Audio Mixer

[Adrian]

Hi,

Can anyone recommend a stereo audio mixer? The immediate and primary
purpose of the same will be to mix the output from three microphones.
It will be good if I had the ability to direct the output one or both
output channels.

The need is to record small public meetings commencing with some live
music (piano) followed by a talk.

However, at some point I would like to be able to mix turntable and
line inputs at home. It seems wasteful to buy two mixers when one
might suffice. For this secondary purpose I need two turntable inputs
and/or two or three line inputs. Switchable turntable/line inputs
would be acceptable.

Output will be to a Behringer UCA202 and a Notebook computer.

Many thanks for your input to my thought process!

Adrian

[Ron Hardin]

Adrian wrote:
>
> Hi,
>
> Can anyone recommend a stereo audio mixer? The immediate and primary
> purpose of the same will be to mix the output from three microphones.
> It will be good if I had the ability to direct the output one or both
> output channels.
>
> The need is to record small public meetings commencing with some live
> music (piano) followed by a talk.
>
> However, at some point I would like to be able to mix turntable and
> line inputs at home. It seems wasteful to buy two mixers when one
> might suffice. For this secondary purpose I need two turntable inputs
> and/or two or three line inputs. Switchable turntable/line inputs
> would be acceptable.
>
> Output will be to a Behringer UCA202 and a Notebook computer.
>
> Many thanks for your input to my thought process!
>
> Adrian

I feed a Behringer UB1204-PRO directly into a Dell notebook mic jack,
which remarkably doesn't seem to mind it, at low volume.

It seems like a nice mixer, though I prefer the older and now-unavailable
models with the wall wart power supplies, as they generate less RFI
than the newer switching supply ones. But it doesn't matter, if you
don't use them right next to radios.

It doesn't seem to come with a wiring diagram, so you're left extrapolating
from older models that do come with them, as to what goes through what control
to where.
--


On the internet, nobody knows you're a jerk.

[Dave Plowman (News)]

In article . com>,
Adrian > wrote:
> Can anyone recommend a stereo audio mixer? The immediate and primary
> purpose of the same will be to mix the output from three microphones.
> It will be good if I had the ability to direct the output one or both
> output channels.

> The need is to record small public meetings commencing with some live
> music (piano) followed by a talk.

> However, at some point I would like to be able to mix turntable and
> line inputs at home. It seems wasteful to buy two mixers when one
> might suffice. For this secondary purpose I need two turntable inputs
> and/or two or three line inputs. Switchable turntable/line inputs
> would be acceptable.

Sounds like you're into a disco mixer if you want cartridge inputs.
Personally I'd go for a Behringer or Mackie and use external pickup
pre-amps.

For recording speech you want a mixer with a half decent
compressor/limiter.

--
*Never miss a good chance to shut up *

Dave Plowman London SW
To e-mail, change noise into sound.

[Eeyore]

Adrian wrote:

> Hi,
>
> Can anyone recommend a stereo audio mixer? The immediate and primary
> purpose of the same will be to mix the output from three microphones.
> It will be good if I had the ability to direct the output one or both
> output channels.
>
> The need is to record small public meetings commencing with some live
> music (piano) followed by a talk.
>
> However, at some point I would like to be able to mix turntable and
> line inputs at home. It seems wasteful to buy two mixers when one
> might suffice. For this secondary purpose I need two turntable inputs
> and/or two or three line inputs. Switchable turntable/line inputs
> would be acceptable.
>
> Output will be to a Behringer UCA202 and a Notebook computer.
>
> Many thanks for your input to my thought process!

The only mixers that have magnetic cartridge inputs are 'disco' mixers. These
will be overkill for your original application and 'disco gear' is almost
invariably of lower audio quality than purpose designed microphone mixers, hence
not a good choice since it'll also not be optimal for your original application.

I do know of one example where quality has not been sacrificed .............
(since I designed it !)
http://www.studiomaster.com/fusion.html

But you may find it difficult to find one. You don't say where in the world you
are for example !

The alternative would be to buy a cheap but adequate mic mixer and ditto disco
mixer. Look at Behringer for example. Maybe for example ....
http://behringer.com/UB1202/index.cfm?lang=eng
http://behringer.com/DX626/index.cfm?lang=eng

Graham

[Eeyore]

"Dave Plowman (News)" wrote:

> For recording speech you want a mixer with a half decent
> compressor/limiter.

Many ppl have managed without compressors just fine.

