Okay,

as promised .

First I should add that many of the parts used in these are what I happened to have around - I was trying to make these as cheaply as possible.

I built the cabinets years ago allowing space to later add amps in the back - which shortly after I did, some based on the design by Johan Sorensen (http://hem.passagen.se/johanps/).

No overly happy about these i set about designing my own inspired by his design.


From the front - Some fairly rough n ready looking DIY speakers.


From the rear - the one on the right houses the mains PSU ( A toiroid transformer (approx 350VA from memory - thogh not sure) for the 50V rail and a small 15V SMPS for the control voltage and battery charging).

The one on the left houses the batterys, amps and control circuit.

Battery bank

50 Cells (not 60 as earlier stated). They are configured as 5 banks of 12 Volt (2500mAh). 4 banks go in series to provide a nominal 48V (about 55 when fully charged) and the final bank provides the control voltage. When plugged in to charge the bank of relays configure each with a constant current regulator and each set of battery and regulator in parallel so will charge from around about 15 volts.

Control circuit

This has several functions - there is an MCU (atmega48p which controls the startup and shutdown procedure by switching transistors (which in turn switch relays) and monitoring supply and speaker rails for correct operation.
It also has a few LED's to show operating status and any fault conditions - including clipping - excessive clipping leads to automated shutdown in order to protect the connected speakers.
Clipping detection is currently crude - but is effective. It simply monitors each speaker rail (full bridge design so both for each speaker) if they get to close to 0V or the power rail a clip is assumed)

The amps

The amps are a full bridge design allowing for needing only one main power rail. A separate lower voltage (10v regulated) rail drives the logic, op amp, comparators and FET drivers/FET gates.
The power rail level has no effect on the gain of the amp - so is able to run from pretty much any voltage (between 10 and about 80) - this should with some extra effort make it possible to only run the large toroid when lots of power is required.
The design is a self oscillating type which oscillates at around 500kHz (with the help of a resistor/capacitor - it tries to run at about 1.6MHz left to its own devices which dissipates to much energy due to switching).
The power FETS are tiny!! 4mm by 4mm yet can deliver incredible power considering their dimensions. There is nothing more than a area of copper (reinforced by some thick copper conductors) on which they are mounted in way of a heatsink.

It was some time ago so i cant recall exact numbers but I think with a 1kHz sine wave dissipating 40Watts RMS into a test load resistor I measured approximately 95% efficiency.

I am using these for full range - not just to drive the bass units!

Speaker ocnnections
I have allowed for connecting the amps to other speakers. Whilst the speakers themselves are likely to be better than your average cheap home "HiFi" speakers - they are certainly no contender to Propper HiFi speakers.

These connection allow the amps to be connected to decent speaker so the amplifiers can be compared directly with others on a set of decent speakers.

Speakers
As you can see the cabinets are built from MDF. They have been designed according to the Thiele/Small parameters for the drivers - which are them selves some cheap Skytronnics things. Despite their costs (£15 for bass/mid driver - £8 for the tweaters) they are pretty good performers.




This is what i lashed up to make it easier to control - I initially had the pre-amps and volume knob on the rear of the speakers but this quickly proved inconvenient when used in the car. So this litte unit now contains the preamps, volume knob, and a USB DAC IC. There is a switch to select between analog/RCA in and the USB DAC.

Despite its appearance this setup sounds pretty incredible! I have had a number of audio buffs from various backgrounds (Some home HiFi enthusiasts (my dad included!) another electronics engineer who has worked with audio, and a guy who works with professional audio equipment for recording) listen to this and all have been amazed.