ELECTRONICS tidbits

0. Extra

At the time when I was looking for 2 amplifiers to drive the subwoofers, I did not know Dick Smith Electronics was clearing out their 500W monoblock amplifiers for only AU$100 (US$50) each!!! I completely missed the sale!

1. Electronics Australia Pro Series Three power amplifier kit

-- Jaycar Electronics is offering one final batch of this amp kit (or so they say). I'm not sure of the weight of the amp, but I'd estimate it to be over 8kg (or 17.64lbs.) while the amp itself is 12"x16"x3" big. Here are some pictures of my amp.

Here is the amp with the top cover removed. Each toroidal transformer has a diameter of a compact disk's [diameter].

Here is a closer look at one of the amp's amplifier modules. Thanks to Jaycar Electronics for predrilling all the holes for these kits.

I must say the stock name sounds a little "uncool." Moreover, it would have been cool if the power-on light was green or blue instead of red.

Here is the back of the amp showing the mains input/output sockets, fuse holders and gold input/output terminals for each amp channel.

Click pictures for larger photos.
(pictures were captured from an old compact-VHS video cam)

PERFORMANCE OF PROTOTYPE
Power output (per channel, with both channels driven)

Continuous:
185W RMS into 8ohms
255W RMS into 4ohms		 IHF (short term):
240W RMS into 8ohms
380W RMS into 4ohms

THD:

0.005% at 100W RMS into 8ohms
0.008% at 180W RMS into 8ohms
0.009% at 240W RMS into 4ohms

 IMD:
(50Hz/7KHz 4:1 ratio)
0.005% at 180W RMS into 8ohms
Frequency Response:
-3dB points: 10Hz to 100KHz		 S/N Ratio (unweighted):
>100dB with respect to 100W RMS
Slew Rate:
Approx. 40V/us
(defined by input filter)		 Damping Factor:
>300 at 180W RMS into 8ohms
Input Sensitivity/Impedance:
0.8V/33K-ohms for 100W into 8ohms		 Overload Indicator:
Activated if output THD exceed approx.
0.05% (regardless of load impedance)


The real advantage with this amplifier is that it has a lot of grunt and that it is cheaper than buying two dedicated subwoofer amplifiers (even after I've built/bought a suitable active crossover filter). Moreover, I could use it for full range sound reproduction.

From tearing the component bags in the box, soldering and assembling everything to trying it out with music, it took me 24 hours to build the kit (counting breaks and trips to the local electronics store because I ran out of heatshrink tubing and the kit I got was missing one 33K-ohm resistor!!! Still, a missing resistor is better than a missing output transistor). I used the amp to break-in my two subwoofers (for 30minutes at a time) with a continuous 20Hz signal at full cone excursion. The right channel has a DC offset of 10.5mV, while the other channel has an offset of 10.6mV -- not bad (!!) considering the driving transistors' hfe were not close to each other.

to be continued...