Corcom EMI/RFI filters
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Grainger49
New member
I have used Corcom in the past but haven't used them with Bottlehead equipment.
Paul Joppa
Moderator
I'm looking into it for a future project. There is a great variety of models, and it's quite a pain to figure out what the differences are - I've downloaded far too many data sheets! Based on various notes from the late John "Buddha" Camille, who really knew a great deal about these things, you want decent attenuation down to basically as low a frequency as you can afford ... :^) ... I figure I'll know more in six months or so, once I digested some of the information I've been gathering.
mcandmar
New member
I haven't used Corcom specifically but have used other brands in various projects. From what i have seen the sizing of the choke is what really matters, the caps from live to neutral really only stop clicks and pops. i.e. if you hear noises turning lights on/off etc. I've also never really liked the concept of the caps between each phase and neutral as they inject voltage/current into the earth circuit. Interestingly "hospital grade" versions of these filters don't have those Y caps.
Its also worth reading the "Felix Filter" thread on Audio Circle, i built a similar filter using parts i salvaged from old computer ATX power supplies, it was a lot more effective than the prebuilt units at cleaning up noise from switching power supply's. In my case i have a bunch of cell phone chargers and various other wall bricks in the same room that all contribute to the noise, some to a hilarious degree. There is also the argument that all this noise is so far above what we can hear that's its irrelevant.
I look forward to your findings Paul, no better person to get to the bottom of all this..
Its also worth reading the "Felix Filter" thread on Audio Circle, i built a similar filter using parts i salvaged from old computer ATX power supplies, it was a lot more effective than the prebuilt units at cleaning up noise from switching power supply's. In my case i have a bunch of cell phone chargers and various other wall bricks in the same room that all contribute to the noise, some to a hilarious degree. There is also the argument that all this noise is so far above what we can hear that's its irrelevant.
I look forward to your findings Paul, no better person to get to the bottom of all this..
mcandmar
New member
Forgot about this, so how is the digestion coming along Paul 
I'm still experimenting with this myself, i only recently picked up a second hand Belkin PureAV. Its just a basic passive filter inside with a some common mode chokes, but with four separate channels so in theory its providing some isolation between devices. The reason i bought the unit was to have something sitting in front of my Bottlehead amps. I do plan to modify it (surprise surprise), and move my two felix filters into the same enclosure.
The voltage monitor is interesting, even back in the days of using opamp based headphone amps i always knew they sounded best from ~1am to 6am in the morning, now i can clearly see thats the only time of the day where i get 240v, from 6am to midnight my mains is down ~230v.
The PS audio powerplant is a very interesting device, from what i understand its basically a big amplifier than creates an AC signal to sit on top of the mains to correct the peaks, basically giving you a true sinusoidal sine wave again instead of the flat tops which is so common theses days due to switching supplies. I assume it voltage regulates too? Why any of that makes a difference to a device that converts AC to DC i don't know, but i like the theory
I'm still experimenting with this myself, i only recently picked up a second hand Belkin PureAV. Its just a basic passive filter inside with a some common mode chokes, but with four separate channels so in theory its providing some isolation between devices. The reason i bought the unit was to have something sitting in front of my Bottlehead amps. I do plan to modify it (surprise surprise), and move my two felix filters into the same enclosure.
The voltage monitor is interesting, even back in the days of using opamp based headphone amps i always knew they sounded best from ~1am to 6am in the morning, now i can clearly see thats the only time of the day where i get 240v, from 6am to midnight my mains is down ~230v.
The PS audio powerplant is a very interesting device, from what i understand its basically a big amplifier than creates an AC signal to sit on top of the mains to correct the peaks, basically giving you a true sinusoidal sine wave again instead of the flat tops which is so common theses days due to switching supplies. I assume it voltage regulates too? Why any of that makes a difference to a device that converts AC to DC i don't know, but i like the theory
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Paul Joppa
Moderator
I was doing this study for the long-delayed SR45. On balance, I chose the Corcom EC series, specifically the 3-amp version. The higher current ratings have less rejection below 1MHz so if I needed more than 3 amps I might go through the catalogs again.mcandmar said:Forgot about this, so how is the digestion coming along Paul
....
The late John "Buddha" Camille provided an extensive discussion in an old VALVE issue, under the title "Buddhafied Afterglow". Following those ideas, I am implementing a post-filter to get the attenuation down to a few kHz. Still no direct experience - I should probably put the whole assembly in a box for A-B comparisons.
So, no proven results but that's where it stands right now.
mcandmar
New member
Thanks Paul, i have a bunch of Valve issues achieved that were on the old website so i'll see can i find that article.
