Audio baluns for sound card input?

[John Woodgate]

I read in sci.electronics.design that Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote (in
<4244B890.28B6BA4D@hotmail.com&gt about 'Audio baluns for sound card
input?', on Sat, 26 Mar 2005:

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.

What Y caps? For a 2-wire, there is no point in including a Y cap.
--
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]

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

 

[Nico Coesel]

"j.b. miller" <invalidjbmiller@cogeco.ca> wrote:

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

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.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl

 

[Jim Gregory]

Or why not just change the switched-mode(?) power supply to something really
repectable to activate the laptop?
From your description of its filthy waveforms superimposed, it sounds
verboten to deliver decent clean DC outputs.
Jim

 

[Fred Bloggs]

Joerg 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

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.

 

[Pooh Bear]

John Woodgate wrote:

I read in sci.electronics.design that Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote (in
4244B890.28B6BA4D@hotmail.com&gt about 'Audio baluns for sound card
input?', on Sat, 26 Mar 2005:

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.

What Y caps? For a 2-wire, there is no point in including a Y cap.

See some applications schematics at www.powerint.com. I'll see if I can
dig out the relevant ANs in the office.


Graham

 

[Pooh Bear]

peg@slingshot.co.nz wrote:

This or similar might help
http://www.rohm.com/products/databook/audio/pdf/ba3121.pdf

If you're going to have active circuitry a simple differential input
op-amp configuration will do the job at better quality.

Graham

 

[Pooh Bear]

John Woodgate wrote:

I read in sci.electronics.design that Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote (in
4244B890.28B6BA4D@hotmail.com&gt about 'Audio baluns for sound card
input?', on Sat, 26 Mar 2005:

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.

What Y caps? For a 2-wire, there is no point in including a Y cap.

Correction. Not in the EMI filter.

See the following example....
http://www.powerint.com/images/schematic/di43.gif


Graham

 

[John Woodgate]

I read in sci.electronics.design that Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote (in
<42457645.774C127C@hotmail.com&gt about 'Audio baluns for sound card
input?', on Sat, 26 Mar 2005:

peg@slingshot.co.nz wrote:

This or similar might help
http://www.rohm.com/products/databook/audio/pdf/ba3121.pdf

If you're going to have active circuitry a simple differential input
op-amp configuration will do the job at better quality.

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).
--
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 Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote (in
<42457611.BFD23784@hotmail.com&gt about 'Audio baluns for sound card
input?', on Sat, 26 Mar 2005:

John Woodgate wrote:

I read in sci.electronics.design that Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote (in
4244B890.28B6BA4D@hotmail.com&gt about 'Audio baluns for sound card
input?', on Sat, 26 Mar 2005:

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.

What Y caps? For a 2-wire, there is no point in including a Y cap.

See some applications schematics at www.powerint.com. I'll see if I can
dig out the relevant ANs in the office.

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.
--
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

 

[Michael A. Terrell]

John Woodgate wrote:

I read in sci.electronics.design that Michael A. Terrell
mike.terrell@earthlink.net> wrote (in
4244DC9E.AA25E0E4@earthlink.net&gt 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.

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

1: I did this because it was usually the only decent audio transformer
available when I needed to build another interface in a hurry. I just
use the pair of pots when there is no hum problems. BTW, the highest
wattage tap on the transformer has the lowest voltage. If you use the
16 ohm winding and a 5 watt tap the voltage doesn't go up very much.
The highest voltage is on the lowest tap, or 25 volts. Not only that,
but the voltage only reaches 25 volts at the full rated output of the
amplifier.

2: A good 600 ohm to 600 ohm transformer can be expensive and hard to
find in a hurry. I have a pile of crappy mil spec 600 ohm to 600 ohm
transformers that roll off a little over 2.5 KHz and others that aren't
much higher quality.


--
?

Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

Pooh Bear wrote:

peg@slingshot.co.nz wrote:

This or similar might help
http://www.rohm.com/products/databook/audio/pdf/ba3121.pdf

If you're going to have active circuitry a simple differential input
op-amp configuration will do the job at better quality.

Graham

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

Michael A. Terrell
Central Florida

 

[John Woodgate]

I read in sci.electronics.design that Michael A. Terrell
<mike.terrell@earthlink.net> wrote (in
<42458123.93B95ED7@earthlink.net&gt about 'Audio baluns for sound card
input?', on Sat, 26 Mar 2005:

I did this because it was usually the only decent audio transformer
available when I needed to build another interface in a hurry.

