My gig last night - need ideas

[midifidler]

Do you use an external supply for either your audio 8 or vci?

[DvlsAdvct]

Nope. Figured that was the next recommendation. Don't want another wall wart if I can avoid it, though (external hard drive and lappy already...)

[BentoSan]

Id be following midifidlers advice, he it THE MAN when it comes to all this sorta stuff.

[Monika.mhz]

The grounding issue is tricky as the USB standard specifies that the peripheral device shield (or chassis in this case) is not to be connected to the ground.

Unfortunately, the usb line on the VCI itself is not grounded. so you've got an ungrounded datastream going from the VCI to the laptop.

The usb standard is SUPPOSED to be the part that grounds. but if that doesn't...there can be problems! This is why the USB standard is so unstable, is because it's grounding issues are so volitile.

[slyooney]

Useful tip when you experience USB problems on windows (XP) : Sometimes, the USB controller just F*ck up for no reason. I won't explain the whole process (too many language lacks)
But I experienced the problem twice with 2 XP-10 on WinXP SP2.

I fixed the issue by trashing the driver (on the system settings/peripheral window) then reboot - it reinstalls itself automatically when you reboot.
Everything was back to normal after that.

[Jo3]

The grounding issue is tricky as the USB standard specifies that the peripheral device shield (or chassis in this case) is not to be connected to the ground.

Connecting the chassis to an ground or separate earth could actually make the problem worse as it will increase the common mode noise.

I'm really not sure why the Vestax engineers included the gnd screw.

In the manual it states the grounding screw shall be used to suitably ground the case in a scenario where a laptop has no earth terminal on the socket.

[DvlsAdvct]

In the manual it states the grounding screw shall be used to suitably ground the case in a scenario where a laptop has no earth terminal on the socket.

if that's the case then that makes sense...

I'm assuming a separate power supply with an earth terminal will work as well, correct?

[Jo3]

if that's the case then that makes sense...

I'm assuming a separate power supply with an earth terminal will work as well, correct?

It depends on the power supply used for the VCi, some transformers do not have an earth on the secondary winding (SELV) therefor no earth would be present on the side the VCi connects. I simply use my USB to power the unit so I'v never taken a proper look at it. Just don't cut the earth out of your laptop socket and you shouldn't have a problem.

[DvlsAdvct]

my laptop socket, for my old laptop, doesn't have an earth connection. My new one does so there shouldn't be a problem, but I gotta wait on bringing that one out.

Well, I guess it'll be a week or two of troubleshooting.

[midifidler]

Unfortunately, the usb line on the VCI itself is not grounded. so you've got an ungrounded datastream going from the VCI to the laptop.

The usb standard is SUPPOSED to be the part that grounds. but if that doesn't...there can be problems! This is why the USB standard is so unstable, is because it's grounding issues are so volitile.

In a usb plug you have 5 connections, +5V, Data -, Data +, GND, and the shield tab.

The shield is typically a metal foil spiraled around the inner cables and connected to the metal on the outside of the USB connector.

The data stream is grounded, the shield should only be connected to ground on the host ie your computer, not the VCI, if the VCI ground was connected to the USB shield pin this would make matters worse as it would create a ground loop for noise picked up by the shield.

This is different to the hum problem that the earth wire on a turntable will fix, a turntables data stream is at audio frequencies (roughly 20 Hz to 30KHz), as is the mains supply, (50 Hz here and 60 Hzin the US).

A decent turntable has many large metal parts, these will effectivley pick up any mains generated noise at 50 Hz and the first few harmonics, now electrons are homesick in that they all really want to get home, and will take the easiest route home (which is to be at GND or 0V).

Without an earth connection to the metal parts the easiest way home is to jump ship on to the signal wires and cruise through the speakers creating a hum. However if the metal parts are connected to the earth stake on the back of your mixer, or any true earth this provides a very low resistance path to GND or 0V, so rather than cruising through your audio they can slide straight home down the earth wire producing no hum on your system.

However USB data has a frequency in the MHz, providing proper return paths and shielding at these frequencies is a totally different can of worms to the extremely low frequencies of AC and its significant harmonics.

Connecting the shield to ground at the VCI end would actually create/ exacerbate the ground loop problem rather than fix it.

Remember a GND connection does not actually imply an earth connection.
A GND is at 0V, and an earth is a direct connection to the actual earth via a pipe or stake in your basement/backyard. So an earth is a GND, but an GND is not always an earth.

Im by no means an expert on this stuff, so I may get some of the specifics wrong, but I prefer to understand the problem rather than just relying on rule of thumb. I hope you all learn from this discussion, because I certainly am.