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From: Eeyore on 7 Sep 2008 08:05


"Ron(UK)" wrote:

> 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.

That'll doubtless be a consequence of the French Law that limits output to 10mW or
something absurd so as not to kill kids' hearing. Trouble is, in noisy places you
can't even hear the music ! Especially if you use real headphones. I can't abide
those ghastly 'buds'.

Reputedly you can can firmware upgrades for some of these that over-ride the French
( i.e everything they sell in EU) requirement.

Graham

From: Ron(UK) on 7 Sep 2008 11:45
Eeyore wrote:
>
> "Ron(UK)" wrote:
>
>> 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.
>
> That'll doubtless be a consequence of the French Law that limits output to 10mW or
> something absurd so as not to kill kids' hearing. Trouble is, in noisy places you
> can't even hear the music ! Especially if you use real headphones. I can't abide
> those ghastly 'buds'.
>
> Reputedly you can can firmware upgrades for some of these that over-ride the French
> ( i.e everything they sell in EU) requirement.
>

Well that doesnt bother me, I never actually listen to the thing, I
just use it for preshow music etc, straight into a line input.

Ron
From: Tim Perry on 7 Sep 2008 14:30

"Eeyore" <rabbitsfriendsandrelations(a)hotmail.com> wrote in message
news:48C2C1B3.17B5C0AD(a)hotmail.com...
>
>
> 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
>

The z match transformers use a step up turns ratio which does increase
signal.



From: liquidator on 7 Sep 2008 15:21

"Tim Perry" <timperry(a)nospammeadelphia.net> wrote in message
news:ga16o6$fn0$1(a)aioe.org...
>
> "Eeyore" <rabbitsfriendsandrelations(a)hotmail.com> wrote in message
> news:48C2C1B3.17B5C0AD(a)hotmail.com...
> >
> >
> > 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
> >
>
> The z match transformers use a step up turns ratio which does increase
> signal.
>


I'm sure you know, not correcting you so much as clarifying, just increases
voltage. Which is what is needed.


From: George's ProSound Company on 7 Sep 2008 20:47

"jakdedert" <jakdedert(a)bellsouth.net> wrote in message
news:NFcwk.23343$Ep1.10309(a)bignews2.bellsouth.net...
> 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

Sirius Subscription radio was unlistenable with a passive combiner
sounded like a cd skipping several dozen times a second
using just one side work ok for the application, until they played a Beatles
song , due to the extreame panning of the cut we lost the vocals
had to create a second wire (rca to 1/4 inch) and use 2 mix channels
George


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