How to add a power switch to front panel?

[EarthTone]

Not sure this is the best place to post this but… Here goes!

I’ve built a bunch of DIY preamp rackmount boxes over the years, and have generally always just plugged them into a Furman or power strip and used that for on/off power switching duties.

On my latest build, I can’t really do that as easily because of where in my rack it will be placed. I want to add a power switch to it. Unfortunately I don’t know how!

Specifically, this unit uses an external switching power supply with 5 pins. The pinout is pictured below, but it is:

Pin 1 Shell/Floating Ground
Pin 2 Common
Pin 3 +16V
Pin 4 -16V
Pin 5 +48V

The PSU feeds an internal filtering PCB which then distributes clean power to the rest of the unit.

So where, how, and what type of switch can I use to achieve this? Do I need a relay between the PSU and the switch or something? I literally have no idea how to do it.

The unit runs on 16V and the PSU will always stay plugged in. But I want to be able to turn the unit off and on from the front panel.

Would really appreciate some advice! I’ve read all sorts of confusing stuff about how to do this and whether or not it will cause audio problems.

For example, can I use something like this? Gebildet 0.87''/22mm Stainless Steel Latching Push Button Switch 12V-24V/5A Power Symbol LED 1NO1NC SPDT ON Off Waterproof Toggle Switch with Wire Socket Plug (Blue LED) https://a.co/d/0GEjZj8

Or does it need to be like this? Limited-time deal: Nilight 90012E Heavy Duty Rocker Toggle 15A 250V 20A 125V SPST 2Pin ON/Off Switch Metal Bat Waterproof Boot Cap Cover-5 Pack, 2 Years Warranty https://a.co/d/a8dRXLn

I’d really prefer something with a light on it, or the ability to add an LED to it somehow. I can only drill round holes, no squares. No tools for that.

Attached below is a picture of what I’m building, although that is not my unit, it is the same thing I’m making. I’m almost done so figuring out the final details now.

Thanks!

 

[gyraf]

Perhaps a humble Lorlin CK1032 - https://mou.sr/484hS45 - set to two positions

In there you have four switches

Use three to interrupt your +/-16V and +48V lines, i.e. between the incoming xlr5 and your circuits - on the Red, Brown? and Green lines in your drawing

No reason to interrupt Ground or Shield

But the best would be to turn off mains before the switching supply anyways, these have limited life expectancy and probably shouldn't run 24/7, also for power-economic reasons.

/Jakob E.

edit: darn, it's expensive when bought from that place - but otoh shipping may or may not be free

 

[EarthTone]

Perhaps a humble Lorlin CK1032 - https://mou.sr/484hS45 - set to two positions

In there you have four switches

Use three to interrupt your +/-16V and +48V lines, i.e. between the incoming xlr5 and your circuits - on the Red, Brown? and Green lines in your drawing

No reason to interrupt Ground or Shield

But the best would be to turn off mains before the switching supply anyways, these have limited life expectancy and probably shouldn't run 24/7, also for power-economic reasons.

/Jakob E.

edit: darn, it's expensive when bought from that place - but otoh shipping may or may not be free

Thank you, Jakob! Big fan of your work. I have a g22 you made, it's been stunning!

I'll try to understand that switch and go from there. I don't understand it looking at the datasheet on it yet, but hopefully with some study, I will.

Is it difficult or unreasonable to try to add a light to the power switch to indicate "on"? Does that cause some sort of inherent audio problem? How would you do that, like even just a small LED? Lots of my other gear has this so it would be a nice feature to let you know it's on.

Oh, and in regards to your thought about the PSU staying on all the time, agreed, and the switching PSU stays plugged into a power strip which is usually "off". So the PSU wouldn't be on all the time. But there's already a hole marked "power" on the faceplate and that same main power strip is often on for other purposes and I wouldn't want the preamp box to be on all the time when I'm not using it, hence the need for a power switch on the unit.

 

[gyraf]

thanks for the kind words!

..you can always just feed the power led LED from e.g. the +16V line, through a suitable resistor e.g. 4K7

 

[EarthTone]

thanks for the kind words!

..you can always just feed the power led LED from e.g. the +16V line, through a suitable resistor e.g. 4K7

Thanks Jakob. This option (a resistor in between the +16v line and the LED) in fact occurred to me, but I don't understand where to place the resistor so that it doesn't also subtract voltage from the mains for the circuit boards? I guess I really don't know as much as I thought... Could I take it off of the last preamp in the chain? Would that hurt anything? Or where would you place the resistor/LED combo in order to let +16V still pass through the power switch uninterrupted into the PCB's?

 

[gyraf]

Yes, you can grab the +16 anywhere after the power switch (if you want it to indicate "turned on")

..from +16V, to 4K7 resistor. From other end of 4K7 to + on LED. From - on LED to Ground/0V

 

[EarthTone]

Yes, you can grab the +16 anywhere after the power switch (if you want it to indicate "turned on")

..from +16V, to 4K7 resistor. From other end of 4K7 to + on LED. From - on LED to Ground/0V

Ah I see, thank you so much Jakob! Makes sense to me. I will try it! Have a good weekend.

