Why the dislike of external power supplies?

[IPunchCholla]

Are you building a class-D power amp? If so, it makes no sense to use a linear power supply. Linear PSUs are inferior to SMPSs almost in every aspect, provided that a good quality SMPS is used. Especially if you want a small form actor. You also want to avoid long connection cables which will pick up more noise and may cause instability due to parasitic inductances.

Yes, it is class D, but I'm not comfortable building an SMPS (since none of my simulations ever work as expected with those).

ETA: I should also note that this is in no way a practical project for me. I could buy a SMPS from Connex and be done with it, for cheaper. This is me doing something because I am curious about doing it.

 

[IPunchCholla]

As a side note, I just touched the enormous brick that powers my dead quite PA5 after it being in standby mode overnight. It is cold. But that is SMPS

 

[Doodski]

What's wrong with lots of DC current?

It increases the conductor length from the load to the supply by the length of wire from the supply to the outputs. I suppose a few more feet of conductor won't make a lotta difference.

 

[fpitas]

It increases the conductor length from the load to the supply by the length of wire from the supply to the outputs. I suppose a few more feet of conductor won't make a lotta difference.

The main reasons I've done it, is to get the AC out of the main circuitry box, and if power supply safety certification is desired.

 

[JeffGB]

External power supplies are inferior to internal power supplies because the output impedance of the PSU includes the wire between said supply and amplifier. If the output stage draws 1amp for instance, during a music signal, you will create a fluctuating voltage drop (E=I x R) that will be applied to all the other stages of the amplifier creating distortion. This is why many high power amplifiers make sure to have thick, short traces or wires between the PSU and the circuits being powered.
This will vary depending on what kind of PSU filtering and regulation is local on the powered device.
An ideal PSU would have an output impedance of zero and the various amplifier stages would not interact in any way other than that intended by the designer.

 

[Doodski]

The main reasons I've done it, is to get the AC out of the main circuitry box, and if power supply safety certification is desired.

Yes, I'm aware of that. It's a great system for designers and manufacturers alike. Have standardized power supplies is good for everybody.

 

[IPunchCholla]

External power supplies are inferior to internal power supplies because the output impedance of the PSU includes the wire between said supply and amplifier. If the output stage draws 1amp for instance, during a music signal, you will create a fluctuating voltage drop (E=I x R) that will be applied to all the other stages of the amplifier creating distortion. This is why many high power amplifiers make sure to have thick, short traces or wires between the PSU and the circuits being powered.
This will vary depending on what kind of PSU filtering and regulation is local on the powered device.
An ideal PSU would have an output impedance of zero and the various amplifier stages would not interact in any way other than that intended by the designer.

I understand the principle, but question the actual effect, particularly if that impedance has been taken into account on the receiving end. In other words, PSU impedance related distortion doesn't seem to show up in measurements of many amplifiers with external supplies. Or at least it is present in a small enough amount not to be audible.

 

[IPunchCholla]

Man, now I have to go look up noise caused by AC within the case and how one shields it and weigh that against the impact of wire impedance from an external supply? Good times. I was going to joke about this being like climbing Everest (a hard task that can kill you and that has already been accomplished by many others and I have no hope of improving upon), but now I'm not sure it is a joke (starting out 1.5 years ago with basically no knowledge of electricity, much less electronics and educating myself in my spare time).

 

[Doodski]

I understand the principle, but question the actual effect, particularly if that impedance has been taken into account on the receiving end. In other words, PSU impedance related distortion doesn't seem to show up in measurements of many amplifiers with external supplies. Or at least it is present in a small enough amount not to be audible.

It is a matter of what kind of power output and what current capability your amp will have that determines where the power supply is located. If it's a beast of a amp requiring 40A for peaks then maybe the power supply would be better near the amp section. If it's a smaller capability amp then it doesn't matter as much and has the benefit of removing the AC from the audio section and using standardized power supplies..

 

[soundtrane]

I use external supplies professionally. The real trick is a good connector. The little barrels are cute and easy, but not real reliable.

Switchcraft has high current barrel connectors. i think it goes to 10A. 15A (24V)

High Amperage Power Jacks & Plugs | Switchcraft

www.switchcraft.com

15 Amp Series Sealed Plug, 0.225" [5.7mm] Max Cable Size | Switchcraft

www.switchcraft.com

15 Amp Series Sealed Jack | Switchcraft

www.switchcraft.com

I was thinking of using DIN? Connectors. Barrel connections always seem to fail over time. Any connectors you recommend?

not so, if you use Switchcraft locking connectors. they are rock solid.

 

[mhardy6647]

I am OK with external power supplies.
Here're a couple that are always "on deck" here for DC needs.

 

[restorer-john]

External power supplies are common due to products getting very small and needing to be sold in various markets, with different voltages, regulations and plugs.

