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Why some preamps have external PSUs?
Old 14th November 2009
  #1
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DONNX's Avatar
 
🎧 10 years
Why some preamps have external PSUs?

Hello Slutz.

Just curious if anyone knows why certain preamp designers choose to make
external psu's verses internal psu's?


I just notice A-designs Pacifica has an external PSU version. Vintech does the same. Never had any issues with my original pacifica having the internal PSU built in.

Any reasons for this concept? Thanks

PS. I just found out that the original first editions of the pacifica had the external..my bad.
Old 14th November 2009
  #2
Gear Nut
 
🎧 10 years
You can get a good few dBs less noise/hum with an external PSU. Moving the power transformer away from audio especially

Oh and possibly can power more than one rack too.
Old 14th November 2009 | Show parent
  #3
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nosebleedaudio's Avatar
 
🎧 15 years
I build my supply (JM-130) external for several good reasons; it removes heat and weight from chassis, removes magnetic fields, enables more than one unit to be powered from same supply.
It cost MORE to do the external supply; another chassis, connectors and cable.
If there is a problem with supply I can replace it with out replacing the whole unit..
Can think of a few others that do the same thing; GML for one..
Old 14th November 2009 | Show parent
  #4
RTR
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🎧 10 years
Oh ya..It also causes you to pay a lot more, Lets pretend you did not read all the BS when ordering a new pre, you get it home, and WTF, it need a PS..Why sell it separate, I have never seen a price with a TOTAL including the PS..what bunch of BS
Old 14th November 2009 | Show parent
  #5
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mexicola's Avatar
 
🎧 10 years
Unless you're powering more than 4 channels, I don't really see the need for an external psu. If the psu is incorporated into the same pcb as the audio circuitry, it can cause potential noise if proper decoupling techniques are not practiced or if the circuit is poorly designed. This can be avoided simply by using two pcb's in the same chassis - one for power, one for audio. However most classic gear has power and audio on the same pcb.
I agree that seperate external psu's for single or dual channel units, like Vintech's for example, are totally unnessecary and in my opinion nothing more than a boutique high end marketing strategy to make more money and to make their gear seem more esoteric and high end-y.
Old 14th November 2009 | Show parent
  #6
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nosebleedaudio's Avatar
 
🎧 15 years
Quote:
Originally Posted by RTR ➑️
Oh ya..It also causes you to pay a lot more, Lets pretend you did not read all the BS when ordering a new pre, you get it home, and WTF, it need a PS..Why sell it separate, I have never seen a price with a TOTAL including the PS..what bunch of BS
My site includes price for both...
The fact is it cost ME more to build external, I lose money...I prefer external for reasons I mentioned, in SOME cases, others it's better to include it. IMHO...
Old 14th November 2009 | Show parent
  #7
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surflounge's Avatar
 
🎧 15 years
internal noise, and EU regulations
Old 14th November 2009 | Show parent
  #8
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mexicola's Avatar
 
🎧 10 years
Quote:
Originally Posted by nosebleedaudio ➑️
My site includes price for both...
The fact is it cost ME more to build external, I lose money...I prefer external for reasons I mentioned, in SOME cases, others it's better to include it. IMHO...
Do you really lose money on an external psu? How complex are your power supplies?
That doesn't sound like a good business plan, no offense.
Vintech's external supplies sell for like $300 for a PSU!!!! What's in them for that kind of price?!
I can build a 1U highly regulated three rail supply with enough current capacity for 8 channels of discrete pre's for around $100. If I built them in quantity I could probably bring the price down even more.
I can't imagine there's not money to be made by seperating the power supply. Not to mention the marketing angle.
Old 15th November 2009 | Show parent
  #9
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1 Review written
🎧 10 years
Quote:
Originally Posted by mexicola ➑️
Do you really lose money on an external psu? How complex are your power supplies?
That doesn't sound like a good business plan, no offense.
Vintech's external supplies sell for like $300 for a PSU!!!! What's in them for that kind of price?!
I can build a 1U highly regulated three rail supply with enough current capacity for 8 channels of discrete pre's for around $100. If I built them in quantity I could probably bring the price down even more.
I can't imagine there's not money to be made by seperating the power supply. Not to mention the marketing angle.
It probably costs $50 for the rackmount case, then $75 or so for the other electronic parts, then figure in labor charges. The cheapest external supply that is rackmount is probably the chameleon labs product and I think that was about $150.

