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'Noise' is a classic misconception about SMPSSpeaking properly, there is no noise in SMPS, since noise by definition is a signal of random nature and what SMPS produce on their output is periodic 'ripple' as any 50/60Hz supply. We could call this 'conducted ripple'This ripple is usually a sawtooth waveform and it may have some RF ringing on transients [on the peak and valley of the sawtooth cycle]. There's not much difference from 50/60Hz supplies, except the ripple frequency is about 1000 times higher.As in 50/60Hz supplies, ripple is easily filtered with pi filters and it may be attenuated as desired [even below noise floor], but with the advantage of size since 100Khz pi filters are much smaller and cheaper than 100Hz pi filters...
The effectiveness of magnetic shielding is generally rated in dB. The transformer is placed in an external magnetic field of known strength, generally at 60 Hz. Its output without and with the shield is then compared. For example, a housing of 1/8" thick cast-iron reduces pickup by about 12 dB and a Mumetal can by about 30 dB. Where low-level transformers operate near strong magnetic fields, several progressively smaller shield cans can be nested around the transformer. Two or three Mumetal cans can provide 60 dB and 90 dB of shielding respectively. In very strong fields, because high-permeability materials might saturate, an iron or steel outer can is sometimes used. Toroidal power transformers can have a weaker radiated magnetic field than other types. Using them can be an advantage if audio transformers must be located near them. However, a toroidal transformer must be otherwise well designed to produce a low external field. For example, every winding must completely cover the full periphery of the core. The attachment points of the transformer lead wires are frequently a problem in this regard. To gain size and cost advantages, most commercial power transformers of any kind are designed to operate on the verge of magnetic saturation of the core. When saturation occurs in any transformer, magnetic field essentially squirts out of the core. Power transformers designed to operate at low flux density will prevent this. Often a standard commercial transformer, when operated at reduced primary voltage, will have a very low external field.
Again, your amps were effected by those changes here as well. We have also found that A/C power conditioning and filtering to be pretty tricky. Too much can cause as much of an issue as not enough. I've tried power cables with a high level of filtering of RFI and EMI plugged straight into the wall on a piece of gear and got fairly good results. But plugged into the balanced power supply it was too much and sucked the upper detail, spacial ques, and life right out of the music. But a power cable with much less filtering characteristics worked great with the balanced power supply...
...The unit proposed here is comprised by two sections – a DC Blocker/Trap/Filter and a Common Mode Filter (CMF).The DC trap section will remove or at least lower the toroidal transformer buzzing. Schematic is similar to this one used in well known Vladimir Shushurin’s Lamm-1 amplifier. An article with in-dept explanation of how DC blockers work can be found on Rod Elliot’s site ( http://sound.whsites.net/articles/xfmr-dc.htm ).The Common Mode Filter will deal with the high frequency pollution in the AC Mains Network. It was inspired by the very successful “Felix project” ( https://www.audiocircle.com/index.php?topic=25757.0 )
...Once installed, it took a few days for me to really begin to hear improvements, but now, a week in, those improvements have gone from subtle to transformative. The best word I can think of to describe the sound I'm getting now is "effortless". Any trace of stridency, boominess or glare that was present is gone. The sound is more clear, wide open and "fuller", with uncanny 3D depth and the deepest bass I've ever heard, low level details are floating in the air. These are exactly the kinds of improvements I had hoped good power conditioning could provide, but it's much more than I expected...
...The unit has following abilities:DC Blocker SectionIt is calculated to handle max. current of up to 16A– On the board are mounted 6 discrete high-power diodes 10A4 which yield the max. DC Blocking voltage of approx. 2 Vdc.– two MASSIVE 47,000 uF EPCOS capacitors (the bigger is capacitance, the higher are handled currents).– one 10W power resistor.– one bypass WIMA MKS4 400VAC capacitor.Common Mode Filter SectionIt is calculated to have a corner frequency of approx. 20 kHz and max. handled current of 20A with the parts used– 4 pcs. X2 type safety polypropylene capacitors– 2 pcs. Y2 type safety polypropylene capacitors– Triad Magnetics Common Mode Choke, rated at 20A– AC input/output connectors can be of the following types:– 3-pins terminal blocks with lead spacing 5 mm.NOTE: Some parts of the unit (DC Blocker’s electrolytic capacitors and diodes, Common Mode Choke, X2/Y2 capacitors, Input/Output terminals) can be replaced with another ones upon customer’s request, as it’s shown on the pictures.
