I'm going to begin a build for an amplifier consisting of an SMPS and some class-D modules. One thing I forgot to buy is a switch to turn the darn thing on and off. The SMPS has a universal 120/230V 50/60Hz input, so the switch should be as well. I thought of a couple of options:
1. Rocker switch on back panel with indicator light on front
2. Illuminated latching pushbutton switch on the front (must not be too difficult to depress!)
3. Good old toggle switch on rear with indicator light on front
This is just a prototype, so I am probably going to build the chassis from wood for now and the switch can't be one of those snap-in types that only work for thin metal panels. Also, cutting a square hole is a total PITA, otherwise I would consider using one of those integrated rocker switch, IEC AC receptacle, and fuse holder things. So I probably need to figure out these other AC power components too... I do have some parts around somewhere that I should be able to use for this purpose for now.
The other thing to think about is inrush and arcing of the switch. Which type is best against this, or how should I protect the switch? Am I over thinking that?
If the amp build works out I will probably move it into a 3U slimline chassis from the DIYaudio Store, and then I can incorporate better quality AC mains connections and fusing, etc. At that time I will need to make a hard decision on the type and location of the power switch. For now I need to get something working and test it all out, including the switch type and location.
Your one or two cents are appreciated. Thanks!
1. Rocker switch on back panel with indicator light on front
2. Illuminated latching pushbutton switch on the front (must not be too difficult to depress!)
3. Good old toggle switch on rear with indicator light on front
This is just a prototype, so I am probably going to build the chassis from wood for now and the switch can't be one of those snap-in types that only work for thin metal panels. Also, cutting a square hole is a total PITA, otherwise I would consider using one of those integrated rocker switch, IEC AC receptacle, and fuse holder things. So I probably need to figure out these other AC power components too... I do have some parts around somewhere that I should be able to use for this purpose for now.
The other thing to think about is inrush and arcing of the switch. Which type is best against this, or how should I protect the switch? Am I over thinking that?
If the amp build works out I will probably move it into a 3U slimline chassis from the DIYaudio Store, and then I can incorporate better quality AC mains connections and fusing, etc. At that time I will need to make a hard decision on the type and location of the power switch. For now I need to get something working and test it all out, including the switch type and location.
Your one or two cents are appreciated. Thanks!
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Switches of any kind on the back panel are a unnecessary self chosen handicap. User unfriendly and nearly always regretted afterwards. Switched/fused/filtered IEC inlet is nice but then combined with a standby circuit + power on/off PCB + front switch for power on/standby. Makes remote control a possibility as well and devices can be 100% separated from mains if one wants to. Even if I have to file a square hole, I do it with pleasure except when stainless steel is used. In fact I have never done it any other method. My personal method is to use high current rated NOS/NIB industrial switches of the known brands, either rotary or push button (10 or 16A rated) but also toggle as long as they have 6.3 or 4.8 mm Faston connectors. That is simple a taste question although toggle switches sometimes have an undesired lag in switching. Too much choice in switches but it suffices to say that most of the nice looking modern Chinese switches are a faint shadow of the old reliable EU/US produced industrial switches. I have bought vandal resistant stainless steel switches that have plated steel contacts.....
For prototyping it all does not matter much as it will be replaced by the final version after all. You could even put a switched/fused/filtered IEC inlet and all the connectors on the front for ease of testing 🙂
For prototyping it all does not matter much as it will be replaced by the final version after all. You could even put a switched/fused/filtered IEC inlet and all the connectors on the front for ease of testing 🙂
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I have built two of these for mono bloks I am building. (https://www.diyaudio.com/community/...ains-relay-includes-soft-start-h9kpxg.354971/) I really like them. Used an RGB LED Anti-vandal switch which is blue in stand-by and red when turned on. This includes the soft-start. Not sure you need soft start with an SMPS.
On my amp camp amp build (see profile photo), pushing the glass tile on the front activates a latching switch circuit. The latching circuit is powered by the smps (19V, regulated down) and operates a relay. The relay switches the smps voltage, not the mains voltage. Perhaps more complexity than you want, but it is aesthetically inoffensive (no visible switches was one of my design objectives).
