Ground Connections

[Phredy1]

I couldn't find any dual channel active DI boxes that looked decent and got good reviews. I found some single channel boxes for $140 each. The only dual channel DI box at Guitar Center had got a review of R & L channels bleeding together and was only $40.

I think I am going to try a Rat Shack ground loop isolator between the sound card and the mixer and see if I can get off cheap ($17). If it doesn't work I can return it and I'm not out anything but some time and gas.

From the sound card it is unbalanced and I can over drive my mixer easily now, so if I loose some with the isolator I would still be ok - as long as it does not reduce the audio quality.....

It probably won't work but worth a try. I will post results of my the cheap fix in a few days.

-Gene

[daedal]

Another thing you can do to minimize the risk of problems is to power the projector and the computer with the controller off the same 110V circuit. Even if you have to run an extension cord from a power strip out to the projector, at least the length of the ground loop will be minimized to double the length of the cable between them.
...
Adam

Or just put the whole computer, QM2000, and everything else inside the projector

--DDL

[Mr.Coffee]

you can get the whirlwind EDB-1 (economical direct box) for $20-30 dollars. it is a pretty good passive direct box.

the iso transformers you get from wal-mart or car audio stores can work, but you have to ground them (they have ground wires for this, if not then you're acutally buying some sort of choke.)

D.I boxes don't technically function as iso transformers, but you can lift the ground between the input and output, so sometimes that will kill the noise. regardless of that fact, they are the best option for connecting unbalanced high-impedance audio to balanced, low-impedance inputs. Check ebay and you can get some great deals on them,but like I said, the edb-1's are cheap and work well (in both directions, btw). you can also get iso transformers by themselves. The sescom Il-19 is the industry standard, but pricy at ~$80 per channel. You can buy jensen iso transformers by themselves, and make whatever you want, just make sure you get the proper impedance.

of course, now a days, you can get professional audio interfaces on the cheap, so you could just buy one of those and feed the system the signals it deserves. (I bought an echo gina off ebay in 2003 for $100, couldn't give it away now (and wouldn't, she still works great!))

[buffo]

Phredy1;

I tried a pair of passive boxes at first, and ended up taking them back. Trust me, you won't be happy with the loss in signal level that you get with a passive box.

Here's a link to the Active Direct Box that I bought at Guitar Center. (You'll need two of them though, as these are single-channel boxes.) When I bought them, they were around $80 each, but apparently they've come down in price a bit. (List price is just $59.99 now.)

I don't know if Live Wire makes a dual-channel box or not. Guitar Center didn't seem to have one from them, though they did stock other dual channel units from Radial Engineering... They were just too expensive.

And as Mr. Coffee pointed out, all you need to do is flip the "ground lift" button on each of the boxes and you're good to go.

Adam

[Phredy1]

Anyone have any feedback on BBE active DI boxes?

I found a BBE DI-400 4 Channel Rack Mounted Active Direct Box for less than $200 and would do what I want and more. Another plus for this is no batteries or 48V phantom power to deal with.

Better pictures here

-Gene

[djlorenz]

interesting post... i have to make wiring in my new lasers...
what i must do? i wanna a nice solution that doesn't give me problems with standard hardware...

connecting al COM / Ground / AC earth / ilda connector pin / together?
and another thing... do you usally connect the 25 pin Connector chassis to ground?

thanks

[DMills]

One (possibly slightly radical answer) to the pain that I have used a few times is to basically follow AES 48 grounding practises (ILDA 25 straight to case ground as close as possible, internal signal ground to case ground at ONE point), and high common mode impedance differential line receivers on all signal pairs.
Goes without saying that power ground connects to case ground.
Sure you get an earth loop, so what? The signal is not referenced to earth (except in a common mode range sense).

Job done, no ripple, hum or other issues.

I used THAT corp balanced line receivers which are bootstrapped to have meg ohm common mode impedances (which means that you get some balanced line goodness even with mismatched source impedances).
On the audio side, coming out of the PC on adat or spdif optical solves that one, as does using a proper audio interface, in a pinch I bought some Lundal line output transformers on fleabay that solve this.

It took the audio game a long time to learn from the instrumentation guys, I suggest me may do well to learn the same lessons.

So I would go with 1, but do the interface right.

Regards, Dan.