So I have an idea to add a small stereo audio amp to some of my engines using a cheap chinese made amp found on ebay...which operates on dc voltage between 7.5 and 12 volts.
Can anyone post up a circuit diagram or suggest a source for a constant voltage power supply I could rig up to run this off track power?
It almost seems like the onboard 9 volt charging circuit and a rechargeable battery from the mth ps2 would work...but I'm not an electronics guy...
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How much current does your amp need? I created a circuit board to wrap around an eBay switching board. It takes track power and adds DCS protection and of course the rectifier and capacitors to filter it. It piggybacks on the eBay adjustable power module and makes a compact power source capable of several hundred milliamps.
The thing that limits the current my little package puts out is the 300uf of bulk capacitance. So, I've laid out, but not built yet, one with a 680uf capacitor that should give you about 300-350ma. It uses the same switching module from eBay.
An LM7809 fixed voltage reg would do the job easily, and no adjustment required.
I have a board designed for this exact purpose; shown below:
It includes provision for a 22uH choke so as not to interfere with DCS signals. It also includes bridge rectifier and filter for clean DC power. You can also select full wave or half wave rectification. Power handling is 500 ma.
I can mail you one if you like. Let me know.
Rod
I suggest you steal unregulated DC voltage from just after the bridge rectifier on your engine's electronics. In round numbers you won't be stealing more than, say, 5 Watts of power for any reasonable audio amplifier application. This should not be an undue burden on the bridge rectifier. Then use one of the 99 cent DC-to-DC regulator modules to generate 7.5-12V DC - it should have several hundred uF of capacitance whether already on-board or added to it if it doesn't already have it (e.g., the DC-to-DC regulator board GRJ shows on the left).
If done this way, the new amplifier and the source of the audio will share a common ground. Some folks will claim that's why you put a coupling-capacitor between the source output and amplifier input. That's correct, but not the entire story. Without getting into the nuts and bolts of hum-rejection from floating grounds, I'd just go with a common ground.
Stan, the common ground may or may not be at the bridge rectifier! For TMCC, it's frame ground. However, for PS2 or PS3 and newer Legacy with the RCMC, it's NOT frame ground.
But that's exactly my point. If possible I suggest using a common ground between whatever DC power supply the audio amp is using and whatever DC power supply the source of the audio is using. Presumably the source of the audio is coming from some DC-powered IC chip where ground is the DC- from the bridge rectifier of the engine electronics (Lionel, MTH, whoever).
Valid point Stan, and you sure want the ground to be the same. The trick is making sure you have the proper common DC ground.
The amp is a PAM8610 from ebay...
I figured on turning down the output volume of the lionel or mth speaker output so as not to overload the amp input...and use the amp volume control to control volume overall...
What I notice on the err type aftermarket kits is a lack of output power...sometimes overwhelmed by the mechanical noise of the train...
Truthfully, the ERR RS Commander has sufficient power for the job, what you see is a lack of a proper speaker. A good speaker and proper baffle will make the RS Commander as loud as almost anyone could want it to be.
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