Graham

[Dave Plowman (News)]

In article >,
Eeyore > wrote:
> "Dave Plowman (News)" wrote:

> > For recording speech you want a mixer with a half decent
> > compressor/limiter.

> Many ppl have managed without compressors just fine.

Depends on how you define 'fine'.

The OP suggests it will be for recording public meetings with multi-mics.
So by nature no real chance to pre-set levels at a rehearsal - especially
if there are questions from the audience. Of course if recording to good
digital you could simply record leaving plenty headroom. But then
you'll likely end up with a dynamic range far too great for home listening.

I record speech (as well as other things) for a living and even on drama
where you do get a rehearsal I'd end up with clipping on occasion without
the use of a compressor. In my case, an SQN mixer - which has probably the
finest one available for this sort of thing.

Of course like all these aids you need to know what it does and how to use
it.

--
*Why are they called apartments, when they're all stuck together? *

Dave Plowman London SW
To e-mail, change noise into sound.

[Peter Larsen]

"Dave Plowman (News)" wrote:

> In article >,
> Eeyore > wrote:
> > "Dave Plowman (News)" wrote:

> > > For recording speech you want a mixer with a half decent
> > > compressor/limiter.

> > Many ppl have managed without compressors just fine.

> Depends on how you define 'fine'.

My defintion of fine is "avoided disturbing modulation of background
noise".

> The OP suggests it will be for recording public meetings with multi-mics.
> So by nature no real chance to pre-set levels at a rehearsal - especially
> if there are questions from the audience. Of course if recording to good
> digital you could simply record leaving plenty headroom. But then
> you'll likely end up with a dynamic range far too great for home listening.

And what issues may there be that either freeware or modestly priced
software, say sam-ultralite, aka magix home studio or sam lite, aka sam
9SE or something to that effect can not solve?

> I record speech (as well as other things) for a living and even on drama
> where you do get a rehearsal I'd end up with clipping on occasion without
> the use of a compressor.

You *do* manage to avoid clipping the mic input pre, right?

> In my case, an SQN mixer - which has probably the
> finest one available for this sort of thing.

IMO the questionee needs a "12 channel" Behringer mixer sans digital
effcts and the required number of external phono-pres. He can even get
one tossed in with one of the software packages that comes to mind,
Magix Audio Restoration suite (or something to that effect), multiple
distribution versions, one of those comes with phono-pre amp. There's a
neat lil' sound editor included, as I recall this with compression
capability. There is also Adobe Audition for those that want to use more
money and of course also SAM9.

> Of course like all these aids you need to know what it does and how to use
> it.

True, the simpler the better, not just for the novice user, for any
user.

> Dave Plowman London SW


Kind regards

Peter Larsen

[Arny Krueger]

"Dave Plowman (News)" > wrote in
message

> For recording speech you want a mixer with a half decent
> compressor/limiter.

They are relatively rare, particularly if you're talking equipment that is
not fairly expensive.

[Arny Krueger]

"Adrian" > wrote in message
oups.com


> Can anyone recommend a stereo audio mixer? The immediate
> and primary purpose of the same will be to mix the output
> from three microphones.

Check out the lower end of Behringer's mixer line. You should be able to
find something for less than $100.

> It will be good if I had the
> ability to direct the output one or both output channels.

Direct???

Do you mean control the volume?

> The need is to record small public meetings commencing
> with some live music (piano) followed by a talk.

Pretty straight forward.

> However, at some point I would like to be able to mix
> turntable and line inputs at home.

Unless you want to accept the limitations, overhead and extra cost of a DJ
mixer, you probably want to provide your own RIAA preamp for the turntable.


> Output will be to a Behringer UCA202 and a Notebook
> computer.

What's wrong with Berhinger mixers?

[Dave Plowman (News)]

In article >,
Peter Larsen > wrote:
> "Dave Plowman (News)" wrote:
>
> > In article >,
> > Eeyore > wrote:
> > > "Dave Plowman (News)" wrote:
>
> > > > For recording speech you want a mixer with a half decent
> > > > compressor/limiter.
>
> > > Many ppl have managed without compressors just fine.
>
> > Depends on how you define 'fine'.

> My defintion of fine is "avoided disturbing modulation of background
> noise".

So you just preset levels and let things happen? Because every time you
move a fader the background will change too. Personally I'd rather have
well balanced voices with a sensisible dynamic range. Intelligibility is
likely to be the order of the day with this sort of recording. Oh - and a
good compressor used sensibly won't produce objectionable pumping.

