From TB thread on the BLI board replacement with an ESU board and speaker:
RedRiverRR4433 said: ↑
Nice work John. I have too many BLI units to even consider replacing the sound decoder. I might just try to replace the speaker. I have a multitude of the Knowles Donau speakers and will try to replace several factory installed speakers to see how the factory installed decoders sound in various BLI units.
Having fun with it........
Shades
Shades,
Notice that the round speaker I took out says "50 ohms" on it. The Knowles Donau is an 8-ohm speaker. It is possible that the audio amplifier in the Paragon will blow up trying to output to an 8-ohm load, which requires far more current than 50-ohm speaker. I probably wouldn't try just replacing the speaker unless I was prepared to go "all in" on an ESU transplant if the worst happens . . . (well, actually, if you DO blow up your Paragon, I know where you can get a used Paragon 2 decoder board cheap 
)
John C.
Yes, just to follow up - the stock speaker is marked 50 ohms; my guess is that if you replaced this with an 8-ohm speaker, you'd either get very low volume, or else you would blow up the amplifier circuit of the Paragon. Which is a shame, because I suspect that a speaker transplant alone would result in a huge improvement in the stock Paragon sound.
I really don't know why manufacturers continue down the "cheap round speaker" route. The advantages of the cell-phone-type rectangular speakers are now well-known in the hobbyist community. Yes, it probably would cost $1 more to use these than the round ones, but when you're paying $200 or more for a sound-equipped loco, what's another buck, especially if it results in a major sound improvement. I also don't know why some sound decoder manufacturers insist on skimping on the audio output stage, which then requires using something like a 50-ohm speaker. ESU's version 3 (I think) used a 100-ohm, until they wised up and built an audio amp that could handle "normal" speaker loads (4-16 ohms). I was very surprised to see the 50-ohm marking on the stock BLI speaker.
If someone wants to try a speaker transplant only, however, I have a couple of spare Paragon 2 PA-1 sound boards that I would get rid of cheap if the worst happens!
John C.
