• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Power Digital Piano with Firewire power

Not open for further replies.


New Member
First let me say I'm new to these forums and I'm a musician, building a mobile piano rig. I'm looking for some advice on powering a digital piano from an external Firewire port.

The digital piano is a Yamaha CP33, which uses the Yamaha PA-3C power adapter.

I have a (Presonus Firebox) that is using Firewire Bus power from a Macbook pro, and has an extra Firewire 400 port for daisy chaining.

What I'm wondering is - can I run this cable - which extracts power from a firewire port - from the Presonus Firebox to the CP33, instead of the PA-3C?

I've looked into Firewire power specs and they seem close to the 12V/700mA output of the PA-3C

Any advice on figuring this out would be greatly appreciated.


- ben


New Member
What exactly are the Firewire specs?

I would think that if the voltage is the same and the Firewire port can source enough current to supply all the devices attached to it then you will not have a problem.


New Member
Forum Supporter
It looks like the voltage is a bit of a grey area and can be just about anything from 9 to 30V depending on the hardware:
IEEE 1394 interface - Wikipedia, the free encyclopedia
I would measure it before going any further.
Another thing to think about is how much current the Presonus Firebox is already drawing off the firewire buss. There may not be enough capacity left to also power the Yamaha CP33 since it looks like the Yamaha CP33 will be drawing near the max rating already.
Last edited:


New Member
FireWire Specs

I found this (here):

Section of the 1394 spec details the power availability. In
1394, a node could provide a maximum current of 1.5A with a maximum
voltage of 40V. The self-id packets give detail about what a node
provides and requires from a bus in terms of power. The 1394a spec has
changed some of these values (e.g. max voltage is now 30V).

And most firewire pinout diagrams say "30V unregulated". I tried to put a meter on Pins 1 and 2 of the port I'd be connecting to, but whenever I touch pin 1, the attached devices react badly (shut off).

So short of getting lucky and finding the device i'd be attaching to outputs 12V / 1A, then it seems I'd be relying on the CP33 handling unregulated voltage like an iPod does when connected via Firewire. However unlike an iPod the CP33 was never designed for Firewire input. Would I be risking damage to the CP33 by trying it?

Otherwise, how difficult would it be to make a custom cable with a DC to DC regulator like this?

Thanks for your help.


New Member
Forum Supporter
If you look at Apple's spec for the Macbook pro:
Legacy: FireWire Developer Note: FireWire Product-Specific Details
You'll see that the spec for the firewire is:
15-inch MacBook Pro Computers (January 2006)

The 15-inch MacBook Pro computers introduced in January 2006, based on the Intel Core Duo microprocessor, provide one FireWire 400 port supported by an Open HCI FireWire controller with an integrated FireWire 400 PHY (Physical Layer). The port supports IEEE 1394a with a maximum data rate of 400 Mbps (50 MBps). The Open HCI controller provides the FireWire Link layer and DMA (Direct Memory Access) through the 32-bit 33 MHz PCI interface on the South Bridge. The integrated PHY implements the electrical signaling protocol and arbitration defined in the IEEE 1394a standard.
FireWire power is present anytime the AC adaptor is powering the system, including shutdown. On battery power, FireWire power is present only during system run and is un-powered in sleep and shutdown to prevent unintentional battery drain.
The 15-inch MacBook Pro's six pin FireWire connector provides unregulated 9 to 12.6 V @ 0.9 A maximum (fused). Developers should design to < 7 W maximum sustainable power.
Output voltage follows the system's battery power, such that voltage is dependent on the state of the battery's charge, as listed below.

  • When the system is receiving AC power, with either a fully charged battery present or no battery present, output voltage is nominally 12.6 V. FireWire power is on in run, sleep, or shutdown.
  • When the system is receiving AC power, and the battery is charging, output voltage will follow the battery voltage (unregulated 9V – 12.6 V). FireWire power is on in run, sleep, or shutdown.
  • When the system is not receiving AC power, the output voltage follows the battery voltage (unregulated 9 V – 12.6 V), and only when the system is running. FireWire power is turned off in system sleep or shutdown when no AC power is present.
The 15-inch MacBook Pro has a single FireWire port, hence, there is no repeater function.
Last edited:
Not open for further replies.

Latest threads

EE World Online Articles