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Can't find the original instructions. Need to know if the resistor is needed and why. I will be using lots of capacitance. Thanks, Tweaker
Follow Ups:
http://www.AudioAsylum.com/audio/tweaks/messages/43988.html
http://www.AudioAsylum.com/audio/tweaks/messages/44145.html
Steve Eddy schematic (top picture)
my additional "tweak":
http://www.AudioAsylum.com/audio/tweaks/messages/47160.html
Huge thread at DIY Audio:
http://www.audiocircle.com/circles/viewtopic.php?t=18443
Note that use of a very large capacitor WILL cause some current loading, and thus, you can literally "use up" the capacity of the transformer with the loading from the cap due to the current it draws, unless the transformer has a very large load capacity, or you keep the capacitor size reasonable.
Note that several uF IS a very large capacitance relatively speaking, to be able to use without the typical penalty of leakage current that would normally go with that size of a cap,
Note that a more typical size for an across the line cap to avoid excessive leakage current (in excess of UL requirements, or to avoid tripping a GFI outlet) is 0.01 uF or less.
Jon Risch
Huge thread at DIY Audio:
Jon:
Thanks for the info. I'm getting a 404 error on the above link and, despite searching for an age, cannot find the thread for myself. Any chance you could check the link?
BTW, having put off trying a DIY isolator for years, this thread finally got me going. As a quick test with two 50VA toroids (w inter-winding screens) and 2uF in the middle was encouraging, I'd like to do a better quality build.
Dave
See:
http://www.audiocircle.com/index.php?topic=25757.0
and subsequent pages.
Note that the Felicia project turned my Super Quick & Dirty Digital filter into a balanced power system; this is NOT necessary, or even desirable if the rest of your system is not connected to balanced power.
I believe they had another project called Felix which was not balanced power tacked on.
I still disagree with the CMC approach to filtering, and find the Surge suppressor design and the SQ&D Digital Filter to be quite sufficient on systems that do not use balanced power.
Jon Risch
I still disagree with the CMC approach to filtering . . .
Many thanks for that. You're right - the thread does go on a bit.
Whatever, I'm now using two isolators assembled as per instructions using bits taken from the proverbial box under the bed, one driving the PSUs for the 1541A board in my DAC, the other driving its I/V stage (each drawing approx 8 watts, output voltage identical to input, seems not to waver).
Though I flatter myself I'd prior paid attention to mains quality (two dedicated lines, pro-audio filters and enough MSA leads to confuse an octopus), the prototypes have made a very noticeable difference to the sound.
All for free or freeabouts. Delighted.
Dave
Couldn't paste these formulas but .1uf is not even close the max capacitance that could (and should) be used in this circuit. 360uf is the aprox. capacitance that draws 15 amps from a 120VAC supply. Havn't done the numbers yet but at 1/30th of this would still be 1.2uf. Why doesn't one "need" to use X type safety caps on lower voltage circuit (24-28VAC). Any idea what type of resistor sounds the best( or very good) in this circuit?? Thanks, Tweaker
Tweaker456,
You need to READ my posts.
When I spoke of a 0.01 uF cap, it was with regard to the maximum leakage current that UL and other Safety Agencies will allow from the H to N or from H to G. A larger sized cap will exceed those limits, and thus would not conform to the Safety Agencies requirements. On a very practical note, a larger cap would very likely cause a modern GFI outlet to trip either all the time, or with maddening regularity whenever there were any "burps" on the line.
It has nothing to do with the maximum current draw of 15 amps, which, if you managed to achieve that much capacitive current loading, would leave no current left over for the electronic device you wish to run!
From a strictly regulatory and insurance standpoint, one MUST use an "X" grade capacitor across the full 120 VAC line, but then, through the transformer/s in my circuit, the cap is not directly across the full 120 VAC line anymore either.
In fact, at lower voltages, all kinds of things are allowed that won't pass muster on a direct connected 120 VAC line.
RE the resistor, all the usual requirements of a good quality audio grade resistor are present, with the added requirement that the resistor NOT choke off RFI, thus, a wirewound (such as a Mills, or the common cement bathtub resistors used in speaker crossovers) resistor is not a good choice.
Jon Risch
I'll have to look into the leadage current thing but I am of the notion that any amount of capacitance across an ac voltage is safe up to the amount of current that the circuit is rated for and that they are safety caps. My calculation for .5A @ 24VAC is 55uf. I have been using what I am told by the manufacturer are Type X caps for over a decade at the amount of 330uf with out ever tripping the 15A, 120VAC breaker. No one has ever told be if and or why large amounts of capacitance from hot to neutral is unsafe. The caps I use are lighting caps made for AC. Once again can you tell me why or is it safe to not use safety caps across 24-28VAC. I'm pretty sure one of your privious post stated one didn't need to use safety caps on the RS tranny (24VAC) Good info on the risistor. Thanks, Tweaker
Tweaker456,
Safety Agencies DO NOT allow any unlimited amount of capacitance to be placed either across the AC line (H-N), or from Hot to Grd.
Placing large amounts of capacitance at these locations can result in potentially fatal current flow through a consumer if they are grounded while touching electrical equipment chassis or input/output jacks.
As far as I can remember, the leakage current limit for UL in North America is 3.5 mA. That flow would be the result of ALL capacitance's within the equipment, including X and Y AC line caps.
Equipment used in Hospitals or other sensitive areas have even lower leakage current limits, somewhere around 0.3 mA.
Most North American GFI AC outlets trigger at a leakage current of 5 mA, thus, any current that exceeds that would trip the GFI breaker.
Note that it is standard procedure to deliberately reverse the H and N lines during the testing for leakage currents.
Is this a common knowledge kind of thing? NO.
But it IS mandated by UL/ETL/CSA etc., and thus most insurance companies will void your insurance if they find out you deliberately modified equipment that then exceeds this amount of leakage current, and this caused a fire, death or injury.
From a practical real world standpoint, unless there is a grievous fault condition in a modern piece of audio equipment, relatively large amounts of capacitance placed across the AC line are not LIKELY to involve a negative result, but there is no guarantee that this will be the case for all scenarios, thus the Safety Agency stance on the matter.
For more on what leakage currents are, see:
http://www.powerlines.com/pq2005paper.pdf
and
http://www.mddionline.com/article/leakage-current-standards-simplified
Obviously, you as an individual can do whatever he wants, you can defeat a circuit breaker or fuse, you can add hundreds of uF of capacitance across the line, just don't expect to be covered by your insurance if you do these things, or be able to successfully defend yourself in a court of law if someone ever gets hurt if they are involved with your modified audio equipment.
Jon Risch
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