Personally I like having the power supply built into the unit just to have less things taking up space. The newer Pacifica appears to have a metal divider inside the rack case that separates the power supply section from the pre-amplifier section. With toroidal transformers I think noise isn't much of a problem.
Old 15th November 2009 | Show parent
  #10
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🎧 15 years
Quote:
Originally Posted by mexicola ➑️
Unless you're powering more than 4 channels, I don't really see the need for an external psu. If the psu is incorporated into the same pcb as the audio circuitry, it can cause potential noise if proper decoupling techniques are not practiced or if the circuit is poorly designed. This can be avoided simply by using two pcb's in the same chassis - one for power, one for audio. However most classic gear has power and audio on the same pcb.
I agree that seperate external psu's for single or dual channel units, like Vintech's for example, are totally unnessecary and in my opinion nothing more than a boutique high end marketing strategy to make more money and to make their gear seem more esoteric and high end-y.
But the most common problem is the power transformer. In many cases, no matter how you arrange things, having the transformer anywhere near the preamp electronics and input transformer (if there is one) causes added noise. In that case the only solution is to put it in an external chassis -- and at that point you may as well put the all the PSU electronics in the external chassis.

Toroidal transformers are much quieter and can be a solution if you can find a suitable one, but for tube circuits, the search can be difficult. A manufacturer can have any transformer made that they like, but in DIY situations, the options are more limited.

Yes, it can easily cost a manufacturer $300 to build a decent, regulated, safe power supply.
Old 15th November 2009 | Show parent
  #11
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nosebleedaudio's Avatar
 
🎧 15 years
Quote:
Originally Posted by mexicola ➑️
Do you really lose money on an external psu? How complex are your power supplies?
That doesn't sound like a good business plan, no offense.
Vintech's external supplies sell for like $300 for a PSU!!!! What's in them for that kind of price?!
I can build a 1U highly regulated three rail supply with enough current capacity for 8 channels of discrete pre's for around $100. If I built them in quantity I could probably bring the price down even more.
I can't imagine there's not money to be made by seperating the power supply. Not to mention the marketing angle.
It makes no difference if you believe me or not.
Is that $100.00 supply a switching supply?
Then why don't you build supplies and get rich...
Old 15th November 2009 | Show parent
  #12
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Mylithra's Avatar
 
🎧 10 years
Till I started building gear and really until I got a O-scope, I really didnt understand what was in a power supply. I though, whats the big deal.. just a transformer and an regulator, but It wasnt until I started building things and seeing how under designed, under delivered power supplies cause really bad results and not just in recording but in most forms of electronics. (Cant tell me an under powered computer power supply wont cause calculation errors. Ive see it) And truth be told, a lot of the gear I see out today really isnt that bad.. they've just horribly shortchanged themselves on the power supply. Once you get to see it all on a O-scope, you can see the power supply ripple getting into the signal chain.

So to get a really good sounding piece of audio gear, you have to have very clean and ample power. The easiest way to get the cleanest power is to externalize the power supply. (Less EMI from the transformers or switching noise) That being said, I can easily see how in a good piece of equipment, the power supply is 1/4 -1/3 the cost of the unit itself.

Take the SCA preamps and chassis. Now Tim's power supply is top notch and ultra clean. Ive actually thought about getting one for my own projects in fact.. but its $260 for just the PS. Each module is roughly $375. Take pair of N72s and a power supply and you see that the power supply is more than 1/4 of the units cost.

Heres just an idea on external power supplies.. How many of you guitar players have a lot of pedals on your pedal board. Is it cheaper to buy a battery for each pedal, an external wall wart for each pedal or a single external power supply like a One Spot and power everything?
Old 15th November 2009 | Show parent
  #13
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ulysses's Avatar
 
🎧 15 years
Quote:
Originally Posted by surflounge ➑️
internal noise, and EU regulations
No and no.

