Since you are using separate batteries for the sound chip and the amp you can try the same thing that worked for me: power the amp with the separate batteries and the only connections between the amp and the sound chip would be with two wires: from the sound chip’s two speaker driver connections to the amps input and the amp’s ground.
Do NOT connect the amp’s ground to the sound chip’s ground or any other “ground” or common wire or metal component that may get back to the sound chip. The sound chip will be driving the amp’s ground, but that is fine as long as it is floating (not connected to some other ground).
I looked at the signals from the sound module and it is a differential PWM output. A differential input on an amp should work OK, but may also need a low pass filter, depending on how good the amp and speakers are.
The sound from the module is just not loud enough outside, so I added an amp this weekend. The amp is a simple fixed gain amp with single ended inputs. The sound was very distorted if it was driven directly from either side of the sound module’s speaker driver. I looked through my parts bins and found an LM386 dual differential op amp, so built a small circuit to convert from the sound module’s output to a more normal single ended output.
Here is the circuit diagram that converts from the sound chip speaker driver outputs to a single ended usable by most amps output. I am running the sound module at about 4.5V, so needed to reduce the output by a factor of 2 to get the maximum volume out of my amp without too much distortion.
If your amp can take a different range, or the sound is too loud at max or too soft at max, just change R5 and R6 to the desired gain. Gain = R5 / 200K, so in the schematic, the gain is 1/2 (100K / 200K).
I just used a couple of standoffs and mounted it on top of the small amp. The battery (I am using an 9.6V RC battery) connection should be the same as the amp, not the sound module.
So heres a small tidbit for you. I bought the 7w canakit amp, and detached the pot and put it on a length of cable (was going to make one of the gun knobs a volume control). Tons of static.
Bought a new kit, tried it. Zero static.
Reattached the pot on the first amp to the amp on maybe 2-3" of wire.. zero static.
I’m about to try some shielded, twisted wire for the pot. Otherwise, I’ll give up on having it separate. You may wanna give that a try, though.
It’s just a hunch, but your power supply may be inadequate. According to my calculations, to put out 8w at 12v requires 0.66 amps. The AA batteries can supply that, but only for around 1.25 hours, and within only one hour, the voltage they output will have dropped from 12v to 8v which is the minimum the amp needs. (And it will put out less wattage with less voltage.)
Your batteries here may be effectively dead, even though you can hear the sound. They may not be supplying adequate current to the amp.
This site shows you what I’m talking about. Look at the 500mA discharge rate chart:
And here’s some more charts. From these I can deduce that if you used D cells, they’d last around 8 hours:
NiMh will give you more bang for your buck, but NiMh AA’s will still run out after 2 hours (see energizer chart 25% of the way down the page):
Of course none of this is evidence that the batteries are your issue. If they are fully charged then it seems like they should be able to put out enough power.
If you have a multimeter, set it to V and stick it across the battery terminals and see what you get.
“I will get myself an old headphone jack and cut that up, to see if the amp still sounds scratchy from that.”
Careful. You don’t know what the impedance of those headphones are, or how much wattage they can take. You could end up frying your amp.
Then again it may be perfectly safe. I don’t know enough about amps and speakers to say for sure. All I do know is that less resistance = more current, and too much current = fried electronics.
Power amplifiers tend to have high impedance inputs, so current would not be an issue. You just need to make sure the volume is turned down on whatever you’re amplifying since the gain is typical an order of magnitude (if not more).
Spongeface is 100% correct with the circuit he posted. Unfortunately though, most people aren’t interested in going that detailed. If you’re up for making that circuit, then do it. I would bet you most, if not all, audio issues would be resolved with it.
Pardon my noobness, but I’m just getting into electronics and having some trouble with your schematic. The protoboard circuit in the photo only has one LM386, but your schematic has two… can you clarify?
EDIT: nevermind, just noticed you have pins 1,2,3,4 and 8 on one and 5,6 and 7 on the other. So it IS just one LM386, just drawn that way for clarity, yes?
I too have been having static problems but have been using a 7w+7w stero amp. As soon as both were wired up, problem solved.
I kind of wish I hadn’t wasted my time with amp and speakers as I have discovered that my x-mini portable speakers sound super loud and crisp direct off the CRIX board. They are tiny speakers with amp/bass built in, easy to use and rechargeable.
The only downside is that the swithes to turn these on are on the sides so it can be inconvenient to turn them on/off if mounted hidden inside your pack.
SO I’ve removed the two 4 inch speakers and am gonna be returning them (or maybe using them for something else down the road, who knows).
Instead, I’ll soon be ordering a pair of these:
8-ohms each, so that SHOULD help out, too. ALSO, I’m gonna be acquiring one of the really handy-looking amp-modules Spongeface designed! Cross your fingers!
I’m gonna be testing this out later today, but I wanted to be clear on a few things first–
Pre-Amp Power Supply - I saw it mentioned earlier, but I’ll ask again - I just run this off the same batteries I have for the amp? (I picked up a lot more AA’s today, and can put fresh AA’s on the AMP as well as give this pre-amp it’s own battery supply if need be. Please advise about min/max wattage for the pre-amp, etc.)
Pre-Amp placement - probably a no-brainer, but I wanted to be sure.
This module is to be wired AFTER the sound kit, BEFORE the amp, right?
Or is it to be wired AFTER the amp, before the speakers?
I’d rather be safe than sorry, so I’m doublechecking.
I had the same idea (volume control on the gun box), and I had the same problem with the static when wiring the pot any longer than a foot or so - I’m curious to know if the shielded wire works out, as I’d still like to make that happen.
Here is a suggested hookup, though you must have already done something like this:
The battery connection on the pre-amp can handle up to about 30V, so should work with the same battery being used to power the amp being used. I am not sure what voltage rating I had for the C4 cap, so if you want to go up to the 30V, a higher rated electrolytic may be needed.
No luck. When I put the pot at the end of a long enough cable, even shielded, it’s like the pot isn’t there at all. Full volume, tons of distortion. If I re-attach the pot just with some jumper cables between the amp and the pot (they’re about a foot long) - clear sound. I guess it’s time to give up on this idea. Maybe ill use the crank as the volume knob or just mount it within arms reach on the mobo or something…
