[[email protected]]

Hi,

I'm building a balun for my 600 ohm unbalanced line level input equipment to match with my balanced line level output equipment.

I can't find any actual numbers for the impedance of balanced line anywhere. It's all referred to as LoZ but what exactly are the numbers? I need to know so I can order the right transformer. I have all the other parts already, this entire project relies on this transformer.

I have several small audio transformers in my junk box, I may even have the right one already I just don't know because I can't find any information on what the actual impedances are with balanced audio gear.

Thanks.

[Don Pearce[_3_]]

On Sat, 26 Aug 2017 08:11:06 -0700 (PDT), wrote:

Hi,

I'm building a balun for my 600 ohm unbalanced line level input equipment to match with my balanced line level output equipment.

I can't find any actual numbers for the impedance of balanced line anywhere. It's all referred to as LoZ but what exactly are the numbers? I need to know so I can order the right transformer. I have all the other parts already, this entire project relies on this transformer.

I have several small audio transformers in my junk box, I may even have the right one already I just don't know because I can't find any information on what the actual impedances are with balanced audio gear.

Thanks.

Do you need to do this? Try using one of the balanced inputs from the
unbalanced output. If it sounds OK with no hum or interference, leave
it that way. A transformer will always degrade sound quality. It will
roll off bass and treble, and it will increase distortion in the low
bass.
If you really need a true balanced to unbalanced conversion, do it
with good op-amps, configured as an instrumentation amp. The only time
a transformer might possibly win is if you have interference so severe
that it is dominating the signal. Only then might the slightly
superior transformer CMRR win out.

d

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[Don Pearce[_3_]]

On Sat, 26 Aug 2017 15:17:00 GMT, (Don Pearce) wrote:

On Sat, 26 Aug 2017 08:11:06 -0700 (PDT), wrote:

Hi,

I'm building a balun for my 600 ohm unbalanced line level input equipment to match with my balanced line level output equipment.

I can't find any actual numbers for the impedance of balanced line anywhere. It's all referred to as LoZ but what exactly are the numbers? I need to know so I can order the right transformer. I have all the other parts already, this entire project relies on this transformer.

I have several small audio transformers in my junk box, I may even have the right one already I just don't know because I can't find any information on what the actual impedances are with balanced audio gear.

Thanks.

Do you need to do this? Try using one of the balanced inputs from the
unbalanced output. If it sounds OK with no hum or interference, leave
it that way. A transformer will always degrade sound quality. It will
roll off bass and treble, and it will increase distortion in the low
bass.
If you really need a true balanced to unbalanced conversion, do it
with good op-amps, configured as an instrumentation amp. The only time
a transformer might possibly win is if you have interference so severe
that it is dominating the signal. Only then might the slightly
superior transformer CMRR win out.

Disregard the configuration I suggested there. One op amp (5532?) is
all you need configured as a unity gain inverter. Feed one input
directly, and the other from this op-amp.

d

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[Scott Dorsey]

wrote:

I'm building a balun for my 600 ohm unbalanced line level input equipment =
to match with my balanced line level output equipment.

If it really IS 600 ohm unbalanced in, you will want a 600:600 ohm transformer.
However, you should know that it's pretty rare to see such low input
impedances today in the 21st century.

I can't find any actual numbers for the impedance of balanced line anywher=
e. It's all referred to as LoZ but what exactly are the numbers? I need to =
know so I can order the right transformer. I have all the other parts alrea=
dy, this entire project relies on this transformer.

Are you talking about the characteristic impedance of the cable? That doesn't
matter unless you're dealing with thousands of miles of cable (and is likely
in the 100 to 150 ohm range depending on the cable you're using).

In the 21st century, most devices have high impedance inputs and low impedance
outputs and don't match. Back in the 1950s, matching for maximum power
transfer was a good plan but these days it's seldom done because drive power
is cheap.

Most of the time if you have consumer gear, the easy solution is to take signal
and ground and connect them to pins 2 and 3 of the XLR connector respectively,
so that the differential input can effectively remove noise without having to
actually drive the output differentially. This will often not work for very
long cable runs into inexpensive inputs with comparatively small range, but
for most applications it's fine.

But, if you are dealing with long runs, a transformer is always a good plan.
Typically today we'd use a 1K to 1K transformer, and a 1K termination resistor
on the secondary. This means that the output device only has to drive a 1K
load instead of a full 600 ohm load, the transformer is matched into the
termination resistor, and the very high impedance input is happy.

