Hobbyist audio engineer wants some more in-depth info on Firewire
I'll start this thread off with the disclaimer that I am pushing some limits. Well, actually, I'm smashing some limits with a sledge hammer. Let me explain.
I don't have a studio. I have an apartment with a room in the back that has enough room to fit a drum kit, a few amps, and a PA system. There isn't enough room for a desk with a computer and a monitor and near-field monitors, so I use my living room as a control room. I'm the type of person that doesn't have cable TV, so I have a PC connected to my TV anyway, and having the near-field monitors and a sub in the living room is also great for watching Netflix, etc.
I recently upgraded my PC. Previously I was using a laptop with a docking bay, an HP Elitebook 8760w. It has a built-in 4-pin Firewire port, and I also used a ExpressCard Firewire adapter that has two 6-pin ports. The reason for having the second Firewire adapter is because I have two audio interfaces - a Mark of the Unicorn (MOTU) 896HD, and a MOTU 896 mk3 Firewire - and they behave much better together when they are on separate Firewire busses. The HD was in the livingroom/control room connected to the near-fields, and the mk3 was in the "live" room, connected with a SEVENTY FIVE FOOT FIREWIRE CABLE.
This is where I'm pushing limits, I know. Firewire is spec'd at 15 feet. Thing is, it worked. It worked great, in fact. I was able to send 24 channels of 24-bit audio from the live room to the living room, and 24 channels back, on a single Firewire cable, and it behaved no worse than it would have if I was using a standard 15 foot cable. The only problem is that the laptop just didn't have the raw computing power to run the kind of effects and routing that I needed to provide the musicians with even a single decent headphone mix, let alone separate mixes for each musician.
So I upgraded to a i9 9900k with 32 gigs of RAM. I know there's always a bigger fish but the 9900k has at least been in the conversation of top-of-the-line processor for some time and it's a huge improvement over the i7 2670QM that was in the laptop. The problem has been finding a Firewire adapter that will allow me to use the 75-foot cable. If I had never had it working properly with another system, I wouldn't even bother asking, but obviously it's possible, so I'm trying to educate myself more on how Firewire works, on top of doing research on audio-centric discussion forums and losing re-stocking fees by taking blind stabs on Amazon and eBay in the hopes of finding something that works.
So far I've tried 3 different PCI-E adapters, and I have another one on order -
axGear Firewire PCI-E Firewire Controller Card IEEE 1394 Adapter
(I think axGear is Amazon's own brand and they don't have a product page as such, so this is as good as it gets)
This one I bought because it was the cheapest one I could find and I had no reason to think that it wouldn't work. It works fine with the HD on a standard 15 foot cable but with the mk3 on the 75 foot cable, it shows up in Device Manager like it would with a standard 15 foot cable, but it doesn't pass audio. I did some reseach and found out that MOTU devices were built around Texas Instrument chipsets, so I bought this one...
StarTech PEX1394A2V2
https://www.startech.com/en-ca/cards-adapters/pex1394a2v2
...and got the same behavior. So I did some more research and found out that there are two different types of PCI-E adapters - those with native PCI-E chipsets, and those with PCI chipsets with a PCI-to-PCI-E bridge chipset. At some point I opened up the ExpressCard adapter I was using with my laptop and found that it had a JMicron JMB381 chipset, which is a native PCI-E chip, so I thought that must be the solution. In the MOTU forums a user said he was using this card (albeit with a standard 15 foot cable)...
StarTech PEX1394B3
https://www.startech.com/en-ca/cards-adapters/pex1394b3
...and it had a Texas Instruments native PCI-E chipset so I gave it a try. No luck. Same behavior. Then I did some more research and found out that since Windows 10, a lot of people have been having issues with TI Firewire chipsets, so I decided to try and find an adapter that had the only chipset known to have worked with the 75 foot cable, so I have this one on order...
StarTech PEX1394A2
https://www.startech.com/en-ca/cards-adapters/pex1394a2
...which is a discontinued product that I was lucky to find on eBay that has the JMicron JMB381 chipset.
I'm not naive enough to assume that this is going to work, so I'm here hoping that someone will shed some light on why this cable works so reliably on my laptop but not at all with my desktop. Of course, I'd love for someone to just tell me "USE THIS ADAPTER AND IT WILL WORK", but beyond that I'd like to learn a little more about the inner workings of Firewire connections so that I can be a better troubleshooter in the future.
Oh, and before I forget, yes, I have tried using the "legacy" firewire driver, and not only does it not make the 75 foot cable work any better, it actually makes my interfaces not really work at all even with standard 15 foot cables, and at any rate, I had never even heard of the legacy driver before I upgraded to this desktop because the 75 foot cable worked fine with the laptop with whatever driver it installed by default.
Anyway, thanks in advance for any insight.