Audio baluns for sound card input?

Hello Graham,

Could be but that printer thing is glued shut. Sometimes when I have to look at switchers I get the impression that there are designers who don't even know the difference between CCM and DCM anymore. Let alone the RHP issue.

Regards, Joerg

Hello Tony,

That's a good idea. Actually I have CM chokes with several mH.

Regards, Joerg

Hello Bob,

audio.http://www.maplin.co.uk/Module.aspx?ModuleNo=33172&TabID=1&source=15&WorldID=&doy=1m3

Yes, that looks very similar to the RS version, except that they also throw in 3.5mm to RCA adapters which is nice for laptops.

Regards, Joerg

Hello John,

Well, when run on the battery all noise is gone.

They are only called baluns by the audio people. It's just an isolation transformer that can also be used for balun situations such as a symmetrical mike into a grounded amp input etc.

Regards, Joerg

Really ? I thought it was an RF term ! Been in audio from hobbyist level onwards for over 35 yrs and never heard an audio type use the term.

Funnily enough I was just about to go to dictionary.com to see if I could find an explanation for the term.

Aha - BALUN Balanced/Unbalanced

Yup, I'd call it an isolation transformer too. You really need an UNBAL !

Graham

What brand of laptop? Does any of "racket" get back into the rest of the church audio system? If you hold a small portable radio close to the line operated power supply or the computer, do you pick up a lot of noise? (I'll be surprised if you do! The FCC get pretty upset about these things creating a lot of RFI.)

From your sig, I assume you have easy access to a decent oscilloscope. Try looking at what's on the lines with the laptop operating of line power.

Personally, I suspect a lot of 60Hz, etc. pickup. If the garbage is only a few volts or less, you could easily build a differential amplifier out of three transistors, a few small capacitors and a 9V battery. The third transistor is for a current source to supply the emitter current for the diff-amp. This will give very good common mode rejection.

Ted

......... and practical experience in solving problems helps

The last adapter I built cost less than $6 for the parts. I always have a small pile of empty project boxes and the line matching transformers so all I had to buy was the two pots, a knob and one connector. It takes about 30 minutes to drill the holes, mount the parts and solder all the wires. I still have one I made 20 years ago with a R.L. Drake tuning knob on the box. I built it and used it to record radio spots from a satellite feed and sent tapes out to a number of radio stations every month. No one ever said a word about the audio quality. Since John is so worried abut stepping the voltage up less than a 1 to 3 ratio you can turn it round and lose a couple dB up front.

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

What Dell says and what is true are not the same. I suspect it will fail rather soon.

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

AFAIK, they are only called baluns by **RF** people, not audio people.

Hear, hear, we always called them 600 ohm:600 ohm telephone-line repeaters or isolating xformers. Baluns (RF) are often added to a TV/radio receiver to convert 300 ohm ribbon antenna to 75 ohm coax input.

stepping up from loadspeaker o/p to line impedance.... By the way, is your experience with posting on newsgroup about the same level as your missed technical experience?

Hello Graham,

True but you can buy them. The Muxlab versions are pretty good but AFAIR they were about $40 a pop.

Regards, Joerg

Hello Graham,

With the good old uA733 in the first stage? I designed a lot of stuff with these because they were an absolute bargain.

Regards, Joerg

How is your track record in putting mission critical systems back on line and keeping them operating while meeting all specifications? As far as newsgroups I've been online for at least five years. BTW, the special DC powered Microdyne 700 series receiver I worked on for NASA is still in use aboard the International Space Station. Now stick your nose back up your ass and piss off.

Over here, one of the better small commonly available 'line level transformers' you can get is made by OEP.

RS components stock some of them. I don't know if you meant Radio Shack or RS components when you said you were getting a transformer form RS.

Graham

Hello Fred,

That's a good idea to test a ground loop w/o the power supply. I suspect it'll be clean though because we also use other gear there, such as a cassette deck for recording. Those are grounded and work fine.

The laptop is said to work ok with its power supply and a mike, just not when connected to the other (grounded) equipment.

Regards, Joerg

Hello Graham,

Thanks. That is not very expensive at all. We'll see what the RS transformer does. It should at least improve things noticably but if it leaves noise then, yes, it will be time for a DI box. But maybe a passive one because the Ultra-DI needs phantom power (which we have but it increases the number of cables) or a 9V battery.

Regards, Joerg

Hello Ted,

Dell. I don't know about that one but I just held an AM radio to the DC cable of my Inspiron 2500. If closer than a few inches I even lost local AM stations which were replaces by the typical "wheeeeshhhhh".

I hope to avoid having to schlepp a big HP or Tek to church but will if needed. This audio room is very packed and just squeezing in there with a scope will be a challenge.

It was higher frequency stuff, the typical switcher noises. I'll try passives first because anything with batteries is a hassle. Murphy's law says they'll exhaust in the middle of the sermon. That has already been a big problem with our wireless mikes until we found nifty uC controlled charge stations and 9V NiMH that can pack 250mAh.

Regards, Joerg