I have several small audio transformers in my junk box, I may even have th=
e right one already I just don't know because I can't find any information =
on what the actual impedances are with balanced audio gear.

Depends on the gear. It's likely a very high-Z in, though, so you make your
own load impedance with a termination resistor.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Mike Rivers[_2_]]

On 8/26/2017 11:11 AM, wrote:
I'm building a balun for my 600 ohm unbalanced line level input equipment to match with my balanced line level output equipment. I can't find any actual numbers for the impedance of balanced line anywhere. It's all referred to as LoZ but what exactly are the numbers? I need to know so I can order the right transformer. I have all the other parts already, this entire project relies on this transformer.

Do you really have 600 ohm unbalanced inputs? In fact, do you have 600
ohm balanced outputs?

I've written a few articles about the subject so I won't go into detail
here, but simply stated, there's no relationship between nominal level,
balanced/unbalanced configuration and impedance. Line level is line
level (but that's conventionally either -10 dBV or +4 dBu). Old gear
with an input and output transformer that was built for broadcast or
telephone applications are frequently 600 ohm impedance, but what's
really important is the operating level.

Most modern solid state gear, whether balanced or unbalanced, has an
output impedance of 100 ohms or less (usually around 30 ohms these days)
and an input impedance of 10,000 to 20,000 ohms.

If you tell us what you're connecting to what (make and model number)
perhaps we can give you more specific information. The most likely
answer, though, is "Oh, it doesn't matter, and you probably don't need a
transformer anyway."

--

For a good time, call http://mikeriversaudio.wordpress.com

[Randy Berry]

On Saturday, August 26, 2017 at 11:29:52 AM UTC-4, Scott Dorsey wrote:
If it really IS 600 ohm unbalanced in, you will want a 600:600 ohm transformer.
However, you should know that it's pretty rare to see such low input
impedances today in the 21st century.

Yes, It's an amatuer radio transmitter. The specs direct from the manufacturer say 600 ohm line level input. The only Hi-Z components I have in the chain are the microphones. That mismatch is taken care of by the mic preamps..

I have a full lineup of balanced audio gear to feed the transmitter assembled in the same rack so lengths really don't exceed 2 feet.

If it's just a 1:1 at 600 ohms I won't worry about an xformer I'll just go direct. I know how to do that. I was just curious as to what the advantages/disadvantages would be if I used a balun. I don't want to lose any bass or treble in the audio or induce any distortion. It's only voice, but still I strive for broadcast quality audio.

I assumed cable impedances were around 100-150 ohms I just didn't know if that was the common for equipment as well.

Thanks.

[Don Pearce[_3_]]

On Sat, 26 Aug 2017 09:31:35 -0700 (PDT), Randy Berry
wrote:

On Saturday, August 26, 2017 at 11:29:52 AM UTC-4, Scott Dorsey wrote:
If it really IS 600 ohm unbalanced in, you will want a 600:600 ohm transformer.
However, you should know that it's pretty rare to see such low input
impedances today in the 21st century.

Yes, It's an amatuer radio transmitter. The specs direct from the manufacturer say 600 ohm line level input. The only Hi-Z components I have in the chain are the microphones. That mismatch is taken care of by the mic preamps.

I have a full lineup of balanced audio gear to feed the transmitter assembled in the same rack so lengths really don't exceed 2 feet.

If it's just a 1:1 at 600 ohms I won't worry about an xformer I'll just go direct. I know how to do that. I was just curious as to what the advantages/disadvantages would be if I used a balun. I don't want to lose any bass or treble in the audio or induce any distortion. It's only voice, but still I strive for broadcast quality audio.

I assumed cable impedances were around 100-150 ohms I just didn't know if that was the common for equipment as well.

Thanks.

If this is for a transmitter, a far more important component is a
common mode choke. Use something like a ferrite ring, and feed the
whole audio cable through it. Loop it through as many times as the
centre hole will allow. Put it as close to the destination kit as you
can get it.

d

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[Mike Rivers[_2_]]

On 8/26/2017 12:31 PM, Randy Berry wrote:
It's an amatuer radio transmitter. The specs direct from the manufacturer say 600 ohm line level input. The only Hi-Z components I have in the chain are the microphones. That mismatch is taken care of by the mic preamps.

So you're connecting the output of a mic preamp to the line input of the
transmitter? Unless it's an antique tube preamp, it'll probably drive
600 ohms just fine as long as you don't have to push the preamp to its
maximum output level to get full modulation of the transmitter.

