Usually a headphone output on devices are very low volume, which makes sense because we need to put headphones on, which are usually right on our ears. If you think of a hifi, the headphone out socket is a lot softer than an aux out or another output.

Does your keyboard not have another output jack? I think that'd work.

Or, it may work to plug your keyboard into one of the XLR ports, those channels have more gain as far as I know. Which would work.

A number of things to consider:
- Aux inputs typically don't have any gain.
- Headphone outs are stereo, your aux input is mono, if you're using a mono cable, you are throwing away half the piano's output power.
- The amp is 100W stereo, you're using one speaker. Once again wasting half the power.
- Amp is 100W per channel into 4 ohms. You are using a single 8 ohm speaker on one channel, which = 50W max. To get full output you need a 4 ohm load on each channel (i.e. two speakers in parallel on each channel = four speakers total).
- Pianos are quite dynamic. If you're playing softly you'll need more gain at the mixer.

To get the most out of what you have already - Use a stereo jack to two mono jack cables, plug into two inputs and pan both to the side where the speaker is. Don't use a stereo input (or plug each into the left input of a separate stereo input channel. If you need to make the piano louder, you can raise the level on both input channels.

Ideally - Get a second speaker and put it on the other output channel, you can plug the two piano outs into one of the stereo line inputs

A lot to assimilate here, so if you have questions, ask...

using a set of headphones, check that output on the keys is nice and loud. then are you using a stereo or mono cable? as if you use a mono cable, only the left (usually) channel is working... so you say yo are only using one speaker? try the other speaker output as what you are hearing is probably just some bleed on the wrong side.

if you are using a stereo cable still try the speaker terminal swop, and if that doesnt cure it then maybe try pulling the cable ''halfout'' as it may just be out of phase and then converting to mono...

cant hurt to try these things.

Just dont plug things in and out with amp at full volume, or if there is no volume control for aux, then switch off between each cable pulling variation. just to protect the speaker from those nasty pops.

cheers

You guys are legends ?

I mangaged to squeeze out about an extra 60% more power, by reading through your comments and using the old noodle. First here's a pic of the suspect in question
[/img]http://www.8thstreet.com/images/phonic-ppod620.jpg[/img]

Dunno if this method is legit, but here is my Mcguyver -
My piano only has Headphone output, but it has 2 of them. I got hold of some extra cables (not sure if they're mono or stereo) and put
them in both piano h/phone output jacks. The mixer has only one AUX input, so I tried putting both in the 6th line input (A and B port) - one closest to the aux input. Instead of using the speaker out I plugged to cables in the main out and two in the speaker. I should have enough power now,
so its just a matter of setting the eq's (so the high notes don't "crackle" and the lows dont "muddle") when I do a soundcheck at the actual venue.

Any other tips you guys willing to offer, since its goldust.

Shot Gents

The headphone outs are stereo, so inserting a mono cable only gives you one channel (left IIRC). Check by playing high and low registers on the piano - you'll find the one side will be louder than the other. What you can do to get around this using mono cables is insert one of them only to the first "click", which will give you the other channel through that mono cable.