Chip damage & speaker impedance

[philiprporter]

I've just installed sound into a new Heljan class 47 using a Zimo chip (MX699KV) from another loco and frustratingly have 1 x 4 ohm speaker and 1 x 8 ohm speakers spare which I had intended fitting (as I like to fit two speakers to all my O gauge locos). However, the manual says that for this chip, I should either use 2 x 8 ohm speakers wired in parallel or 1 x 4 ohm.

 

If I was to wire the 8 and 4 ohm speakers in parallel I would get 2.6 ohms impedance (approx) - I'm assuming this will risk damaging the chip, but I can't find a definitive answer as to whether it would or wouldn't and wondered if anyone knew the answer and whether wiring these two speakers up in parallel would land me in an expensive puff of smoke?

 

Thanks, Phil. 

[pheaton]

You are correct you will either damage the chip or shorten its Lifespan quite dramatically. 

[pauliebanger]

Agreed. A 4ohms and an 8 ohms in parallel is a potential disaster in the making.

 

IF, you keep the volume level low, you could probably get away with doing so, but it would be so easy to forget and to turn the wick up some time in the future which will definitely cause damage. The 699 has a 10W amplifier so danger is lurking!

 

You could use these speakers in series, giving 12ohms total, which would be safe. There will be a small reduction in maximum sound level attainable, but at 10W, you will probably not usually be running sound at maximum, so that's kind of irrelevant.

 

Best regards,

 

Paul

[philiprporter]

Thanks guys that's really helpful - I may try them in series and see how that sounds. Many thanks. Best wishes, Phil.