Audio baluns for sound card input?

[Michael A. Terrell]

Joerg wrote:

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

I believe that it was the 4C series. It has the finger hole for
quick tuning, but someone tried to be helpful and laid a hot soldering
iron on it during an emergency repair at a Cable TV Headend.

I have a friend who worked QC at Drake in Miamisburg and it was
rejected for a minor scratch on the inlay. I also got a handful of
scrap UV3 frequency display boards that were run through their wave
solder machine before it was at the proper temperature. They were just
starting up the production line and didn't have the profile set up
right. One had over a pound of excess solder on it. Some IC's were
completely covered with solder. That board was a real challenge to
repair with nothing but the IC data sheets and the pinouts for the
board. I got most of them working but I don't remember what I did with
them.
--
?

Michael A. Terrell
Central Florida

 

[Pooh Bear]

Joerg wrote:

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.

That figures.

What does the interference sound like when it's connected to grounded
equipment ?

Graham

 

[Pooh Bear]

Joerg wrote:

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.

I have to admit I prefer 'passive' DIs myself. I'm surprised Behringer don't do
one.

Good luck anyway.


Graham

 

[Pooh Bear]

Joerg wrote:

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.

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

http://www.oep.co.uk/

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

 

[Joerg]

Hello Graham,

What does the interference sound like when it's connected to grounded
equipment ?

I haven't heard it much but the person who did the recording said it is
hash (not just 60Hz plus harmonics).

Regards, Joerg

http://www.analogconsultants.com

 

[Pooh Bear]

Rich Grise wrote:

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".

If it's power supply noise, how is a transformer supposed to help?

Thanks,
Rich

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.


Graham

 

[Joerg]

Hello Graham,

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

http://www.oep.co.uk/

Nice. I think it is great that some smaller companies still make good
audio iso transformers. It is no problem to produce RF versions but
audio with hundreds of turns is a pain and I'd rather buy them.

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.

Sorry, I meant Radio Shack. Should have known since I have lived in
Europe and have dealt with RS.

Regards, Joerg

http://www.analogconsultants.com