Audio baluns for sound card input?

Correction. Not in the EMI filter.

See the following example....

Graham

I read in sci.electronics.design that Pooh Bear wrote (in ) about 'Audio baluns for sound card input?', on Sat, 26 Mar 2005:

But those have very poor CMRR for radiated RF! Just what is NOT wanted in this case (if what the OP thinks is the cause is indeed the cause).

I read in sci.electronics.design that Pooh Bear wrote (in ) about 'Audio baluns for sound card input?', on Sat, 26 Mar 2005:

I don''t know what you wanted me to look at but I looked at the EPR11 schematic, which is for a 2-wire and ... no Y-cap.

How does this remove the hum? one input of the op amp will be grounded because it is an unbalanced source.

remember when they started local radio in this area (like BRMB or Radio City 199), they had no understanding for unbalanced equipment and balanced telphone lines,we got a lot of complaints. Transformers cured the problem. I don't understand what is so difficult about transformers, you find them in allmost any sorts of modems

-JM

that link again

I read in sci.electronics.design that Joerg wrote (in ) about 'Audio baluns for sound card input?', on Fri, 25 Mar 2005:

I don't know exactly what you are doing (e.g. how many microphones and how long are the cables), but I think you need to do some tests before you assume that the power supply is the problem. While these things emit into the mains supply, they don't normally emit enough radiation to cause problems with audio unless the audio and power supply cables are much too close together.

How are you proposing to use 'baluns'?

I read in sci.electronics.design that Joerg wrote (in ) about 'Audio baluns for sound card input?', on Fri, 25 Mar 2005:

It sounds as if it is faulty. Does it do the same thing when used elsewhere with a different signal source? If so, It IS faulty.

I read in sci.electronics.design that Michael A. Terrell wrote (in ) about 'Audio baluns for sound card input?', on Sat, 26 Mar 2005:

I REALLY would not recommend this. Why transform the audio up to 25 V or more only to attenuate it again?

I read in sci.electronics.design that J M Noeding wrote (in ) about 'Audio baluns for sound card input?', on Sat, 26 Mar 2005:

I hope you are not correct in that assertion. The local commercial stations had to meet ITC requirements, and they were not crude.

I read in sci.electronics.design that Michael A. Terrell wrote (in ) about 'Audio baluns for sound card input?', on Sat, 26 Mar 2005:

The differential stage still has common-mode rejection, and the hum is common-mode. This technique is widely used for video on coax, less so for audio.

Assuming your mixer and other apparata are earthed/grounded to a reputable ground, try connecting audio screen to mains-operated (grounded) destins *only* at receiving ends, so dissing them (o/c) at mixer send end, ie, use cores only which you say are commoned. But keep the screen for the laptop feed as unbalanced and it can then be experimentally isolated with a 10k:10k i/p transformer at *receiving* end. J

I doubt if the car stereo chip the previous poster suggested will be any better than a standard audio grade op-amp in differential mode ( especially since you can use close tolerance Rs with the discrete solution ).

I'm unclear if the problem has been definitively resolved as being RF though. Heard of plenty of similar scenarios where it's basically 50/60 Hz.

Graham

Transformers with *respectable audio performance* are neither especially cheap nor common. Not much demand for them these days either.

Graham

Funny you should mention that John. Back in 1989/90 I designed a simple differential video buffer for EMI studios to solve just such a problem. They used bucketloads of them. I'm not aware if there was an equivalent 'off the shelf' product ( certainly at a sensible price ) that could do the job.

Graham

Note my other post with link to

It's the Y cap from pri to sec that's the cause of the leakge current of course, not actually the EMI filter.

Graham

It depends on the quality of the transformer. Where I used to work we used a particular type/brand of these telephone transformers for everything including hifi (roll-off above 20kHz). Also beware not to saturate a transformer.

I read in sci.electronics.design that Pooh Bear wrote (in ) about 'Audio baluns for sound card input?', on Sat, 26 Mar 2005:

Yes, our messages overlapped. I'm not up on SMPS and I wonder what that cap actually does, and whether that's the best way to do whatever it does.