> > The OP suggests it will be for recording public meetings with
> > multi-mics. So by nature no real chance to pre-set levels at a
> > rehearsal - especially if there are questions from the audience. Of
> > course if recording to good digital you could simply record leaving
> > plenty headroom. But then you'll likely end up with a dynamic range
> > far too great for home listening.

> And what issues may there be that either freeware or modestly priced
> software, say sam-ultralite, aka magix home studio or sam lite, aka sam
> 9SE or something to that effect can not solve?

If he's going to multitrack then of course it can be sorted later. But
there's no need to go to these lengths.
>
> > I record speech (as well as other things) for a living and even on
> > drama where you do get a rehearsal I'd end up with clipping on
> > occasion without the use of a compressor.

> You *do* manage to avoid clipping the mic input pre, right?

Of course. Mic amp clipping isn't a problem with decent gear- if you know
how to use it.

> > In my case, an SQN mixer - which has probably the
> > finest one available for this sort of thing.

> IMO the questionee needs a "12 channel" Behringer mixer sans digital
> effcts and the required number of external phono-pres. He can even get
> one tossed in with one of the software packages that comes to mind,
> Magix Audio Restoration suite (or something to that effect), multiple
> distribution versions, one of those comes with phono-pre amp. There's a
> neat lil' sound editor included, as I recall this with compression
> capability. There is also Adobe Audition for those that want to use more
> money and of course also SAM9.
>
> > Of course like all these aids you need to know what it does and how to
> > use it.

> True, the simpler the better, not just for the novice user, for any
> user.

--
*Change is inevitable, except from a vending machine*

Dave Plowman London SW
To e-mail, change noise into sound.

[Dave Plowman (News)]

In article >,
Arny Krueger > wrote:
> "Dave Plowman (News)" > wrote in
> message

> > For recording speech you want a mixer with a half decent
> > compressor/limiter.

> They are relatively rare, particularly if you're talking equipment that
> is not fairly expensive.

Still? I'm not terribly up to date on the cheaper end of the market but
expected 'they'd' have got this sorted by now. Although I can quite
understand Behringer expecting you to buy an outboard one from them as
well. Although those are often far to complex for a simple task like this.

--
*A plateau is a high form of flattery*

Dave Plowman London SW
To e-mail, change noise into sound.

[Eeyore]

"Dave Plowman (News)" wrote:

> Arny Krueger > wrote:
> > "Dave Plowman (News)" > wrote
>
> > > For recording speech you want a mixer with a half decent
> > > compressor/limiter.
>
> > They are relatively rare, particularly if you're talking equipment that
> > is not fairly expensive.
>
> Still? I'm not terribly up to date on the cheaper end of the market but
> expected 'they'd' have got this sorted by now. Although I can quite
> understand Behringer expecting you to buy an outboard one from them as
> well. Although those are often far to complex for a simple task like this.

Inbuilt comp/limiters seem to be unique to expensive mixers designed for
location recording like your own.

Graham

[Arny Krueger]

"Dave Plowman (News)" > wrote in message
...
> In article >,
> Arny Krueger > wrote:
>> "Dave Plowman (News)" > wrote in
>> message
>
>> > For recording speech you want a mixer with a half decent
>> > compressor/limiter.
>
>> They are relatively rare, particularly if you're talking equipment that
>> is not fairly expensive.

> Still?

True.

>I'm not terribly up to date on the cheaper end of the market but
> expected 'they'd' have got this sorted by now.

While there are a lot of cheap mixers with EFX, its all reverb-oriented.

I think that the only mixers that Behringer makes that has built-in
compression/limiting are digital.

> Although I can quite
> understand Behringer expecting you to buy an outboard one from them as
> well.

A lot of mixers are used for live sound, and compression and limiting can
make live sound very complex and hard to manage, when feedback starts being
an issue.

Most compression and limiting I see used for SR is packaged as amplifier
management, along with the crossovers.

> Although those are often far to complex for a simple task like this.

That's just it. The OP's basic need could be filled by a sub-$100 mixer,
particuarly if he didn't have clients he wanted to impress with an expensive
piece of equipment.

[Dave Plowman (News)]

In article >,
Arny Krueger > wrote:

> "Dave Plowman (News)" > wrote in message
> ...
> > In article >,
> > Arny Krueger > wrote:
> >> "Dave Plowman (News)" > wrote in
> >> message
> >
> >> > For recording speech you want a mixer with a half decent
> >> > compressor/limiter.
> >
> >> They are relatively rare, particularly if you're talking equipment
> >> that is not fairly expensive.

