Large Scale Central

Blew my Sierra Sound Board running two Speakers

Electronics Power and Sound
#1

I have (2) USA GP38s. The 1st loco has a Sierra Soundtraxx system installed in the fuel tank with the supplied speaker from Sierra. (A 2-1/2” round speaker made by Kobitone, 8 ohms, 0.5 watts numbered 49211). I wanted to trainline the sound into the 2nd loco when they run together. As a test… I connected a Phoenix speaker (A 2-1/2” round speaker, 8 ohms, ?? Watts, number SP-2.5SQ: 824-660) in parallel to the Sierra speaker. Well… the sound was coming out of both speakers for about 30 seconds when a puff of smoke came off the Sierra board followed by a bright glowing component. Needless to say … the board was cooked.

After reading about ohms on the Internet (should have done this first)… I discovered that hooking up two 8 ohm speaker in parallel changes the ohms to 4. I’m assuming the Sierra couldn’t handle this and blew.

Has anyone ever hooked up two speakers in one locomotive or trainlined the sound to a 2nd unit?

To add to the challenge… I noticed there is a place to mount a 2” speaker under the rear fan in the top of the locomotive. Is there a way to wire the sound board to run a speaker in the fuel tank and a speaker under the rear fan in the first locomotive so that the locomotive can run solo… but be capable to run a third speaker in the 2nd unit when both locomotive are operated together?

Can a Sierra card handle the power needed or would a Dallee 11 watt amplifier be needed?

I’m not very knowledgeable about this stuff (if I was, I wouldn’t have cooked the board ).

Any help or thoughts would be greatly appreciated!
Thanks,
Russ

#2

Easy peasy.
Forget about the 3rd speaker.
Wire two 8 ohm speakers in SERIES.
That will give you 16 ohms which a Sierra can easily handle. Volume may be decreased slightly.
If you unplug the second speaker insert a jumper in the socket so that a circuit is maintained.
The loco speaker will then be 8 ohms. Just what the Sierra was designed for.

#3

Hi Tony,
I like the idea of putting a jumper in to complete the circuit.
Thanks,
Russ

#4

Would you hook up two or more speakers with Phoenix the same way?

#5

Would or could?
As long as the two speakers are about 8 ohms each and wired in SERIES, yes you could.

#6

Hmmmm
I just looked up the Phoenix instructions and they say parallel. ???
http://www.phoenixsound.com/pdf/spkr.pdf

Could they be wrong?

I’ll contact John Weaver and verify this.

#7

John.
Yes according to those Phoenix instructions you can wire two 8 ohm speakers in parallel.
For more than two they need to be in series and parallel.

Personally I would not wire two 8 ohm speakers in parallel.

#8

The Phoenix works just fine with two 8 ohm speakers in parallel. The board is rated for 4 ohm output. If using two 8 ohm speakers on a Phoenix, I’d use parallel to maintain the volume level. Series will work, but you then present a 16 ohm load to the power amp and it can’t deliver the same output. What you end up with is less sound from two speakers than you had with one. My Cheesy Sound Car uses a 2K2 and two large 8 om speakers in wired parallel…

(http://www.cvsry.com/images/SoundCar-3-640.jpg)

It has lots of volume and the power amp chip never gets hot. Last summer I decided I wanted train line sound in my 3 RS-3 locos driven from the Cheesy Sound Car. I worked out a series-parallel circuit with a three wire train line that kept the boards load above 4 ohms while driving 5 speakers. Creative use of jumpers allows units to be cut out of the consist without dropping the amp load below 4 ohms. The Sierra must be rated for 8 ohms, and be borderline at that to fry in just a few minutes with a 4 ohm load. For speakers wired in Series - add the impedance of all the speakers together. For speakers of the same rating wired in Parallel, divide the rating of one speaker by the number of speakers. Series-Parallel and parallel wiring of speakers with different ratings gets a little more complicated.

#9

Hey,
I just got a Cheesy car like that! :slight_smile: :slight_smile:

#10
John Bouck said:
Hey, I just got a Cheesy car like that! :) :)
But it hasn't got those big honkkin' speakers inside (I hope, checking to be sure I sent the right one)
#11

Ow. That hurts.

Yes, an amplifier will be designed for a specific load. With more or less ohms it won’t produce as much sound. With less ohms, it could very well zorch.