GlassWare Audio Design
Thanks for Supporting the Tube CAD JournalNew Balancer PCB and Kit
New DC-Block Kit
Product Description
For decades I have wanted to make a DC-Block PCB. Why? I often use toroidal power transformers. Toroids offer many advantages, such as a much smaller, flatter size, and less radiating hum—all of which is the result of having a tight magnetic circuit in their wound steel-strip cores. Sadly, this also leads to their problem: an inability to sustain a DC offset. Yes, power transformers are never supposed to encounter any DC on their primary. Alas, the wall voltage can harbor a small DC component, due to all the other current-drawing equipment and machines attached to the same feed, such as refrigerators, light-dimmers, computers…solar cells that directly connect to the grid without intervening transformers.
The DC-Block circuit blocks the small amount of DC from entering the power transformer. What is needed is a huge coupling capacitor, which is simply impractical, as 10,000uF/400V film capacitors might be made, but they would be bigger than a garbage can and cost a fortune. The workaround is to use two high-valued but low-voltage electrolytic capacitors in series with safety voltage clamps that prevent over voltages.
Two rectifier bridges are used to double the maximum amount of DC that can be blocked to four rectifier voltage drops, about 2.8V. The two 22kuF/16V capacitors are in series, which effectively creates a non-polarized electrolytic capacitor and are shunted by a 1uF/630V polypropylene capacitor (C4). In addition, I added a House-Ground circuit. (If we are going to fix one wall-voltage problem, we might as fix two problems.)
The DC-Block circuit is placed in series with the neutral lead. Many prefer to place in series with the "live" or "hot" lead, but either position works equally well. The difference is that neutral should be at house-ground potential. Wall sockets can be mis-wired, however, so at all times the the DC-Block should be sealed up away from probing fingers (or inquisitive paws).
Bear in mind that adding a DC-Block to an existing piece of commercially-made audio gear will no doubt void the warranty. Moreover, this is not a project for the beginner. Indeed, do not even think of using if you are not an experienced electronics practitioner.
The kit includes the PCB and all the parts needed to populate the PCB, along with four hex standoff and screws and instructions.
The DC-Block circuit blocks the small amount of DC from entering the power transformer. What is needed is a huge coupling capacitor, which is simply impractical, as 10,000uF/400V film capacitors might be made, but they would be bigger than a garbage can and cost a fortune. The workaround is to use two high-valued but low-voltage electrolytic capacitors in series with safety voltage clamps that prevent over voltages.
Two rectifier bridges are used to double the maximum amount of DC that can be blocked to four rectifier voltage drops, about 2.8V. The two 22kuF/16V capacitors are in series, which effectively creates a non-polarized electrolytic capacitor and are shunted by a 1uF/630V polypropylene capacitor (C4). In addition, I added a House-Ground circuit. (If we are going to fix one wall-voltage problem, we might as fix two problems.)
The DC-Block circuit is placed in series with the neutral lead. Many prefer to place in series with the "live" or "hot" lead, but either position works equally well. The difference is that neutral should be at house-ground potential. Wall sockets can be mis-wired, however, so at all times the the DC-Block should be sealed up away from probing fingers (or inquisitive paws).
Bear in mind that adding a DC-Block to an existing piece of commercially-made audio gear will no doubt void the warranty. Moreover, this is not a project for the beginner. Indeed, do not even think of using if you are not an experienced electronics practitioner.
The kit includes the PCB and all the parts needed to populate the PCB, along with four hex standoff and screws and instructions.