In case its of interest to you this is the choke used in the Felix filter http://www.coilcraft.com/pdfs/comoco.pdf , obviously you have to add the capacitors around it to complete the CLC circuit.
In case its of interest to you this is the choke used in the Felix filter http://www.coilcraft.com/pdfs/comoco.pdf , obviously you have to add the capacitors around it to complete the CLC circuit.
Buddafied Afterglow is in Volume 6, Numbers 3 & 4
I've been intending to use those components in front of a 5kVA transformer wire for balanced output.
I have a 1.5kVA transformer with balanced output in use in front of my BottleHead gear, but without any filtering. I have the advantage of being at the end of my power line with a step-down transformer for my house only. Even with my older amps and 95dB speakers, noise hasn't been a problem therefore my procrastination.
I'll be interested to see what changes, if any, that PJ makes.
Grainger, thanks for pointing out my mistake on the transformer ratings. One other point, for balanced power, the transformer rating should be at least twice what would be required for the load it will be supplying. You are using the transformers at half the designed voltage, so to be safe the max current rating of the transformer should be 4x the actual current draw. I hope this is clear.
I've been intending to use those components in front of a 5kVA transformer wire for balanced output.
I have a 1.5kVA transformer with balanced output in use in front of my BottleHead gear, but without any filtering. I have the advantage of being at the end of my power line with a step-down transformer for my house only. Even with my older amps and 95dB speakers, noise hasn't been a problem therefore my procrastination.
I'll be interested to see what changes, if any, that PJ makes.
Grainger, thanks for pointing out my mistake on the transformer ratings. One other point, for balanced power, the transformer rating should be at least twice what would be required for the load it will be supplying. You are using the transformers at half the designed voltage, so to be safe the max current rating of the transformer should be 4x the actual current draw. I hope this is clear.
mcandmar said:
Well those are two routes I've been looking at myself... Belkin PF60 or building a few of the Felix filters. I was thinking of just going cheap a simple with a couple of the Tripplite Isobars, but something about those things doesn't sit well with me. Perhaps they are just not audiophile approved enough for me
Oh, and yes, the PS Audio Powerplants do voltage regulation, it's one of their key features.The PF60 has six separate filters, one for each of the six duplex outlets, and one is a high-current filter so it would meet all my needs. Also has trigger/delay capabilities which is a plus and you can get them for $200 through Belkin. Seems like a lot of features packed in for that price, which makes me wonder where are they skimping.
johnsonad said:
I had forgotten all about the Hammond Choke Tweak. Thought about doing it years ago but never got around to actually ordering one. Didn't think it was necessary with my PS Audio Powerplant Premiere in the mix. After years of reliable use the powerplant went bad on me so I got it repaired and then sold it off since I could cover the repair and still pocket enough to play around with some other options. I may end up regretting it, but that's all part of the journey.
I'm thinking of several different options right now.
- Off-the-shelf EMI/RFI filter boxes (like those from Corcom or others) wired to separate outlets in a DIY power strip/distribution box
- Felix filters instead of he off-the-shelf boxes (think it will probably give me better filtering at lower frequencies)
- Hammond 193 Choke Tweak - probably do this regardless as it is not exclusive of those other approaches
- Belkin PF60 - well that's the easiest with the most ready-to-go features and flexibility, but where's the fun in that?
mcandmar said:
For the same reasons that the coil of wire that makes up the primary of a power transformer also doesn't appear as a short to an AC line supply. (The choke can be considered a power transformer with one winding, and an airgap)
mcandmar
New member
krikor said:Well those are two routes I've been looking at myself... Belkin PF60 or building a few of the Felix filters. I was thinking of just going cheap a simple with a couple of the Tripplite Isobars, but something about those things doesn't sit well with me. Perhaps they are just not audiophile approved enough for me
The PF60 has six separate filters, one for each of the six duplex outlets, and one is a high-current filter so it would meet all my needs. Also has trigger/delay capabilities which is a plus and you can get them for $200 through Belkin. Seems like a lot of features packed in for that price, which makes me wonder where are they skimping.
The unit i got is the PF40 which is the four channel version, if you look at the internal pic i posted, the far right channel is the "digital" section with two chokes, the two channels in the middle are identical (audio&video) except for the left one is switched, and the far left channel is also switched and only has two caps and a ferrite bead, thats the "high current" output.
The two switched channels can be turned on/off with the power button on the front, or you can feed it an AC or DC signal in the back to trigger them. The delay function is a set time, once triggered it waits 3-4 seconds before turning on those two channels.
