Inside Reface DX and Reface CS

With so much to do and learn, it’s been a long while since I’ve taken a peek below the hood of an electronic musical instrument.

Yamaha caught the world by surprise with its Reface series of portable keyboards. So far, there are four models in the series: Reface YC (organ), Reface CP (electric piano), Reface CS (analog modeling synthesizer), and Reface DX (4-op FM synthesizer).

Before I get to the DX and CS, here’s a few thoughts about the YC and CP. According to Yamaha specifications, the Reface YC tone generation engine is “AWM (Organ Flutes)”. This suggests to me that the YC uses a standard AWM tone generation integrated circuit (IC) like the SWP70. Hammond-like “Organ Flutes” have been part of the mid- and upper-tier arranger workstations like Tyros for a very long time. Thus, I suspect that the YC implementation is an updated implementation of the arranger technology.

The Reface CP tone generation engine is specified as “SCM + AWM2”. SCM or “Spectral Component Modeling” is the modeling technique first employed in the flagship CP-1 stage piano. SCM and AWM2 are also used in the CP-4 and CP-40 models. The CP-1 uses three tried-and-true SWP51L tone generation ICs: master, slave and effects. The master and slave generate the base piano tones and the two ICs share the same WAVE ROM. Total WAVE ROM size is 1024Mbits or 128MBytes (organized as 16-bit words) which is a ridiculously small amount of memory for a top quality piano. Such is the power of SCM!

The CP-1’s samples are stored in two Lapis Semiconductor MR26V51252R devices (32M by 16-bit words each). The processor is a Yamaha SWX02 (SH-2A CPU core operating at 135.4752MHz). There’s not much to the CP-1 user interface, so a relatively light-weight, low-cost processor is enough for the job. The SWP51Ls handle all of the heavy computation.

Thus, the Reface YC and Reface CP are relatively uninteresting from a technologist’s point of view. The YC and CP use proven technology from other Yamaha products. That leaves the Reface CS and Reface DX.

Although the CS and DX implement two different tone generation techniques — analog physical modeling vs. frequency modulation (FM) — they are fraternal twins at the hardware level. They share much of the same base hardware design with a few variations to handle their unique user interface requirements.

The CS and DX both use a Fujitsu MB9AF141LAPMC1 processor to handle key and panel scanning. Here’s a quick summary of its characteristics:

    CPU                 Cortex-M3
    CPU Frequency       40MHz

    On-chip flash memory   Main area   64KBytes
    On-chip flash memory   Work area   32KBytes
    On-chip SRAM           SRAM0        8KBytes
    On-chip SRAM           SRAM1        8KBytes

    Peripheral interfaces:
        DMAC            8 channel
        Serial I/F      8 channel
        Base timer      8 channel
        Dual timer      1
        Realtime clock  1
        Watch counter   1
        12-bit A/D      12 channel

This processor is a good choice for embedded control applications where low power and low cost are important. To my knowledge, this is the first product line using an ARM embedded microcontroller.

The Reface CS and Reface DX both use the proprietary Yamaha SSP2 (uPD800500F1-011-KN9-A) for tone generation. The SSP2 is Yamaha’s designated hitter for DSP tasks and is incorporated into many products. The SSP2 has an SH-2A CPU core operating at an internal clock speed of 135.4752MHz. The SSP2 has its own ADC, GPIO, UART, USB and serial audio interfaces. The SSP2 UART handles 5-pin MIDI communications. The SSP2 USB interface handles external USB communications.

The SSP2 has two memory interfaces:

  • DSP RAM: Connecting to 8MBytes of DSP SDRAM.
  • CPU bus: Connecting to 8MBytes of program ROM and 16MBytes of SDRAM.

Memory sizes and devices are the same in both products.

The AUX IN and audio out hardware design is also the same across the two products:

  • PCM1803ADBR ADC: AUX IN analog-to-digital converstion
  • AK4396: Digital-to-analog conversion for OUTPUT L/R and PHONES OUT
  • YDA176 D-Amp: DAC and amplification for internal speakers

This shouldn’t be any surprise. All of the Reface series products ahare the same external jack, power and key switch boards.