> > Still?

> True.

> >I'm not terribly up to date on the cheaper end of the market but
> > expected 'they'd' have got this sorted by now.

> While there are a lot of cheap mixers with EFX, its all reverb-oriented.

> I think that the only mixers that Behringer makes that has built-in
> compression/limiting are digital.

> > Although I can quite understand Behringer expecting you to buy an
> > outboard one from them as well.

> A lot of mixers are used for live sound, and compression and limiting
> can make live sound very complex and hard to manage, when feedback
> starts being an issue.

Oh indeed. But I wasn't saying it was compulsory to use one - all those I
know can be switched out of circuit. But even in a 'live' situation a
limiter can prevent over driving the power amps and possible damage to the
speakers, etc. I also think foldback chains should have a catcher again to
prevent nasties down the line when things go wrong.

> Most compression and limiting I see used for SR is packaged as amplifier
> management, along with the crossovers.

Ah.

> > Although those are often far to complex for a simple task like this.

> That's just it. The OP's basic need could be filled by a sub-$100 mixer,
> particuarly if he didn't have clients he wanted to impress with an
> expensive piece of equipment.

Even for the most simple sound recording on location I use my SQN mixer.
The compressor /limiter on that is either off or on. It's really just a
'soft' limiter. And I really wouldn't be without it. For more complex
stuff I have an 8 channel Audio - that too has a built in limiter.

All you have to do is listen to a large percentage of interviews on TV
news etc to realise just how essential a *decent* mixer with limiter is.
And of course an operator who knows how to use one.

--
*All generalizations are false.

Dave Plowman London SW
To e-mail, change noise into sound.

[Adrian]

On Aug 31, 12:53 pm, Ron Hardin > wrote:
> Adrian wrote:
>
> > Hi,
>
> > Can anyone recommend a stereo audio mixer? The immediate and primary
> > purpose of the same will be to mix the output from three microphones.
> > It will be good if I had the ability to direct the output one or both
> > output channels.
>
> > The need is to record small public meetings commencing with some live
> > music (piano) followed by a talk.
>
> > However, at some point I would like to be able to mix turntable and
> > line inputs at home. It seems wasteful to buy two mixers when one
> > might suffice. For this secondary purpose I need two turntable inputs
> > and/or two or three line inputs. Switchable turntable/line inputs
> > would be acceptable.
>
> > Output will be to a Behringer UCA202 and a Notebook computer.
>
> > Many thanks for your input to my thought process!
>
> > Adrian
>
> I feed a Behringer UB1204-PRO directly into a Dell notebook mic jack,
> which remarkably doesn't seem to mind it, at low volume.
>
> It seems like a nice mixer, though I prefer the older and now-unavailable
> models with the wall wart power supplies, as they generate less RFI
> than the newer switching supply ones. But it doesn't matter, if you
> don't use them right next to radios.
>
> It doesn't seem to come with a wiring diagram, so you're left extrapolating
> from older models that do come with them, as to what goes through what control
> to where.
> --
>
>
Thanks Ron,

I have located the more recent Xenyx 1204, which seems to fit the bill
very well.

Adrian

[Adrian]

On Aug 31, 4:31 pm, "Dave Plowman (News)" >
wrote:
> In article . com>,
> Adrian > wrote:
>
> > Can anyone recommend a stereo audio mixer? The immediate and primary
> > purpose of the same will be to mix the output from three microphones.
> > It will be good if I had the ability to direct the output one or both
> > output channels.
> > The need is to record small public meetings commencing with some live
> > music (piano) followed by a talk.
> > However, at some point I would like to be able to mix turntable and
> > line inputs at home. It seems wasteful to buy two mixers when one
> > might suffice. For this secondary purpose I need two turntable inputs
> > and/or two or three line inputs. Switchable turntable/line inputs
> > would be acceptable.
>
> Sounds like you're into a disco mixer if you want cartridge inputs.
> Personally I'd go for a Behringer or Mackie and use external pickup
> pre-amps.
>
> For recording speech you want a mixer with a half decent
> compressor/limiter.
>
> --
Cartridge input seems to just cloud the issues these days. I will
either use turntables with pre-amps, or forgo turntable input
altogether. I have very little vinyl.

