LM358N or other IC for balanced input?

[chozo4]

Just a curious question as I've not exactly worked much with balanced inputs at all. Currently my amp is connected with unbalanced inputs (TRS jack) and as such grounded through the input sleeve. Disconnecting the ground for it results in a fair bit of signal loss but power will not run through there and rather the power ground instead. I have cleaned up the rail noise with a ripple filter but would like to isolate the input ground and power grounds from each other next. Using resistors on either ground do not do any good in this regard.

I'm wondering if an LM358 or other such 8pin package IC can be used for converting an unbalanced input (unbalanced ground to both IN- pins) to a balanced one to isolate the input ground from the power ground in a single rail amp. Has anyone experience with doing the such or would a specifically designed differential amp be a necessity for the purpose instead?

[budm]

Re: LM358N or other IC for balanced input?

So let me get this correcly, the AMPLIFER you have has only Un-balanced input (Tip (hot) and Sleeve (gnd)) but you want the Amp to have Balanced input for the differential signal input?
Or explain what you have and what you are trying to do.

[chozo4]

Re: LM358N or other IC for balanced input?

What I'm trying to do is isolate the input ground from the unbalanced input of an amp. I had a topic on the issue before on a slightly related issue (power rail noise) and is an amp I'd built based on the TEA2025B Opamp. The input ground and power ground share the same rail and the power ground needs to be otherwise disconnected to avoid a ground loop. Both the input device and amp share the same power source so the power source grounds through the input ground of my amp.

I'm wondering if an lm358 or another type of IC would do the trick.

edit: I also realized I made the new topic in the completely wrong forum. Would explain why it didn't show up in the audio equipment discussion forum as intended. My apologies.

[budm]

Re: LM358N or other IC for balanced input?

OK, so you have unbalanced input, even if you have balanced input but the external Source is un-balanced which means the source GND is still connected to the chassis and connected to the safety GND and your receiving amp also has audio circuit GND tied to safety GND, then you will still get the GND loop. You need to lift the circuit GDN from chassis GND, if you look at pro audio with 3-prong power plug, you will see GND lift switch (not the safety GND lift) that will disconnect the audio circuit GND from the chassis GND. if they do not have switch then you will see that they use washer on the input/output jack to float the circuit from the chassis.
If you draw up the wiring between two or more piece of equipment that has 3-prong plug and the AUDIO circuit GND is attached to the chassis, then you can see how the GND LOOP current flows between the equipment. What ever you do, do not lift the SAFETY GND.
Balanced source to balanced input, then you do not have to worry about loop because the signal is no longer reference to GND, differential signal is the key.
http://sound.westhost.com/earthing.htm

[montemcguire]

Re: LM358N or other IC for balanced input?

A 1:1 line input transformer is simple and foolproof. They aren't cheap if you want very high quality, but you can get several hundred volts ground isolation easily, something that an electronically balanced input stage will not do so easily.

The Jensen Isomax series is designed for consumer and pro gear to solve this problem. You don't have to think - just plug it in series with the input. Here's a link to get started: http://www.jensen-transformers.com/h...ter/isolators/