Putting the power supply a few feet away is one way to keep PSU EMI out of the audio circuits. Another method is to improve the design and construction of both.

And there's nothing at all in the CE directives that pushes you into an external power supply. I suspect some manufacturers are intimidated by their own lack of understanding of the CE directives and choose to avoid dealing with it by buying a 3rd-party power supply.
Old 16th November 2009 | Show parent
  #14
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DONNX's Avatar
 
🎧 10 years
Thanks to all. I am following the thread. But its seems there is no hard reason why or its a must do thing to eliminate hum/noise issues.

You got so many pieces of pro audio gear that don't use the external route.
And for me at least, I never had any issues with hum or noise. At least audible in the tracks.

I actually did have hum issues with the vintech X73, X73i eq preamps. Wish I didn't. I loved the eqs on these things and the preamp isn't bad at all. But I just couldn't deal with the hum it came with... So I sold them for the reason alone and dealing with digital audio. I rather have the cleanest signal I can get. Stepping up to a AMS neve rack and neve preamps...virtually no noise, clean as white laundry. And the PSU is only inches away from the preamps.

With that said, Vintech for example has an external power supply, but I am still getting noise, EFI, whatever you want to call it. I thought this is supposed to get rid of that issue?

Still will like to find out from more posters if external power supplies have any benefit for a cleaner signal or not. Space requirements makes total sense.

Thank you.
Old 16th November 2009 | Show parent
  #15
Gear Nut
 
🎧 15 years
Quote:
Originally Posted by ulysses ➑️
No and no.

Putting the power supply a few feet away is one way to keep PSU EMI out of the audio circuits. Another method is to improve the design and construction of both.

And there's nothing at all in the CE directives that pushes you into an external power supply. I suspect some manufacturers are intimidated by their own lack of understanding of the CE directives and choose to avoid dealing with it by buying a 3rd-party power supply.
I agree with you. My feeling is that it's also a matter of making more money.
I don't think it's too hard to design proper psu when you are making series of gear, they done it 50 or more years ago with very bad components/technology compared to what we have available today.
I use external supplies in cases when i have high quality but too big power transformer. This way i can still use it and save some money.

Some time ago i was reading a post where someone said that companies use external psu-s because you don't need all certificates for the unit if psu already have one. I don't remember about what certificates they were talking about, can someone explain this to me please? IIRC it was about CE.
Btw, i have a friend who ordered power amp from US and when it arrived custom office didn't want to give it to him because it didn't have CE sign. It looks like we can't import gear from US to Europe even if it's vintage. I'm a bit off topic here, but this is somehow related.

Miha
Old 16th November 2009 | Show parent
  #16
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mexicola's Avatar
 
🎧 10 years
Quote:
Originally Posted by David Kulka ➑️
Yes, it can easily cost a manufacturer $300 to build a decent, regulated, safe power supply.
It might cost $300 to build a decent regulated PSU for a console (like an Acopian), but not for 1 or 2 channels of preamplification. A power one HDD-15-5A can be had for about $150. And that's 5 Amps of +/-15VDC - enough to power a console. For a couple preamp channels you might need half an amp. If Power One can do a psu that size for $150 and make money, you can't tell me that I need to spend $300 on vintech's or jmk's PSU for one or two preamp channels. That's laughable.

I do a LOT of DIY and I've never had issues with noise using internal PSU's.
But then I also decouple like it's my religion, and use much larger (and if possible, more) filter caps than are required.
That's something that most manufacturers skimp on.
Old 16th November 2009 | Show parent
  #17
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🎧 15 years
But the HDD-15-5A is just an open frame power supply with everything exposed, not a complete unit. For somebody to finish it as a marketable external supply you need to add the chassis, machining, cords, connectors, fuses, indicator(s), switch, labor. Add the costs of the safety testing. Maybe an output cable. Also, add an additional section if you want phantom. In my opinion the $300 figure is about right but if you disagree, well...