Adrian

[Adrian]

On Aug 31, 7:04 pm, Eeyore >
wrote:
> Adrian wrote:
> > Hi,
>
> > Can anyone recommend a stereo audio mixer? The immediate and primary
> > purpose of the same will be to mix the output from three microphones.
> > It will be good if I had the ability to direct the output one or both
> > output channels.
>
> > The need is to record small public meetings commencing with some live
> > music (piano) followed by a talk.
>
> > However, at some point I would like to be able to mix turntable and
> > line inputs at home. It seems wasteful to buy two mixers when one
> > might suffice. For this secondary purpose I need two turntable inputs
> > and/or two or three line inputs. Switchable turntable/line inputs
> > would be acceptable.
>
> > Output will be to a Behringer UCA202 and a Notebook computer.
>
> > Many thanks for your input to my thought process!
>
> The only mixers that have magnetic cartridge inputs are 'disco' mixers. These
> will be overkill for your original application and 'disco gear' is almost
> invariably of lower audio quality than purpose designed microphone mixers, hence
> not a good choice since it'll also not be optimal for your original application.
>
> I do know of one example where quality has not been sacrificed .............
> (since I designed it !)http://www.studiomaster.com/fusion.html
>
> But you may find it difficult to find one. You don't say where in the world you
> are for example !
>
> The alternative would be to buy a cheap but adequate mic mixer and ditto disco
> mixer. Look at Behringer for example. Maybe for example ....http://behringer.com/UB1202/index.cfm?lang=enghttp://behringer.com/DX626/index.cfm?lang=eng
>
> Graham- Hide quoted text -
>
> - Show quoted text -

You designed a nice mixer. However it is overkill for my needs. I am
going for a Behringer.

Thanks for advising

Adrian

[Adrian]

On Sep 1, 1:24 am, "Dave Plowman (News)" > wrote:
> In article >,
> Eeyore > wrote:
>
> > "Dave Plowman (News)" wrote:
> > > For recording speech you want a mixer with a half decent
> > > compressor/limiter.
> > Many ppl have managed without compressors just fine.
>
> Depends on how you define 'fine'.
>
> The OP suggests it will be for recording public meetings with multi-mics.
> So by nature no real chance to pre-set levels at a rehearsal - especially
> if there are questions from the audience. Of course if recording to good
> digital you could simply record leaving plenty headroom. But then
> you'll likely end up with a dynamic range far too great for home listening.
>
> I record speech (as well as other things) for a living and even on drama
> where you do get a rehearsal I'd end up with clipping on occasion without
> the use of a compressor. In my case, an SQN mixer - which has probably the
> finest one available for this sort of thing.
>
> Of course like all these aids you need to know what it does and how to use
> it.
>
> --
Sounds like I have a real learning curve ahead.

[Adrian]

On Sep 1, 4:07 am, "Arny Krueger" > wrote:
> "Adrian" > wrote in message
>
> oups.com
>
> > Can anyone recommend a stereo audio mixer? The immediate
> > and primary purpose of the same will be to mix the output
> > from three microphones.
>
> Check out the lower end of Behringer's mixer line. You should be able to
> find something for less than $100.
>
> > It will be good if I had the
> > ability to direct the output one or both output channels.
>
> Direct???
>
> Do you mean control the volume?
>
> > The need is to record small public meetings commencing
> > with some live music (piano) followed by a talk.
>
> Pretty straight forward.
>
> > However, at some point I would like to be able to mix
> > turntable and line inputs at home.
>
> Unless you want to accept the limitations, overhead and extra cost of a DJ
> mixer, you probably want to provide your own RIAA preamp for the turntable.
>
> > Output will be to a Behringer UCA202 and a Notebook
> > computer.
>
> What's wrong with Berhinger mixers?

Thanks Arny,

Found myself a Behringer Xenyx 1204 for just under USD100.00.

Adrian

[Adrian]

On Sep 1, 4:07 am, "Arny Krueger" > wrote:
> "Adrian" > wrote in message
>
> oups.com
>
> > It will be good if I had the
> > ability to direct the output one or both output channels.
>
> Direct???
>
I want to be able to direct input from a mic. to the left of a piano
to the left stereo channel, and the right to the right. When I am
speaking I want to send the mic. input to bboth channels in even
proportions. Do I sound new to this? There is a reason for
that! :-)

Adrian

[Arny Krueger]

"Adrian" > wrote in message
ups.com...
> On Sep 1, 4:07 am, "Arny Krueger" > wrote:
>> "Adrian" > wrote in message
>>
>> oups.com
>>
>> > It will be good if I had the
>> > ability to direct the output one or both output channels.
>>
>> Direct???
>>
> I want to be able to direct input from a mic. to the left of a piano
> to the left stereo channel, and the right to the right. When I am
> speaking I want to send the mic. input to bboth channels in even
> proportions. Do I sound new to this? There is a reason for
> that! :-)

These are the sorts of things that even the more basic mixers do well.

