Audio baluns for sound card input?

J

Joerg

Guest
Hello Folks,

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?

I know the Muxlab (Montreal) versions which have great frequency
response. However, these are rather bulky devices that are ok for a
fixed installation. But this one needs to be small and portable even if
it's not 100% "hifi".

Ok, of course I could make one. But if there is a smaller of-the-shelf
version that would be better.

Regards, Joerg

http://www.analogconsultants.com
 
How about using the common 'telephone 600r-600r' type transformers ? Easy to
find,just hack any old PC modem card.or if you have access to an old Amtelco
concentrator, they have great audio transformers in there!
jay
 
The pulses within the PSU may be playing havoc. Try it again running off
mains, but make sure the PSU is as far away as the cable allows - so its
electromagnetic radiation won't influence the sound card at all. Orientation
of laptop may also minimise the extraneous pulses.

What type of mic (assuming it's a mic) cable and what length is being run
into laptop?
Balancing transformer (it's not that big) not encouraged yet until we have a
scenario.
 
Usually, if tiny, the modem xformers have the mid-band freq response of a
telco line (200Hz to 4kHz); that's all they ever need to isolat!
 
Hello Jim,

The pulses within the PSU may be playing havoc. Try it again running off
mains, but make sure the PSU is as far away as the cable allows - so its
electromagnetic radiation won't influence the sound card at all. Orientation
of laptop may also minimise the extraneous pulses.
Click to expand...
We did try that. The noise didn't change.

What type of mic (assuming it's a mic) cable and what length is being run
into laptop?
Balancing transformer (it's not that big) not encouraged yet until we have a
scenario.
Click to expand...
It is out of the main mixel panel at line level. This source feeds other
things such as a speaker amp, hearing wands etc. Those didn't get
disturbed so it looks like the laptop is "self polluting".

Regards, Joerg

http://www.analogconsultants.com
 
Hello Jay,

As Jim hinted these are for telephone line bandwidths. I tried them
before and while some modem xfmrs do exceed 4kHz substantially they did
roll off below 300Hz.

Regards, Joerg

http://www.analogconsultants.com
 
Joerg
You say the pre-mixed feed also goes to several other destins. Literally in
parallel with the line level to laptop i/p, or are these from different
facility ports/interfaces? Are these balanced o/ps (floating, ground-free),
and do your other bits and pieces have bal or unbal i/ps?
Is your i/p level into laptop too high? 200mV should suffice. Has it got agc
or has it got adjustable (via software) sensitivity?
 
Ratshack anyone.

they have an audio isolator that is good quality for non audiohpile
applications.


"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:pi11e.15481$C47.4811@newssvr14.news.prodigy.com...
Hello Jim,

The pulses within the PSU may be playing havoc. Try it again running off
mains, but make sure the PSU is as far away as the cable allows - so its
electromagnetic radiation won't influence the sound card at all.
Orientation of laptop may also minimise the extraneous pulses.

We did try that. The noise didn't change.

What type of mic (assuming it's a mic) cable and what length is being run
into laptop?
Balancing transformer (it's not that big) not encouraged yet until we
have a scenario.

It is out of the main mixel panel at line level. This source feeds other
things such as a speaker amp, hearing wands etc. Those didn't get
disturbed so it looks like the laptop is "self polluting".

Regards, Joerg

http://www.analogconsultants.com
Click to expand...
 
Hello Mook,

Radioshack is what I vaguely remembered. I didn't know they called it
isolator. Their web site doesn't offer a lot of tech info, could it be
this one?

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=270-054

Regards, Joerg

http://www.analogconsultants.com
 
On Fri, 25 Mar 2005 23:39:27 +0000, Joerg wrote:

Hello Jim,

The pulses within the PSU may be playing havoc. Try it again running off
mains, but make sure the PSU is as far away as the cable allows - so its
electromagnetic radiation won't influence the sound card at all. Orientation
of laptop may also minimise the extraneous pulses.

We did try that. The noise didn't change.

What type of mic (assuming it's a mic) cable and what length is being run
into laptop?
Balancing transformer (it's not that big) not encouraged yet until we have a
scenario.

It is out of the main mixel panel at line level. This source feeds other
things such as a speaker amp, hearing wands etc. Those didn't get
disturbed so it looks like the laptop is "self polluting".
Click to expand...
If it's power supply noise, how is a transformer supposed to help?

Thanks,
Rich
 
Hello Rich,

If it's power supply noise, how is a transformer supposed to help?
Click to expand...
An audio transformer can cut down on common mode noise currents quite a
bit. Just hook an EMC current clamp onto the DC line from the power
supply into the laptop. Then look at the analyzer when you connect
anything else to the laptop. You can even see it on the scope and the
picture ain't pretty. This stuff propagates onto almost any cable that
connects to the laptop.

