Floor monitor speakers

Last September the ceilidh band I play with (the Greenbank Buskers) were doing a gig in a hall which was filled with lots of noisy dancers (etc!). We have usually managed fine in the past but found that the fiddles were having difficulty hearing the accordions, and vice versa. We had amplification but only for the hall.

Having done other gigs where we had (gasp!) a sound tech and even (gasp again!) floor/stage monitor speakers, I knew there was a solution to our problem – but commercially at cost – and we are just a band that plays for charity. However, I remembered that I had an ancient guitar amp I made with a couple of really nice speakers in it …

The amp had not been used for years. Here it is, in use as a table for wine glasses:

I decided to chop it up and recycle what I could into two floor monitors. I would use the speakers and the power amplifiers at least. Here’s the rear view before I started to take it to bits:

With the back off and the amp moved onto the top of the cabinet you can see the speakers fully, and the power supply boxes on one of the back panels below:

It may be obvious to the cognoscenti that at least part of the amp used valves – as all the best early guitar amplifiers did!

You can also see a heatsink – the power amp section used two transistor amplifiers I had built for my (third I think) old hi-fi system. It used the circuit of the Practical Wireless “Texan” amplifier, uprated to 30 + 30W. Here’s the underside of the chassis:

and the controls:

After lots of work with the hacksaw, the power section was separated, the power supply for the power amp re-used, the supply for the preamp discarded along with the valve preamp, and a new preamp made from a couple of Chinese preamp boards bought through eBay. Here’s the inside of the amp box, which now includes the toroidal transformer for the preamp power supply:

The preamps are in their own box:

Once assembled, the electronics worked as expected, using the mixer I also found on eBay as a source (which is what I will use with microphones on stage). Here’s the lash-up:

Everything could now be put into the newly made floor cabinets – this is the main cab with the speaker board (front) off:

This is the rear view of the external speaker cabinet:

Here’s the main cabinet rear view. Note Speakon connectors! The preamp controls are nicely recessed, and work fine. It’s more than sensitive enough.

That’s it finished! We now need to try it out before it gets used in anger at a gig.