Ok Now things well get more interesting - here I want to explore the LPS solutions available - focusing on the less expensive options (under $250). But first a quick primer on the last main component of these LPS units - the filter capacitors. WARNING – POWER SUPPLIES CONTAIN LETHAL HIGH VOLTAGE! NEVER OPEN THE CASE OF YOUR POWER SUPPLY. SEEK A COMPETENT TECHNICIAN TO MAKE ANY ADJUSTMENTS OR CHANGES TO YOUR EQUIPMENT! I take no responsibility for anyone who ignores this warning! LPS Capacitors: There are many types of capacitors, but linear power supplies generally use electrolytics, due to their ability to withstand high voltage spikes and reasonable performance. These caps are rated for voltage, and capacity, as well as expected life, temperature rating and physical size. But other important criteria is the caps ESR rating, PSRR and impedance - more on this in a bit. Generally the aluminum electrolytic types are preferred. https://en.wikipedia.org/wiki/Aluminum_electrolytic_capacitor "The basic unit of electrolytic capacitors capacitance is the microfarad (μF, or less correctly uF)", that and voltage are two main parameters for use. "Electrolytic capacitors are polarized capacitors and generally require an anode electrode voltage to be positive relative to the cathode voltage. To minimize the likelihood of a polarized electrolytic being incorrectly inserted into a circuit, polarity has to be very clearly indicated on the case, see the section headed "Polarity marking". Now for some details on why these capacitors are used in a LPS and how to select the better versions: Impedance: It's my understanding that a lower impedance is generally better for use as a filtering cap. ESR and dissipation factor tan δ: Here a lower value is generally better. Ripple current: Here again higher is better. I have had good success replacing the stock capacitors on inexpensive LPS's. I look for long life - 10,000 hours preferred (most of the cheaper LPS from China use 2,000 hr or less rated caps), low ESR, high PSRR and low impedance for the respective capacitor value. I also try and find capacitors rated for 105C temperature, if possible. The cost for these better caps is minimal compared to the overall cost of the LPS. One note more and larger filter caps in a LPS will give a higher level of AC noise or ripple rejection - all other things being equal. The larger number and size will slightly increase the noise fed back into the local AC mains (still orders of magnitude less then a SMPS). Here is a TeraDak X1/X2 with the stock Panasonic FC 25V 1500uf caps (rated at 5000 hrs, 105C Temp) - from Digikey (although they show a different color) Impedance: 30mOhm, Ripple: 1.55A@120Hz, they do not show an ESR rating for these. With Nichicon HW 25V 1500uf - 10,000hr (105C), low impedance: 16mOhm, Ripple 1.56A@120Hz. Other possible caps I could have used that are excellent: United Chem KZ (5000hr - 18mOhm, 2.7A) $1.00each Pannasonic FM (7000hr - 15mOhm, 2.55A@120Hz) $1.40each Pannasonic FR (10,000hr - 18mOhm, 2.08A@120Hz) $1.01each I have the FMs and may switch the caps in this little unit at some point - more on this LPS later. Existing LPS available for low cost - under $250: Just a note on linear power supplies - they do come in both regulated and unregulated versions. Typically the unreg will be cheaper wall wart looking devices. Do to the lack of regulation they are not recommended, their voltages can swing by wide amounts and even damage some equipment. All the following are of the regulated variety. In PART 1,2,and 3 we have explored the three main components of a linear power supply: the transformer, the regulation circuit, and the power filtering capacitors. So what to look for? Well for me I really like the R-Core transformer for it's AC noise (ripple) rejection superiority over toroidal or EI transformers. A high quality LDO with low DC noise and high current capacity (an issue with many of the ultra low LDO's available). You have to look at what your current and voltage needs are, when choosing a replacement power supply. If you're powering a USB DAC or DDC - is 500mA enough? Many draw in excess of this - the PUC 2 Lite for example with a 800mA draw. Most external XMOS DDC's will draw less and abide by the 500mA USB std. I would prefer a LPS that can provide at least 1A 5VDC(the std USB voltage). Many LPS's also have adjustable voltage pots - so their voltage can be changed as