iFi SilentPower DC Blocker - Blocks any DC offset, IEC Connector

Product Information

It started to get worse and you could hear the hum when sitting down when not being used despite having a decided mains supply to the hi-fi system. I put this down to the mains coming into the house as around us, we have a significant amount of civil engineering going on around us due to new railway infrastructure. Where I live, we have four compounds for the new East West Rail line and within four miles there is a massive compound for the High Speed 2 rail line, plus numerous others in the vicinity. It will be nice when all is completed, I must admit. It's worth noting that the mains 'DC' observed (measured across the diode/capacitor network) varied by about ±25mV worst case - at least while I was watching!. However, this was measured in a residential area, and there is no doubt that much higher voltages occur from time to time. I expect that a circuit that has been tested to work with over 250mV as shown here will be more than sufficient for most installations. Please note that our couriers will try to deliver as arranged but we will not be held responsible for any costs incurred because of non-delivery or factors introduced by third-parties. This service is based upon best endeavour and is not guaranteed. Please note that the descriptions and calculations presented here are for (nominal) 240V 50Hz mains. For Europe, the mains is 230V 50Hz (and so is Australia now - but it's a

y k = ( 1 − ω ) ⋅ ( x k − 3 x k − 1 + 3 x k − 2 − x k − 3 ) + 6 − 7 ω 2 − ω ⋅ y k − 1 − 6 + ω 2 − ω ⋅ ( 1 − ω ) 2 ⋅ y k − 2 + ( 1 − ω ) 2 ⋅ y k − 3 The circuitry described is intended to remove DC offset when the transformer is operating with no (or light) load. This is when it's most likely to growl if DC is present, and attempting to cater for full-load current is both pointless and ill-advised. A 1kVA transformer will draw 4.4A RMS at full load, and expecting electrolytic capacitors to handle that is unrealistic. At full load, whether temporary (transient) or permanent would require an extremely large capacitance, and it's not needed. When the load increases, the diodes shown in the schematics below take over, and they pass the load current, shunting the capacitors. Mains electricity has a fundamental influence on the audio signal as it passes through a system, from source to amplifiers to speakers. After the asymmetrical (R ext and D ext) load has done its job, a simulation shows the positive peaks of the 240V AC waveform reach 338.35V, but the (unloaded) negative peaks reach the proper value of 339.28V. This is a tiny bit less than the theoretical value of 339.41V because of the transformer load resistance and simulator resolution. The difference between the peak voltages is 0.93V, but the mean (average) DC voltage is -275mV. It is the mean value that appears as 'DC' on the mains. It can also be measured, but to do so requires that one works on live components. This is not recommended as it is inherently dangerous. Tests were done using a 500VA toroidal transformer with very close to the example values given above. With 240V AC mains, 50Hz, 264mV DC offset created by DC injection (see Figure 6), and at no load, the current was seen to rise from 16mA to 218mA. The test was done at no load because this is the worst possible case. As load increases, the effective primary voltage falls - the voltage dropped across the winding's resistance is 'lost' to the transformer. 264mV DC offset causes a current of 132mA DC in the transformer primary. This is probably the maximum offset that you will encounter in real life, although some areas may be worse. I have no data on this.The current waveforms are shown below. These were taken from the mains input to the transformer, using an in-line current monitor. The waveforms were captured using a PC based oscilloscope, and RMS currents in Table 1 were measured using a Tektronix digital oscilloscope. This is effective in reducing both differential-mode noise (exacerbated by cheap switch-mode power supplies used by many home appliances) and common-mode noise (aggravated by airborne interference from phones, Wi-Fi networks and Bluetooth).

circuit (see Figure 8) is easily adapted - the changes needed are described in the conclusion text. The mains voltage is more-or-less immaterial unless it climbs by more It may seem that we need to know the amplifier power rating, and also that of the transformer. We already know that the transformer will be subjected to considerable inrush current, both to set up the magnetising current and initially charge the filter caps. At this point, use of a soft start circuit (see Project 39) is highly recommended. Figure 2 shows some numerical simulations. It turns out that α = 0 is in fact a good choice. Positive α leads to flatter curve shape of the transfer function, whereas a negative α may result in a peak of | H(Ω)| 2. Both is not desired. A slightly improved curve shape may be obtained for small negative α ≈ −(1− b) 2/8 = − ω 2/16.

