VHF EXTENSION SPEAKER

[AlanPound]

Valve amplifier output stages can blow if driven into no load (ie. no speaker connected).

Transistor output stages (and lets hope your VHF has transistors!) will be fine with no load - no load == no heat generated (migh be a bit quiet though).

... (in a former life I used to design 1000W audio power amplifiers for sound reinforcement purposes)

Alan

<hr width=100% size=1>

 

[EdEssery]

Thanks for your response -- I am aware of the dangers of driving into no load.

If you look at the <A target="_blank" HREF=http://www.essery.demon.co.uk/VHFSpeaker.pdf>circuit</A> closely you will realise that it is not possible to configure the switches so that both speakers are off and therefore there is NO danger with this circuit of driving into no load.

The switches allow one or other speaker to be on or both can be on together. So long as your VHF can cope with a 4-8 ohm load and the two speakers are both 8 ohm, there is NO danger of damaging your VHF set.

Regards,

<hr width=100% size=1>

 

[StephenW]

Hi Riccardo - I also have an older Icom VHF and have fitted an external Navico waterproof cockpit speaker. I noticed that if you don't push the extension speaker jack plug all the way in i(sort of half way in) t enables both VHF speaker and extension to work simultaneously!

Very handy when to-ing and froing between below and the cockpit.

Looks like that's what you want to do, though you'll need to experiment.



<hr width=100% size=1>

 

[AlanPound]

Ed
Sorry to be a pain, but (as far as the speakers go) there is *NO* dangers involved in driving into no load.... Please read my posting again....

Believe me, unless you recovered your VHF from the Ark (not the ARC, I mean Noah's Ark), you don't have valves (valve ciruitry typically doesn't like humidity anyway).... so...

*Don't Panic* Your wiring won't actually cause any problems, but won't really be any more practicat than using two SPST switches (with common ground) feeding two separate speakers....

...except of course, insofar as it won't allow the VHF to be totally isolated from at least one speaker, you won't end up with wondering why you can't hear any radio checks anymore, and thinking, erroneously, that the coastguard actually *had* stopped responding to calls for radio checks....

... ah well....

<hr width=100% size=1>

 

[Guest]

Switch ....

Why not just put a three way switch in ..... 1-both-2 ......... why the double switching and all the palaver ?

Better still have a series of jack plug sockets around so you can plug in where you want ???

OR even better still - have wandering lead speaker !


<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[EdEssery]

Re: Switch ....

I agree that a 1-both-2 switch would be better but I was unable to source a suitable toggle switch from RS or Maplin. The closest I could get was an On/On/On switch which is, of course, no good...

<hr width=100% size=1>

 

[EdEssery]

Transistor or Valve(!), I'm sure the VHF manufacturers wouldn't think it a good idea to disconnect the internal speaker by plugging in the cable for an extension one and then not connect it.

But of course the real purpose behind the circuit is covered by your second point -- to avoid the situation where you think the VHF is on ('cos you can see the display) but miss broadcasts 'cos both speakers are individually turned off. So far as possible, systems should be designed to prevent human error. For the additional switch costs of about a £1, I'd recommend my proposed approach every time...

<hr width=100% size=1>

 

[AlanPound]

<So far as possible, systems should be designed to prevent human error. >

... I take your point, but in that case it seems rather a shame that most VHF sets are fitted with a volume control...

8)

Alan

<hr width=100% size=1>