High frequency noise.

Tweakers' Asylum

Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

In Reply to: Technically, what does the Hammond 193 choke filter? posted by pete1 on September 22, 2010 at 05:36:12:

The choke has some series resistance in the winding wire and some stray capacitance due to the winding wires being close together. This makes it a parallel L-C tank circuit with some losses due to the resistance.

Inductor impedance rises linearly with frequency, but the choke impedance will reach a maximum value at a frequency determined by the stray capacitance interacting with the choke inductance. Above that frequency the impedance becomes capacitive and will fall as the frequency continues to rise. See the Wikipedia article for a summary.

Connecting the choke to the AC line provides a resistive path for the radio frequency noise, since the capacitive impedance will be very low. This allows the noise to be dissipated and not simply reflected. The choke works primarily on the normal-mode noise (noise currents are balanced on hot and neutral AC wires) and not so much on the common-mode noise. Alan Maher's Circuit Breaker Filters work primarily on the common-mode noise, so it may be worthwhile sticking some CBFs on the chokes.

The chokes draw a small amount of current at the power frequency. This is why it is important to use chokes with inductance greater than 5 henrys for 120 volts and 10 henrys for 240 volts.

It is important to keep in mind that most AC tweaks for audio work by dissipating noise energy. Pure reactances (inductances and capacitances) cannot absorb energy and only reflect it. There are some expensive devices that use nothing but shunt capacitors, and I do not recommend these. They may decrease the noise level at one point by making it higher elsewhere.

Wikipedia article on L-C resonant circuits. (Open in New Window)

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Follow Ups Full Thread

Topic - Hammond Choke 193 Tweak Revisited - Are 2 Better Than 1? - pete1 21:49:19 09/20/10 (9)

Absolutely. I have 4 on the line, and improvement was clearly... - carcass93 12:54:47 09/21/10 (0)

RE: Hammond Choke 193 Tweak Revisited - Are 2 Better Than 1? - wushuliu 12:24:48 09/21/10 (0)

193D is too small. - Al Sekela 10:37:33 09/21/10 (6)

Technically, what does the Hammond 193 choke filter? - pete1 05:36:12 09/22/10 (4)

High frequency noise. - Al Sekela 12:50:06 09/22/10 (3)

RE: High frequency noise. - pete1 13:39:34 09/22/10 (2)

No. - Al Sekela 11:20:36 09/23/10 (1)

RE: No. - RayBan 13:54:11 09/24/10 (0)

Thanks... - pete1 21:54:55 09/21/10 (0)

Follow Ups

High frequency noise. - Al Sekela 12:50:06 09/22/10 (3)

RE: High frequency noise. - pete1 13:39:34 09/22/10 (2)

No. - Al Sekela 11:20:36 09/23/10 (1)

RE: No. - RayBan 13:54:11 09/24/10 (0)

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