European Countries

That's a fairly large capacitance, and can only be economically realised using an electrolytic capacitor. This raises a new quandary - electrolytic caps can operate for many years without a polarising voltage, but only at very low voltages. This means that the maximum voltage across the cap(s) must be limited to less than 1V, or they will fail. To be sensible, it will be necessary to use a pair of electrolytic capacitors, wired in 'anti-parallel'. However, in this configuration it may be impossible to keep the voltage across each capacitor low enough to prevent eventual failure. A normal series connection with the two negative (or positive) terminals joined will work, but reduces the available capacitance and maximises ripple current through both caps. Nonetheless, this is preferable (see conclusion). The traditional way to limit the voltage is to use a number of high current diodes in parallel with the caps. Unfortunately, our Installation Service excludes all gas appliances. It is the customer’s responsibility to find a gas safe engineer to connect the appliance. Any work conducted by a third part gas safe engineer will be at the customer’s expense and we will not accept any liability for their work.

For the sake of the exercise, we'll use the 500VA transformer as shown in Table 1. Maximum long-term input current is ... PA20, PA21, PA22, PA23, PA24, PA25, PA26, PA27, PA28, PA29, PA30, PA31, PA32, PA33, PA34, PA35, PA36, PA37, PA38, PA39, PA40, PA41, PA42, PA43, PA44, PA45, PA46, PA47, PA48, PA49, PA50, PA51, PA52, PA53, PA54, PA55, PA56, PA57, PA58, PA59, PA60, PA61, PA62, PA63, PA64, PA65, PA66, PA67, PA68, PA69, PA70, PA71, PA72, PA73, PA74, PA75, PA76, PA77, PA78, PA79, PA80 There are any number of different machines that can create a mains supply DC offset. Most will be totally outside your control, many DC 'events' will be transient in nature, but one common theme applies - they will all load the mains supply asymmetrically for a period of time that ranges from a couple of cycles to minutes at a time. Figure 1 shows a typical (small) example that you may even have in your house - the transformer (shown within the dotted line) is your toroidal transformer. Many older hairdryers (and some heat guns as well) had a switch for 'half power' that simply switched a diode in series with the mains. For a 240W element at 240V, that equates to a resistance of 240 Ohms (example only - actual power will vary widely).Electrical safety is of utmost importance with a circuit such as that described here. Never rely on the electrolytic capacitor outer plastic sleeve for insulation. All parts must be meticulously mounted, with special consideration to personal protection from live components and separation of all low voltage conductors from anything at mains potential. How do they do this? They guarantee, by design, that no significant surge currents flow, which would place the bridge diodes in their high current, high Vfwd regime. These components are easy to spot on the Bryston 6B-SST schematic (LINK). The triac is reference designator Q3, part number BTB-24800B (datasheet), and the microcontroller is reference designator IC1. To see the earlier version with the washing machine controller IC, look at the schematic of the Bryston 3B. As you can see, the normal idle current is not a sinewave. The small peaks at the right side of the half-cycles become larger as the transformer is pushed further towards saturation, indicating that the transformer is just on the verge of saturation in normal operation. This is deliberate. If a transformer is built using enough primary turns to ensure that no saturation effects are visible, it will have very poor regulation because the primary resistance will be too high. If the 500VA transformer is driven to full power (RMS current for the waveform shown is 2.06A), the ripple current through the capacitors will be the same as the transformer's current draw, but we determined the capacitance based on light loading. With 5.5A peaks, even high current diodes can be expected to have a forward voltage of at least 1V, and considerably more during the power-on inrush period.