 

[scott2000]

Yes, you can grab the +16 anywhere after the power switch (if you want it to indicate "turned on")

..from +16V, to 4K7 resistor. From other end of 4K7 to + on LED. From - on LED to Ground/0V

Also between +16 and -16 ?

 

[MidnightArrakis]

Not sure this is the best place to post this but… Here goes!

I’ve built a bunch of DIY preamp rackmount boxes over the years, and have generally always just plugged them into a Furman or power strip and used that for on/off power switching duties.

On my latest build, I can’t really do that as easily because of where in my rack it will be placed. I want to add a power switch to it. Unfortunately I don’t know how!

Specifically, this unit uses an external switching power supply with 5 pins. The pinout is pictured below, but it is:

Pin 1 Shell/Floating Ground
Pin 2 Common
Pin 3 +16V
Pin 4 -16V
Pin 5 +48V

The PSU feeds an internal filtering PCB which then distributes clean power to the rest of the unit.

So where, how, and what type of switch can I use to achieve this? Do I need a relay between the PSU and the switch or something? I literally have no idea how to do it.

The unit runs on 16V and the PSU will always stay plugged in. But I want to be able to turn the unit off and on from the front panel.

Would really appreciate some advice! I’ve read all sorts of confusing stuff about how to do this and whether or not it will cause audio problems.

For example, can I use something like this? Gebildet 0.87''/22mm Stainless Steel Latching Push Button Switch 12V-24V/5A Power Symbol LED 1NO1NC SPDT ON Off Waterproof Toggle Switch with Wire Socket Plug (Blue LED) https://a.co/d/0GEjZj8

Or does it need to be like this? Limited-time deal: Nilight 90012E Heavy Duty Rocker Toggle 15A 250V 20A 125V SPST 2Pin ON/Off Switch Metal Bat Waterproof Boot Cap Cover-5 Pack, 2 Years Warranty Amazon.com

I’d really prefer something with a light on it, or the ability to add an LED to it somehow. I can only drill round holes, no squares. No tools for that.

Attached below is a picture of what I’m building, although that is not my unit, it is the same thing I’m making. I’m almost done so figuring out the final details now.

Thanks!

Perhaps I have lived a "sheltered" life, but.....this is the first schematic I have seen where the power-switch is on the -- SECONDARY -- side of a power-transformer and -- NOT -- on the primary-side!!! I would think that doing things in this way would violate some type of UL code along the way, even despite there being a fuse in the primary-side circuit. Just looking at this schematic gives me the "heebie-jeebies"!!!

/

 

[gyraf]

It's common with wall-wart supplies

..yeah as mentioned not the best of ideas, but when what you're given is an external smps, it makes sense. No, it won't qualify for EU regulations on low standby power, but this is no commercial design, intended for personal use..

/Jakob E.

 

[C H]

Perhaps I have lived a "sheltered" life, but.....this is the first schematic I have seen where the power-switch is on the -- SECONDARY -- side of a power-transformer and -- NOT -- on the primary-side!!! I would think that doing things in this way would violate some type of UL code along the way, even despite there being a fuse in the primary-side circuit. Just looking at this schematic gives me the "heebie-jeebies"!!!

/

Mission Cyrus amp switches *that way* too!!!

 

[nsalis]

I am also of the opinion that you should switch the mains before the power supply so that the power supply does not simmer constantly until it dies an early death.

A safe solution would be the Lowell RPC-15 (see attachment).

You can easily install the associated low-voltage switch with a built-in LED power indicator in the front panel of your device, as the voltage with which it is operated is harmless. There would be at least a three-pin built-in plug in the back of the device. A cable with a suitable cable socket would be plugged into this and lead to the Lowell.

A suitable switch would have to be able to reliably switch the small switching current of 37 mA. This means that its switch contacts should be gold-plated. It must also be latching and have a built-in LED with a series resistor for 24VDC.

At the moment, switches with gold contacts are not available anywhere. You can temporarily use a switch with silver contacts and replace it later, if necessary by one with gold contacts.

A suitable switch with gold contacts would be, for example, TE Connectivity Nbr. 3-2213764-6 (Mouser No. 655-3-2213764-6).

The identical temporary solution with silver contacts would be e.g. TE Connectivity Nbr. 3-2213764-5 (Mouser No. 571-3-2213764-5).


ns

 

[nsalis]

I am also of the opinion that you should switch the mains before the power supply so that the power supply does not simmer constantly until it dies an early death.

A safe solution would be the Lowell RPC-15 (see attachment).

You can easily install the associated low-voltage switch with a built-in LED power indicator in the front panel of your device, as the voltage with which it is operated is harmless. There would be at least a three-pin built-in plug in the back of the device. A cable with a suitable cable socket would be plugged into this and lead to the Lowell.

A suitable switch would have to be able to reliably switch the small switching current of 37 mA. This means that its switch contacts should be gold-plated. It must also be latching and have a built-in LED with a series resistor for 24VDC.

At the moment, switches with gold contacts are not available anywhere. You can temporarily use a switch with silver contacts and replace it later, if necessary by one with gold contacts.

