Power supply for diy projects safety

[mattenylander]

Hi!
I’m fairly new to electronics but I have started, for some time ago, building circuits like simple Mic pre amplifiers with transistors on breadboards with a supply V of +12V and such, as a way to learn the art of electronics.

I see in many schematics for say API, Neve preamps etc that they relying on say+18/-18V or + 24V or something around that numbers.

My goal is to be able to make a standalone mic preamp with +48V so my question as a beginner of electronics is.

1. What are some good ways to make a power supply for this types of projects and be able to let it run a stand alone unit?
2. What am I allowed to to as a hobbyist regarding the power supply wiring?
3. How do I wire it safe?

 

[rock soderstrom]

2. What am I allowed to to as a hobbyist regarding the power supply wiring?
3. How do I wire it safe?

Where are you from? Many regulations and legal requirements depend on the national location.

 

[mattenylander]

Where are you from? Many regulations and legal requirements depend on the national location.

Hi!
I live in Sweden (Europe)

 

[Tubetec]

The regulations probably apply more to the mains installation itself , thats not really a concern in this case . Theres a handfull of PSU boards made available by members here specifically destined for audio usage , that might be a good place to start .

The basic safety is important to get right in any case , its simple enough , you have Live , Neutral and Earth , Brown, Blue and green /yellow respectively .
The live wire will go to a fuse first then the on/off switch ,then the transformer or smps input , Neutral goes direct , then the ground /earth also called PE is bonded to the chassis near the IEC input socket , see diagram below .

 

[mattenylander]

The regulations probably apply more to the mains installation itself

Thanks for your reply! Ok so it is allowed for my own use to wire up a device like that?

Neutral goes direct

Do you mean that the neutral goes directly to the smps or transformer?

If I would use say, a 24V ac adapter as my power supply, or a 15V DC adapter as my power supply. Would the same internal wiring you described earlier apply in that case as well? Even though it’s just 2 plugs coming from these supply’s?

 

[rock soderstrom]

The regulations probably apply more to the mains installation itself , thats not really a concern in this case .

That's not quite right, at least in Germany. As soon as a integrated mains transformer is involved, it is simply not permitted for non-experts to set up and operate an DIY electrical device.

Not everyone adheres to this and I know some really competent people who do not have the appropriate licence and still build very safe devices.

This is not a problem as long as nothing happens.

In the event of a fault with material damage or even personal injury, things look very different.

Find out what rules apply in Sweden.

 

[Newmarket]

Thanks for your reply! Ok so it is allowed for my own use to wire up a device like that?

Do you mean that the neutral goes directly to the smps or transformer?

If I would use say, a 24V ac adapter as my power supply, or a 15V DC adapter as my power supply. Would the same internal wiring you described earlier apply in that case as well? Even though it’s just 2 plugs coming from these supply’s?

If the plug has only two connections then the device is "double insulated" and is designed mechanically to be safe without it. Should be a square in a square symbol on it to indicate this.

 

[mattenylander]

thanks for the replies!
Ok so a good starting point for my diy builds might then be to use say a 24V AC adapter as power supply for my projects instead?

 

[JohnRoberts]

I like the idea of commercial self contained switching power supplies with IEC plug sockets.

The power supplies meet all safety agency criteria.

JR

 

[Tubetec]

Hmmm , maybe ......
I just replaced an aftermarket laptop psu with an original , the aftermarket part spewed out all kinds of RF garbage which interfered with my radio reception . Upon dismantling I found the aftermarket unit didnt even have a common mode filtering choke at the mains input . Not all Smps's are made equal thats for sure . Fortunately here the members have sussed out the better types to use in audio , Mean-Well being a consistantly good performer by all accounts .

 

[rock soderstrom]

I like the idea of commercial self contained switching power supplies with IEC plug sockets.

The power supplies meet all safety agency criteria.

this or

Ok so a good starting point for my diy builds might then be to use say a 24V AC adapter as power supply for my projects instead?

or these are good solutions for safe working as you don't have to worry about the mains voltage. If you work with quality suppliers here, then these devices also have the right safety certifications and you have a few less worries and you can take care of your low-voltage circuit.

AC voltages above 50V with more than 50mA are considered potentially life-threatening in Germany, anything below that does not exempt you from working safely, but the situation is much more relaxed. That's why external power supplies or prefabricated PSU solutions are very good, because you can't normally come into contact with dangerous voltages.

 

[mattenylander]

the aftermarket part spewed out all kinds of RF garbage which interfered with my radio reception . Upon dismantling I found the aftermarket unit didnt even have a common mode filtering choke at the mains input

Ok that’s good to know, I’ll definitely check those out!

 

[mattenylander]

AC voltages above 50V with more than 50mA are considered potentially life-threatening in Germany,

Ok so the phantom power is up there I guess?

Then I’ll start with a good AC/AC adapter as my power supply.

 

[mattenylander]

By the way, what’s some pros and cons of choosing one power supply setup vs another, say, the mains transformer power supply setup vs a double insulated adapter power supply setup? Since I see so many pro audio level gear comes with that mains transformer setup…

 

[Tubetec]

An old style mains transformer will have 50/60 hz radiated magnetic feild , that can get into other signal transformers , good wiring schemes , metal sheilding and carefull layout are important to minimise it . The good thing about the old style transformer psu is with good design it can give a lifetimes usage .
Switchmodes will have some LF noise but mainly noise at the switching frequency .
Theres some good tips around here on reducing SMPS noise , in general the higher the frequency the easier it is to filter , the downsides of Smps's are limited lifespan , low quailty components shoe horned into a tiny plastic enclosure magnify the effect due to heat build up .

A lot of consumer electronics nowadays is designed to fail after a few years , then you chuck it in the bin and get the new model . The waste mountain created by this throw away society runs into tens of millions of tonnes , it screws the planet and the consumer to keep the wheels of industry from falling off the wagon .
I have a few old tube radios and hifi amps dating back to the 50's , they are more or less as they left the factory , mostly original components and they still work to spec .

 

[mattenylander]

The good thing about the old style transformer psu is with good design it can give a lifetimes usage .

Thanks for sorting that out!

 

[HP200CD]

There are a number of ready made power supplies with triple outputs (+16V, -16V, +48V) intended to power 500 Series racks which can also be used on the bench when developing microphone preamps. For example, here are links for two of them, so you can search for one available locally to you in Sweden.

https://www.diyrecordingequipment.com/products/external-power-supply
https://www.sweetwater.com/store/de...-power-supply-for-r1600-workhorse-and-firefly

 

[warpie]

Since we're on that. I read that the LVD applies to devices with 50-1kVAC or 75-1.5kVDC.

Is this for the sum of different voltages or for the maximum "per rail"? For example does a 500 module require LVD because 32Vdc(+/-16) + 48V= 80Vdc? Or it doesn't because 48V is the highest voltage?

 

[HP200CD]

warpie, to answer your question:

Yes, the LVD applies to any mains powered device, because the LVD specified ranges apply to both the INPUT and the OUTPUT voltages.

the specified ranges are: 50 to 1kV AC or 75 to 1.5kV DC

Since the mains may be 120VAC (US) and 240VAC (europe) any mains powered device is subject to the LVD unless the output exceeds these ranges.

Low Voltage Directive (explained)
https://single-market-economy.ec.eu...g-industries-eei/low-voltage-directive-lvd_en

 

[mattenylander]

There are a number of ready made power supplies with triple outputs (+16V, -16V, +48V) intended to power 500 Series racks which can also be used on the bench

Wow Thanks! Didn’t know that!
Will definitely buy that!