But about those high impedance microphones . . . most mic preamps expect
a low impedance source and have an actual input impedance of 1500 to
3000 ohms. A high impedance mic won't be too happy with that.

Or does your preamp have a high impedance mic input?

Since when do amateur transmitters have line level inputs? I haven't
looked for 50 years, so maybe nowadays they expect that people might be
using other than "communications" mics, though I don't know why.

This advice would be a lot more certain if you specified the make and
model of the transmitter and preamp, and maybe pointed to web sites with
pictures and specifications. This isn't an amateur radio group, but
audio is audio.


--

For a good time, call http://mikeriversaudio.wordpress.com

[Scott Dorsey]

Randy Berry wrote:
On Saturday, August 26, 2017 at 11:29:52 AM UTC-4, Scott Dorsey wrote:
If it really IS 600 ohm unbalanced in, you will want a 600:600 ohm transf=
ormer.
However, you should know that it's pretty rare to see such low input=20
impedances today in the 21st century.

Yes, It's an amatuer radio transmitter. The specs direct from the manufact=
urer say 600 ohm line level input. The only Hi-Z components I have in the c=
hain are the microphones. That mismatch is taken care of by the mic preamps=

So, then, it's not line level at all. It's a microphone input you are wanting
to drive?

I have a full lineup of balanced audio gear to feed the transmitter assembl=
ed in the same rack so lengths really don't exceed 2 feet.=20

Well, then just use pin 2 to drive the unbalanced line, and pin 1 and 3 to
ground. However, you will want a substantial pad in order to reduce the
signal level, which will be much much higher than what a microphone input
would expect.

You may still want an isolation transformer to allow you to break grounds
for RF isolation. A 600 to 600 ohm transformer would be fine. Don't
forget to pad it down, though.

I assumed cable impedances were around 100-150 ohms I just didn't know if t=
hat was the common for equipment as well.

No, nobody cares about cable characteristic impedances for audio except
the phone company. And these days with local loops no longer than a
mile or two, even the phone company doesn't care anymore.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Phil Allison[_4_]]

Randy Berry wrote:


I'm building a balun for my 600 ohm unbalanced line level input
equipment to match with my balanced line level output equipment.

I can't find any actual numbers for the impedance of balanced line
anywhere. It's all referred to as LoZ but what exactly are the numbers?
I need to know so I can order the right transformer. I have all the
other parts already, this entire project relies on this transformer.



** When dealing with audio, you have to forget "ham radio think" entirely.

Audio source and load impedances are not "matched" by same value - cos that causes 6dB of signal loss. Generally, an audio source is connected to a load 5 to 10 times higher in impedance so minimising signal loss and distortion.

With reasonably short cable runs, a cable's characteristic impedance is meaningless with audio. The only thing that sometimes matters is the total *capacitance* of a cable causing loss of high frequencies with a high impedance source - like a 50kohm mic.

Since you are not supplying specific details of your gear we cannot give detailed advice. Your unsupported opinions of what maker's specs say and what matters is unhelpful.


...... Phil

[geoff]

On 27/08/2017 4:31 AM, Randy Berry wrote:
On Saturday, August 26, 2017 at 11:29:52 AM UTC-4, Scott Dorsey wrote:
If it really IS 600 ohm unbalanced in, you will want a 600:600 ohm transformer.
However, you should know that it's pretty rare to see such low input
impedances today in the 21st century.

Yes, It's an amatuer radio transmitter. The specs direct from the manufacturer say 600 ohm line level input. The only Hi-Z components I have in the chain are the microphones. That mismatch is taken care of by the mic preamps.

Given the application it really doesn't matter one iota how matched
anything is. As long as it works and is not noisy or tonally spoiled in
some way (unlikely) just plug in whatever a talk away.

geoff

[[email protected]]

On Saturday, August 26, 2017 at 11:11:11 AM UTC-4, Randy Berry wrote:
Hi,

I'm building a balun for my 600 ohm unbalanced line level input equipment to match with my balanced line level output equipment.

I can't find any actual numbers for the impedance of balanced line anywhere. It's all referred to as LoZ but what exactly are the numbers? I need to know so I can order the right transformer. I have all the other parts already, this entire project relies on this transformer.

I have several small audio transformers in my junk box, I may even have the right one already I just don't know because I can't find any information on what the actual impedances are with balanced audio gear.

Thanks.

I used to use the D-104 mic, very common. Specs here...
http://www.bellscb.com/products/micr...104_Specs.html

Jack