[Ron Hardin]

Adrian wrote:
> Thanks Ron,
>
> I have located the more recent Xenyx 1204, which seems to fit the bill
> very well.

You'll also need a bunch of 3.5mm to 1/4" adapters, in various combinations
of stereo and mono, and a couple for RCA as well.

Then you'll find you get enormous AC hum when you connect to your computer,
owing to a ground loop. Put a Radio Shack ground loop isolator in that line
(cat 270-054). I keep a bunch of them around to isolate every different thing
that's plugged in on AC mains.
--


On the internet, nobody knows you're a jerk.

[Ron Hardin]

Ron Hardin wrote:
>
> Adrian wrote:
> > Thanks Ron,
> >
> > I have located the more recent Xenyx 1204, which seems to fit the bill
> > very well.
>
> You'll also need a bunch of 3.5mm to 1/4" adapters, in various combinations
> of stereo and mono, and a couple for RCA as well.
>
> Then you'll find you get enormous AC hum when you connect to your computer,
> owing to a ground loop. Put a Radio Shack ground loop isolator in that line
> (cat 270-054). I keep a bunch of them around to isolate every different thing
> that's plugged in on AC mains.

Oh, and finally some brush-on Deoxit, to keep the adapters working. I get mine
here http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=341-215

A tiny bottle lasts forever. It fixes everything, from battery charger terminals
to audio connectors to mains plugs on high current devices that get hot (plug in
and out until the contacts come out clean).
--


On the internet, nobody knows you're a jerk.

[Adrian]

On Sep 4, 5:36 am, Ron Hardin > wrote:
> Ron Hardin wrote:
>
> > Adrian wrote:
> > > Thanks Ron,
>
> > > I have located the more recent Xenyx 1204, which seems to fit the bill
> > > very well.
>
> > You'll also need a bunch of 3.5mm to 1/4" adapters, in various combinations
> > of stereo and mono, and a couple for RCA as well.
>
> > Then you'll find you get enormous AC hum when you connect to your computer,
> > owing to a ground loop. Put a Radio Shack ground loop isolator in that line
> > (cat 270-054). I keep a bunch of them around to isolate every different thing
> > that's plugged in on AC mains.
>
Is that true even if I utilize the USB link into my Notebook?

> Oh, and finally some brush-on Deoxit, to keep the adapters working. I get mine
> herehttp://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=341-215
>
> A tiny bottle lasts forever. It fixes everything, from battery charger terminals
> to audio connectors to mains plugs on high current devices that get hot (plug in
> and out until the contacts come out clean).
> --
Thanks, I will check this out.

Adrian

[Ron Hardin]

Adrian wrote:
> > > Then you'll find you get enormous AC hum when you connect to your computer,
> > > owing to a ground loop. Put a Radio Shack ground loop isolator in that line
> > > (cat 270-054). I keep a bunch of them around to isolate every different thing
> > > that's plugged in on AC mains.
> >
> Is that true even if I utilize the USB link into my Notebook?

Yes, it's a problem in the connecting audio cable. The computer and the audio components
don't have quite the same idea of what ground potential is. The slight difference is made up
by a current down the ground shield of the audio cable. There's a slight voltage drop
across the shield as a result, and this voltage drop is shared with the audio input circuit.

So you hear the slight ground difference in the audio signal, as AC hum.

An isolation transformer breaks the ``DC'' path in the audio cable, so there is no
shared current between power and audio circuits.

No hard trying it without, but if you get a hum, that's why.

--


On the internet, nobody knows you're a jerk.

[Eeyore]

Ron Hardin wrote:

> Adrian wrote:
> > > > Then you'll find you get enormous AC hum when you connect to your computer,
> > > > owing to a ground loop. Put a Radio Shack ground loop isolator in that line
> > > > (cat 270-054). I keep a bunch of them around to isolate every different thing
> > > > that's plugged in on AC mains.
> > >
> > Is that true even if I utilize the USB link into my Notebook?
>
> Yes, it's a problem in the connecting audio cable. The computer and the audio components
> don't have quite the same idea of what ground potential is.

That's the traditional reason for 'hum loops'.

