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Got a technical problem? Can't understand a piece of jargon or some technical principle? Drop us a line and we'll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097 or send an email to silicon@siliconchip.com.au

Battery amplifier for single loudspeaker

I’m trying to source an amplifier to take the output signal of my MP3 player and drive a single 8-ohm speaker (rated at 40W max). I want to be able to run the amplifier from batteries or from a plugpack and I want the amplifier to be relatively small so I can place it in a compact enclosure.

I found the Mighty Midget amplifier (SILICON CHIP, March 2002) but I understand this is no longer available. I have found other amplifier modules at Jaycar Electronics but these require dual supply rails, making it much more difficult to use batteries.

Can you please suggest a suitable amplifier? Since I only have a single speaker, can I use a smaller rated amplifier than 40W? (G. W., via email).

• The Mighty Midget can still be made. The PC board can be purchased from RCS Radio (www.rcsradio.com.au), while the TDA1562Q amplifier IC is available from Dick Smith Electronics (Cat. ZA-2098).

Charging controller current query

I saw the Charging Controller for 12V Lead Acid Batteries in the Circuit Notebook pages of the August 2008 issue and am wondering what the circuit’s own power consumption is. The reason for this question is that I have a small solar panel that produces up to 100mA in full sun. Its open-circuit voltage is in the order of 22V which is probably not much good for 12V car batteries. (T. T., via email).

• The quiescent current of the Charging Controller would be very close to 13mA.

Note that this current is drawn from the battery, although your solar panel will need to supply this as part of the charging current, when the circuit turns on transistor Q1.

Magnetic Cartridge Preamp Equalisation

I am constructing the Magnetic Cartridge Preamplifier described in your August 2006 issue. As a slight variation on the design, I wish to use a 12-position switch to select between all the equalisation curves because I have a number of different 78 RPM record types. However, to save space, I would like to leave the level potentiometer out and replace it with a trimpot or fixed resistors.

If I do this, when I switch between the various equalisation settings, will the level vary so much that I will need to re-adjust it for each setting? If this is the case, I will need to include the level control but if this is not the case, I can leave it out. (C. R., Tuebingen, Germany).

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