I use a DIY power cord for my amp (two-prong), so it's a little different from the design initially posted, but the two wires are shielded and the shield is connected to 'Earth' at the mains. Chris Venhaus has some info for this design, except I didn't build it exactly as his design, I used shielded solid-core and twisted that (hard to do).
The original generic power cord is relegated to lying unused somewhere because the DIY one provides a larger frequency bandwidth, which we noticed more clearly in the extension of the bass area.
The DIY power cord is big and not very flexible.
The original generic power cord is relegated to lying unused somewhere because the DIY one provides a larger frequency bandwidth, which we noticed more clearly in the extension of the bass area.
The DIY power cord is big and not very flexible.
One thing you can be absolutely sure about: the apparent extension of the bass area (or any other larger frequency bandwidth) has absolutely nothing whatsoever to do with the presence of a mains cable shield. If the LF extension is real then this means that your amp PSU is somewhat lacking, but has had a small boost via lowering the cable resistance.
Power cords which are not very flexible may violate local electrical codes. If so, this may invalidate your home insurance.
Power cords which are not very flexible may violate local electrical codes. If so, this may invalidate your home insurance.
Local electrical codes around here have nothing to do with power cords. Safety lab test is required for some locations to comply with their insurance policies. But never heard of any issue in residential use.
Any shielded power cord will have more capacitance which will provide a reduction in high frequency line noise both going into a power amplifier and coming out from it. The power supply in an amplifier can actually put out line noise above 5 MHz. So this high a frequency of distortion could indeed be affected by added capacitance. How this affects your other equipment is one issue often ignored.
Any shielded power cord will have more capacitance which will provide a reduction in high frequency line noise both going into a power amplifier and coming out from it. The power supply in an amplifier can actually put out line noise above 5 MHz. So this high a frequency of distortion could indeed be affected by added capacitance. How this affects your other equipment is one issue often ignored.
“Rhodes is here, here is where you jump!”
Ask anyone who believes he can discriminate a big or small difference in the sonic performance of an amplifier who has been fitted with a Power Cord with braided Shield to accept a blind test with 5 exactly the same amplifiers but one of them is fitted with that special cable. The test consists of an audio switcher which has a common audio source input and a common pair of speakers. Switching between the amplifiers takes place instantly. I really doubt if anyone is capable to discriminate any difference!
Ask anyone who believes he can discriminate a big or small difference in the sonic performance of an amplifier who has been fitted with a Power Cord with braided Shield to accept a blind test with 5 exactly the same amplifiers but one of them is fitted with that special cable. The test consists of an audio switcher which has a common audio source input and a common pair of speakers. Switching between the amplifiers takes place instantly. I really doubt if anyone is capable to discriminate any difference!
There are two major coupling mechanisms, magnetic and capacitive (EM). The shield will not help with any magnetic coupling issues, but I would suspect it might be useful in attenuating the 'E' field provided it was grounded. For standard linear transformer audio applications I would not expect much benefit off the top of my head though.
I once did a 10 W SMPS running at 100kHz that sat about 10 mm from a front end signal conditioning circuit that took T/C and RTD inputs directly. The major noise problem I had to overcome was the noise and HF garbage being radiated from the mains cable and back to the input. Filtering to block noise going out on the mains cable and on the input solved the problem. The housing by the the way was completely plastic and the meter resolution 19 bits (16 bit dual slope A-D and a 3 bit gain ranging amplifier on the front end). Henry Ott, ground planes and some of the older experienced engineers helped me on that one.
I once did a 10 W SMPS running at 100kHz that sat about 10 mm from a front end signal conditioning circuit that took T/C and RTD inputs directly. The major noise problem I had to overcome was the noise and HF garbage being radiated from the mains cable and back to the input. Filtering to block noise going out on the mains cable and on the input solved the problem. The housing by the the way was completely plastic and the meter resolution 19 bits (16 bit dual slope A-D and a 3 bit gain ranging amplifier on the front end). Henry Ott, ground planes and some of the older experienced engineers helped me on that one.
The noise source is inside the amplifier! It is not line noise going into the power amplifier as much as it is amplifier power supply noise going back and into the other stages such as preamp and CD player.
A power line filter introduces extra loss. That is an issue with power amplifiers. Capacitance in the power cord adds no AC line loss.
Attached is a DC to 12 MHz. spectrum of power supply noise. The power source was a sinewave generator into a power supply. All of the noise comes from the linear power supply under test.
Also attached is the noise created just by a power transformer.
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With a typical inductance of a microhenry or so and a shield to conductor capacitance of 1.2 nF for a 2M shielded power cord you would have filtering in the cable from 2.5 MHz and up. It also is effectively a balanced pair for the noise calculation as the common or neutral or grounded conductor has more than enough inductance at those frequencies.
Now for filtering that should be done in the preamp circuits as the added AC power line loss is unimportant.
By using the power cord as a filter you do not add any additional resistance to the AC power line. A discrete inductor would also have some additional resistance. That would lower the surge current to a power amplifier. Using the "Free" inducance of the power cord avoids additional loss.
In a lower power device like a preamp the loss isn't important so a discrete filter is a better choice. But even then a filter power cord prevents higher frequency EMI from even making it into the case.
That's why the can type filters locate the filter OUTSIDE the Chassis.
But back to your "free" filter.
If the impedance of the cable is less than the impedance of the real filter then the filtering effect will be less.
If the "free" filter has no impedance, then there will be no attenuation.
Most PSUs aren't very well made when it comes to audiophile reproduction.
Which one precisely?
Ha, not that again, please. The difference is not even close to warrant a statistical analysis.
Indeed, I spend a lot of time researching, thinking about and investigating Electromagnetic Compatibility these days.
I have started building an AC Filter box, much like Jon Risch's original filter design, so it will be interesting to see what effect if any the DIY power cords do post-filter or even for powering the filtering or combinations thereof.
The more I investigate, the more this simple AC Filter box is becoming more of a full-fledged and customised AC Conditioner!
Some great results with only 3 filter lines already: very tall and large soundstage, and great separation of harmonies (e.g. separate people in backing vocals).
I think there's all that: noise coming in, noise coming out, it's quite complex, especially when it comes to EMI/RFI and ground plane noises with digital equipment.
I've looked into doing parallel filtering for the amp if necessary, or else removing it from the filter box altogether and let it use its own power outlet.
Interesting stuff, Simon, and may explain why some people still recommend a filter even with linear PSUs.
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