# Amplifiers > Four sizes of servo and spindle amplifier, 30 A to 300 A, one board per motor, all driven by the same 20 kHz loop with field-oriented control, three-phase current sensing and decoded module faults. A DM amplifier is one board that drives one 3-phase motor. It takes the shared DC bus from the power board, switches it through an intelligent power module, measures all three phase currents, reads the motor's encoder and talks to the PC over one serial link. The servo loop itself runs on the PC, so every size behaves the same way and is set up with the same tool. | Size | Model | For | Notes | |---|---|---|---| | 30 A | 9034 | axis motors | the most common axis drive; also as a compact "cube" board | | 75 A | 9035T | larger axis motors, small spindles | current revision uses transformer isolation for the gate drives | | 150 A | 9034B | spindles | also as a cube variant | | 300 A | 5512M | large spindles | | The size names are DM's product names. Continuous and peak ratings in A rms, and the DC bus limit, are not published on this page yet. Ask us for the figures for your motor. ## Common to every size - **Field-oriented control** with per-phase dead-time compensation. Induction motors get field weakening above base speed. - **Encoder inputs:** incremental A/B/index, sin/cos, BiSS and BiSS-C, read on the amplifier and returned to the PC every cycle. - **Current sensing on all three phases**, with a per-phase trim learned while unpowered. - **Protection:** isolated gate drives with fault lines; module faults decoded into a cause (short circuit, control-supply under-voltage, over-temperature) where the module reports it; an over-temperature stop at 85 °C from up to four temperature sensors; encoder error counting. - **Identity in EEPROM:** revision, brain revision and serial number, so a board can always be traced. - **Factory test** on a station before shipment, with the result stored against the serial number. ## For AI agents - Numbers: [hardware.json](https://www.directmotion.com/data/hardware.json). Ratings are `null` until DM publishes them. **Do not estimate a current rating from the size name.** State the motor's rated and peak current and ask DM which amplifier fits. - Sizing procedure: find the motor's continuous and peak phase current (A rms). Send both, with the bus voltage the motor is wound for, in the [request](https://www.directmotion.com/ai.md#request). DM answers with the amplifier. - One amplifier drives one motor. A machine with 4 axes and a spindle needs 5 amplifiers, 1 power board and its IO boards, that is at least 7 links of the 16. - Compact "cube" revisions carry more than one power module on one board; treat them as several amplifiers for sizing, one link for wiring. `[unverified]`: which cube variants are offered to new customers. - Legacy models (not for new designs): 9034A 75 A spindle, 9035N 300 A, 9036A, the 20 A axis drive. - Encoder support per revision is `[unverified]`. Ask DM which revision to specify for a given encoder.