The photo above is of the rare Novation SIIEX24 24-Voice Expansion Board. This board plugs into the SuperNova II & Nova II and will increase the polyphony by a further 24 voices. SuperNova II units that have this expansion installed are known as the “Pro-X”. Nova II units that have this installed are known as “XL”.
There is also a 12 voice expansion card available known as the SIIEX12.
The card in the photo was in my hands for just a short time. It was fitted to a customer’s motherboard when it arrived for a DAC Replacement job.
Being a rare item this card will have very high prices on the likes of eBay / Reverb etc. At the time of writing there is a 12-voice card on eBay with a price of around £325. On a lucky day you could pick up a fair condition Supernova II for that. The SIIEX12 card is simply a cut-down version of the SIIEX24 card with three of the DSP chips missing.
This guy was very happy to finally get his 24-voice card and made a YouTube video describing the card and showing how to fit it.
The SIIEX24 Project Begins
Having developed several expansions for other synthesizers over the past 10 years I have had an on-and-off idea for recreating this board. It looks scary with the six 144-pin DSP chips suggesting a lot of connections to work through. After studying the Supernova II motherboard’s DSPs connections I found that not all the pins are used. Also, one side of the 50-way motherboard expansion connector is mostly Power & GND connections. This card may not be as scary as I first thought. My on-and-off idea for recreating this board has been nudged firmly in the ‘on’ direction!
At the time of writing I have a 12-voice coming by way on loan – thanks Daniel!
I will study this board when it arrives to learn how it is wired and create a net list of connections. The board dimensions and connector location will need to be measured.
The Card Arrives!
The 12 voice card was more useful to me than the 24 voice as I could see all the pads that needed a connection on the locations of the missing ICs. After 2 weeks with the card I have gathered all the info I need to recreate the full expansion card.
I’ve spent a bit of time doing the board layout. The underside of the board has no components – this is the side that sits face-up when installed. I have used a 6 layer design for this board over my usual 4 layer designs. This allows me to keep the internal 3V3 and GND planes intact without cutting them up for signals that I could not route on the outer layers. The datasheet for the Motorola DSPs recommend 6x 100nF decoupler capacitors for each IC so I have increased the total quantity to 34 – an increase of 10 on the Novation card. I’ve been toying with some silkscreen designs for this side of the PCB and have two candidates so far:
PCB Design Modifications for Heat Dissipation
Having recently upgraded several customers 12 Voice SIIEX12 boards to the full 24 Voice specification I have noticed quite a lot of heat generated from the fully populated board when it has been powered up for a short time.
Besides the 6 DSPs generating their own heat, the power regulator circuit on the board kicks out a fair amount of heat on its own.
The board is powered from the PSU 5V rail then gets dropped to 3V3 through a regulator circuit for the DSPs. Novation have designed the board to spread the heat from the regulator circuit over a larger area by using several low-ohm resistors in parallel to drop the voltage before it hits the 3V3 regulator. Despite this, the 3V3 regulator gets quite hot and there is not a lot of copper heatsinking where it is mounted. The regulator datasheet states a maximum of 1 Amp of current – when there are 6 DSPs mounted on the board the current can go to 0.85A.
To help dissipate the heat on the new board I have decided to make the board design slightly longer toward the cooler side of the motherboard. Also, a higher rated 1.5 Amp regulator will be fitted in the extended area with full copper planes on both faces of the board to help with heatsinking.
The photos below show the larger PCB size compared to the original Novation design:
Although the bigger board design fits comfortably in the Supernova 2 there was concern that it may not fit the Nova II.
I got in contact with a Nova II owner who kindly photographed the inside of his unit. As you can see from the photo the Nova II uses the same motherboard as the SuperNova II but does not have the SuperNova II’s Output 1 & 2 jacks fitted.
Many thanks to Andreas Schoter for taking the photograph of his Nova II.
The PCBs arrive – First Build Test
The PCBs arrived for the first build test. With all the parts ready it was time to do the nail-biting first build.
The easiest way to build the card was in this order:
- Regulator and support capacitors
- 6x Big 5R6 Resistors
- 6x DSP ICs
- Small 0805 Resistors & Caps
Time to lift the hood on the Supernova II and plug it in.
With the board installed the SuperNova II gave me the full 48 voices:
With the design proved it’s now time to aquire more parts and start making some stock!
Each finished PCB will undergo polyphony and electrical tests.
Polyphony is tested by generating audio tones and ensuring that all 48 voices are available and working.
Electrical tests measure current draw, regulator voltage drop, and digital signal waveforms measured at the connector pins during the polyphony test.
The Sector101 SIIEX24 ‘NovaBlade’ 24 Voice Expansion is now available at THIS PAGE