needed. Some of the external USB gizmos like the Regen and Recovery need a higher voltage then the std USB +5VDC, as they have their own on board LDO regulators that will then step down the required voltage to 5VDC - in the case of the Regen 7-9V is optimal and the W4S Recovery needs 9VDC. Feeding a USB DDC like the F-1 can be done with a split USB cable (the data and power leads are separate), taking the power from the LPS and the data from the PC's USB. As for capacitors - not as big of an issue for me as they are fairly easy and cheap to upgrade. But it would be nice to have the better Panasonic, Nichicon, or Chemcon caps. So here are a few I own, or look interesting to me. First I want to discuss a neat little gadget: iFi DC iPurifier: http://ifi-audio.com/portfolio-view/accessory-dcipurifier/ This attaches to the end of the DC feed cable before the device and filters the DC power by many factors. I have had very good success using one of these with a low cost LPS bought on Ebay. iFi claims tremendous DC noise filtering from this unit - 316X under 1Khz, up to 100,000x above. They claim they are able to achieve this with an active noise canceling circuit used in military radar. I wonder if this type of circuit isn't being used on chip for these >1uv LDO IC's to get the DC noise levels down? They are not cheap - around $80 from Music Direct: https://www.musicdirect.com/power/ifi-dc-ipurifier-power-conditioner But the big question is - do you need an ultra low noise regulator (>4uv) in your LPS if you use one of these? As you'll see there are many decent and cheap LPS's on Ebay - some for less then $100. If one uses the LT1083 or LT1084 LDO regulators (see Part 2 for a comparison of LDO's) with 180uv of DC noise - but that then gets filtered down by a DC iPur at least 317 times - that would leave less then .5uv of noise to the device! This is the lowest noise level I have seen in a plain IC LDO. So for around $160 you can have a nice ultra low noise package. That is if the DC iPur works as advertised. OK On the LPS's: Generic R-Core LPS: This unit I own uses the LT1083 regulator mounted on a nice large heat sink - uses one 50V 3300uf filter cap, 4 of the new Vishay B560 Ultra Fat, Ultra Low Loss Rectifiers, and a 12V R-Core transformer. The LT1083 does not have very good noise numbers rated at 180uv, and lowly PSRR. But with an R-Core maybe high PSRR is not as necessary? With the iFi DC iPur - the DC noise can be reduced to virtually nothing. This is a high current unit - and not appropriate for a USB device - the lowest setting is 9V(3A) and can go as high as 24V(1A). So if high current and voltage is needed this looks like a great low cost solution. Note the iFi DC iPur is rated to just 24VDC - and over heated when I tried it this unit at that voltage, but has worked well at much lower voltages. $77 Delivered. http://www.ebay.com/itm/30W-30VA-HiFi-Linear-power-supply-PSU-DC9V-12V-15V-16V-18V-20V-24V-for-choose-/161870356771?hash=item25b039a123 I will explore the DIY option in a later part 4. But this could be the 'bones' for just such a project. Just replace the LDO with some thing like this (the existing board is 75X50mm): http://www.ebay.com/itm/142115498378?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT Ultra low noise LT3042 .8uv - very high PSRR 79dB @ 1Mhz. This board is rated at 6-12V input and 1.5A 5VDC output. So the existing R-Core could be used. The size is 69x47mm - so it would fit as well. $60 shipped. So with a little effort this could be a killer good USB DDC or DAC power supply. The voltage is non-adjustable. TeraDak X1/X2 LPS: Neat little unit - EI transformer - LT1084 LDO (180uv 30dB PSRR)- Panasonic FC caps 25V 1500uf (8 total), AC common mode filter coil, MOV surge protectors, etc... $80 shipped. http://www.ebay.com/itm/TeraDak-TeraLink-X1-X2-DC8-5V-1A-USB-DC5V-port-Hi-Fi-Linear-Power-Supply-/181467993450?hash=item2a4055d56a:g:LzQAAOxyVVJR~9Nv Upgrade the caps - as pictured - or use the stock caps and add a iFi DC iPur and you have a neat low cost LPS solution. Nice feature - has two DC power ports - one a USB set for 5VDC and the other a 2.5mm barrel which has adjustable voltage. Product Specification Output : 8.5V DC + USB-A 5 VDC Port @ ~ 1A With a total of 1A 5VDC - I would not use both power ports simultaneously. But 1A for 5VDC is more then adequate for XMOS USB DDC use. TeraDak DC-30W (old design): Nice copper shielded R-Core