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Dear Jon,On November 2001, you posted a thread with the topic "Latest Tweak to Digital AC Line ISO Trans Filter".
http://db.audioasylum.com/cgi/m.mpl?forum=tweaks&n=47160&highlight=Latest+Tweak+to+Digital+AC+Line+ISO+Trans+Filter&r=&session=
In this thread you recommended "to add a 220-270 Ohm 10W wire wound resistor across the secondaries along with the cap/caps to reduce any tendency for the caps and transformer windings to want to resonate". This resistor value is suitable only for the 25VAC transformer from RS that proposed by you.
I am now using your isolation transformer filter with transformers having primary voltage of 220VAC and secondary voltage of 110VAC. Would you please advise what value and power rating of the resistor that I should use to reduce the resonate of the transformer windings ?
Thanks in advance for your help.
Follow Ups:
One of the idea's behind my Digital AC Iso Filter was to get the intermediary voltage down low enough to use caps that are not AC line rated, as well as larger value caps, and not incur a lot of AC line leakage currents, this also allowed the use of a relatively "small" value damping resistor, because the current through it would be low as well for a given value.In your implementation, the voltage step-down is not that much, even if you are using it on a 120VAC input. I have to assume that you may be using it with a 220V inoutm, and that the secondaries are operaring at 120VAC. Thus, in order to keep dissipation down below 10W ( a common and handy resistor wattage size), the value would have to be 1.47 kohms or larger. I would recommend that the value be more like 2.2 kohms to 2.7 kohms, as this allows some safety margin (many resistors will not run at full rated power indefinitely, even at room temperature).
Jon Risch
Dear Jon,Thanks for your quick reply.
You are right that I am using a transformer with a 220V input and that the secondary is operating at 110VAC. I use a higher secondary voltage in order to minimize the drop of the voltage at the outlet of the isolation transformer.
I will try the value of resistor that suggested by you.
Jon: I have my digital equipment on one of your line filters and the rest on two others. Should I use this back to back transformer in combination with the other line treatment?
thanks
Les
Les,The Digital AC Iso Filter was designed to address digital components specificaly, and to address other issues, such as excessive leakage currents when using large caps across the line.
While the original RS transformers are no longer available, othrs of a similar voltage and rating can be used. I would recommend trying to keep the secondary voltage down, and to use a high enough current rating (e.g., 24VAC at 2.5 amps or better, etc.) so as to be able to power most any digital component. The amount of isolation achieved is related to how much capacitance is present across the line, as well as the exact nature of the transformer, for example, toroids ARE NOT recommended, they couple too well, regular E-I core transformers are the best for this kind of application.
Any way, yes, you can use these in conjunction with my AC Line Filter & SS circuit, but I would recommend that they only be used on digital components, due to the In and Out isolation they provide, and the limited power capacity inherent to dropping the voltage down and back up.
Other folks have used higher voltage secondaries, such as diyaudiophile, but these have the disadvantage of requiring full AC line rated caps, and the use of larger resistor values to damp the secondaries, this result is less damping.
For the original info on these:
http://www.AudioAsylum.com/audio/tweaks/messages/43988.htmlhttp://www.AudioAsylum.com/audio/tweaks/messages/44145.html
Steve Eddy schematic (top picture)my additional "tweak":
http://www.AudioAsylum.com/audio/tweaks/messages/47160.htmlHuge thread at DIY AUdio:
http://www.audiocircle.com/circles/viewtopic.php?t=18443
Jon Risch
Thanks Jon. Just what I needed.
regards.
Les
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