I installed a Digitrax SDH164D into a Bachmann GP7 however I found that the supplied 32 ohm speaker was just a little too large(28mm) for the fuel tank location. I need a 20mm. speaker.
Finding a smaller 32 ohm speaker seems to be impossible so I thought that from a review of previous threads I possibly could use an 8 ohm speaker so as an experiment I wired up a 28mm Digitrax 8 ohm speaker I had but there was zero sound. I do know that using a 4 ohm speaker for a stereo system with an amp designed for 8 ohms is a bad idea so I suppose the same applies for this decoder, i.e. using a speaker with a lower ohm rating.
Can I go up in the ohm rating and use say a 100 ohm Lok speaker? There doesn't seem to be anything in between.
I realize I could use a different sound decoder but I can' t see spending $100 on a $50 loco. The Digitrax sound was fine for what I wanted but I would like to be able to have the fuel tank cover the speaker up.
Thanks in advance for any help.
CN Charlie
I have bought Kobitone speakers from Mouser. They have a 20mm round for 32 ohm.
http://www.mouser.com/catalog/catalogusd/644/1947.pdf
Another source.
http://www.allelectronics.com/make-a-store/item/SK-230/20-MM-32-OHM-SPEAKER/1.html
http://search.digikey.com/us/en/products/CLS0231MA3E-L152/102-1557-ND/1630871
I have put 28mm speakers up inside HO diesels over the rear truck.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
You could add a resistor. Since you've got the 8 ohm, assuming it's not burned out--test with battery--give it a try.
BTW, this is just one reason we don't use Digitrax sound anymore. Soundtraxx and QSI both use 8 ohm speakers and they can be put in parallel.
Richard
CNCharlie ....Finding a smaller 32 ohm speaker seems to be impossible so I thought that from a review of previous threads I possibly could use an 8 ohm speaker so as an experiment I wired up a 28mm Digitrax 8 ohm speaker I had but there was zero sound. I do know that using a 4 ohm speaker for a stereo system with an amp designed for 8 ohms is a bad idea so I suppose the same applies for this decoder, i.e. using a speaker with a lower ohm rating. Can I go up in the ohm rating and use say a 100 ohm Lok speaker? There doesn't seem to be anything in between.....
....Finding a smaller 32 ohm speaker seems to be impossible so I thought that from a review of previous threads I possibly could use an 8 ohm speaker so as an experiment I wired up a 28mm Digitrax 8 ohm speaker I had but there was zero sound. I do know that using a 4 ohm speaker for a stereo system with an amp designed for 8 ohms is a bad idea so I suppose the same applies for this decoder, i.e. using a speaker with a lower ohm rating.
Can I go up in the ohm rating and use say a 100 ohm Lok speaker? There doesn't seem to be anything in between.....
The optimum power transfer to the speaker occurs when the amplifier output impedance matches the speaker impedance (usually a couple of hundred ohms). OTOH, a low speaker impedance allows stronger magnetic fields due to higher current draws to move larger volumes of air. But the lower the speaker impedance, the higher the current draw on the output stage of the amp/decoder, and because of the impedance mismatch between speaker and amp, the heat of the wasted energy is in the amp, not the speaker. That's why powerful audio amps have massive heat sinks and cooling fans.
So the design challenge becomes to set the speaker impedance at a low enough point that will not burn up the output stage of your decoder/sound amplifier, yet still have reasonable audio efficiency. Our decoders have very little room for heat dissipation, which is why decoders tend to require higher impedance speakers than a good stereo amplifier. And small speakers can be designed to work well at higher impedances - it's just not as easy.
My best guess is that the 8 ohm speaker simply tripped the internal overload protection of your decoder, (assumes the output amp didn't fry) and that's why you got no sound. A 100 ohm speaker will work with your decoder, although the sound output may not be as high a volume as you would like.
my thoughts, your choices
Fred W
You can use anythign 8 ohms or greater with that decoder. Probably have to run the volume down for an 8 ohm speaker. The amplifier is apparantly optimized for 32 ohms, so use one of those speakers mentioned, but connecting the 8 ohm should not have blown anything, unless you shorted teh speaker output wires. If there was no sound, something else is probably wrong - if you hook the 32 ohm back up, does it work again? One issue with small speaker, if you hold the sodlering iron on too long to solder the wires from the decoder, it can unsolder the wires to the voice coil on the other side of those terminals, rendering the speaker dead.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Thanks for all your replies!
Rich, I never thought of such suppliers, only DCC sellers. A good friend of mine lives very near Thief River Falls so I will get him to pick up a speaker at Digikey. Thanks for the link.
Fred, thanks for the excellent explanation.
Randy, I did try 2 different 8 ohm speakers with the same result, no sound. I use a 15w iron to minimize the heat and I don't think I damaged the speakers with it. When I re-installed the 32 ohm speaker the sound was back.
Again thanks for your input.
rrinker You can use anythign 8 ohms or greater with that decoder. Probably have to run the volume down for an 8 ohm speaker. The amplifier is apparantly optimized for 32 ohms, so use one of those speakers mentioned, but connecting the 8 ohm should not have blown anything, unless you shorted teh speaker output wires. If there was no sound, something else is probably wrong - if you hook the 32 ohm back up, does it work again? One issue with small speaker, if you hold the sodlering iron on too long to solder the wires from the decoder, it can unsolder the wires to the voice coil on the other side of those terminals, rendering the speaker dead. --Randy
Randy is right about the 8ohm speaker. I talked to a Digitax tech a couple years ago about their sound quality of the 32 ohm speakers. And he commented that an 8 ohm speaker will work fine in any of their sound decoders. I beleive most of their newer sound decoders have 8 ohm speakers in them.
Truck.
I've heard that the 8 ohm speaker is suppose to work ,but its hit and miss.litchfield says use a resistor and I think Tony's use to have a tip page that went with that same idea of it didn't seem to work w/8 ohm speaker. ...I guess try and see ..Jerry
Just thought I'd post an up-date.
I installed an 100 ohm ESU 32 mm speaker and it works just fine. I had to turn up the volume a bit but I have no complaints. In spite of some claims otherwise an 8 ohm speaker does not work with this decoder.
Thanks for all your help.
Correction, it was a 23 mm speaker.