Regards, Joerg

http://www.analogconsultants.com
 
Hello Graham,

Common problem with laptops. The psu is usually a 2 wire job , so there's no nice
clean earth for the Y caps in its EMI filter.

Connect it to an earthed device ( such as much audio gear ) and the current from
the Y caps likes to go there instead.
Click to expand...
My impression is that it got worse with the three-wire versions.

Regards, Joerg

http://www.analogconsultants.com
 
Joerg wrote:

Hello Graham,

Common problem with laptops. The psu is usually a 2 wire job , so there's no nice
clean earth for the Y caps in its EMI filter.

Connect it to an earthed device ( such as much audio gear ) and the current from
the Y caps likes to go there instead.

My impression is that it got worse with the three-wire versions.

Regards, Joerg
Click to expand...
From experience or are you conjecturing ?


Graham
 
On Fri, 25 Mar 2005 22:12:03 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello Folks,

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?

I know the Muxlab (Montreal) versions which have great frequency
response. However, these are rather bulky devices that are ok for a
fixed installation. But this one needs to be small and portable even if
it's not 100% "hifi".

Ok, of course I could make one. But if there is a smaller of-the-shelf
version that would be better.

Regards, Joerg

http://www.analogconsultants.com
Click to expand...
I've used common mode chokes successfully in this situation, and also
in the serial port connection, since this too seemed to be necessary.
Compared with an isolating transformer, at very low frequencies, the
transformer has great isolation but poor response, whereas the CM
choke has no isolation but great response, and this seems to be more
appropriate. They are similar at HF, but as the load impedance can be
quite high, there should be no real problem at HF. Try anything that's
available, eg I've recently come across some very cheap CM chokes for
ethernet applications that are 4.7mH with 4 windings. Others are up to
47mH (better still).

Tony (remove the "_" to reply by email)
 
Joerg wrote:
My impression is that it got worse with the three-wire versions.

Regards, Joerg

http://www.analogconsultants.com
Click to expand...
One thing to be considered is to buy an external USB2 soundcard for the
laptop, because the usual input is only meant for an electret mike and mono.
Even if there are line inputs, they are usually not well shielded and the
interference with the digital noise is at elevated levels. Another
possibility is the use of a wireless link with line inputs. These would
eliminate the need for galvanic connection and solve the A/D conversion as
well.
--
ciao Ban
Bordighera, Italy
 
hi joerb,
this unit is ideal for this use stereo 2 isolating transformers in one
box, used for car
audio.http://www.maplin.co.uk/Module.aspx?ModuleNo=33172&TabID=1&source=15&WorldID=&doy=1m3
availible from radio shack i think
regards
bob

On Fri, 25 Mar 2005 22:12:03 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello Folks,

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?

I know the Muxlab (Montreal) versions which have great frequency
response. However, these are rather bulky devices that are ok for a
fixed installation. But this one needs to be small and portable even if
it's not 100% "hifi".

Ok, of course I could make one. But if there is a smaller of-the-shelf
version that would be better.

Regards, Joerg

http://www.analogconsultants.com
Click to expand...
 
that link again

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




On Fri, 25 Mar 2005 22:12:03 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello Folks,

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?

I know the Muxlab (Montreal) versions which have great frequency
response. However, these are rather bulky devices that are ok for a
fixed installation. But this one needs to be small and portable even if
it's not 100% "hifi".

Ok, of course I could make one. But if there is a smaller of-the-shelf
version that would be better.

Regards, Joerg

http://www.analogconsultants.com
Click to expand...
 
I read in sci.electronics.design that Joerg
<notthisjoergsch@removethispacbell.net> wrote (in
<T001e.1641$FN4.1140@newssvr21.news.prodigy.com>) about 'Audio baluns
for sound card input?', on Fri, 25 Mar 2005:

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?
Click to expand...
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'?
--
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
 
I read in sci.electronics.design that Joerg
<notthisjoergsch@removethispacbell.net> wrote (in
<Pi11e.15481$C47.4811@newssvr14.news.prodigy.com>) about 'Audio baluns
for sound card input?', on Fri, 25 Mar 2005:

It is out of the main mixel panel at line level. This source feeds
other things such as a speaker amp, hearing wands etc. Those didn't get
disturbed so it looks like the laptop is "self polluting".
Click to expand...

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.
--
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
 
I read in sci.electronics.design that Michael A. Terrell
<mike.terrell@earthlink.net> wrote (in
<4244DC9E.AA25E0E4@earthlink.net>) about 'Audio baluns for sound card
input?', on Sat, 26 Mar 2005:
No. You need to take the brute force method. An isolation
transformer connected to the PA amp's speaker outputs and a two stage
attenuator to reduce the level to what you want. get a 25, 70 or 100
volt audio line transformer and connect the low impedance side to the
speaker line.
Click to expand...
I REALLY would not recommend this. Why transform the audio up to 25 V or
more only to attenuate it again?
--
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
 
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