external psu?
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kelly

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What are some arguments for and against external PSUs in headphone amplifiers?

I have some ideas myself but since I have nothing to back it up with but speculation, I thought I'd throw the question out to the experts.

What do you guys think?
 
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CaptBubba

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Having the PSU in a separate enclosure can help cut down on noise in the amp. Also this means that you can use a noisier transformer (ie. use a traditional one instead of a torriodal), and noiser transformers are cheaper in general than quiet ones.

Also it gives more room for the PSU, allowing it to be larger and more powerful. Also there is more room for filter capacitors and such.

But, because you can use cheaper parts in an external PSU, there could be the problem of using too cheap of parts and the PSU will either deteriorate or fail in time. This is assuming that the PS is adequate for the amp to begin with.

Also, the power has to travel further than it would if the PS was onboard, so a capacitor bank should be added to allow the amp to deal with transients.

And you have two enclosures, ect.
 
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aos

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I use ps in a separate enclosure. One reason to do so is if you're doing DIY it's FAR easier to just build another amp and use your "old" PS then to build a new PS every time. So this one PS can be made very good and expensive if wanted.

CaptBubba's observations are right as well. It should also cut down the noise as the transformer will be far away, and you would need additional caps in the amp since the regulators would be far away. I read somewhere here that some high end designers use separate PS and then put another level of regulation in the amp itself, this does sound like a good thing to do.
 
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Anders

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I am really not an expert in audio engineering. But have two components with external PSUs. The first is the turntable with the PSU in a little, external box. The idea here is to reduce the electro-magnetic induction from the PSU. The signal strenght is very low in the cartridge and the tonearm cable, very sensitive to external noise. The other is the Musical Fidelity phono preamp with the external X-PSU. External PSUs are rather common in turntables and phono preamps, as well as battery operation in the latter. I assume that the EMI problem is not so critical for components with higher signal strengts as headphone amps, although it could elevate performance.
There is another advantage of external PSUs that one don't need to be an audio engineer to understand - upgradability. Musical Fidelity is not a good example here because they have discontinuded the PSU before the products it is intended to serve. But you can combine the Naim headphone amp with power supplies of different qualities. There are different PSU options for the Creek. Or you can buy a Trichord phono preamp with a wall-wart and later upgrade to an external PSU, etc...
External PSUs seem to be most popular in UK.
 
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jarthel

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What type of connector (banana plug, spade, etc) do you use to connect the psu to the amp?

Thanks

Jayel
 
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eric343

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DIN or barrel plug, usually.
 
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KurtW

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Phono preamps have high gain so an external power supply to reduce noise makes sense. This is less important in a headphone amp. As aos states, external supplies make a lot of sense for DIY people because they can easily be reused, or potentially even power several things at once.

The Neutrik or Switchcraft XLR connectors are nice for power supply connectors since they are locking. One drawback of of the three conductor ones is that they could be mistaken for a balanced audio input or output. This can be avoided by using their 4 connector plugs.
 
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aos

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I use XLR connector, but cheap one from local store. In fact I didn't even know it's called XLR and what that is when I build this PS two years ago, I just looked around store for something that looked good, and this one has three pins (+ - and ground) plus the earth so it was perfect.
 
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Nezer

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As near as I can tell the 'de facto' standard is 5-pin DIN.

I would avoid XLR because of it's common use in high-end audio gear. The last thing you want is some moron plugging your power supply into balanced input/output of a high-end CDP or amp.
 
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eric343

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Ouch. I think I'll stick with DIN...
 
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kelly

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Not that anyone cares, but I'd prefer Kurt's suggestion because it is both locking AND unlike any other connector you'd use. Locking connectors are just cool.
 
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Anders

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I have also seen Lemo plugs being used for this.
The X-PSU has some type of mic/headphone connector, I think smaller than the standard 3.5 mm.
Suspect that the Lemo is to prefer (have only seen it on units with limited power demands).
 
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eric343

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Or better yet, how about using the Neutrik SpeakON or PowerCON connectors? I've used the Speakons before (I do some of the teching for the school theatrical department), and they're HEFTY. And rock-solid. And strong. And VERY VERY locking...
 
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aos

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Actually no, I'd go with DIN. In fact I got a few such sockets from Digikey when I was considering using them in a device that uses two separate power supplies supplies. There are also options to use more than 5 pins if needed.

Problem with exotic stuff is that you may buy it today but tomorrow it's out of stock forever or it may be hard to get. No point in complicated the DIY'ers life which is complicated enough already
.
 
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CaptBubba

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I use one of those power connecters from the back of a computer (not the regular power input on, but the one that you can use to chain devices together with) for stepped down AC power. It is easy to find cords for it, but nobody uses them.

For DC I use Dean's plugs (often found in electric RC cars). I use these because they grip well, are gold plated, come in 2 and 4 prong varieties, and I know they can conduct a lot (20A or so) of current. Plus they are small and cheap.

I normally just locate the transformer externally, and do the rectification and regulation inside the amp. This gives me a setup that isn't very noisy and I can hide the transformer in a out of the way location because it doesn't get switched on/off that often.
 
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