No power switch for the TwinTen amplifier

I have read the article in the February 2005 issue on the TwinTen amplifier. One thing struck me as a bit strange, especially with your fixation about turning things off when not in use – it doesn’t have a power switch.

To turn it off you either have to pull the power connector out of the back panel or turn it off at the wall GPO. With the intended use of this project as a kids’ auxiliary amplifier, it will run all the time unless one method or the other is used to shut it off and if other kids’ bedrooms are like my kids, the wall socket is "buried".

Sure, a power switch in the low-voltage AC circuit will not turn off the power pack but at least it will cut current draw to that which is the idle current of the plugpack.

I also am slightly bemused by the comment that this amplifier performed well on your staff member’s "huge" stereo. I would not expect otherwise if this person’s speakers were reasonably efficient – say in the order of 98dB/1W/1m). Any small amplifier will do well on speakers of this type. In the "olden days", pro speaker systems had efficiencies of 105dB/1W/1m) and they filled a whole auditorium full of people with just 50W.

However, when amplifiers are connected to today’s rather abysmally inefficient speakers, an amplifier with this output runs out of "puff" really quickly.

Please don’t get me wrong. The intended purpose of this amplifier is fully understood and I’m not knocking it; I just wanted to point out a couple of things. As an auxiliary amplifier, your new design is just what the doctor ordered . . . however, you can’t turn it off!

Brad Sheargold,
via email.

Comment: as indicated in the article, the TwinTen was presented as a project for high school and college students. Many such schools will not let their students build anything with mains wiring in it, so using a plugpack is the only practical approach.

Certainly, running the plugpack continuously is a waste of electricity. And it does go against our philosophy of turning everything off because as you point out, laziness will mean that many such units will always be plugged in and never turned off.

If people want to, it would be reasonably straightforward to install a miniature toggle switch near the AC input socket but as you point out, that still leaves the plugpack powered up.

The TwinTen was tried with reasonably efficient loudspeaker (90dB/1W/1m) in a very large listening room.