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From: jakdedert on 5 Sep 2008 12:02
Rupert wrote:
> On Sep 5, 6:28 am, jakdedert <jakded...(a)bellsouth.net> wrote:
>> George's ProSound Company wrote:
>>
>> <snip>> and do not "Y" the ipod's channels into one input one the LG
>>> strange things happen to a line level stereo signal when passivly "y"ed
>>> George
>> That's good to know. Some stereo line-outs don't mind being tied
>> together, although I never do it if there's an option. Lately I've been
>> getting a lot of ipods and stereo laptop outputs. Fortunately we've got
>> dedicated A/V DIs, with isolated stereo lines-in to a single balanced out.
>> jak
>
> The reason why it's not a good idea is because you're only suppose to
> drive high impedance inputs from low impedance outputs. When you "Y"
> to outputs together directly, each output tries to "drive" the other
> regardless of the input your connected to. Since the outputs are much
> lower impedance than what the circuit is really designed to drive,
> excessive current is sourced from each output to drive the other which
> can cause distortion. In extreme cases you can damage the output
> circuit. That said, my understanding is that in relatively modern gear
> there may be resistor networks built-out on the outputs to prevent
> overloading the outputs in the event they're "Y"ed together or shorted
> out. Either way, it's still bad practice in my opinion. There are
> simple passive resistor summing networks that you can make to ensure
> proper loading when tying 2 output together:
>
> http://www.rane.com/note109.html
>
> Rupert

I understand both the pros and cons...and the right and wrong way to do
it. In a pinch, you do what you can with what you have. Often it's
better to use just the left or right out, and let the other
float...depends on the program material. With music, it should sum to
mono. If the sound quality doesn't deteriorate when connecting l+r
together, then likely there is also no overload damage potential. It
depends on the particular gear. Use your ears....

jak
From: Joe Kotroczo on 5 Sep 2008 16:17
On 5/09/08 14:31, in article 48c12686$1(a)news.alcatel.com, "crevitch"
<crevitch(a)none.com> wrote:

> I have a lab gruppen lab 300 PA amplifier.
> http://www.labgruppen.com/downloads/product/LAB300_manual_rev2.pdf
>
> It has balanced TRS phone and XLR inputs. I am trying to connect
> standard line level outputs to these inputs (i.e. IPOD) but find that
> the output level from the speakers is very low. I am using a cable that
> converts mini-stereo phone to 2 - 1/4" mono phone plugs. Since the 1/4"
> connectors only have tip/ring and not TRS, I assume I am grounding one
> of the balanced inputs with the ring.
>
> What is the reason for the low output? Should this work properly?

Your Ipod has consumer line level, which is -10 dBV.

Being a professional amp, the amp wants to see pro line level. It has a gain
switch that let's you choose between +4 dBu and O dBu.

You'll need a preamp of some sort.


--
Joe Kotroczo kotroczo(a)mac.com

From: Tim Perry on 6 Sep 2008 13:06

"crevitch" <crevitch(a)none.com> wrote in message
news:48c12686$1(a)news.alcatel.com...
> I have a lab gruppen lab 300 PA amplifier.
> http://www.labgruppen.com/downloads/product/LAB300_manual_rev2.pdf
>
> It has balanced TRS phone and XLR inputs. I am trying to connect
> standard line level outputs to these inputs (i.e. IPOD) but find that
> the output level from the speakers is very low. I am using a cable that
> converts mini-stereo phone to 2 - 1/4" mono phone plugs. Since the 1/4"
> connectors only have tip/ring and not TRS, I assume I am grounding one
> of the balanced inputs with the ring.
>
> What is the reason for the low output? Should this work properly?
>
> Thanks

Get a cheap volt meter. Put it on the 2 volt AC scale. Measure the output of
the playback device. It may not be super accurate at Audio frequencies but
will give you a ballpark idea of what's coming out.

If you don't see a reading time to check the device or the cable.

Use the ohm meter function to check the cable conducts from the tip of the
"stereo plug to the tip of one 1/4" plug and from the ring of the plug to
the other plugs tip

A lot depends on what you mean by "very low". Perhaps simple Z matching
transformers , low to high inserted on the inputs will give the gain you
want for full volume.



From: Eeyore on 6 Sep 2008 13:45


Tim Perry wrote:

> "crevitch" <crevitch(a)none.com> wrote in message
> > I have a lab gruppen lab 300 PA amplifier.
> > http://www.labgruppen.com/downloads/product/LAB300_manual_rev2.pdf
> >
> > It has balanced TRS phone and XLR inputs. I am trying to connect
> > standard line level outputs to these inputs (i.e. IPOD) but find that
> > the output level from the speakers is very low. I am using a cable that
> > converts mini-stereo phone to 2 - 1/4" mono phone plugs. Since the 1/4"
> > connectors only have tip/ring and not TRS, I assume I am grounding one
> > of the balanced inputs with the ring.
> >
> > What is the reason for the low output? Should this work properly?
>
> Get a cheap volt meter. Put it on the 2 volt AC scale. Measure the output of
> the playback device. It may not be super accurate at Audio frequencies but
> will give you a ballpark idea of what's coming out.
>
> If you don't see a reading time to check the device or the cable.
>
> Use the ohm meter function to check the cable conducts from the tip of the
> "stereo plug to the tip of one 1/4" plug and from the ring of the plug to
> the other plugs tip
>
> A lot depends on what you mean by "very low". Perhaps simple Z matching
> transformers , low to high inserted on the inputs will give the gain you
> want for full volume.

It's hardly an impedance match problem it's a LEVEL match problem.

Graham


From: Ron(UK) on 7 Sep 2008 06:52
Eeyore wrote:
>
> Tim Perry wrote:
>
>> "crevitch" <crevitch(a)none.com> wrote in message
>>> I have a lab gruppen lab 300 PA amplifier.
>>> http://www.labgruppen.com/downloads/product/LAB300_manual_rev2.pdf
>>>
>>> It has balanced TRS phone and XLR inputs. I am trying to connect
>>> standard line level outputs to these inputs (i.e. IPOD) but find that
>>> the output level from the speakers is very low. I am using a cable that
>>> converts mini-stereo phone to 2 - 1/4" mono phone plugs. Since the 1/4"
>>> connectors only have tip/ring and not TRS, I assume I am grounding one
>>> of the balanced inputs with the ring.
>>>
>>> What is the reason for the low output? Should this work properly?
>> Get a cheap volt meter. Put it on the 2 volt AC scale. Measure the output of
>> the playback device. It may not be super accurate at Audio frequencies but
>> will give you a ballpark idea of what's coming out.
>>
>> If you don't see a reading time to check the device or the cable.
>>
>> Use the ohm meter function to check the cable conducts from the tip of the
>> "stereo plug to the tip of one 1/4" plug and from the ring of the plug to
>> the other plugs tip
>>
>> A lot depends on what you mean by "very low". Perhaps simple Z matching
>> transformers , low to high inserted on the inputs will give the gain you
>> want for full volume.
>
> It's hardly an impedance match problem it's a LEVEL match problem.
>

Dunno about ipods, but I have a Creative Zen which when plugged
directly into the average power amplifier (Yamaha P5000 say) and with
the volume up to max, barely gives a listening level enough for the
average large living room (I realise that there are a lot of variables
here, but they just arent designed to drive power amplifiers directly
from the headphone sockets.

Ron(UK)
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