impedance problem?

[BigPapaFly]

impedance? Actually, I really don't know what that means...but here's the deal. I have a very skeletal set-up...a laptop running Cakewalk to a midi keyboard, which generates all my tones (the keyboard does, that is)...and the keyboard going out to a TASCAM 788. I monitor the 788 through a home stereo by running out of the TASCAM into the AUX ins on the stereo unit. It works, BUT, I get nasty buzzing through my speakers. The buzzing is only there when the cable from the keyboard is plugged into the TASCAM, so its not a problem with the TASCAM alone. I've had some problem with the OUT on the keyboard, having to jiggle it and whatnot, but when the midi chords are disconnected from the keyboard, and only the connection between the keyboard and the TASCAM remain, the buzzing stops. So, I bought a new power strip and plugged everything into the same strip- laptop, keyboard, laptop speakers, tascam, even the cdr attatched to the keyboard is running through the same power strip now...

Any ideas?

Thanks for any help.

 

[AlChuck]

It's not impedance...

 

[Track Rat]

Sounds to me like a ground loop. You've already done what would be my first suggestion, plug all the power chords in at one power strip. You might try a ground lift on the patch cables from the keyboard.

 

[Qwerty]

viagra?

 

[BigPapaFly]

Track Rat: when you say "ground lift on the patch cables from the keyboard." what do you mean? The cable running from the keyboard to the tascam is about four feet off the ground- running along the exterior of my work space.

 

[James Argo]

...Track Rat didn't say Ground as earth you're standing on... although it's very close related. He's talking about Electrical "ground". It means one of your gear (the keyboard is the main suspect here...) is not "electricaly grounded" propherly. There's should be three cables in the power strip. (+) (-) and (ground). Some strips don't have three but just two. All you have to do is make sure each of your gear connected to propher grounded power strip...

 

[skippy]

If I read this correctly, the noise problem exists whenever the keyboard is connected to the TASCAM _and_ the MIDI cables are connected from the keyboard to the computer. That's the key, right there: the keyboard is quiet as long as the MIDI cables are disconnected, right?

What you have here is a ground loop that is letting noise (probably ground noise and crud from the computer) sneak into the audio paths. Computers are horrific EMI/RFI generators, by and large: the digital switching noise can really wreak havoc with audio systems.

Here's a test: if the laptop has a battery in it, try disconnecting the AC adapter and letting it run on battery. If the noise remains, it is switching noise from the laptop. If it goes away, it may be because the laptop has a really cheap and nasty switching power supply in its AC adapter, and noise from _that_ is causing the problem. In any case, if it's a laptop, the computer itself doesn't have a ground connection (the AC adapter is almost certain to be a 2-pin plug, right?). If this is the case, the only way the laptop has to get grounded is through the shield on the MIDI cable, and there's where your noise injection might be coming from.

If things quiet down when you're running on battery, the next step is to figure out some way to get real grounding set up for the laptop. That could be as simple as running a wire from some chassis ground point on the laptop (say, one of the jackscrews for the serial or parallel port) to the same ground point on the power strip. That's getting ahead of the game, though. First, try the battery test, and let us know how it goes...