With low current devices, that can run on low voltages, the external power supply is a sensible option, albeit a terribly ugly and messy choice.

If you start talking about power amplifiers, there is no good reason to persist with external power supplies, and when the supply is two or three times the size and weight of the amplifier, it's just ridiculously stupid in my view. A few proper HiFi amplifier manufacturers produced integrated amplifiers with external PSUs, but they were plagued with issues, not the least of which was a high current snake of cables between the power supply and the amplifier boxes.

That's not to say a heap of full size gear of the past really wasted internal space, just to incorporate a mains power transformer to make the components truly separate. I have tuners where they are mostly fresh air inside the casework- all due to the 'need' to physically match other components.

The thing with separate outboard umbilical connected supplies is idle consumption and the complete lack of control of the outboard supply. Gone are all the 'smart' controls of front end supplies like many of the newer class D amps. They can shut down the power supply in the case of faults.

 

[sq225917]

Never had any issue with external psu. With sufficient local decoupling, good regulation, remote kelvin sense and neat wiring it's possible, in some cases, to improve upon an onboard psu. It's no panacea however.

 

[IPunchCholla]

Switchcraft has high current barrel connectors. i think it goes to 10A. 15A (24V)

High Amperage Power Jacks & Plugs | Switchcraft

www.switchcraft.com

15 Amp Series Sealed Plug, 0.225" [5.7mm] Max Cable Size | Switchcraft

www.switchcraft.com

15 Amp Series Sealed Jack | Switchcraft

www.switchcraft.com

not so, if you use Switchcraft locking connectors. they are rock solid.

Those are nice and reminded me I was forgetting the locking barrel connector on my PA5.

 

[MRC01]

Aren’t internal supplies always on if plugged in? All my devices that use them (barring our infrared toaster oven) are.

Technically, it depends on where the switch is in the circuit. But generally speaking, no. Often enough, when you turn off most audio preamps or power amps (not just standby, but OFF while plugged in), the internal power supply is not energized, the caps have no voltage, it generates no heat, it has no power draw.
Of course there will always be exceptions.

 

[IPunchCholla]

External power supplies are common due to products getting very small and needing to be sold in various markets, with different voltages, regulations and plugs.

With low current devices, that can run on low voltages, the external power supply is a sensible option, albeit a terribly ugly and messy choice.

If you start talking about power amplifiers, there is no good reason to persist with external power supplies, and when the supply is two or three times the size and weight of the amplifier, it's just ridiculously stupid in my view. A few proper HiFi amplifier manufacturers produced integrated amplifiers with external PSUs, but they were plagued with issues, not the least of which was a high current snake of cables between the power supply and the amplifier boxes.

That's not to say a heap of full size gear of the past really wasted internal space, just to incorporate a mains power transformer to make the components truly separate. I have tuners where they are mostly fresh air inside the casework- all due to the 'need' to physically match other components.

The thing with separate outboard umbilical connected supplies is idle consumption and the complete lack of control of the outboard supply. Gone are all the 'smart' controls of front end supplies like many of the newer class D amps. They can shut down the power supply in the case of faults.

Good points. I wonder about the idle consumption issue though. Is that limited to linear external supplies? The SMPS I have are cold to the touch if the device is in standby. Also is there an inherent issue with communication? I was planning on using IcePower 300A modules which can shut down the power supply and either using a custom control board with relays to disconnect the supply or, if I decide to do my own power supply for funnies, providing comunication to the external supply to turn off the PSU. I get that would be a nightmare for manufacturers in that they would either have to standardize on communications and would increase housing costs.

 

[IPunchCholla]

Technically, it depends on where the switch is in the circuit. But generally speaking, no. Often enough, when you turn off most audio preamps or power amps (not just standby, but OFF while plugged in), the internal power supply is not energized, the caps have no voltage, it generates no heat, it has no power draw.
Of course there will always be exceptions.

Hmmm. I’m going to have to see how many of my devices actually have off switches vs standby switches. I would have thought, off the top of my head, that most were standby. Certainly, anything with a remote isn’t really turned off in everyday use?

 

[MRC01]

If it has a remote, then it usually also has a "hard" on/off switch. When turned off by the remote, the "hard" switch is still on so the device is not really off, and the power supply is most likely energized.

 

[Doodski]

Certainly, anything with a remote isn’t really turned off in everyday use?

Usually there will be a standby transformer with 5VDC and maybe some ~12VDC sort of thing too that are powering the brain and the circuitry to support remote turn ON and then engage the relay(s) and power ON.

 

[CJH]

Those are nice and reminded me I was forgetting the locking barrel connector on my PA5.

You need plug/jack rated for at least 40VDC, preferably 50VDC for PA5 38VDC supply. These are hard to find.
CJH