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March 13, 2012

Glassware Audio LV-Regulator Power Supply

Wallwarts... you know them as the little black plastic boxes that take up precious real-estate on your wall outlet or your surge protector. These little devices are generally mass produced overseas as a cheap method of converting your house's AC (alternating current) to usable DC (direct current) for whatever device they'll be powering. This process requires transformation, rectification and filtering in order to make the power worthwhile for your device. Transformation is the process of converting the voltage from 120v (in the U.S.) to whatever the device is calling for, whether it be 9V, 12V, etc. Rectification periodically reverses the direction of AC to convert it to DC, usually using diodes or vacuum tubes in some circumstances. Filtering is reducing the power ripple to produce stable power and reduce EMI (electromagnetic interference), often times making use of capacitors.

Not all power supplies are created equally. Many high-end electronics shrug off the little wallwarts and have a dedicated power supply built-in, or even in a separate chassis. Using higher quality transformers and better filtering circuits improves the quality of power entering your equipment, which will hopefully improve the listening experience if all goes according to plan. As many forum members agree, there are a number of devices that can benefit from a dedicated power supply, such as the Squeezebox, Cambridge Audio DACMagic, Wadia 170 and 171 iTransport and the Musical Fidelity X-Series and V-Series components. 

This brings us to the Glassware LV-Regulator (LV standing for Low Voltage) which can be configured for 5v, 9v or 12v DC output and makes use of a 3A low-dropout regulator (LD1085). As stated by John Broskie on the Glassware website: "The LV-Regulator uses a simple RC filter (1 ohm & 10kµF) as a pre-filter before the LDO regulator and holds bypass capacitors for all the electrolytic capacitors and a 4.7µF/400V polypropylene shunting capacitor at the output. The 1-ohm resistor is a 4W device, so the maximum current output is 2A. The RC filter before the voltage regulator unburdens the regulator from having to deal with sharp transients."

The Glassware LV-Regulator board (copyright Glassware)

This board, when combined with a suitable transformer, will make a nice power supply for low voltage devices like many mentioned above. The one being assembled in this particular post will be 9v and making use of a center-tapped Hammond transformer. Below is the initial board assembly and the Hammond 166M10 3A transformer. Because the transformer is center tapped, the board would be configured as full-wave center-tapped. 

Transformer and LV-Regulator Board

Aside from the transformer and board, a few other things will be necessary, including a chassis, IEC inlet, power outlet, umbilical power cable, pilot light, and on-off switch. The IEC inlet will be a EMI/RFI filtering type that should help further clean up the power. For the power outlet, a Neutrik Powercon connector will be used. For the chassis, I'll be using a custom 8" x 5.5" chassis from Keith (Ebay member po1019). Below is a quick initial chassis layout for the build.  

Custom 8" x 5.5" chassis with mahogany panels

Initial chassis layout

Below is a photo of the chassis after the holes were drilled and it was powdercoated a cream color. I have a nice Greenlee punch for handling the Neutrik Powercon connector (it handles the Powercon, the locking 1/4" jack and other similarly shaped panel mounted jacks). The IEC inlet has to be cut with a Dremel cutting disc which requires a bit more time and effort. I typically drill four holes in the corners, then cut between them with the cutting disc, then finally use a hand file to smooth out the cuts. All the other holes on the chassis were created with a drill press. 

The LV Regulator Chassis

Next comes the process of adding the parts and the populated circuit board to the chassis. Thankfully everything fit without issue. 

Parts added to chassis

With everything in place, the circuit could be wired up. 16 gauge silver-plated copper in PTFE was used for all wiring, aside from the pilot light which was 18 gauge. The wood side panels were then slipped in place and screwed in. 

The LV Regulator all wired up

With the wiring complete inside the unit, there will be a need to get the amps to the transport it will be powering via a cable. The cable from a power supply to the unit it is powering is typically called a "umbilical" cable. The center of this cable is a twisted pair of 18 gauge silver plated wire, one for power and one for return. This was carefully wired to a small 3 pin power connector that closely matches the Wadia 171i input. Multiple layers of heatshrink were used to ensure to possibility of a short within the plug. 

Creating an umbilical cable for the power supply

I decided to shield this cable, so some additional steps are necessary. The twisted pair was covered with Teflon tape, then a bus wire wrapped around it. This bus wire will conduct to the foil shield that will be wrapped around it. 

The foil tape is made by 3M and is a basic way to reduce EMI (electro magnetic interference). I used it rather than copper mesh to keep the cable from getting too bulky. 

3M foil tape wrap

The cable then gets another layer of teflon tape on top.

More to come...

The Fine Print:
Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 


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