Sound amplifiers.

Model Railroader Electronics and DCC
1

Hi All,

Does anyone know if there is a such thing as an amplifier for DCC sound decoders?

The reason I ask is that I did a recent sound install and used a “Mega Bass” speaker that is rated for 2 watts…most all decoders only put out 1 watt of power for speakers.

Thanks.

2

What you would actually need is an audio amp booster. There is already an amplifier on the board and tapping into the signal before the onboard amp would be impossible to accomplish. You could build yourself a line level booster for it, but that would just be yet another circuit board you would have to shoe horn into your engine … hardly worth it for a mere gain of one watt.

That being said, have you actually played your speaker at full volume through your decoder ? Should be plenty loud ! If it’s because you want to improve bass response instead of sheer volume, your enclosure will have more to do with that than anything.

Still, if you are determined to experiment, here’s a simple line level audio amp circuit that utilizes a common LM386 amp that will boost your power and also improve bass response …

  • The amplifier circuit is designed to be fed by a headphone output, so the input impedance set by R1 is a relatively low 100Ω. This helps load down the source and eliminate noise. Use a 10KΩ resistor for R1 if you’ll drive your speaker from a line-level source like a home stereo CD player.
  • Most small speakers need bass boost. Components R2 and C1 provide a high-pass feedback loop to boost bass by reducing frequencies above 200Hz. If the sound is too bassy with your speaker, R2/C1 can be eliminated or disconnected.
  • For the best bass in a 4Ω speaker, C3 can be increased to 1,000µF. In a 16Ω speaker, C3 can be 470µF or reduced to 250µF without losing bass performance.
  • R1 provides a load for the signal source and ground reference for the
3

the basics of speaker construction is to mount the loudspeaker on the side of an air tight box. Is there a good seal around the louadspeaker? are there leaks in the back cavity (e.g. tender)?

4

And then on top of Mark’s circuit you will need a rectifier and LOTS of filtering to get a power supply for the amp from DCC track power. Lots of filtering because otherwise you will get DCC frequency buzzing in the speaker.

The the real question - will it all fit inside an HO loco? If the room is there, I posit you would get a bigger improvement by using the extra volume to make the speaker enclosure larger, rather than fill it up with audio amp and power supply.

–Randy

5

Using a high quality speaker and enclosure will produce better results than trying to add an audio amplifier. I put two large oval speakers into a dummy diesel B-unit connected to the output of a LokSound Select decoder, and the volume can be set to an almost deafening level without the need for an amplifier.

This new software doesn’t allow the cut and paste function to provide links to other sites, but Litchfield Station sells a speaker with their stock number of SP-18X53BR-08 that provides plenty of volume.

6

Not a problem. New software works just fine for links.

http://www.litchfieldstation.com/xcart/product.php?productid=999003109

Rich

7

I’m getting ready to add under layout sounds for a Trackmobile and have been doing some research on how to accomplish this. I found this Technical Note showing a more simple amplifier:

http://www.noarail.com/members2/d/1323-1/undertable_dsx.pdf

The Audio Output Transformer and the potentiometer are about $4 each at Radio Shack; I believe the SoundTraxx decoder comes with the capacitor…which RS doesn’t carry (the DSX is discontinued, replaced by the DSD series).

Without having it in front of me, the transformer is a little smaller than about a cubic inch; probably too big for inside a loco, but maybe will fit in a dummy. I haven’t hooked up mine yet (waiting for the decoder to arrive) so will better understand the whole thing once I start soldering wires together.