[joe h]

Hello,

I ordered the Focusrite ISA 430 MK II. I'm in the process of sourcing
the digital output card:
ISA430/220 ADC

Mr. Rivers kindly told me that I guessed correctly on the toslink/
spdif cable.

But in the meantime, before my card arrives, I ordered an analog cable
to go into the 1/8" MacBook Pro analog input:

http://www.guitarcenter.com/Live-Wir...19-i1166818.gc

It has a single-black on the 3.5mm. I thought a mono tip on the 3.5mm
would be the safest to avoid an electrical short or something (the
Focusrite is intending the three-pin to mean balanced, but I think the
Macbook would interpret the double-black tip to mean stereo input).

Do you think this is a safe cable to plug into the MacBook Pro from
the Focusrite?

The Macbook pro is a recent one, like this one:
http://www.apple.com/macbookpro/specs.html

I'm not worried about "awesome" right now. I'm worried about safe and
usable-enough until I get the digital card stuff sorted out.

Thanks!

[joe h]

This webpage has a link at the top that has a PDF of the ISA 430 MK II
with a picture of the back (it shows the xlr output).
http://www.focusrite.com/downloads/i...mkii_brochure/

[Mike Rivers]

On 8/30/2011 11:19 PM, joe h wrote:

But in the meantime, before my card arrives, I ordered an analog cable
to go into the 1/8" MacBook Pro analog input:

It has a single-black on the 3.5mm. I thought a mono tip on the 3.5mm
would be the safest to avoid an electrical short or something (the
Focusrite is intending the three-pin to mean balanced, but I think the
Macbook would interpret the double-black tip to mean stereo input).

Well, which picture do you believe? The second picture of
the four in the link to the cable you ordered shows a
two-circuit ("balanced" or "stereo" depending on the
application) plug but the other photos including the wiring
diagram show a "mono" plug. I'd tend to believe the diagram,
which indeed is for unbalanced wiring.

Do you think this is a safe cable to plug into the MacBook Pro from
the Focusrite?

It's certainly safe. Nothing will blow up. But I don't know
the characteristics of the audio input jack on your
computer. Is it at mic or line level? Is it mono or stereo?
The specs say only "Audio line in." If that means it's line
level, that's better, for this application, than mic level.
I don't know what an iPhone headset is or how it connects
but I suspect that's a different input connector and not
relevant here. I don't know how Macs are built, but with
most Windows computers, the mini audio input jack is stereo
(though some are used in mono when selecting Mic input, if
that's possible). If it's a stereo jack, then you'll see
audio coming in on only one channel. The other channel input
will be shorted out by the sleeve of the plug. This is OK,
but you'll need to know how to configure your DAW or other
recording program for mono recording from the "left channel"
source. (I think the tip of a stereo jack is conventionally
the left channel)

If the cable turns out to have a two-circuit plug and is
wired for a balanced connection, and if the jack on the
computer is expecting a stereo input, then, if the output
configuration of the Focusrite preamp is, as I suspect,
differential, you'll get a signal on both the left and right
channels, but they will be of opposite polarity (180 degrees
out of phase at all frequencies). You can use it this way,
but you can use only one channel of the stereo pair.

In any case, the line level input (if that's indeed what it
is) will be expecting a maximum level quite lower than the
Focusrite is capable of putting out. You will probably have to

I'm not worried about "awesome" right now. I'm worried about safe and
usable-enough until I get the digital card stuff sorted out.

You can surely get something out of this that you can use,
but it might be more complicated than simply plug and play.
Or maybe it will be simple.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[James Perrett[_3_]]

The main issue is what happens to pin 3 on the xlr. It can either be connected or disconnected and, if you make the wrong choice you could either end up with more noise or you could end up shorting out the output stage of the Focusrite and damaging it. Check the Focusrite manual to see what they recommend and then check to see if the cable is wired according to their recommendations.

James.

[Arny Krueger[_4_]]

"joe h" wrote in message
...
Hello,

I ordered the Focusrite ISA 430 MK II. I'm in the process of sourcing
the digital output card:
ISA430/220 ADC

Mr. Rivers kindly told me that I guessed correctly on the toslink/
spdif cable.

But in the meantime, before my card arrives, I ordered an analog cable
to go into the 1/8" MacBook Pro analog input:

http://www.guitarcenter.com/Live-Wir...19-i1166818.gc

It has a single-black on the 3.5mm. I thought a mono tip on the 3.5mm
would be the safest to avoid an electrical short or something (the
Focusrite is intending the three-pin to mean balanced, but I think the
Macbook would interpret the double-black tip to mean stereo input).

Do you think this is a safe cable to plug into the MacBook Pro from
the Focusrite?

The Macbook pro is a recent one, like this one:
http://www.apple.com/macbookpro/specs.html

I'm not worried about "awesome" right now. I'm worried about safe and
usable-enough until I get the digital card stuff sorted out.

Don't worry about safe, just worry about effective.

Line outputs of audio gear are designed to work into shorts - otherwise
there would be a big equipment repair bill everytime a cable got shorted due
to damage, or in the case of phone plugs, merely inserted.

Unless the output of the preamp has a floating transformer output, you can
think of each XLR as having two active output pins with opposite polarities.
If you short one pin either nothing happens or in some cases the signal
voltage at the other one doubles.

Similarly, it is generally very difficult to actually damage an input by
applying the wrong voltage within reason. Obviously, hooking up the 120-240
volt power line to an input might cause damage. Or it might not.

[joe h]

Wow, thanks everyone.

I learned a lot.

Ironically, it might be simplest for me to buy the digital card first
and go from toslink to spdif, rather than guess wrong on the analog.

I'm not sure by looking at the inside of the Focusrite what the pin
assignments would be, and the cable is probably going to be molded-
end, which would make analysis difficult on that as well.

The one really valuable thing I picked up from this discussion is that
there can be many possibilities. Simply going XLR out from a
"standard" channel strip out into a "standard" xlr1/8" mono cable
doesn't make sense, because there is not a guaranteed standard of how
the internal polarity stuff is addressed for this type of
circumstance.

[PStamler]

There's also the factor that the A/D converter in the Focusrite is
likely to be WAY better than the analog-input-plus-A/D-converter in
the Mac.

Peace,
Paul

[Mike Rivers]

On 8/31/2011 10:25 PM, joe h wrote:

The one really valuable thing I picked up from this discussion is that
there can be many possibilities. Simply going XLR out from a
"standard" channel strip out into a "standard" xlr1/8" mono cable
doesn't make sense, because there is not a guaranteed standard of how
the internal polarity stuff is addressed for this type of
circumstance.

The problem is that when it comes to cables with different
connectors on each end, there are some conventions, but no
real standards. For example, when going between XLR and TRS
(big or little) connectors, the convention is:

Pin 1 - sleeve
Pin 2 - tip
Pin 3 - ring

The missing information (which you could fill in either with
some research or experimentation) is how the tip, ring, and
sleeve are used by the computer. It's really not that hard
to figure out, but you need to understand what you're
looking for. It's also not hard to make a custom cable wired
in a way that it will work with whatever you have, and if
you don't have the tools or skills, it's not hard to find
someone to make one for you. But you need to provide the
wiring information.

It's your decision as to what's more trouble than it's
worth. And as Paul says, the A/D converter in the Focusrite
is better than the one in your computer.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff