• on Audio/Video/Photography
  • Published in issue 11/2004 on page 0
About the article

Noise Suppression

For ClariTy and other final amps

Noise Suppression
In the three-part article for the ClariTy 2 x 300-W final amplifier, the various input and output filters were not described. In this article we remedy that situation. The circuits described here can also give excellent results when used with other designs. Extremely high currents at relatively high frequencies are present in amplifiers such as our ClariTy design (Elektor Electronics June, September, October 2004). In such situations it is recommended to take measures to suppress interference signals (electromagnetic interference, or EMI for short). This can be done by using additional filters for all connections to the outside world. For an amplifier, three different types of filters are necessary. They are respectively used for the loudspeaker connections, the signal inputs and the 230-V mains connection.
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Products
Resistors:
R1,R2 = 470kOhm
R3,R4 = Varistor 275V (Epcos SIOV-S20K275, Farnell # 580-284)
Capacitors:
C1,C2,C3,C6 = 390pF
C4,C5,C7,C8 = 100pF
C9,C10,C13,C14 = 1nF 400V, lead pitch 5mm or 7.5 mm
C11,C12,C15,C16 = 10nF 400V, lead pitch 5mm or 7.5 mm
C17,C18 = 10nF 275 VAC, Class X2, lead pitch 15mm
C19,C20 = 100nF 275 VAC, Class X2, lead pitch 15mm
Inductors:
L1,L2 = 2 x 1 turn (bifilar) 0.5mm dia. (SWG26) enamelled coppper wire on Ferroxcube core TL10/6/4-3E5 (Farnell # 305-6960)
L3,L4 = 2 x 18 turns (bifilar) 1.5mm dia. (SWG16) enamelled coppper wire on Ferroxcube core TX36/23/15-3E25 (Farnell # 305-7021)
L5 = 2 x 16 turns 1.5mm dia. (SWG16) enamelled coppper wire on core TN36/23/15-3E5 (Farnell # 305-7010)
Miscellaneous:
K1,K2 = PCB mount cinch socket (T-709G from Monacor/Monarch)
K3 = 3-way PCB terminal block, lead pitch 7.5mm
K4 = 2- way PCB terminal block, lead pitch 7.5mm
8 x spade terminl (fast-on), PCB mount, 3mm screw mounting
PCB, order code 030217-1
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