Radio/CD player - power consumption and reception?

[Duffer]

SWMBO very kindly bought me a replacement CD/radio for Christmas, as the last one was playing up. Two questions:

(1) Both it and its predecessor are supposed to have AM (MW and LW) reception but nothing is received. I thought these car stereos had built in AM aerials with plug in FM aerials but is this wrong i.e. do car aerials also provide AM reception? (We fitted a VHF/FM splitter which has significantly improved FM reception.)

(2) The new stereo was supposed to have a fairly standard 25 watts per channel but the new one has been uprated by the manufacturer to have 45 watts per channel (up to 4, we have 2 speakers connected). Does this mean it uses nearly twice the power of the old one, or only if we have it twice as loud?

Many thanks

PS Happy New Year to all Forumites!

 

[Ruffles]

If it's a car radio it won't have an internal ferrite antenna for AM (LW+MW) 'cos then it would be directional. You would have to tack while driving! It will use the external antenna.

The VHF/FM splitter will assuredly block low frequency AM and LW. You may get somewhere by tacking a short piece of unscreened wire into the aerial plug that connects to the unit. This may impact FM performance - it may also affect the VHF reception if the splitter is passive.

You are correct that the increase in max audio output power does not necessarily mean increased battery drain. The amplifiers tend to be very efficient - mainly so that the manufacturers don't need to fit a heat sink.

Does the radio need a permanent 12v supply to maintain the security code? Some do, some don't. Can be a pain. I connected mine to the battery meter on my switch panel.

 

[mikefleetwood]

(1) AM reception will need some sort of aerial. The internal "ferrite rod" aerial used in portable AM radios does not work in the enclosed metal box of a car, so they always use an external aerial. You don't need to go to the trouble of buying something special, just a few metres of wire stuck in the socket will do. Although a cheap "replacement" aerial from Halfords will look better.

(2) Power output ratings for this kind of equipment tend to be a little fanciful. Actual power will, of course, depend on how loud you have the volume and how many speakers you connect in parallel. I would think you can expect to draw little more than about 1A at "normal" levels.

 

[steve_cronin]

No car radios don't have an internal aerial. If you think about it, how would that work in a metal car? You are maybe confusing the situation with that of portable radios which have internal ferrite rod aerials for AM but a rod (usually telescopic) for the VHF (which gets called FM these days buit that only describes the modulation system)

Your set needs an external aerial for Amplitude Modulated signal reception in the medium and long wavelength bands as well as for the VHF or very short wavelengths.

In a plastic boat, so long as you don't want to receive say radio4 198khz (1515 metres) from a long way away, any old bit of wire pushed into the central hole of the plug will work but there may be need to "trim" the tunable length of the with a small variable capacitor provided for the purpose near the socket.

Basically, as I'm running out of time now, the power consumption will increase as you increase the volume but NOt necessarily in a linear relationship.

As to power outputs, these are quoted in "music power2 (or peak power) by cheap set manufacturers whereas the quality end of the market uses the more accurate root mean squared (RMS) which will give a lower but more honest indication of output.

Wish i had time to go into more detail!

sTEVE cRONIN

 

[Duffer]

Many thanks for the replies - I'm glad I don't have to buy a lower powered one for the boat in the sales: about £50 for a Sony from Argos.