The far left board has a metric crap ton of MOV's to withstand a lightning bolt from the hand of god, and the rest of the board is a mystery to me. All i can make out is the transformer runs a positive and negative 12v regular to feed a quad channel opamp, what its doing i have no idea. Apart from the simple remote trigger logic, the front panel displays voltage & current, and that's about it. Its a nicely made unit but there is nothing clever or "expensive" inside the unit, i would say the bulk of the cost is the pretty enclosure. The reason i liked it was up until now i was making separate units for different equipment, at least now i can have it all inside the one box, and with the PF40 there is plenty of room inside the case as it has two less channels than the PF60. For example there would be plenty of room to mount a Hammond 193 in there connected to a few outlets.
Caucasian Blackplate said:
That makes perfect sense now you say it. Though that does starts to blur the lines for me on the differences between a choke and auto former, apart from the take off taps aren't they essentially the same thing being a single winding? Reason i ask is i have a huge 1300watt autoformer here.
Grainger49
New member
mcandmar said:
I can see why this is perplexing. I mean, it looks just like a short, doesn't it? But it isn't.
The difference between the terms resistance and impedance is frequency. DC has no frequency, it never cycles. So when you measure with a meter it measures [DC] resistance. But impedance has a resistive component and a reactive component. That reactive component changes with frequency. So at 60 Hz the impedance of a choke is much higher than just the resistance of the windings.
mcandmar
New member
Excellent explanation, thank you Grainger.
So if i understand this right, as the frequency goes up the impedance goes down, therefore the choke looks like a low impedance path at higher frequencys. So on an AC line its effectually just providing a bypass for the HF keeping them away from other devices on the line?
So if i understand this right, as the frequency goes up the impedance goes down, therefore the choke looks like a low impedance path at higher frequencys. So on an AC line its effectually just providing a bypass for the HF keeping them away from other devices on the line?
Grainger49
New member
Not quite...
Even though 60 Hz is a low frequency, as the frequency goes up the impedance of an inductor goes up. So at very high frequencies it is a brick wall. This is why they are great in a power supply. They will not pass high frequency pulses or high frequency dips. Variable speed drives in industry notch the power line when they turn on.
Thinking back to older cars, a choke (coil in your ignition) resists changes in current through it. In an ignition system the coil "charges" from the 12V battery when the points close. When the points open the coil kicks 10,000 volts to the spark plug.
In a power supply a choke suppresses voltage spikes and fills in notches.
In a crossover a series choke passes low frequencies and a parallel choke shunts low frequencies.
In crossovers capacitors do the opposite. A series cap passes highs and a parallel cap shunts highs.
Even though 60 Hz is a low frequency, as the frequency goes up the impedance of an inductor goes up. So at very high frequencies it is a brick wall. This is why they are great in a power supply. They will not pass high frequency pulses or high frequency dips. Variable speed drives in industry notch the power line when they turn on.
Thinking back to older cars, a choke (coil in your ignition) resists changes in current through it. In an ignition system the coil "charges" from the 12V battery when the points close. When the points open the coil kicks 10,000 volts to the spark plug.
In a power supply a choke suppresses voltage spikes and fills in notches.
In a crossover a series choke passes low frequencies and a parallel choke shunts low frequencies.
In crossovers capacitors do the opposite. A series cap passes highs and a parallel cap shunts highs.
mcandmar
New member
That much i can follow, series wired in DC supplies, crossover theory, and especially car ignition coils as i have been on the receiving end a few times. I still don't really understand what it does across an AC line as it would be parallel to the load, i.e. a power transformer.
To add a little more the formula for inductive reactance is:
RL= 2(Pi)FL
RL=inductive reactance
Pi=3.1417
F= frequency in cycles/sec
L= inductance in Henries
So you can see inductive reactance goes up as the frequency goes up or if the inductance goes up, therefore more resistance to a particular frequency.
Capacitance reactance works inversely:
RC=1 divided by 2(Pi)FC
RC= reactive capacitance
C=capacitance in farads
Reactive capacitance decreases as frequency increases or capacitance increases.
I apologize for the awkward way I wrote the formulas. I know something of AC power because I worked in a power plant for my career and learned now Rl and Rc affected the main generator. I still have not mastered computer symbols.
RL= 2(Pi)FL
RL=inductive reactance
Pi=3.1417
F= frequency in cycles/sec
L= inductance in Henries
So you can see inductive reactance goes up as the frequency goes up or if the inductance goes up, therefore more resistance to a particular frequency.
Capacitance reactance works inversely:
RC=1 divided by 2(Pi)FC
RC= reactive capacitance
C=capacitance in farads
Reactive capacitance decreases as frequency increases or capacitance increases.
I apologize for the awkward way I wrote the formulas. I know something of AC power because I worked in a power plant for my career and learned now Rl and Rc affected the main generator. I still have not mastered computer symbols.
