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Old 9th January 2012, 06:39 PM   #1
Mike P is offline Mike P  United Kingdom
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Default Opinions on the use of plug packs

I'm planning to build a new upgraded power supply for my DAC using the P05 boards available from Rod Elliott Sound Products. These boards create a fairly straightforward PSU comprising of a bridge rectifier, smoothing caps and 7815, 7915 type voltage regulators.
The DAC needs 2x (+15v, -15v, 0v) for the audio section and 1x (+15v, -15v) for the digital section.
The original plan was to use three separate toroidal transformers one for each supply however I noticed that Rod Elliott recommends the use of 16v plug packs instead of transformers on grounds of convenience and safety.
I'm attracted to the idea of using plug packs as it would be super easy and cheap but what are the pro's and con's from a performance point of view given that I'm aiming to make a better /quieter PSU than the original?
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Old 11th January 2012, 10:12 PM   #2
! is offline !  United States
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Three separate toroidal transformers isn't useful, it'll work but no need. "16V plug packs" doesn't tell us what they are except it's in a case and it's 16V. For low current use such as a DAC, yes you can use cheap and commonly available, linear unregulated plug packs with equal success. Assuming they're E-core you'll want to put them a distance away from the DAC, though the regulator boards can be near the DAC or in same casing (which is better).

What will give a bit lower noise is using separate power supply boards with LM317 & LM337 instead of 7815 and 7915, a bit like this one: Power Supply for Preamps except leave off the Aux portion of the circuit, and between the Adj 1 pin on each regulator and ground, place a 10uF tantalum capacitor. Well actually, just ignore his 2nd schematic and use something like the following +/-12V to +/-5V Power Supply Regulator By LM317 and LM337| Circuit Project as there is no need for the RC filter he has before the regulator, nor any need for so much as 4700uF capacitance before the regulator on a DAC to filter 100Hz to 200Hz ripple from a bridge rectifier, no need for the rail to ground diodes, nor any need to parallel two resistors as R4A + R4B & R6A + R6B. It doesn't need to be 15.000000V, 14.8486748V or 15.34V or whatever, is fine so long as it is clean power.

However, how common are 16V plug packs? They are not common at all in the US or anywhere else I am aware of. 12V are common, 24V not terribly uncommon, but I have never seen a 16V unless he is referring to the unregulated peak voltage from a 12VDC rated plug pack which is about 16.nV, but drops with a load and isn't high enough to regulate down to 15V with a linear regulator except possibly a low dropout type.

Oh now I see what he wrote, it was about using a 16VAC plug pack. I don't think they will be easily found nor if you find one will it be attractively priced due to their rarity. However, 24VAC power packs are more common (in the US at least), you could use a couple of those. The real question is what voltage you want, or the DAC's voltage limits. If it doesn't need to be as low as 15V then you can raise the voltage, or if it'll run fine on 12V then you can make the voltage +-12V and use common 12VDC or 12VAC plug packs, in the case of the 12VDC it'll need rated for a fair amount more current than the DAC uses but most will be.
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Old 12th January 2012, 10:21 AM   #3
Mike P is offline Mike P  United Kingdom
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Thank you very much for your reply.
O.K. so it makes sense to buy a single toroidal transformer with enough power to supply all three sections of the DAC (audio L, R and digital). I'll then use three separate PSU circuit boards with LM317 & LM337 type regulators.
As far as I understand the plug packs are just cheap step down transformers which plug directly into the mains wall socket. I have found these on ebay new at 3 each. I suppose they will be noisy but if sited on the wall away from the DAC this would still be an option?
Do you think some high grade regulators like this would be overkill? NewClassD UWB Regulator
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Old 12th January 2012, 10:42 PM   #4
Minion is offline Minion  Canada
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When used with a 16v ac wallmatr in this configuration it is set up as a Voltage doubler which will have 2 x the ripple in the PSU as compared to useing a 16v 0v 16v Transformer .......

You would need twice the capacitance in the PSU when useing 16v to get the same performance as useing 16v 0v 16v .......

So if you use a 16v AC wallmart transformer you might want to double the capacitance in the PSU depending your current draw ......

Cheers
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Old 12th January 2012, 11:27 PM   #5
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How you do it really depends on your goals. Some people will swear they can hear changes and they can, others will swear they hear a change because they want to believe added work and expense "must" improve the sound but they can't blind A/B test and determine which is which.

E-core transformers (as in plug packs) are a little less noisy than toroids, but should be placed much further away (several inches at least). On the wall is fine. The noise difference decreases with capacitance and regulation downstream of them.

Some would use a toroid because it seems more "pro" looking to do so. Some would use only one regulator board, or 2, instead of 3. Some will feel LM7805/7905 are good enough. Some will feel LM317/337 are good enough. Some will feel the regulator boards you linked are worth the money, but I suspect most people won't.

I mentioned LM317/337 because it is a minimal part and cost increase while those linked regulator boards are REALLY expensive. For 3 power supply boards you'll need 6 of them which when I convert to USD for comparison purposes I can relate to, is $224 for regulators alone and possibly a shipping charge on top of that. Personally I could not justify such a high price nor do I think you would hear any difference.

As far as transformer and capacitor choices before the regulator boards, there are many options that will work fine whether you use single output voltage (single secondary winding) transformer and then a voltage doubler circuit with more capacitance, OR two of the same plug packs wired in series, or a dual secondary transformer whether it be e-core or toroidal.

Some consideration might be made as to the size and portability you want. A single plug pack with a voltage doubler circuit, then the doubling circuit and regulator in the same case as the DAC, makes for a smaller more portable combo. If the PSU board is in a separate casing than the DAC, size difference isn't much but still "usually" a little smaller than putting a toroidal transformer in the power supply boards' case. On the other hand if you want to use a particular case due to price or size or that it matches your DAC case, how big it is will lead to a decision about which power supply transformer arrangement will work well with the available space. If a transformer will fit in the case it's bigger and less portable to use a plug pack plus the case than to have the transformer in it.

All the options are valid ones, so people have done it many different ways with success.
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Old 13th January 2012, 12:00 AM   #6
! is offline !  United States
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I might add, that on one headamp I built, I took two plug packs, one a bit larger than the other, opened them both and put the smaller transformer in the larger pack case which left enough room for a regulator board I made to fit in the available space. It situated the regulator at the edge of the board so I could cut a little ~ 1 x 2cm hole in the plug case and mount the regulator on a heatsink attached to the outside front of the plug case. Compared to other regulated supplies I swapped back and forth on the same headamp, I can't hear any difference.
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