A suitable switch with gold contacts would be, for example, TE Connectivity Nbr. 3-2213764-6 (Mouser No. 655-3-2213764-6).

The identical temporary solution with silver contacts would be e.g. TE Connectivity Nbr. 3-2213764-5 (Mouser No. 571-3-2213764-5).


ns

For European 230VAC users, the equivalent is

Canford Optoswitcher #42-6701

https://www.canford.co.uk/CANFORD-OPTO-SWITCHER-Mk.2
ns

 

[abbey road d enfer]

A suitable switch would have to be able to reliably switch the small switching current of 37 mA. This means that its switch contacts should be gold-plated.

Not necessarily. Actually, gold contacts are recommended/necessary when very low current <1mA) is to be controlled. Silver contacts are perfect for 37mA.

You can temporarily use a switch with silver contacts and replace it later, if necessary by one with gold contacts.

I very much doubt it would be necessary.

 

[thor.zmt]

On my latest build, I can’t really do that as easily because of where in my rack it will be placed. I want to add a power switch to it. Unfortunately I don’t know how!

Ok, an easy way is to use a power strip with a "slave" circuit. This has one "master" socket and many slave sockets, put a load (eg. DAW or Mixer) on the "Master" and all slaves turn on.

You can also build this yourself, I did so at a flat a few years ago, where I wanted the TV projection screen to come down and stay down while the projector was on (actually the projector lamp to be more precise) and to automagically funk off when not needed.

Specifically, this unit uses an external switching power supply with 5 pins. The pinout is pictured below, but it is:

Pin 1 Shell/Floating Ground
Pin 2 Common
Pin 3 +16V
Pin 4 -16V
Pin 5 +48V

Modern SMPS tend to be rated for 24/7 connection and usually include "green mode" meaning they will consume almost no power when the load is disconnected. This is mandated, but you may want to check the details of your supply.

So cutting the incoming DC feed is fine.

It is common to use MOSFET switches.

But I have - in a similar situation - used "capacitor multiplier" circuits to clean up noise. These are ideal as added power switches, you can use generic (e.g. "817 Spec") opto couplers to remove the base bias for these Gyrators and then you can just a single contact and resistor and front panel LED plus the Opto-coupler LED's to turn on the system and with "soft turn-on" to boot.



As you can see, there is a soft start where the power supply ramps up slowly and there is over 50dB noise suppression from ~ 100Hz - 1MHz (above 1Mhz the fairly large size film/ceramic cap at the output becomes inductive and noise suppression falls off, we could add a ferrite and small SMD ceramic cap if that is a concern.

Thor

 

[oran.outan]

JLMaudio have made that power switch corresponding to your need...

https://www.jlmaudio.com/shop/fet-power-switcher-kit.html?display_tax_prices=1

 

[nsalis]

JLMaudio have made that power switch corresponding to your need...

https://www.jlmaudio.com/shop/fet-power-switcher-kit.html?display_tax_prices=1

Interesting what you found there. They even have a "Power Switch Kit" that goes with it.

https://www.jlmaudio.com/shop/power-switch-kit.html?display_tax_prices=1

 

[nsalis]

Not necessarily. Actually, gold contacts are recommended/necessary when very low current <1mA) is to be controlled. Silver contacts are perfect for 37mA.

I very much doubt it would be necessary.

In my experience, 1 mA is not enough to reliably switch with a silver contact (be it relay or switch) for years. We were often called to systems where the audio system could no longer be switched on or could no longer be switched on reliably because the contractor had used a switch with a silver contact to control a dry contact input on an AMX, Crestron or other PLC control. Such control inputs allowed a current of just under 10 mA to flow.

Basically, I always followed the recommendation from the Siemens relay book 1992 and did well with it: Use hard gold-plated contacts with currents up to 200 mA @ 24 V, do not use silver contacts with currents under 50 mA.

 

[EarthTone]

Thanks for all the great replies! I have one final question which may be something others can benefit as well so thought I’d ask:

In my specific case, I am using a Collective Cases PSU filtering PCB between a switching PSU and my project PCB’s. Should the switch interrupt 16V, -16v, and 48V *before* or *after* the PSU filtering PCB?

My initial thought line is it probably doesn’t matter, but in case one way would add more noise than the other, I thought I should ask before wiring it up.

I got the Lorlin switch @gyraf mentioned and it works great! Thanks!

The options are:

1. Interrupt power straight off the 5-pin XLR power jack

OR

2. Interrupt power between the PSU filter board’s outputs and the device’s main PCB’s.

Is one way better than the other? And if so, why?

Thanks!!

Matt

 

[abbey road d enfer]

Should the switch interrupt 16V, -16v, and 48V *before* or *after* the PSU filtering PCB?

It shouldn't matter.
However, it depends on the PSU's behaviour when unloaded.
If it goes in "hiccup" mode, there is a constant start-stop cycle that results in transients. If the filter is connected, it results in spurious currents that may radiate into adjacent equipment.
As a precaution, I would wire the switch "before" the filter.
But as a researcher, I would investigate both possibilities.