Model Boat Mayhem

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: BarryM on July 23, 2007, 04:43:06 PM

Title: Mono/Stereo SFX Hook-up
Post by: BarryM on July 23, 2007, 04:43:06 PM
I like my electronics to come in little sealed boxes with nothing but terminals marked 'in' and 'out'. This query is more complex (to me) and I think I know the answer but I'd rather have a second opinion before I produce an unintended smoke generator.

I have gunfire recorded on a MP3 player, an 8 ohm speaker and a 6V. supply. I believe I will need to fit both a pre-amplifier and amplifier in between  MP3 and speaker and have Maplins N46FL and N64AW in mind.

Questions
a) are the above pre-amp/amplifier considered suitable or would alternates be better?
b) the MP3 player has a stereo output; is it OK to feed the stereo input into the pre-amp by splitting L&R channels and connecting paired cables into the pre-amp? - Or will this just cause 'them what know' to throw up their hands and scream "Numpty"?

Thanks in advance for all help.

Barry M
Title: Re: Mono/Stereo SFX Hook-up
Post by: Tug-Kenny on July 23, 2007, 08:23:41 PM
Hi Barry

The word you're looking for is NO

You cannot connect the left and right channels directly together. You're options are to use a stereo amplifier  (Maplins part number K4003 30W Stereo Amplifier)   or,  only use the left  (or right)  output alone to the Mono system you propose.   You could build a mixer but this would only be extra weight and it isn't as if its a Hi Fi unit you're building.

The difference in Gunfire between stereo or Mono is negligible, I would have thought  (unless it's aimed at you  ;D)

You do not actually have to use a preamp at all, as the output can be sent direct to the main amp. The volume would then controllable by the MP3 player.

Hope this helps


Cheers...Ken
Title: Re: Mono/Stereo SFX Hook-up
Post by: malcolmfrary on July 23, 2007, 09:42:35 PM
Connecting the left and right direct can be a bit iffy, but there are alternatives.  You could insert a resistor, value not really critical, but I would go for 47ohm each or greater into each of the signal legs, and then common the pair.  Optionally, this common point can be connected to the -ve line via another resistor of the same value.  The resistors are about 13P each.
This will effectively stop the left and right MP3 player amps from tryng to feed each others outputs.  The combined outputs are now ready to connect to a mono input.  
The MP3 player will do all of the preamplifying you need.
The N64AW is a magic brick.  Mine has had all manner of abuse, including being well dunked in salt water, and still works.
Of course, if you have two MP3 players, you could get one sound from the left of one and the right of the other..........

Title: Re: Mono/Stereo SFX Hook-up
Post by: BarryM on July 25, 2007, 07:30:15 AM
Ken and Malcolm - Thanks for info; you have saved me time and money.

Barry M
Title: Re: Mono/Stereo SFX Hook-up
Post by: BarryM on July 26, 2007, 01:37:24 PM
Ken,

Followed your advice as the simpler option and it all worked first time.  :)  :)  :)

Barry M
Title: Re: Mono/Stereo SFX Hook-up
Post by: Tug-Kenny on July 26, 2007, 07:32:12 PM

Only to glad to help.   .................Boom Boom


Ken