unbalanced input grounds..?

[jeth]

With all this fantastical pro equipment being diyed my searches have failed to come up with the answer to this question...

How is it best to make ground connection for unbal***ed (thought that may be a dirty word in these parts) equipment? Do the shield/negative connections go to the input circuits signal ground, or should they all be bussed together and connected back to star ground(or just straight to chassis)?

 

[analag]

Look at any Behringer rack unit manual, it gives instructions on how to terminate your connections.

 

[jeth]

Afraid I don't have a Bringer manual to hand...or was that meant to be a Joke? :roll:

 

[TedF]

The theory of unbalanced input grounding is quite simple and easily understood...... The audio signal IS the exact voltage between the unbalanced input wire and its ground; so to get an accurate clean signal into the input amplifier, the ground has to be connected directly to the ground reference point electrically nearest to the input device: If it's an IC, then it's fairly simple, if it's a discrete amplifier, then it can be a little less easy.

Looking at it the other way around:.....
When connecting unbalanced outputs to balanced inputs, it's often worth treating the unbalanced output and its ground connection as a balanced pair, this can usually eliminate hum problems.... provided that the balanced input is truly 'balanced' and has good common mode rejection properties.
There's a lot to be said for sticking to transformers! :guinness:

 

[skipwave]

[quote author="TedF"]There's a lot to be said for sticking to transformers! :guinness:[/quote]

Somebody shout "Amen!"

 

[jeth]

There's a lot to be said for sticking to transformers!

Would love to go trafo, unfortunately new family arrival means I'm totally broke....I'd rather build something to fit my needs than nothing at all. There's alaways the aspiration that I can upgrade it all oneday....

 

[ciminosound]

Here's some tech notes from Rane that may answer some questions.

http://rane.com/note110.html

http://rane.com/note151.html

 

[jeth]

Thanks criminosound, but I've read through the rane notes and I'm familiar with different cable connections as I know a fair bit more about sound system connections than I do electronic circuits. I'm mreally trying to find out how to make the in the box connections between the incoming cables and the circuit itself. Nice one for the input tho'

 

[skipwave]

[quote author="jeth"] Would love to go trafo, unfortunately new family arrival means I'm totally broke....I'd rather build something to fit my needs than nothing at all. There's alaways the aspiration that I can upgrade it all oneday....[/quote]

You might be surprised by how cheaply you can get some trafos. Edcors are $11 for outputs, and depending on the application you can find some very nice inputs on evilBay if you look for the lesser known brands. Forgot UTC and Altec/Peerless. Go to the Transformer Meta and find the other brands, then search the forum to see what data has been presented here, what projects people have used them in, etc. You may not have time for all that, but my point is that it is possible if you are willing.

 

[jeth]

I'm very willing but there are several factors working against me...

First, I'm stuck in deepest mexico where few parts are available, if they were they'd be pricey due to their specialist nature and low demand. I have practically no cash to throw at this but i desperately want to do something. The cost of mailing in parts from the states or elsewhere is just too high. So I have to face the fact that I'll be playing around with TL072's for the time being, that's really all i can lay my hands on. But it'll do me to learn and test my layout till i can rebuild in the uk with quality parts.
I'm a relative beginner to electronics, though I've probably chosen too complex a project to learn with (see my "most unusual mixer project" thread). This is because I enjoy researching the design issues and feel I'll learn a lot more than just building up existing projects. Despite this I think it's best to keep my circuit blocks simple and relatively cheap whilst I'm still experimenting and learning fundamentals. So I'm afraid it's opamps for now.

You probably didn't need such a thorough explanation, but there it is! Cheers for the tips though...good to know for future ref.