Common Mode Filter SectionIt is calculated to have a corner frequency of approx. 20 kHz and max. handled current of 20A with the parts used– 4 pcs. X2 type safety polypropylene capacitors– 2 pcs. Y2 type safety polypropylene capacitors– Triad Magnetics Common Mode Choke, rated at 20AThe PCB is mounted in a steel enclosure with following characteristics:– Schurter IEC power inlet with fuse– Schneider AC Power outlet (Schuko, French, Euro-American, United Kingdom or Italian).– steel case black powder coated– 4 small rubber feet underneath the case.Dimensions of Combined module DC Blocker & EMI/RFI/CMF: 125x165x75 mm. (WxDxH).Weight: ~ 1.25 kg.
It retains most of the previous unit’s abilities but for the first time now the customer can chose a board with 6 discrete diodes which increases the ability for DC blocking up to 2 Vdc.DC Blocker is built with following parts:– MASSIVE 47 000 uF EPCOS capacitors (upgrade over the older 33000uF)– Six high-voltage diodes 10A4 (2V DC Blocking voltage) or one bridge rectifier (1.4V DC Blocking voltage)– 10W power resistor– WIMA MKS4 400VAC capacitor– MOLEX 3-terminal connectors for AC input/output– Schurter IEC power inlet with fuse– Schneider AC Power outlet (Schuko, French, Euro-American, United Kingdom) or IEC C14 outlets– steel case black powder coated– 4 small rubber feet underneath the case.
This has been (and will be) a long story that started back in the year 2008 when I started with intensive testing of various opamps concerning their susceptibility to electromagnetic fields in the air or from the inside of the instruments. Quite a long row of opamps was tested, including uA741, uA1458, LM358, OP97, TL071, TL072, AD829, AD844, AD797, AD825, LT1028, LT1122, OPA134, OPA2134, OPA627, OPA211, OPA827, LM6171, LM4562, LME49710, LME49720, NE5532. So they were both BJT and JFET input stage opamps, slow and fast, low supply current or standard supply current. Some of them performed very well and were almost unaffected by a “normal” lab or home environment EM field that surrounded the test PCB or box, some were performing “moderately” and some were performing very poorly, reacting to a slightest change of EM field in their vicinity, like changing their position on a test bench or approaching a hand or just a move of the air or of the body at a 1m distance.In general, JFET input opamps have had no problems and the behavior of BJT input opamps was very different, from excellent immunity to horrible sensitivity to a slightest change in their vicinity. As a conclusion, absolutely worst behavior was that of the LM4562/LME49710/LME49720 family, bought several times in the past 12 years, directly from the manufacturers or authorized distributors.No fakes, no cheap buys. Every time I published some of the results, it started strong reactions and dissatisfaction, especially of the people involved in audio production who have been using those parts that did not perform well...
As a conclusion, there was never a problem with JFET input opamps, there was never a problem with bipolar input opamps AD797, LT1028, AD844, there were slight issues with LM6171 and NE5532 and there were big issues, always, with the LM4562/LME497X0 family. This family of opamps is extremely sensitive to EM fields in their vicinity, mains frequency 50Hz triggers them during zero crossing and they send narrow spikes to their output, in 100ms distances and of amplitude that depends on shielding.This can be cured extremely well shielded box that shields not only against electric field component, but also against magnetic field component. The problem may remain hidden, sometimes it disappears with respect to momentary EM field conditions, but can be seen also for gains as low as -1 in the professional TI LME49720NABD evaluation board. The problem was observed by various soundcards and PCs in 2 independent measuring places and also by using analog and DSO scopes. It looks like a duck, it quack like a duck, so it would be a duck.
