NOTE:  THE AUTHOR SHALL NOT BE HELD RESPONSIBLE IN ANY WAY FOR THE
USE OF THE INFORMATIONAL CONTENT OF THIS ARTICLE, OR DAMAGES OR
INJURIES ARISING FROM THE USE OF SAID CONTENT.  THE AUTHOR URGES
ALL POSSIBLE SAFETY PRACTICES AND THAT GOOD CONSTRUCTION TECHNIQUE
BE USED SHOULD THE READER DECIDE TO CONSTRUCT A DEVICE FROM THE
INFORMATION CONTAINED HEREIN.  CONSULT YOUR LOCAL LIBRARY FOR
INFORMATION ON AC LINE SAFETY PRACTICES, AND GOOD ELECTRICAL
CONSTRUCTION TECHNIQUE.

Schematic Key
  ______ = wire connection

  o = junction where wires or leads are connected/soldered together

  ) = wire connection skipping over another wire, no junction

  H = Hot AC line, the smaller of the two rectangular outlet holes

  G = Ground, the "U" shaped hole on the AC outlet

  N = Neutral, the larger of the two rectangular outlet holes

AC Line Filter Schematic

IN                                OUT

H________o___o___L1____o________H
         |   |         |
        C1  C3         C4
         |   |         |
G________o___)_________)________G
         |   |         |
        C2   |         |
         |   |         |
N________o___o___L2____o________N

AC Surge Suppressor and Filter Schematic

IN                                OUT

H__B1_o___o___o___L1__o___o______H
      |   |   |       |   |
     V1  C1  C3      V2  C4
      |   |   |       |   |
G_____)___o___)_______)___)______G
      |   |   |       |   |
      |  C2   |       |   |
      |   |   |       |   |
N_____o___o___o___L2__o___o______N

For AC Surge Suppressor and Filter Schematic
B1 = Circuit breaker, 5, 10 or 15 amps as appropriate, thermal type.
V1,2 = Harris Metal Oxide Varistor 150 VAC rated
C1,2,3 = 0.047 uF 250 VAC metallized polyester AC line rated for
continuous use across the line, which is designated as "X" type caps.
C4 = 0.01 uF 250 VAC metallized polyester AC line rated cap as above.
L1, L2 = 50 to 100 uH powdered iron rod core inductor with DCR less
than 0.03 ohms.

-Capacitors-
These are metallized polyester AC line rated capacitors, rated for
continuous use across the AC line, UL and other safety agency listed.
For any capacitor placed across the AC line, I recommend use of
fully rated AC line parts, which are designated as an "X" type.
They are 250 VAC rated, and can be used with European voltages as
well as for US lines.

Mallory Series 158X 158X473  0.047 uF, Allied part #852-0484  $.59
Mallory Series 158X 158X104  0.10 uF, Allied Part #852-0475  $.62
Mallory Series 158X 158X103  0.01 uF, Allied part #852-0474  $.56
Roderstein 0.1 uF type F1772410-2000, Newark Part #95K9070 $1.70

Other parts that are "X" rated that can be used:
RIFA brand, part #PME265MA447 0.047 uF (these are my preference)
RIFA brand, part #PME265ME610 0.10 uF

Siemens MKP series part #B81128-C-B145 0.01

I do not recommend the use of ceramic capacitors for audio grade
filters and suppressors.  The above listed parts are all
low-inductance metalized polyester types.

-Inductors-
Preferred units:  these are 50 uH 15 amp powdered iron or ferrite
core inductors with very low DCR.
Dale #8401, J.W. Miller #5524, and Renco RL-2226-15-50.  Even
though these are all rated at 15 amps DC, these particular models
were tested by UL for AC use when selected for use in a commercial
surge suppressor, so I know they can handle it.  Unfortunately, I
have been unable to find a ready source for these.

Other parts in the series, such as the J.W.Miller #5520, a 100 uH,
10 amp part would be useful.  Available from Allied, #871-7015 for
$6.71 each.  These can handle up to 7 amps AC continuous for a 40
degree C temperature rise, and 10 amps AC for a 60 degree C temp.
rise.  I would recommend not using them for a total equipment load
beyond approx. 5 amps (600 watts) to maintain linearity and a safety
margin.  For power amps, two can be used in parallel for a total
safe margin AC current draw of 10 amps, 14 amps recommended maximum.

To build a filter or suppressor for an entire system, I would
recommend building separate units for the lower power components,
and a separate unit with paralleled inductors for each power amp.

Other inductors can be used, but the two most significant features
are: very low DCR, preferrably below 0.03 ohms for 10-15 amps
current draw, and below .06 ohms for 5-7 amps.  The second is the
proper form factor and core, in this case a powdered iron or
ferrite rod core, not a torroid or bobbin style.  The inductor
must also have sufficient AC current capacity for the total load,
plus a safety margin.

When paralleling inductors, use one's leads for the circuit hookup,
and use the others to stand the second inductor as far away as
possible, by making a little hook in the end of the leads, and
using that to make the connection to the other inductor.  Keep
inductors away from any steel or conductive parts to minimize
inductor distortion.

Alternate sources for inductors:
Marlin P. Jones Assoc. 1-800-652-6733   Surplus parts outfit.
part# 9117-CH, Dale  7 amp 150 uH powdered iron core inductor,
$1.25 each.  Use in parallel for a total AC current capacity of
10 amps maximum AC current draw, 7 amps (860 watts) recommended
maximum loading.

-Varistors-
For US AC lines :Harris V150LA20A,B or C   from $.78 to $1.02

This is a 150 VAC rated part, capable of over 80 joules of transient
energy absorption, and peak currents over 6500 amps.  The maximum
rated clamping voltage is 390V vs. 340V for a 130VAC rated part.
This is a minor difference, and the higher voltage point keeps the
MOV from conducting regularly on high line peak voltages, avoiding
the worst of the wearout mechanism that MOV's are prone to, and
preventing the degradation of the sound.

For 240 VAC use, I recommend the V275LA40A,B or C from $.97 to $1.85
which is capable of over 140 joules of transient energy absorption,
and peak currents over 6500 amps.  Maximum rated clamping voltage is
710 volts @ 100 amps.

Both are available from Allied or Newark, and the manufacturers part
# is also the stock number.

Siemens and Panasonic also make excellent and reliable varistors,
but beware other brands!  There are many cheap and unreliable MOV's
being offered, that can barely take rated surges once!  The Harris
and other two recommended brands can take repeated overloads and
abuse and still keep functioning.  MOV's generally either fail by
permanently short circuiting or exploding!  In severe overload tests,
some brands other than GE/Harris, Siemens or Panasonic tended to explode.
Once a MOV fails in the short circuit mode, the circuit breaker will
trip, and will not reset.  This indicates the need for replacement
of the device.

-Circuit Breakers-
I recommend the use of a Potter & Brumfield W28 series thermal
circuit breaker over that of a fuse.  Less total resistance at
high current draws, and the ability to be reset after a surge.
The W28 series is compact and fits in the same hole as a panel
mount fuse holder.  Available from Newark, see list below.
5 amps, Newark part#75F010 type W28XQ1A-5  $1.69
10 amps, Newark part#75F013 type W28XQ1A-5  $1.69
15 amps, Newark part#75F015 type W28XQ1A-5  $1.69
Rated trip current depends on type of coil used for L1 & L2.

Other thermal circuit breakers can be used, such as the P&B W23,
W31 and W58 series.

The Eaton KD-1 thermal circuit breaker is also suitable,
5 amps, Newark part#29F1605, type KD1-5  $6.17
10 amps, Newark part#29F1610, type KD1-10  $6.17
15 amps, Newark part#29F1611, type KD1-15  $6.17

Schurter TS-710 series is similar in form factor to the P&B W28,
and the Schurter T11 series is suitable.

-Line cords and outlets-
For the line cord, I recommend
Belden #17616 (6 ft) Allied part #214-3616  $8.04
Newark #37F3295 $9.37
Belden #17617 (10 ft) Allied part #214-3616  $11.44
Newark #37F3296 $13.22
These would be captive permanent 14 gauge Beldfoil shielded cords,
which minimize contacts in the circuit.

If you want to experiment with various AC cords, then use an IEC
connector for the input.  Belden #17267A is a 15 amp, 250VAC rated
IEC connector, Newark #37F3023  $2.13
An IEC connector that makes a better connection is:
Inalways from Mouser

IEC Connector for the cord:
Schurter 4300.0603 available from Allied Electronics, Allied PN 509-1215

Alternate source for HD line cord:
Marlin P. Jones Assoc. 1-800-652-6733   Surplus parts outfit.
Part#8323-WI, a 3 foot 14 gauge, 3-wire AC line cord, unshielded,
$2.95

Use Pass & Seymour 5242-I wall outlets OR BETTER for best results.
There is the equivalent AC cord plug, too in that brand, wall plug
Pass & Seymour 5266-X .hospital or industrial/heavy duty
AC outlets for the sockets, these are available from your local
hardware stores.

-Enclosure & Wiring Details-
I recommend a sturdy metal enclosure, with lots of space inside,
and the use of fiberglass circuit board/perfboard to wire
everything up.  Keep in mind that the metal enclosure should have
space between it and electrical components of at least an inch,
and that the coils can have up to a 40 degree C temperature rise
above ambient.  They should be mounted so that they are stood off
the board by their full lead length, and wiring brought to these
lead tips.

The input varistor needs to be wired in as soon as the cord is
terminated on the board, and the loop area kept small.  Don't be
tempted to use a wide open layout until past the input MOV, and
keep the coils physically seperated by a decent amount of distance.

If a power ON/OFF switch is desired, use a heavy duty one rated for
at least 15 amps, and 240VAC.  Indicators such as LED's and
especially neon indicators are not recommended.  If a power ON
indicator is absolutely needed, socket in a 7 watt night light bulb
on the output side.  Not only will this be a benign indicator, it
will actually help damp the output of the filter a little.  Ideally,
a 100 watt bulb will be connected across the output at all times to
load and damp the circuit, but I do not recommend placing such
wattage inside the metal box.  A load resistor of suitable wattage
and resistance can be used, remember that most of these require
heatsinking for such power dissipation levels.  Appropriate values
are 120 ohms at 150 watts or 150 ohms at 100 watts or higher.  This
size of resistor is not cheap, and the 100 W light bulb/lamp in a
lamp fixture is a much more economical method of achieving the loading.

Nationwide Parts Distributors:
Allied 1-800-433-5700 or http://www.allied.avnet.com
Newark 1-312-784-5100 for local phone numbers, or see the web site at:
http://www.newark.com for local info, etc.

All applicable copyright laws apply, all rights reserved, except transmission by USENET and like facilities granted.  Any use or inclusion in print or other media are specifically prohibited.  The informational content is not warrantied in any way or form, and any use of said content are at the reader's own risk, the author shall not be held responsible in any way for any damages or injuries arising from the content of this web site.  Common safety practices are encouraged at all times.  Do not fold, spindle or mutilate.

 ----> E-MAIL ME ! <-----