It's sort of a moot point because most of the time outboard supplies aren't necessary, especially on manufactured gear. For stuff DIY I think it's an issue somewhat more often but then the supply doesn't need to be so finished looking and have all the features of a manufactured unit.

I can't comment on vintech or jmk supplies, have not seen them.
Old 16th November 2009 | Show parent
  #18
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mexicola's Avatar
 
🎧 10 years
Quote:
Originally Posted by David Kulka ➑️
In my opinion the $300 figure is about right but if you disagree, well...
Well, you kinda just re-iterated my point. Yes, I'm aware the HDD-15-5A is open frame (I actually assembled one earlier this year), and I do think you're figure for finishing it and testing it is accurate...but that's a 5 Amp supply, enough to power a console. I'd pay $300 for a supply for my console. (BTW, the main filter caps on it are 23,000uF!!! I'd like to see how the filter caps compare on these little outboard psu's we're discussing.)

What I wouldn't pay is $300 for a PSU capable of supplying a few hundred milliamps for a couple preamps, which should cost significantly less than a PSU that can supply 5 Amps of current for a console.
That's my point.
Old 16th November 2009 | Show parent
  #19
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brianroth's Avatar
 
🎧 15 years
IMHO external supplies exist because of UL and the similar EU testing.

To pass the tests, the power supply has to be sent to a Lab, which then attempts to explode the PSU with extreme voltages.

Hence, most folks decide to select an external PSU which SOMEHOW survived the tests, and won a UL (or whatever) "listing".

Bri
Old 16th November 2009 | Show parent
  #20
RTR
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🎧 10 years
Quote:
Originally Posted by brianroth ➑️
IMHO external supplies exist because of UL and the similar EU testing.

To pass the tests, the power supply has to be sent to a Lab, which then attempts to explode the PSU with extreme voltages.

Hence, most folks decide to select an external PSU which SOMEHOW survived the tests, and won a UL (or whatever) "listing".

Bri
But then they bitch about a wall-wart, come on,,it's for $'s..everything these days is all about $...there are a few pieces of gear I would have bought if the PS wasn't 1/3 of the price of the gear its self!!.A few hundred dollars to power a one channel pre/compressor? come on man!!
Old 16th November 2009 | Show parent
  #21
Gear Guru
Benefits of using outboard psu's or power transformers are reliant on the chops of the designer.

If you use directional field EI power transformers and mic input transformers, you may need an outboard psu. Then again, just re-orienting the iron to the null position would lower PSU hum levels, perhaps below the hiss levels.

If you use shielded torriodal power transformers and place them away from sensitive circuitry and avoid the input transformer, 60 and 120 hz noise can be pushed down to -125 dbu or more. Then the benefits of an outboard supply are lost. With outboard supplies, you do pick up increased impedance and resistance through the cabling. I find sometimes an impedance dropping pass transistor can remove any residuals pickup up between the psu and the audio gear if located internally and drop the impedance back down to pre wiring levels.

An Audio Precision noise vs frequency sweep with a -140 db resolution will find that noise. Whether you can remove it or not is the designer's responsibility.

Jim Williams
Audio Upgrades
Old 17th November 2009 | Show parent
  #22
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🎧 15 years
Quote:
Originally Posted by RTR ➑️
But then they bitch about a wall-wart, come on,,it's for $'s..everything these days is all about $...
We have to do RFI testing on our automotive engine controllers. It costs us $25,000 to go through the tests. If the device fails, you fix the design, and it's another $25,000. Testing/approvals are not cheap.
Old 17th November 2009 | Show parent
  #23
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🎧 15 years
Hi
Having a seperate box can assist with safety approvals if the gear runs at less than about 50 Volts (European directives, not sure about USA). This means that the rack or preamp does not need as much insulation and guarding as for a mains device. This can be seriously beneficial in say a '500' series rack or similar with open busbars and low voltage connectors. Only the PSU box needs the full safety works.
Matt S
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