Audio baluns for sound card input?

[Joerg]

Hello John,

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.

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

How are you proposing to use 'baluns'?

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

http://www.analogconsultants.com

 

[Pooh Bear]

Joerg wrote:

Hello John,

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.

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

How are you proposing to use 'baluns'?

They are only called baluns by the audio people.

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

http://www.acronymfinder.com/af-query.asp?p=dict&String=exact&Acronym=BALUN

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.

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


Graham

 

[Ted Edwards]

Joerg wrote:

When someone at our church tried to record audio into a laptop this
caused a serious racket if line powered. Probably this is due to the
laptop switch mode power supply. Only running the laptop off its battery
produces a decent recording. Is there a simple balun transformer that
you could recommend?

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

 

[J M Noeding]

On Sat, 26 Mar 2005 19:58:44 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:

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

---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/91n.htm

 

[Michael A. Terrell]

J M Noeding wrote:

On Sat, 26 Mar 2005 19:58:44 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:



........ and practical experience in solving problems helps
---
J. M. Noeding

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.

--
?

Michael A. Terrell
Central Florida

 

[John Woodgate]

I read in sci.electronics.design that Joerg
<notthisjoergsch@removethispacbell.net> wrote (in
<1Rk1e.2982$zl.2568@newssvr13.news.prodigy.com&gt about 'Audio baluns for
sound card input?', on Sat, 26 Mar 2005:

Hello John,

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.

Maybe, but it's not my laptop so I'll have to ask. Some "modern" power
supplies seem weird to me. One in a new printer works but produces lots
of EMI and makes inconsistent hissing noises. Like a whining bearing.
Dell said that's "normal".

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

rather soon.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[John Woodgate]

I read in sci.electronics.design that Joerg
<notthisjoergsch@removethispacbell.net> wrote (in
<fil1e.15802$C47.8239@newssvr14.news.prodigy.com&gt about 'Audio baluns
for sound card input?', on Sat, 26 Mar 2005:

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.

AFAIK, they are only called baluns by **RF** people, not audio people.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Jim Gregory]

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.

 

[J M Noeding]

On Sun, 27 Mar 2005 06:19:11 GMT, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

J M Noeding wrote:

On Sat, 26 Mar 2005 19:58:44 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:



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

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?


---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/91n.htm

 

[Michael A. Terrell]

J M Noeding wrote:

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?

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.
--
?

Michael A. Terrell
Central Florida

 

[Joerg]

Hello Fred,

Run the laptop off the battery and run a small jumper from laptop case
ground to the power supply safety ground while it is plugged in. If the
noise is present then a small isolation transformer, in conjunction with
screened twisted pair mic cable, should improve the situation and will
be the best you can do. If no noise is present with the jumper, then you
are wasting your time, the power supply is corrupting the sound card
circuitry itself- nothing you can do except go after that power supply
to increase attenuation of high frequency components by cutting cable
and interposing small box with multiple LC lowpass chain and ferrite
chokes.

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

http://www.analogconsultants.com

 

[Joerg]

Hello Graham,

To cut a long stort short.... Can you afford $30 ? It's small, portable and
does what you want.

Pro audio guys call it a DI box.

http://www.behringer.com/DI20/index.cfm?lang=ENG

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

http://www.analogconsultants.com

 

[John Woodgate]

I read in sci.electronics.design that Joerg
<notthisjoergsch@removethispacbell.net> wrote (in
<rdF1e.2224$FN4.338@newssvr21.news.prodigy.com&gt about 'Audio baluns for
sound card input?', on Sun, 27 Mar 2005:

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

B*****d computer people, never did understand audio and never will!
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Joerg]

Hello Ted,

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.)

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".

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.

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.

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.

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

http://www.analogconsultants.com

 

[J M Noeding]

On Sun, 27 Mar 2005 16:14:16 GMT, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

J M Noeding wrote:

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?


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.

then you might have learned how to follow the thread
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/91n.htm

 

[Joerg]

Hello John,

B*****d computer people, never did understand audio and never will!

Well, yeah, they could hire some pros to take care of this stuff. But
nowadays I have the impression that computers are pieced together using
existing designs. And pieced together in quite a hurry. The MB comes
from this mfg, the drives from that, the sound stuff from another and
the PS from yet another. Slap it all together and you've got a PC. Sort
of. As long as it does video games nicely then 95% or more of the
customers are going to be happy campers.

Heck, even our answering machine (from a BIG US mfg) is full of noise
when the broadband connection runs. Some day I'll fix that, too, but
sometimes I am getting sick of having to polish off the designs that
others were supposed to finish properly. Unless I am paid for it, then
I'll do it with gladness.

Regards, Joerg

http://www.analogconsultants.com

 

[Joerg]

Hello Michael,

... I still have one I made 20 years ago
with a R.L. Drake tuning knob on the box. ...

Ah, Drake. Was it the style of knobs found on the Drake 2B? That was one
of the most beautiful designs I have ever seen. Both from an aesthetics
point of view and with respect to the circuitry.

Regards, Joerg

http://www.analogconsultants.com

 

[Joerg]

Hello Graham,

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

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

Regards, Joerg

http://www.analogconsultants.com

 

[Joerg]

Hello 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.

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

http://www.analogconsultants.com

 

[Joerg]

Hello John,

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

I grew up in RF but was surprised when I heard audio folks asking where
the box with baluns was. The people that rig up the gear for rock bands.
Maybe they aren't the typical audio expert. But they usually did have a
lot of tatoos.

Regards, Joerg

http://www.analogconsultants.com