tube socket pins, terminal strips, the lugs of potentiometers and switches, the terminals of transformers. No printed board carries the connections. The leads of resistors and capacitors often form the connections themselves, and insulated wire joins points that are further apart. It was the normal way to build electronics before printed circuit boards became common, and it is still widely used in hand-built tube amplifiers.

The term is used loosely. Some makers call any hand-wired chassis “point-to-point”, including ones built on tag or turret boards. Strictly, it means that parts are mounted on the pins and anchors they connect, without an intermediate board.

Three ways to build a tube amplifier circuit

Many amplifiers combine methods, for example a board for the power supply or control circuits and hand wiring for the signal path.

Point-to-point wiring vs PCB: what each gives

Point-to-point wiring is not better in itself. It is a different set of trade-offs.

What hand wiring gives

• Serviceability. Every part can be reached, measured and replaced with a soldering iron, with no tracks to lift. A tube amplifier may stay in use for decades, so repairs and part changes are likely over its life.
• Freedom of layout. Parts sit where the circuit needs them: a grid-stopper resistor directly on the socket pin, a coupling capacitor between two stages without a detour.
• Heat and high voltage. Large parts can be mounted in free air, away from hot tubes and with generous spacing for high anode voltages.
• Units built to order. When options are agreed with each customer, wiring by hand avoids designing a new board for every variation.

What it costs

• Time. Wiring a chassis by hand takes far longer than fitting parts to a board.
• Consistency. A PCB fixes the position of every part. With hand wiring, consistency depends on the builder’s discipline and on good documentation.
• Dependence on skill. A carelessly wired chassis can hum, oscillate or be hard to service. A good board layout is better than poor hand wiring.

Owners often report that hand-wired amplifiers sound more open and more alive. Such impressions are hard to separate from the rest of the design. The wiring method is one factor among many, and we would not claim more for it.

Layout, grounding and lead dress

With no board to fix the geometry, the builder decides where every wire goes. A few general principles apply to any tube amplifier, however it is built:

• Grounding. Return currents from different stages should not share a conductor where they can produce small voltages that the input stage then amplifies. Common approaches are a star ground, where the returns meet at one point, and a ground bus, a heavy conductor to which the stages connect in order from input to output. Either works when it is applied consistently; mixing them carelessly is a common cause of hum.
• Heater wiring. AC heater wires are usually twisted together and run close to the chassis, away from the input wiring, so that their magnetic fields largely cancel.
• Separation. Input wiring is kept short and away from output wiring, mains wiring and the power transformer, to avoid hum and the unwanted feedback paths that can make an amplifier oscillate.
• Lead dress. “Lead dress” is the routing and placement of wires and component leads. Short leads where signals are sensitive, wires crossing at right angles where they must cross, and fixed positions that do not shift when the chassis is handled keep an amplifier quiet and stable.

What does “hand-wound output transformer” mean?

The output transformer couples the tubes to the loudspeaker, and in a single-ended amplifier it also carries the DC current of the output tube. A hand-wound transformer is wound on a winding machine by a person who controls the tension, the insulation between layers and the arrangement of the sections. The arrangement matters most. Interleaving divides the primary and secondary windings into alternating sections, which lowers leakage inductance and helps the high-frequency response; the designer balances it against the capacitance between windings. Hand winding does not guarantee a good transformer. What it allows is a transformer calculated for one circuit and built in small numbers.

How a Demograf Audio amplifier is built

This is what we document about our own amplifiers:

• Wired by hand, point to point. The circuit is wired by hand. In the amplifiers, point-to-point wiring takes the place of printed boards in the signal path, and circuits run without global negative feedback wherever the circuit allows it.
• Transformers wound for each circuit. Output, power and interstage transformers and chokes are wound to Demograf Audio specification for each circuit. Output and interstage transformers are wound by hand in interleaved multi-layer sections. Transformers by Hashimoto, Tango or Tamura are available on request instead.
• Internal wiring. The internal wire is the Proprietary “RareCoreFusion” Alloy, a solid-core copper with rare-earth admixtures; other options are available.
• Digital units. Converters such as the Reference Tube DAC combine hand-assembled boards with point-to-point wiring.
• Built and measured per unit. Every unit is made to order in Kazakhstan by Dmitriy Gubchenko, in the workshop. Depending on the model the build takes 6 months or longer. The finished unit is measured (frequency response, noise floor, distortion at working levels) and listened to, and you receive its own measurement report.
• Records by serial number. Circuit diagrams and measurement records are kept for every unit by its serial number, so any unit can be returned to specification.

This is where hand wiring matters to an owner. A chassis whose parts can be reached, together with the diagram and the measurements of that particular unit, makes service straightforward years later. Every piece of gear carries a one-year warranty on materials and workmanship, with extra warranty available for +1 or +2 years; after it, paid repair is available. The warranty page and how to order give the details, including the 50% queue deposit and the balance due after the measurement report.

Which Demograf Audio piece fits

Every Demograf Audio tube amplifier is built single-ended as stock; a push-pull build is available to order. Our guide to single-ended and push-pull and the one on power triodes for single-ended amplifiers help with the choice of circuit.

• Solaria (45 triodes, 2 W) and Eurybia (2A3 triodes, 2 W) are integrated amplifiers for sensitive loudspeakers.
• Atlas is an integrated amplifier on 300B triodes, 5 W.
• Helios MkII (G-811 triodes, 15 W) and Endymion (845, 211 or 805 triodes, 15–25 W) suit loudspeakers that need more power.
• Ether runs on GM-70 Triode / GK-71 Pentode transmitting tubes, 25 W, and Tantal Senior on tantalum 4E27 tubes, 30 W.
• Tantal (3C24 triodes, 3 W) adds an electrostatic headphone output.

If you are unsure which circuit suits your loudspeakers and room, write to us with your loudspeakers, the size of the room and the music you play most.