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Topic: Connecting MP3 to active speaker amp - with pre-amp? (Read 7004 times) previous topic - next topic
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Connecting MP3 to active speaker amp - with pre-amp?

Hi,

I have a portable PA speaker (active) that has line level inputs. I currently connect it to a small DVD player that is used to play audio CDs. The output from the CD player seems perfectly matched to the speaker, but whenever I connect a MP3 player or laptop via their headphone jacks, the volume is never high enough.

Using my MP3 player would be far more convenient for me so I'm looking for a way to get the same output I get from the line outs on my DVD player.

I'm thinking that I'm likely to need some sort of pre-amp to sit between the mp3 player and the active speaker.

Any ideas on what I should use? The smaller the better as I move this system around a lot.

Thanks!

Connecting MP3 to active speaker amp - with pre-amp?

Reply #1 –
A small mixer is probably the easiest/cheapest way to get a preamp.  The line inputs on a mixer usually have some gain.

That's a very strange problem...  Headphone outputs usually have higher than line-level output (with the volume turned-up).

I'm assuming the PA/Speaker system have a built-in mixer????  If you're connecting the DVD outputs and the MP3 player's outputs together with a Y-adapter, that's the problem....  The DVD player is "pulling down" the MP3 player's output...  You should never connect two outputs together.... You need a mixer.

Connecting MP3 to active speaker amp - with pre-amp?

Reply #2 –
What about attenuating the DVD output using some passive resistors instead of actively amplifying the other sources?
 

Connecting MP3 to active speaker amp - with pre-amp?

Reply #3 –
Thanks for the replies!

My PA box doesn't really have a mixer. It has one line level input and a mic xlr input. It also has volume and tone controls but that is it. I've not been using two inputs, when I connect the DVD player I use a straight rca cable and when I connect the mp3/laptop I use a 3.5mm jack -> rca cable.

I'm thinking that I might be best just continuing to use the DVD player. My primary motivation for using an mp3 player is to save space/weight/requirement for an extra plug - but a mixer isn't going to solve that issue.

It's strange that headphone outputs are normally higher than the line out on the dvd player. I've tried a bunch of different mp3 players and laptops and all are significantly quieter.

Does anyone have any experience with something like this:
http://www.incarexpress.co.uk/view_product.php?partno=PC9460

Or headphone amps?

Something small I could run off rechargable batteries would be fine, but perhaps it's just easier to stick with the DVD player.

Thanks for the advice

Connecting MP3 to active speaker amp - with pre-amp?

Reply #4 –
Quote from: DVDdoug on
That's a very strange problem...  Headphone outputs usually have higher than line-level output (with the volume turned-up).

My experience says otherwise. It does depend on what the output is designed for. On many portable players there is insufficient supply voltage to reach line-level. When driving low impedance ear/headphones that's not an issue since they require current more so than high voltage. I have a notebook, CD player, Minidisc player, 2 MP3 players and a cassette-player, and only one of those is (just, barely) able to reach line-level on the headphone jack.

Connecting MP3 to active speaker amp - with pre-amp?

Reply #5 –
I really think the "root problem" is the PA system. 

That line-level booster will probably do the trick.    This is an unusual problem and it's going to take a creative solution.

Quote
It has one line level input...
Is the PA system stereo or mono?  If you're using a "stereo-to-mono adapter", that can foul-up the signal too.

Or, is there any chance that the 3.5mm to RCA adapter cable is some kind of special attenuating adapter?  Have you tried a different cable?  (Attenuators are a "specialty item", so it's very unlikely that you accidently ended-up with one.)

Connecting MP3 to active speaker amp - with pre-amp?

Reply #6 –
Quote from: antz on
Quote from: DVDdoug on
That's a very strange problem...  Headphone outputs usually have higher than line-level output (with the volume turned-up).

My experience says otherwise. It does depend on what the output is designed for. On many portable players there is insufficient supply voltage to reach line-level. When driving low impedance ear/headphones that's not an issue since they require current more so than high voltage. I have a notebook, CD player, Minidisc player, 2 MP3 players and a cassette-player, and only one of those is (just, barely) able to reach line-level on the headphone jack.


Actually, there are five or more different signal levels that are commonly  called "line level". I think the above discussion conflates them all. One "line level" is the line level traditionally used in US consumer audio equipment. It is around 100-300 millivolts. The aux inputs and tape outputs of most hi fi amplifiers are designed to work at this level. Consumer analog tape machines and tuners work at these levels. Professionally, we call it "-10". Another line level is used in professional audio gear - pa systems, mic mixers, etc. It runs around 1.25-2.5 volts. Professionaly, we call it "+4". The two levels are actually about 11 dB apart, since the two profesional level dB designations are referred to two different professional signal voltage standards that are about 3 dB apart. There is also a line level that is used in Europe, and runs around 30-50 millivolts, and is often found on DIN connectors. There is the line level that we find on consumer and pro power amps and CD players. Its from 1.5 to 2.5 volts.  Then there is the line level that we find on PCs that relates to the AC97 standard and is 1 volt.

Portable gear tends to be limited by whatever battery power it uses. While DC-DC converters are readily availble, efficient, and reasonably cheap and small, they still aren't used that much. The three most common levels of battery supply voltage are 1 AAA or AA cell which is 1.2 to 1.6 volts depending on the battery technology, twice that for two cells, and 4.2 volts obtained from Lithium cells.  A portable player based on them might deliver anything from a few 100 millivolts for a 1 cell supply, to over 1.25 volts for a player that is based on a 4.2 volt supply.

If you juggle all the alternatives, you can see that the "line level" coming out of a 1 cell music player will be compatible with the line level inputs on your typical stereo receiver, but will be totally inadequate for the line level input of a mixer or amplifier designed for pro audio use. OTOH, a player that is based on 4.2 volts will put out about a 1.25 volts and will work fairly well with pro audio gear, but will be kinda loud (but manageable) when plugged into an america-standard hifi receiver.