volume control of power amps and Beolabs

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BeoLignage Posted: Wed, Jan 23 2013 3:17 PM

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Hello,

More than once it has been discussed how to connect Beolabs to a non beo amp via line-in or rca-to-PL converter. In connection with this it has been mentioned the issue of internal volume control of Lab5s, leaving them on high volume when using line-in. this has got me more confused than educated.

My question is more general and I hope it at all makes sense asking.

If you in the normal case connect a Beomaster to a BeoLab with a PowerLink(PL) cable, where is the volume controlled. Is PL really only volume controlled line level (pre-out) with a different cord? Or is it constant level and a data signal controlling the amp volume level in the speaker? Are the amps of BeoLabs always on max, like a power amp in a separates set up, or am I even getting that wrong.

And… How does my Beomaster 3500 work if I use a PC-audio out connected to tape1 input, and then lower the volume at the source i.e. on the PC. Is the amp of the BM3500 working as hard as if the volume input was high (BM volume fixed)?

Hope someone has an answer to this, and is willing to sort things out

Thanks in advance

//Goran

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Jeff replied on Wed, Jan 23 2013 6:18 PM

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Since the 5's have a digital input they have an internal digital volume control from what I know. Standard PL carries analog L and R line level variable signals, level controlled by the source component. It also carries a DC low voltage power on signal to tell the Beolabs to turn on. Some versions also carry data for older speakers like the Pentas which have displays on them showing the source selected, CD, FM, etc. 

Ive used PL to RCA converters, back when I first got my Beosound 9000 I used these to drive a classic McIntosh MC240 tube amp and have also used them with an AV7000 to drive an amp for the rear channels. 

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Vienna replied on Wed, Jan 23 2013 6:47 PM

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BeoLignage:

More than once it has been discussed how to connect Beolabs to a non beo amp via line-in or rca-to-PL converter. In connection with this it has been mentioned the issue of internal volume control of Lab5s, leaving them on high volume when using line-in. this has got me more confused than educated.

My question is more general and I hope it at all makes sense asking.

If you in the normal case connect a Beomaster to a BeoLab with a PowerLink(PL) cable, where is the volume controlled. Is PL really only volume controlled line level (pre-out) with a different cord? Or is it constant level and a data signal controlling the amp volume level in the speaker? Are the amps of BeoLabs always on max, like a power amp in a separates set up, or am I even getting that wrong.

PowerLink is an analogue volume controlled (pre-amp line level) signal + trigger for power amps  + display data for older speakers (eg Penta)

No volume control happens in BeoLabs - gain of the power-amps remains always the same.
The actually produced power depends of course on the level of the incoming (pre-amp) signal.

The only exeption are BeoLab5s if not connected via PowerLink - the have a built in IR receiver and a
built in volume control for "Line" and "Digital" mode.

BeoLignage:

And… How does my Beomaster 3500 work if I use a PC-audio out connected to tape1 input, and then lower the volume at the source i.e. on the PC. Is the amp of the BM3500 working as hard as if the volume input was high (BM volume fixed)?[/quote]

In this example your PC is the pre-amp and the volume control of your BM 3500 can be used as an additional volume preset.
The gain of the power-amps BM3500 remains always the same - the actually produced power depends of course on the level
of the incoming (pre-amp) signal.

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Steve at Sounds Heavenly replied on Wed, Jan 23 2013 8:42 PM

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Hello Goran,

Vienna is correct, Powerlink is really only a volume controlled line level (pre-out) with a different cord, as you suggested.  The 8 pin cord has extra contacts which allows for control signals to tell the speakers when to switch on and off.  If you use the fully-wired (mk.2) Powerlink cables, then data is also sent, but for most Beolab speakers this data is not used.

It is because of this fact that Beolab speakers have proven to be so flexible, as they can easily be used with a huge range of non-B&O audio and video products, including pre-amplifiers and AV receivers, as well as any device that has a headphone socket fitted.  The cables to integrate Beolab speakers with non-B&O products are amongst the most popular ones out the hundreds of cables that I produce, showing how popular and adaptable Beolab speakers are.

All Beolab speakers rely on the Beomaster/Beosound unit to set the volume level when connected via Powerlink, ie. the speakers are always set to full volume.  The easiest way to visualise this is to consider that the Beomaster 3500 is a traditional hifi pre-amplifier and the speakers contain a hifi power amplifier as well as the speakers.  Hence, the usual chain of hifi components still exists, but the power amplifier has been moved inside the speakers.  Beolab 5 is a special case, as this speaker has its own pre-amplifier for use on its Line and S/PDIF digital inputs only.

Looking at your example of a PC being used as a source, normal practice would be to set the PC volume level to maximum, so that the Beomaster receives a full line level signal, not a volume-controlled line level signal.  In this way, the PC would behave like a CD player or tuner, allowing the Beomaster to set the volume control.  You could turn down the volume of the PC, but this would just mean that when switching from Radio or CD to the PC input, you would need to adjust the volume of the Beomaster each time.

The headphone output of your PC (or the headphone socket of an iPod, Sonos music streamer, Airport Express, non-B&O TV, etc) can either be set to full volume to give a line level signal for connection into the Beomaster/Beosound pre-amplifier, or it can be turned down and used as its own pre-amplifier when connected directly to a pair of Beolab speakers.  I am listening to music from my PC playing directly into my Beolab Penta speakers (with volume control from iTunes on the PC) as I type this - the cabling is straightforward, making this a nice and simple solution.

If you need any further help, please feel free to ask.

Kind regards, Steve.

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BeoLignage replied on Thu, Jan 24 2013 7:41 AM

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Thanks for all the answers, and a lot of bonus information as well. I did not have the right nomenclature to put the question right.

this quote is spot on what I was after:

Vienna:

No volume control happens in BeoLabs - gain of the power-amps remains always the same.
The actually produced power depends of course on the level of the incoming (pre-amp) signal.

...

The gain of the power-amps BM3500 remains always the same - the actually produced power depends of course on the level
of the incoming (pre-amp) signal.

1) gain of power 2) actually produced power

so a follow-up question: does a power amp work harder with a higher incoming signal. does it consume more electrical current/power. I assume so, otherwise it would always be hot since there is no internal volume control.

I always have the PC set to just below max volume and control the volume on the beomaster, but the above implies that there would be no harm to the beomaster if it was set to 90% volume and then the PC was controlling volume level, the beomaster would still do the same "job" so to speak.

thanks again for clarifying //Goran

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Vienna replied on Thu, Jan 24 2013 9:48 AM

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BeoLignage:

... does a power amp work harder with a higher incoming signal.
does it consume more electrical current/power...

 Yes

BeoLignage:

I always have the PC set to just below max volume and control the volume on the beomaster,
but the above implies that there would be no harm to the beomaster if it was set to 90% volume
and then the PC was controlling volume level, the beomaster would still do the same "job" so to speak.

True for "power consumpion"and "Watt send to the speaker", but ...

If you look at an other topic of any signal path/chain "how to minimise hum and noise",
it is always preferable to send a "robust" signal over the cabling instead of a "weak" one.

Assuming both volume controls have the same layout/scale:

Setting the volume to 20% at PC and 80% at the BM3500 would produce the same
"Watt send to the speaker" and consume the same electrical power as setting the
volume to 80% at PC and 20% at the BM3500.

But hum and other noise breaking through the shielding of your cable and entering the
signal path "through the back door" would be amplified in the first example (20/80)
much more than in the second one (80/20)  ...

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BeoLignage replied on Thu, Jan 24 2013 11:11 AM

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Thanks Vienna, very much appreciated

I feel so educated now

cheers //Goran