That being said, you're designing it, so you can do whatever you want. You could hide a rocker switch on the bottom near the front if there's clearance, or put it on the side. Power indicator lights can go anywhere. I'm partial to rocker switches. A light-pressure mechanical latching pushbutton switch rated for mains voltage probably doesn't exist.
That being said, you're designing it, so you can do whatever you want. You could hide a rocker switch on the bottom near the front if there's clearance, or put it on the side. Power indicator lights can go anywhere. I'm partial to rocker switches. A light-pressure mechanical latching pushbutton switch rated for mains voltage probably doesn't exist.
I think if I wanted to go this route I would roll my own using a low voltage, low current but easy to push momentary button (or perhaps even a capacitive touch switch!) and have an Arduino or Raspberry Pi monitor that for contact closure. It is VERY EASY to do debouncing in code! You just apply a very long time constant filter to the button state. Once the "on" state has been reached the computer hardware can perform all sorts of turn on tricks, like soft start, sequential start, etc. via GPIO pins. I designed a relay PCB for this purpose and have a gross of 10A relays ready to go. I have code that I wrote to do this kind of thing (turn on a power amp) in response to an audio signal, and it could be adapted to work off of the state of a switch very easily, or even monitor both inputs simultaneously. Only the computer hardware would need to remain powered up, and for some of these small platforms like Pi or Arduino the power draw is miniscule.
In fact now that you mention it, I SHOULD do this kind of thing. I previous purchased 10 dual output 5V/12V supplies and have a bunch of small Raspberry Pi boards to go with it. I just have been waiting for the "right" project to come along where I would make use of them. Thanks for the reminder! 🙂
Otoh, I quite like the concept of the amp being placed backwards (frontplate on the rear, connections on the front), and the the switch on the front becomes the switch on the back…
Toggles are the easiest to mount, rockers are a pain due to the rectangular hole. I don’t like push buttons because it’s hard to see from a distance if it’s in or out. If you are using a power strip to turn on all the equipment then on the back is ok but if you are going to turn things on individually then the front is the way to go. Make sure to overrate the switch by at least double.
Putting an RPi near the audio is asking for lots of RF to be a problem. Both the switching power supply and the RPi itself radiate RF.
Yes, SMPS do have huge inrush current. It's listed on the manufacturer's engineering datasheet. For the example SMPS attached below, inrush current is specified as 90 amperes. That might stress the power switch / power relay contacts a bit. Also the fuse or circuit breaker.
I favor the "MS32" line of inrush current limiter devices, made by Ametherm, rated for 250 Joules of inrush energy. Their "MS35" is rated 800 Joules.
If you decide to implement an all-software approach to soft start, why not include all the bells and whistles ever put into an all-hardware soft start. Including
_
I favor the "MS32" line of inrush current limiter devices, made by Ametherm, rated for 250 Joules of inrush energy. Their "MS35" is rated 800 Joules.
If you decide to implement an all-software approach to soft start, why not include all the bells and whistles ever put into an all-hardware soft start. Including
- Support both momentary front panel switches (software creates push-on, push-off) and also toggle/rocker front panel switches
- Front panel multicolor LED indicates OFF - SOFTSTARTING - ON
- Child safety mode: Requires you to press a momentary pushbutton for 20 continuous seconds to turn on. Instant turn off.
- User adjustable time delay between switch-on and end of soft start / beginning of bypass-the-soft-start. 0.1 sec / 0.5 sec / 1 sec / 2 sec etc.
- Soft shutdown / soft "unstart" at power off: Cease bypass-the-soft-start and reinsert the inrush current limiter into the mains circuit, before cutting off
- 12V DC remote trigger input
- European regulatory requirement to switch both Line and Neutral wires, for safety
_
Many of these are good ideas and it is really only your imagination that limits what you can do with a software approach.
The code I have already written to trigger external events (like soft-start of amplification) based on the audio level passing though the plugin code (it's a LADSPA plugin implented under Linux) and has the features described in the attached text file. I can adapt this to instead monitor an external signal connected to a GPIO pin and determine the state of that pin (low/high), taking action on a state change.
For inrush limiting I have a PCB I designed that uses a transformerless power supply that runs a short-duration relay that controls some inrush limiting element like a resistor bank or NTC thermistor
I use a light up momentary button for power on my builds connected to one of these:
https://www.ebay.ca/itm/222483418790
https://www.ebay.ca/itm/222483418790