Yes, the show must go on, of course. I know someone who used a PENCIL
LEAD as an attenuator in those circumstances! But I wouldn't put it
forward as a recommendation.
--
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

 

[J M Noeding]

On Sat, 26 Mar 2005 15:24:48 +0000, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote (in
42457645.774C127C@hotmail.com&gt about 'Audio baluns for sound card
input?', on Sat, 26 Mar 2005:


peg@slingshot.co.nz wrote:

This or similar might help
http://www.rohm.com/products/databook/audio/pdf/ba3121.pdf

If you're going to have active circuitry a simple differential input
op-amp configuration will do the job at better quality.

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).

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

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

 

[J M Noeding]

On Sat, 26 Mar 2005 15:35:11 GMT, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

1: I did this because it was usually the only decent audio transformer
available when I needed to build another interface in a hurry. I just
use the pair of pots when there is no hum problems. BTW, the highest
wattage tap on the transformer has the lowest voltage. If you use the
16 ohm winding and a 5 watt tap the voltage doesn't go up very much.
The highest voltage is on the lowest tap, or 25 volts. Not only that,
but the voltage only reaches 25 volts at the full rated output of the
amplifier.

2: A good 600 ohm to 600 ohm transformer can be expensive and hard to
find in a hurry. I have a pile of crappy mil spec 600 ohm to 600 ohm
transformers that roll off a little over 2.5 KHz and others that aren't
much higher quality.

useful transformers are not difficult to find if you know how an audio
transformer looks like, you probably have a lot of equipment where
they are without considering it. Impedance is not important when the
equipment hasn't been made to a specific impedance

Jan-Martin


---
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 15:35:11 GMT, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:

1: I did this because it was usually the only decent audio transformer
available when I needed to build another interface in a hurry. I just
use the pair of pots when there is no hum problems. BTW, the highest
wattage tap on the transformer has the lowest voltage. If you use the
16 ohm winding and a 5 watt tap the voltage doesn't go up very much.
The highest voltage is on the lowest tap, or 25 volts. Not only that,
but the voltage only reaches 25 volts at the full rated output of the
amplifier.

2: A good 600 ohm to 600 ohm transformer can be expensive and hard to
find in a hurry. I have a pile of crappy mil spec 600 ohm to 600 ohm
transformers that roll off a little over 2.5 KHz and others that aren't
much higher quality.

useful transformers are not difficult to find if you know how an audio
transformer looks like, you probably have a lot of equipment where
they are without considering it. Impedance is not important when the
equipment hasn't been made to a specific impedance

Jan-Martin

I have several hundred transformers and most have poor frequency
response for this application. I also pointed out commercial "DI Boxes"
sold in music stores at high prices.

--
?

Michael A. Terrell
Central Florida

 

[John Woodgate]

I read in sci.electronics.design that J M Noeding <la8ak@online.no>
wrote (in <tf1b419fce1ca35m2geoc7054ma24b85ob@4ax.com&gt about 'Audio
baluns for sound card input?', on Sat, 26 Mar 2005:

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

I hope you are not correct in that assertion. The local commercial
stations had to meet ITC requirements, and they were not crude.
--
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 Michael A. Terrell
<mike.terrell@earthlink.net> wrote (in
<42458170.4E25A467@earthlink.net&gt about 'Audio baluns for sound card
input?', on Sat, 26 Mar 2005:

If you're going to have active circuitry a simple differential input
op-amp configuration will do the job at better quality.

Graham

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

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.
--
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

 

[Pooh Bear]

John Woodgate wrote:

I read in sci.electronics.design that Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote (in
42457645.774C127C@hotmail.com&gt about 'Audio baluns for sound card
input?', on Sat, 26 Mar 2005:


peg@slingshot.co.nz wrote:

This or similar might help
http://www.rohm.com/products/databook/audio/pdf/ba3121.pdf

If you're going to have active circuitry a simple differential input
op-amp configuration will do the job at better quality.

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 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

 

[Pooh Bear]

J M Noeding wrote:

I don't understand what is so difficult about transformers, you find them
in allmost any sorts of modems

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

Graham