Using a Roland LAPC-I without a PC

Question

This is inspired by the video Using an old 8 bit ISA sound card (Roland LAPC-I) without a PC.

I would like to find detailed instructions (for those unlearned in electronics), including a parts list, to replicate the setup in the video, which includes something to the effect of:

• ATX power supply
• wires
• wire couplers
• external ISA bus
• USB-to-MIDI adapter (readily available)

And improvements would be welcome, such as, if possible, a more compact power supply and more elegant wiring to facilitate enclosure of these components with the card.

Operation in Windows 10/11 would suffice but Linux support would be ideal, although this would probably require a kernel module, if emulators such as ScummVM and PCem could use it.

The closest alternative of which I'm aware is the usb2isa-r by ARS Technologies, although price and support may be obstacles.

Answer 1

According to the video description, the creator of the video

connected only to the +5V, -5V and ground lines of an ATX power supply

If you are, as you write, "unlearned in electronics", I'd recommend a slightly different approach:

• Get yourself a dedicated +/- 5 V power supply with no minimum load. Many PC power supplies require some minimum load on at least one rail, which may be a source of problems you don't want. A good choice might be the Mean Well MW RT-65A, which is readily available and also provides +12V (which you don't need for this setup, but might need with other ISA cards).

• Get a passive ISA backplane like this*, which should take care of all the soldering for you. Connect the power rails to your power supply.

• Connect the sound card to your modern PC using a USB to MIDI adapter.

• Connect active speakers or an amplifier to the sound card.

There also seems to be a Midi Connector Box in the video, presumably used as a passive adapter to connect the PC's MIDI out to the card's MIDI in. Depending on what MIDI cables you have at hand, you might need that, or some other kind of passive adapter, as well.

And that appears to be it. Which operating systems are supported depends on your choice of USB to MIDI adapter; the card works a MIDI expander in this context, not as a sound card.

Good luck.

* I'm not affiliated in any way with this particular seller, nor am I familiar with this specific product. It's just an example of what to look for. I chose this as an example because it's comparatively small ‒ you need only one slot, after all ‒ and because of the screw terminals for power.

Answer 2

Michael Graf already pointed out the basic way to get it working, so here a few additional information bits about the LAPC-I that may help to understand the setup involved:

Name

• It's mostly known that LA stands for Linear Arithmetic (Synthesizer)
• Unlike assumed PC stands not for Personal Computer but
  • P complements LA as Processor, while
  • C simply stands for Card.
• Similar is I not not the Roman numeral for one but the letter 'I', for IBM-PC.
• Thus LAPC-I means Linear Arithmetic Processor Card for the IBM-PC

Whats In It?

A LAPC-I is essentially the combination of a

• Roland MT32 Multi-Timbral sound generator
• Roland MPU-IPC-T - MIDI Processor Unit for the IBM PC - which is a combination of the prior
  • Roland MIF-IPC - MIDI Inter Face for the IBM PC - with all of the
  • Roland MPU-401 breakout box except for the connectors

MIF cards were available for many common computer, especially Japanese systems, but also C64 or Apple II. They 'only' provided the MIDI interface, all further electronics were part of the MPU-401 box. The MPU-IPC-T moved much of onto it's card reducing the break out box size.

The MT32 in turn was the syntesizer to be controlled via MIDI. It was considered a 'low end' offering for 'Hobbyist' musicians.

The LAPC-I integrated all of that onto one board needing only the smaller break out box (now called MCB-1 - MIDI Connector Box), as seen in above picture, to support connection with other MIDI devices (Manual).

Why Does It Work Without PC

The MT32 is a stand alone synthesizer controlled over MIDI. It does not need a PC to work. The PC's MIDI interface part will when only powered be strictly invisible to the bus - as shown in the manual:

(From the LAPC-I Manual p.24)

All input at MIDI-IN will be handed to MIDI-OUT and thus the MT32 part. For all that matters it will look and work like any stand alone MT-32.

How To Connect

The LAPC-I became famous for high end gamer setup - and that created one problem for today's usage: Gamers almost never bought the MCB1, which was sold separat. Thus the MCB-1 is a rather rare sight.

But since the connector used (DA-15) is a common one and the MCB-1 insides known a rebuild shouldn't be too hard.

Alternative Solutions

Get Yourself a Standard MT-32 Box.

While 'hacking' a LAPC-I to work as a stand alone MT-32 is nice, it involves a lot of work and at least basic electronic skills if no MCB-1 is at hand. In contrast any MT-32 will already include the necessary connectors, reducing the task to getting an USB to MIDI interface and plug it into PC and MT-32. No ISA setup, no external power supply, no soldering, just plug and play :))

Also, MT-32 are way more common and available at way lower prices than a LAPC-I.

Still Insisting to "Hack" it?

Well, as a quick look at some of my LAPC-I

shows, it connects only

• GND - at B1 / B10 / B31
• +5V - at B3 / B29
• -5V - at B5

for power. Thus a simple 62 Pin Card Edge Connector at ca. USD 2, a +/-5V PSU of your choice (*1) and 6 wires connecting those two will do it.

While it's really a little fun job, I would still suggest to be careful and count everything twice - at least.

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*1 - Quickhack would be to chain two cheap USB wall warts.