Digital audio is transfered serially between the SSP2, the ADC, the DAC and the digital amplifier. The SSP2 generates the master clock (MCLK) and bit clock (BCLK) to synchronize data transfers. MCLK and BCLK are derived from the SSP2 clock, in case you’re wondering about those odd-looking CPU clock frequencies. MCLK is 256*fs and BCLK is 64*fs, where fs is the sampling frequency, 44.1KHz. MCLK operates the AK4396’s digital interpolation filter and delta signal modulator. Data format is I2S and is probably 24-bit as it is in workstation products.

Aside from the other front panel controls, the Reface DX has two major additions: Capacitive sensors for the front panel touch strips and the LCD panel display. The printed circuit board positions for the LCD interface are not populated (i.e., no mount) in the Reface CS as it has no LCD display.

There you have it — two more examples of solid and conservative Yamaha hardware design.

Now, you may find the SSP2 to be incredibly boring. It is, however, a good choice for a low-cost, compact product. The Reface CS and DX need a metal shield over the SSP2, perhaps to control RF emissions, perhaps to radiate heat, or maybe both purposes together. Low power is a vital concern throughout the Reface series due to battery power concerns.

I’m a little hesitant to draw any inferences about future products. The Yamaha Montage supports 128 note, 8 operator FM polyphony. The Reface DX provides a relatively meager 8 note, 4 operator FM polyphony. Thus, there must be considerable hardware resources at work in the Montage. Well-worth the price, one hopes! And speaking of hopes, many people would like an analog modeling extension to the Montage. That would depend, of course, on the availability of spare computational horsepower.

Copyright © 2016 Paul J. Drongowski

Reface YC and DX teardowns

Markus Fuller posted two Yamaha Reface teardowns (YC and DX) to Youtube:

In case you’re not familiar with the term “teardown,” think of a teardown as a casual tour through the insides of a keyboard.

Both Reface keyboards have an ARM FM3 handing the user interface panel. The switch to ARM is major news. In the past, Yamaha used Renesas H8 or SH4 microcontrollers for interface applications. They apparently have decided to ride the embedded cost curve and that curve leads to ARM, the current leader in low-power, high function embedded microcontrollers.

I wonder if Yamaha will adopt ARM in their entry-level keyboards? This would be a smart move. Yamaha currently use their own SWL01 processor in battery-powered entry-level products. Now that Yamaha have sold off their integrated circuit fabrication plant, they are free to move to off-the-shelf parts when it makes sense. ARM is the choice for battery-powered embedded devices. Further, the ARM-resident, XG-capable sound engine in Yamaha Mobile Music Sequencer has a better spec than the entry-level ‘boards. (MMS reference)

Both Reface keyboards have a large metal plate over one or more integrated circuits. This is the honey pot. 🙂 I understand Markus’s reluctance to remove the heat sink. This is, however, where the digital signal processing (DSP) is being performed. Apparently, Yamaha had a minor power dissipation problem and resolved it using a simple heat sink (no fan). Heat is an important product design problem; x86 fans take note. (More on x86 and instrument design.)

Here are some notes about the integrated circuits in the Reface YC:

Winbond W9864G6KH-6 SDRAM  (64Mbits)
    4Mx16 bits = 1M words x 4 banks x 16 bits (8MBytes equivalent)
    Parallel interface
    Burst-oriented accesses

Winbond W9812G6JH-6 SDRAM (128Mbits)
    8Mx16 bits = 2M words x 4 banks x 16 bits (16MBytes equivalent)
    Parallel interface
    Burst-oriented accesses

AKM AK4396VF (Asahi Kasei Microdevices Corporation)
    Digital-to-analog converter (DAC)
    24-bit 192KHz 128x oversampling
    I2S data interface
    Integrated digital filter

Texas Instruments / Burr Brown PCM1803A
    Stereo analog-to-digital converter
    24-bit, 64x or 128x oversampling
    I2S data interface

The circuits are all pretty typical for a Yamaha design. Not enough information here to indicate whether the SWP70 tone generator is in use or not. Yamaha have used W9864G6KH as DSP SDRAM in past designs.

I’m glad that Markus posts his teardowns. I like it when he zooms in and identifies the integrated circuits. One very small quibble with the YC teardown — I believe the “A” stands for “Acetone.”

While you’re here, catch my Reface CP snap review.