1998 SΨREN 15W two box

Class A Amplifier

by Altronics

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very subtle green light, very high quality push button Case was NVA power supply

HEAVY METAL? Finished in Toyota Derwent blue

This amp uses two full length heat-sinks and case is 3mm mild steel.

Built about 6 years ago (Sept 1998) this is probably my best amplifier to date. A two box power amp with a rather unusual fully regulated 21V supply. This amplifier case is constructed from 3mm steel plate and is so well isolated from mains it can safely use unscreened fine silver wire as an input wire. A big thanks to my great friend Nino Sardi who spent a lot of time designing and building this case out of such a difficult material .It is completely free from hum and has extremely low distortion levels. All the extra heat is easily dissipated by two massive full length heat sinks. The power supply features a large 300VA toroidal transformer. Although only rated at 15W per channel it easily sounds like 50W and is extremely entertaining. The output devices are the very well specified Motorola MJL21194 and MJL21193.

SPECS  OUTPUT 15W per channel, Input sensitivity 680mV for rated output, Distortion < 0.004% although typically 0.0006% ( No not a misprint!), S/N ratio 113dB unweighted from 20Hz- 20KHz

The amp kit is available from Altronics Perth, item K5109, regulated PSU K5110

I did modify the power supply, matched the transistors very carefully, used silver solder along with 1 and 3 mm fine silver. The main on off switch has a mechanical life of 1,000,000 operations. The switch light has a large value resistor attached so it glows very dimly. The power supply case and sink get very hot so I would recommend  a very large heat sink here as well as the two on the amp (blue case). You can just about see the sink on the power supply case on the right This amp is normally used with my Passion preamp or the Hemsley passive.

This power supply needs this heat-sink. It gets very hot during summer!

Link wire is all solid silver

OTHER NOTES ADDED JULY 2004.

The power supply case is constructed from aluminium. It started life as an N.V.A. (Nene Valley Audio UK) The regulated supply circuit is the one supplied by Altronics. I did beef up the filtering adding two extra caps (at least twice the size of those used on the PCB) The most difficult job was bolting the regulator circuit to the back of the case. It was quite hard electrically isolating it. The heat sink needs to be large. The power supply runs hotter than the amp. It is absolutely essential to use a good amount of heat transfer compound and to grind the sink down to a flat plane. Even cast heat-sinks tend to be slightly bowed. I did use a rather expensive push button. It has an excellent mechanical and electrical lifetime and can also handle high currents. I wired it up US style. This means it is pushed in to switch off. Since it uses a 12V lamp I experimented with a resistor pair to really reduce brightness. When on the switch is a very dull green. Its silly but it makes me think that it is cool running. During a summer's evening you cannot keep your hand on that heat sink!!!!

 A "soft start circuit" would be worthwhile here. This amp generates a good thump when switched on. TIP detach your positive speaker cable at the end of each use.