In this case the problem is made worse but the use of switching power supplies (certainly in the
computer) and in some audio gear (I'm fairly certain the Behringer model mentioned also has one).
These swiching power supplies have filters on the ac power input that injects a noise current
into the ground conductor. This messes up your grounding arrangements very effectively.

Graham

[Arny Krueger]

"Eeyore" > wrote in message
...
>
>
> Ron Hardin wrote:
>
>> Adrian wrote:
>> > > > Then you'll find you get enormous AC hum when you connect to your
>> > > > computer,
>> > > > owing to a ground loop. Put a Radio Shack ground loop isolator in
>> > > > that line
>> > > > (cat 270-054). I keep a bunch of them around to isolate every
>> > > > different thing
>> > > > that's plugged in on AC mains.
>> > >
>> > Is that true even if I utilize the USB link into my Notebook?
>>
>> Yes, it's a problem in the connecting audio cable. The computer and the
>> audio components
>> don't have quite the same idea of what ground potential is.
>
> That's the traditional reason for 'hum loops'.
>
> In this case the problem is made worse but the use of switching power
> supplies (certainly in the
> computer) and in some audio gear (I'm fairly certain the Behringer model
> mentioned also has one).
> These swiching power supplies have filters on the ac power input that
> injects a noise current
> into the ground conductor. This messes up your grounding arrangements very
> effectively.

I've always been under the impression that the simple presence of a hard
chassis ground was all it took to pretty well guarantee a ground loop, if
there was a second hard chassis ground anyplace in the equipment that was
attached to the PC. IOW, the switching power supply might have made the
ground loop more obnoxious-sounding, but it would be there regardless.

[Eeyore]

Arny Krueger wrote:

> "Eeyore" > wrote
> > Ron Hardin wrote:
> >> Adrian wrote:
> >
> >> > > > Then you'll find you get enormous AC hum when you connect to your
> >> > > > computer, owing to a ground loop. Put a Radio Shack ground loop
> isolator in
> >> > > > that line (cat 270-054). I keep a bunch of them around to isolate
> every
> >> > > > different thing that's plugged in on AC mains.
> >> > >
> >> > Is that true even if I utilize the USB link into my Notebook?
> >>
> >> Yes, it's a problem in the connecting audio cable. The computer and the
> >> audio components don't have quite the same idea of what ground potential
> is.
> >
> > That's the traditional reason for 'hum loops'.
> >
> > In this case the problem is made worse but the use of switching power
> > supplies (certainly in the
> > computer) and in some audio gear (I'm fairly certain the Behringer model
> > mentioned also has one).
> > These swiching power supplies have filters on the ac power input that
> > injects a noise current
> > into the ground conductor. This messes up your grounding arrangements very
> > effectively.
>
> I've always been under the impression that the simple presence of a hard
> chassis ground was all it took to pretty well guarantee a ground loop, if
> there was a second hard chassis ground anyplace in the equipment that was
> attached to the PC.

For this to be the case, there has either to be some source of electromagnetic
induction ( like the stray field from a transformer) imposing itself on a
connecting wire or a current intentionally dumped to ground (as with the EMI
filters). Or, not likely in the context of equipment used in a single room, a
different earth potential at the various power sockets.


> IOW, the switching power supply might have made the
> ground loop more obnoxious-sounding, but it would be there regardless.

The mere presence of a loop doesn't of itself generate any hum. The loop simply
provides a path that's a perfect 'shorted turn' for a magnetic field to create a
current in.

You can in fact very easily have a 'hum loop' like that *inside* a piece of
equipment. I've measured potential differences of the order of tens of uV
between different parts of a steel chassis caused by electromagnetic induction
from the stray field of a large power transformer inside the equipment for
example.

Graham

[Arny Krueger]

"Eeyore" > wrote in message
...
>
>
> Arny Krueger wrote:
>
>> "Eeyore" > wrote
>> > Ron Hardin wrote:
>> >> Adrian wrote:
>> >
>> >> > > > Then you'll find you get enormous AC hum when you connect to
>> >> > > > your
>> >> > > > computer, owing to a ground loop. Put a Radio Shack ground loop
>> isolator in
>> >> > > > that line (cat 270-054). I keep a bunch of them around to
>> >> > > > isolate
>> every
>> >> > > > different thing that's plugged in on AC mains.
>> >> > >
>> >> > Is that true even if I utilize the USB link into my Notebook?
>> >>
>> >> Yes, it's a problem in the connecting audio cable. The computer and
>> >> the
>> >> audio components don't have quite the same idea of what ground
>> >> potential
>> is.
>> >
>> > That's the traditional reason for 'hum loops'.
>> >
>> > In this case the problem is made worse but the use of switching power
>> > supplies (certainly in the
>> > computer) and in some audio gear (I'm fairly certain the Behringer
>> > model
>> > mentioned also has one).
>> > These swiching power supplies have filters on the ac power input that
>> > injects a noise current
>> > into the ground conductor. This messes up your grounding arrangements
>> > very
>> > effectively.
>>
>> I've always been under the impression that the simple presence of a hard
>> chassis ground was all it took to pretty well guarantee a ground loop, if
>> there was a second hard chassis ground anyplace in the equipment that was
>> attached to the PC.

