I have just bought a peavey xr800f powered mixer but unable to get echo on mics any help would be appreciated thanks

Certainly you could.

This is a high output piezo pickup but won't give line level signals expected by some inputs so I would guess you may be going into a line input. If so try a mic input (XLR) instead and see if that works.

http://www.peavey.com/products/index.cfm/item/699/116338/PV%26nbsp%3B20%26nbsp%3BUSB

Look under "Downloads" tab at bottom for owners manual info. In a nutshell...mic to mixer channel #1, mixer connected to power amplifier, amplifier connected to speakers. Start with zero volumes on all equipment, bring up amps 1st (1/2 volume) and then adjust mixer until sound is heard from the microphone.

The48 volt supply is a simple rectifier/filter from the power transformer. The schematics don't even show the switch anyplace that one can find it. It appears they don't even regulate the 48 volts... Some Peavey switches are just in a hole that you have to poke something into with an alternate action button. They use these on some equipment for instance for selecting a powered mixer into L/R or Main/monitor setup. Push in with a match stick... From the manual it lloks like this is supposed to be a tiny square button... these are EASILY broken off but usually you can still actuate the switch with a little stick.

The mixer is stereo and the amp is mono. The line level out of the mixer MAY overwhelm the KB2 regular inputs so try running the mixer into the PA input jack.

First of all confirm if the speaker impedance is not lower then the recommended Ohms at the back of the Mixer speaker socket.You can use an 8 Ohms speaker on a 4 Ohms amplifier but not vise versa .
Next see if the fan on the mixer works. If not the Amp is getting very hot and this will lead to unwanted distortion. You can confirm if its a heat related issue by playing the mixer at low volumes for more than an hour and see if it distorts.

View videos on YouTube regarding "mixer setup". Find the parts of setting up of "effects". Don't worry that you have a different mixer, the principles are all the same for analog mixers. Steps are this: Set the EFX send level for EACH of the input channels (knob above each channel gain) for the proportion you want for each channel. Check that the level you are sending does NOT cause the effect clip light to light very much. Set the effect you want, delay, echo, etc. with the selector knob. Advance the output sent to the power amp with the two knobs in the upper right of the panel. Adjust the "time" knob for the delay or effect depth you want. Then go over the same settings in the same order until you get the sound you want.

You will need at least a 24 channel mixer to give you spare channels. You also need an active crossover and a snake. The advice you need is too much to include here so I am including some links:http://mixonline.com/live/FixIts/, http://en.wikipedia.org/wiki/Live_sound_mixing, http://mixinglivesound.com/blog/tag/outdoor-concerts/,http://mixinglivesound.com/blog/, and http://www.scribd.com/doc/11435651/Beginners-Guide-to-Mixing-Sound. You may need more monitors than you are planning on and you might consider in ear monitoring.

If the subwooofer has only a single input, then connect it to the Monitor output which does a mix, HOWEVER the level will NOT vary with the main sliders, but only with the monitor pots... This is NOT really practical for performances.

There is no mixer built in the unit, so you might make a simple resistive mixer taking the "Master out" left and right using 1K ohm resistor from each to a common point that feeds the subwoofer. Tie the grounds of the sub and mixer together.

FOR SYSTEM SAFETY always power the mixer and active speakers or any interconnnected equipment from the same receptacle or source.

Troubleshooting is always a "process of elimination." Have you tried hooking up your Peavey powered mixer to another set of speakers? How about connecting the speakers to another audio system? Your term "very little sound" could mean audio input problems, mixer/amp settings or failure and possibly speaker damage (internal passive crossovers). Please be more specific.