OK, the image I posted in post #22 is WRONG.
Here's the CORRECT way to connect the end terminals of both the volume and balance pots for anyone who's not exactly sure.
Thank you for clearing that up wapo.
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Your image is still in error -- there is no minus 5 volts involved, only zero volts to plus five volts.
I must be seeing things.
It clearly states +-5V on your board.
What am I missing here?
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While I eagerly wait for my nice shiny new package from across the sea I thought I better sort out the power supply. I have a lot of spare wall warts laying around but I don't really want two power connections on my chassis and my chip amp transformers are 25v ac so I was thinking of stripping the shell off a wall wart and putting it inside my amp for the volume control, do you think this will be ok from a noise point of view or should I be looking at another transformer and building a small basic supply, say 10v ac, 4 diodes and a couple of smoothing caps?
Alan
Alan
That's a bit of a challenge.
As far as I can tell, cutting up a wall-wart is the electrical equivalent of installing a second transformer with diodes, capacitors and, possibly, a regulator, except for the aesthetics. If that's correct, then you can choose simply based on appearances.
If you want to take power from the main PS capacitor after rectification, that's a challenge. That 25VAC turns into 35VDC when rectified and connected to a large capacitor, and that's above the maximum for the 78xx style regulator.
However, there are regulators that will handle above 35VDC input (which is what you'd need to take power off your main capacitors). Have a look at the STMicroelectronics PB137ACV -- TO-220 -- 40V in, 13.5V out. You would probably want to bolt it to a heatsink or the chassis and verify voltages before you commit to using it in this application. Don't now if tab is ground . . .
Many thanks Karl, the wall wart would be an easy approach, the only issue that worries me is noise, I've often read that these things are pretty bad in that dept. The regulator looks like a good alternative, I'm no electronics engineer so if there's no circuit diagram I'm pretty screwed though. I will check it out in the morning.
Ok ive found an old circuit I built many moons ago, its got a linear tech 317at in it so i think I am good to go on the power supply, I cant see any info on the website that states what the power requirement is for the complete kit, Ive got 1.5 amps max at my disposal, im guessing this is enough but confirmation would be helpful?
Alan
Alan
The last line of each board description on the website lists the dimensions and the current draw. The value for the LDR Controller board is < 50ma during operation and < 100ma while calibrating. The RE/IR/Display draws < 100 ma including current for the OLED display. So, published maximum draw is something less than 200 ma for the entire system.
While current capability is very important, the power dissipation capability must be considered. With a 3-terminal regulator, you might be able to deliver a lot of current with a minimal 3-volt in/out differential, but far less current with a 20 volt differential due to heat buildup in the regulator.
Because your input voltage is going to be about 35VDC and the output must be 16VDC or less, you must plan on dealing with the heat generated by dropping 20V or more volts at a maximum of 200ma, which is 4 watts (20V * .2A = 4W). It doesn't sound like much, but that's a lot of heat to deal with in a regulator, and the heatsink must be substantial. This is an unusual situation -- usually when regulating one tries to keep the voltage drop across the regulator to the minimum value possible to avoid the heat problem. This is why the input to the on board regulators is limited to 16VDC max -- to avoid excessive heat in the regulators. Optimal input to the onboard regulators is actually 9~12VDC, and 16VDC is absolute maximum.
There are a lot of variables to consider such as space available, etc, so I can't make a definitive recommendation, but the high input voltage to the 317 and the subsequent heating is something you must take into account.
While current capability is very important, the power dissipation capability must be considered. With a 3-terminal regulator, you might be able to deliver a lot of current with a minimal 3-volt in/out differential, but far less current with a 20 volt differential due to heat buildup in the regulator.
Because your input voltage is going to be about 35VDC and the output must be 16VDC or less, you must plan on dealing with the heat generated by dropping 20V or more volts at a maximum of 200ma, which is 4 watts (20V * .2A = 4W). It doesn't sound like much, but that's a lot of heat to deal with in a regulator, and the heatsink must be substantial. This is an unusual situation -- usually when regulating one tries to keep the voltage drop across the regulator to the minimum value possible to avoid the heat problem. This is why the input to the on board regulators is limited to 16VDC max -- to avoid excessive heat in the regulators. Optimal input to the onboard regulators is actually 9~12VDC, and 16VDC is absolute maximum.
There are a lot of variables to consider such as space available, etc, so I can't make a definitive recommendation, but the high input voltage to the 317 and the subsequent heating is something you must take into account.
I definitely fit into the 'little knowledge' danger camp! I'm off to get a little pcb transformer from maplins, £2.99 for 2x9v,
I will just run a basic full wave bridge and cap config. Job done, thanks Karl.
That sounds like a great solution -- make sure you wire it so you get 12VDC on the capacitor. If you wire the two legs of the transformer in series it'll wind up being 25VDC and you don't want that.
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