> For this to be the case, there has either to be some source of
> electromagnetic
> induction ( like the stray field from a transformer) imposing itself on a
> connecting wire or a current intentionally dumped to ground (as with the
> EMI
> filters).

There always seem to be incidental em fields kicking around places were AC
power is being used.

> Or, not likely in the context of equipment used in a single room, a
> different earth potential at the various power sockets.

Agreed. I've seen a few volts of ground potential differences in adjacent
rooms on different circuits.

>> IOW, the switching power supply might have made the
>> ground loop more obnoxious-sounding, but it would be there regardless.

> The mere presence of a loop doesn't of itself generate any hum. The loop
> simply
> provides a path that's a perfect 'shorted turn' for a magnetic field to
> create a
> current in.

Agreed.

> You can in fact very easily have a 'hum loop' like that *inside* a piece
> of
> equipment. I've measured potential differences of the order of tens of uV
> between different parts of a steel chassis caused by electromagnetic
> induction
> from the stray field of a large power transformer inside the equipment for
> example.

That's one reason why we have separate signal grounds, even inside the
chassis.

[Eeyore]

Arny Krueger wrote:

> "Eeyore" > wrote
>
> > You can in fact very easily have a 'hum loop' like that *inside* a piece
> > of equipment. I've measured potential differences of the order of tens of uV
>
> > between different parts of a steel chassis caused by electromagnetic
> > induction from the stray field of a large power transformer inside the
> equipment for
> > example.
>
> That's one reason why we have separate signal grounds, even inside the
> chassis.

This used to be very popular but is inherently incompatible with good EMC
practice.

I use chassis ground as my reference and I'm VERY careful about stuffing current
into the ground ( i.e I avoid it like the plague ). As a last resort, I also
make some internal connections differential/balanced, which of course entirely
eliminates the complication of questionable ground potentials.

Graham

[Arny Krueger]

"Eeyore" > wrote in message
...
>
>
> Arny Krueger wrote:
>
>> "Eeyore" > wrote
>>
>> > You can in fact very easily have a 'hum loop' like that *inside* a
>> > piece
>> > of equipment. I've measured potential differences of the order of tens
>> > of uV
>>
>> > between different parts of a steel chassis caused by electromagnetic
>> > induction from the stray field of a large power transformer inside the
>> equipment for
>> > example.
>>
>> That's one reason why we have separate signal grounds, even inside the
>> chassis.
>
> This used to be very popular but is inherently incompatible with good EMC
> practice.

Interesting.

> I use chassis ground as my reference and I'm VERY careful about stuffing
> current
> into the ground ( i.e I avoid it like the plague ). As a last resort, I
> also
> make some internal connections differential/balanced, which of course
> entirely
> eliminates the complication of questionable ground potentials.

Interesting.

[Chris Morriss]

In message >, Eeyore
> writes
>
>
>Arny Krueger wrote:
>
>> "Eeyore" > wrote
>>
>> > You can in fact very easily have a 'hum loop' like that *inside* a piece
>> > of equipment. I've measured potential differences of the order of
>> >tens of uV
>>
>> > between different parts of a steel chassis caused by electromagnetic
>> > induction from the stray field of a large power transformer inside the
>> equipment for
>> > example.
>>
>> That's one reason why we have separate signal grounds, even inside the
>> chassis.
>
>This used to be very popular but is inherently incompatible with good EMC
>practice.
>
>I use chassis ground as my reference and I'm VERY careful about
>stuffing current
>into the ground ( i.e I avoid it like the plague ). As a last resort, I also
>make some internal connections differential/balanced, which of course entirely
>eliminates the complication of questionable ground potentials.
>
>Graham
>
>
I have to agree there Graham. If you're going to have a ground in a
piece of equipment, make sure there's only one, and make sure that
everything that connects to it has the lowest impedance path you can
manage.
--
Chris Morriss