A rumble filter simply adds to the bass cut making your already “cut” records sound bass light. Plus, it “time-steps” the bass in relation to the higher frequencies (where our hearing is most sensitive) so much so it can confuse the ear into believing the bass is playing out of tempo. iFi solution: OPTION B ….16 AMP (C19) HIGH CURRENT IEC INLET, SHORT LENGTH OF CABLE WITH C19 HIGH CURRENT IEC CONNECTOR 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. Six independent outlets for source components; power amps, preamps, integrated amplifiers, CD players, DACs, etc. The majority of audio electronic equipment uses a power transformer or transformers for their power supply. Mains power starts out being a pure sine wave at the power station but ends up having a lot of distortion imposed upon it by the time it reaches your equipment at home. The distortion comes from other equipment connected to the same power line and could be industrial or domestic in nature, such as pulse-width modulated electric motors (eg. vacuum cleaners, heat pumps), household heating, washing machines, phase-controlled industrial equipment in factories, light dimmers, etc. What sort of equipment should I connect to it?

Eliminates DC component and low-frequency noises, giving a cleaner power supply and improve sound quality. 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.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. The situation becomes somewhat less clear when we look at the typical current waveform as seen at the primary of a transformer feeding a capacitor input filter (99.99% of all transistor amplifiers use a capacitor input filter). We are not in any position to try to remove DC offset at all power levels - the capacitance needed simply becomes too large. Therefore, at some value of current, the voltage across the capacitor will be such that the diodes conduct. Even without exceeding the transformer's continuous rating, the peak current drawn by a 500VA transformer can exceed 5.5 Amps. This is shown in Figure 5. A large number of amplifiers (including very expensive commercial brands) will cause the transformer to be overloaded if both channels are driven to full power simultaneously. This is perfectly alright - transformers can withstand huge short-term overloads provided the average VA rating is not exceeded long term.

The resonant frequency of the network is well away from the mains frequency, so series resonance is not a problem. While studying various designs I stumbled across a TEAC DAC, that I personally found interesting as it took a grip of the dirty USB cable shield. It lands the USB port at separate pcb, hard coupled to chassis by a screw and just millimeters from the port, minimizing the lead reactans, the entire PCB is grounded to chassis. This is an example of a good design. Others in that DAC could be questioned in my opinion. Could not see, e.g. any signs of a grounded lead out from an electrostatic shield in the transformers. I want to create a safe and extremely robust solution, but don't have the skills to model this, nor the test equipment to do more than PAT type safety stuff. I'm aware of the need to properly rate, fuse, insulate and earth every last aspect.

About this Book

Like so many things in electronics, transformer winding is a balancing act. There are many compromises - more turns lowers the core flux, but increases winding resistance, reducing regulation. Fewer turns gives better regulation, but the transformer will run hot at no-load and even a small over-voltage (or DC offset) will cause even higher no-load current. iFi's approach to noise cancelling in cables uses inverse noise current to cancel out the noise in the mains signal. (Yes, comparable to the tech in noise-cancelling headphones). The capacitors need to be able to handle the maximum worst case current. For the sake of the exercise, it is worthwhile to size the caps so that they are capable of handling the full load current - 2A. On this basis, it is better to select a much higher voltage than needed to ensure that the ripple current rating is high enough. Although 16V caps would seem perfectly alright, 63V caps will have a ripple current rating that's more than double that of the low voltage type. The extra size helps to keep the cap cool, improving life expectancy. A varying DC offset on the AC mains is no longer uncommon. There are many ways that a DC offset can be created, with most being totally outside the control of those who have to try to eliminate it, or put up with the mechanical noise created in (especially) toroidal transformers. It may be counter-intuitive (and some may choose to disbelieve it altogether [they are wrong]), but the maximum flux density in any transformer core occurs at no load. This is also the condition where even a small DC offset can cause the idle current to rise alarmingly, as described further below.

And how do they do THAT? They use a soft start circuit. A triac in series with the transformer primary is controlled by either (i) a soft start IC designed to control AC motors in washing machines {part number TDA1085C (datasheet)} in their early power amp products; or else (ii) a microcontroller {part number PIC16F818} in their more recent power amps. This triac gets fired at just exactly the right phase of the incoming mains waveform, to minimize surge current ("ELI the ICE man"). Then the controller gradually ramps up the conduction angle, across many many cycles of the AC mains waveform. After installing the DC Stopper in circuit with the same transformer as used above, the above shows the current without DC (left) and with DC (right). The plots are almost identical. What is not seen is a very low frequency oscillation after the DC is switched in or out. This is caused by the series resonant circuit mentioned above. While it looks a little disconcerting, it's nothing to worry about and can be ignored. Frequency is as calculated - approximately 0.6Hz (more on this topic below).Each individual live and neutral conductor sports multiple layers of insulation and shielding, too. The cable is completed with a tough yet flexible polymer outer sheath and iFi’s "audiophile-grade" connectors, with oxygen-free copper conducting pins coated in tarnish-resistant 24ct gold. The AC transformers commonly used in home audio equipment cannot tolerate the presence of significant levels of DC voltage without being compromised. Less than 500mV of DC – typical in an average household electricity supply – can be sufficient to cause toroidal transformers of the kind often found in amplifiers to become saturated, which adversely affects sonic performance and may cause audible mechanical vibration.