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

Product Information

Most of the time, the DC offset is transient - it appears for a short while, then goes away again. When it is there, toroidal transformers may complain loudly by making growling or buzzing noises. It is important to understand just how this happens, and what can be done about it if it causes problems.

It has been installed for a couple of days now. I put it on the noisiest 250 and immediately, the hum was reduced. Didn’t cut it out totally, but reduced it so much, that you can’t hear it unless you put your ear right next to the amplifier. The other 250 is still slightly humming, but that was never as bad as the first one, so now I know that it works, I’ll get a second one. The SuperCap, FlatCap and the NAPSCs are all quiet. Additional tests I performed used only diodes (no effect whatsoever), and a 22µF and 1µF capacitor, and both of these were completely useless. Actually, they were worse than useless, by actually creating a DC offset! Without a very detailed examination, it appears that the small capacitance is only capable of averaging the slightly different forward voltages of the diodes, resulting in a few millivolts of offset. Because the cap is not big enough to maintain the AC component to a value well below diode conduction voltage, this small DC voltage then becomes an offset. With 1µF, transformer idle current rose to about 25mA without any external DC, and was 170mA when DC was added (same setup as used for all other tests). Idle current was a little less than this with the 22µF cap, but not by very much. Please note: TV and larger floorstanding speaker deliveries are not available to Northern Ireland, Republic of Ireland, Isle of Man, Isle of Wight, Scottish Islands, and Channel Islands. OPTION D ….EU SCHUKO MAINS PLUG (FURUTECH) TO STANDARD IEC CONNECTOR WIRED WITH 1.5 METRES OF CABLE EACH SIDE 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.

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Note that all current measurements must be made using a true RMS meter. All 'normal' (not using a true RMS detector) meters use an average responding circuit, and this will cause serious errors because the waveforms are not sinewaves. Waveform distortion creates large errors with 'ordinary' meters. A quite cheap and not very sophisticated filter design, offering a substandard DC-filtration, unless the reqtifier bridge is not spec'd with higher forward voltage diodes. The decoupling is very rrudimentory as well and will do some good, but since no resistor loads are implemented it will not cancel possible resonances. 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. The mains supply in a typical home is subject to interference induced by a range of issues, causing the AC waveform to distort before it reaches each component. This creates noise in the audio signal, which degrades sound quality – a situation that continues to worsen with more and more electrical devices being added to the home mains supply.

When a wire simultaneously conducts low-level DC as well as AC current, the result is a distortion of the AC waveform, called DC offset. Audio gear with transformers just don't like dealing with distorted AC sine waves (which is why PS Audio "regenerators" proudly measure their reduction of it in and out). DC in AC can be continuous, intermittent, or random. The culprits? Could be endemic to the power coming to the house. Could be HVAC, the microwave, or our usual suspects, switch mode power supplies. Like a rash, you know it if you have it. H ( Ω ) | 2 = 4 β 2 ⋅ sin 2 ( Ω 2 ) + 4 ⋅ ( b 2 − β 2 ) ⋅ sin 4 ( Ω 2 ) 4 β 2 ⋅ sin 2 ( Ω 2 ) + 4 α ⋅ sin 2 ( Ω 2 ) − 4 α ⋅ sin 4 ( Ω 2 ) + 4 ( b 2 − β 2 ) ⋅ sin 4 ( Ω 2 ) + ( α + β 2 − ( 1 − 2 b + b 2 ) ) 2 ⋅ cos 2 ( Ω 2 ) = 4 β 2 ⋅ sin 2 ( Ω 2 ) ⋅ cos 2 ( Ω 2 ) + 4 b 2 ⋅ sin 4 ( Ω 2 ) 4 β 2 ⋅ sin 2 ( Ω 2 ) ⋅ cos 2 ( Ω 2 ) + 4 b 2 ⋅ sin 4 ( Ω 2 ) + 4 α ⋅ sin 2 ( Ω 2 ) ⋅ cos 2 ( Ω 2 ) + ( α + β 2 − ( 1 − b ) 2 ) 2 ⋅ cos 2 ( Ω 2 ) = 1 1 + 4 α ⋅ sin 2 ( Ω 2 ) + ( ( 1 − b ) 2 − α − β 2 ) 2 4 β 2 ⋅ cos 2 ( Ω 2 ) + 4 b 2 ⋅ sin 2 ( Ω 2 ) ⋅ cot 2 ( Ω 2 ) 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. These are rated for a maximum ripple current of 14 Amps, and it is my intention to use a pair in parallel to give >20 Amps headroom, plus a similarly robust bridge rectifier.With a focus on Class A analogue circuitry and maintaining the audio signal's integrity, iFi Audio's products offer exceptional performance without compromising environmental sustainability. They believe that how a product looks, performs, and impacts the environment all matter, and they strive to deliver audio solutions that meet these criteria. While the common solution found on the Net appears simple, there's a lot more to it than may seem to be the case. The operation is not intuitive, so while you may think that you know how it works, you could easily be mistaken. Also, beware of snake oil - there are vendors who will make outrageous claims about how their 'gadget' will improve the sound in mysterious ways, often accompanied by a 'technical explanation' that only qualifies as word salad. 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). The circuit shown above should not be used unless you are absolutely sure of your ability to take fully isolated measurements, and are fully aware of the serious risk to life if you get something wrong. It can (and will) kill you if you touch anything !

The circuit and design processes described here will work for any size transformer. In most cases, the circuit shown in Figure 3 will be fine for any transformer from 500 to 750VA. DC stoppers are usually not needed in smaller toroidal trannies because their primary DC resistance is high enough to limit the (usually small) DC component so the DC has very little effect.

Cute. Clever.

The normal idle current is shown on the left, and the current with 132mA DC offset is on the right. The asymmetrical waveform with DC present is very obvious - the current is drawn predominantly during the negative half-cycles. If the DC polarity were to be reversed, the positive half-cycles will create saturation. Note that the right current scale is 10 times that on the left. The disadvantage of the latter approach is that you need 4 x the capacitance to achieve the same ripple current handling, which becomes hopelessly expensive and outsized in the case I'm trying to get my head around. PH15, PH16, PH17, PH18, PH19, PH20, PH21, PH22, PH23, PH24, PH25, PH26, PH27, PH28, PH29, PH30, PH31, PH32, PH33, PH34, PH35, PH36, PH37, PH38, PH39, PH40, PH41, PH42, PH43, PH44, PH45, PH46, PH47, PH48, PH49, PH50 Formed in the early 1980s by Philip Swift and Derek Scotland, audiolab earned worldwide acclaim with the 8000A - an integrated stereo amplifier that became a classic ‘step-up’ from the budget models of the time.