transformer, likely the LT1084 LDO's 180uv, 30dB PSRR, Panasonic FC caps 25V 1500uf (10 of them). With the R-Core transformer and it's excellent inherent PSRR - the low LT1084 PSRR may not be as important as when it's used with a toroidal transfomer (see PART 1 on transformers). Rated at 3Amps 5VDC and 1.5A for 12V and with an adjustable voltage - more then enough for almost any DAC or DDC. Great for powering the 7-9 VDC Regen or 9VDC Recovery USB reclockers. TeraDak DC-30W (New design): Nice copper shielded R-Core Transformer, looks like two NPN devices used for power regulation, mine had the Panasonic FC 25V 1500uf caps 3 total and two larger 25V 3300uf Panasonic SU caps (low 2000 hr life), EMI common mode filter and MOV surge protection on board. I see the latest versions have the better Panasonic FC 25V 3300uf caps vs the SU. (On mine I swapped the SU's for 25V 3300uf Nichicon HW's. This made a noticeable improvement in SQ.) $139 shipped. http://www.ebay.com/itm/TeraDak-DC-30W-TOUCH-DC9V-2-5A-Hi-Fi-For-Audio-Linear-Power-Supply-/130906580297?hash=item1e7aa3e549:g:5UoAAOxyo4lRjkus This new design has high current capability - rated at 2.5A @ 9VDC. Also with adjustable voltage - so at say 5VDC plenty of power for any USB DDC and then some. Plenty for the Regen and Recovery etc... I could only find the marking of D44H11 on the regulation devices - there are two. I identified them a NPN devices (OnSemi?) - but was not able to find any DC noise figures on this power supply. Imagine less then 50uv with excellent PSRR. http://www.onsemi.com/pub_link/Collateral/D44H-D.PDF I use mine with a iFi DC iPur to excellent effect on both my modded BURL B2B DAC and with the Singxer F-1 XMOS USB DDC. MEIYAN Ultra Low Noise - High Current LPS: This unit I found on Ebay has me really intrigued - very low noise - 13uv @24VDC - low noise at lower voltages, very high current capability: $192 shipped. http://www.ebay.com/itm/131867485038?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT We have following several kinds voltage for choose (Output voltage / current) 1. 5V /6A 2. 9V /5.7A 3. 12V /5.5A 4. 15V /5.3A 5. 18V /4.4A 6. 19V /4.2A 7. 24V /3.3A Nice copper shielded R-Core transformer - excellent low noise. One downside is the voltage is not adjustable. But it is available in a range of voltages - I will likely order one at some point to try out. Update: The DC voltage is adjustable in a range of 5VDC to 24VDC. So that completes the low cost LPS's I have found - now a few expensive ones: Paul Hynes SR2 & SR3: These highly regarded LPS's are excellent designs - but not cheap the SR2 is approx $250 ($195 English Pounds) and the SR3 $381 (300 English Pounds): http://paulhynesaudio.com http://hifipig.com/paul-hynes-sr3-power-supply/ http://www.paulhynesdesign.com For the SR3, I have seen 5uv @10-100Hz quoted for the SR3 and PSRR of 80dB @ 0-300Mhz! On his Z100A Shunt regulator he quotes 110dB of PSRR from DC to 20kHz! The SR2 used to be much more expensive - and maybe this is the best lower cost LPS to get. The one issue is very long back order que from what I have heard - I'm sure with the recent devaluation in the British pound - maybe even more so today. Note these PS's need to be built to spec as the DC voltage is not adjustable. Teddy Pardo - Teddy Cap PS - These made a name for themselves replacing the NAIM power supplies. Available in a range of voltages - $369 for a 5VDC version. http://www.teddypardo.com/powersupplies/underthehood.html I have not seen noise or PSRR numbers for these power supplies. Uptone JS-2 - $925 Wow! This is a beautifully totl LPS - with multiple DC outputs that have various voltage settings: http://uptoneaudio.com/products/js-2-linear-power-supply R-core transformer! The choice of the R-core here speaks volumes: Have not seen DC noise or PSRR numbers for the JS-2 but I bet they are very good. HDPLEX 100W Linear Power Supply - OK R-Core Transformer - nice. But...the LDO regulator used is the Linear Tech LT1083. High noise of 180uv and only 30dB PSRR at high frequencies - not great for a $395 PS. Says low ripple and 'void of high frequency noise' what ever that means. Any numbers? http://www.hd-plex.com/HDPLEX-Fanless-Linear-Power-Supply-for-PC-Audio-and-CE-device.html I'd prefer going with a TeraDak DC-30W or the MEIYAN for much less money and adding a DC iPur. Or get in line for a Hynes SR3. Next Part - the new SuperCap PS's and Batteries. Cheers!