Phase correct active cross over rev0


An active cross over circuit that reduces distortion, cost, critical components, and the effects of drift in component values.



Crossover designs.

Passive filtering.

Traditional high fidelity speaker systems typically included either a 2 or 3 way passive crossover circuit to split the amplifier output signal based on the frequencies the drivers are designed for. Passive cross over circuits can be expensive and introduces unwanted artefacts.

Active filtering.

Active cross overs involve filtering the signals at line level, and using a separate power amplifier for each of the drivers. Active cross overs are more stable, produce less distortion and are cheaper. However, they do require separate power amplifiers for each driver units. In the past, this held major cost implications, but as the cost of silicon keeps falling year after year, the argument against active cross over becomes less and less relevant with each passing year.


Traditional design drawbacks.

Total system frequency response.

A traditional crossover design filters the highs, lows and mids separately. This makes the tolerance and drift of the components critical, as matching these components affects total system frequency response.

Critical component matching.

The traditional crossover?s reliance on critically matched parts has a huge cost implication. As a passive crossover acts on the amplifiers output signal, the components have to be high current, high voltage, high accuracy, and very stable. In short, although a bad but cheap crossover can be build, a good passive cross over is usually quite expensive.

The Damping Factor.

The damping factor of modern amplifiers may be impressive, but passive crossovers can destroy it at certain frequencies. Around the crossover frequency, the series components in passive crossovers makes amplifier damping factor practically irrelevant as the series impedance increases towards the crossover frequency. Because of poor driver tracking, the result is increased distortion and ringing at these critical frequencies.


A new approach to active crossover design.

The active crossover circuit below does not require high voltage or high current components as it operates at line level. Importantly the circuit achieves a perfect flat total system frequency response, even with components that are neither high tolerance or highly stable. This is achieved by only having one filter circuit to filter one of the outputs, the other is being generated as the difference between the input and the filtered output signal.

This design provides good damping factor, by virtue of being active, providing a direct connection between power amplifier and driver. This ensures optimal driver tracking, reducing distortion.

The circuit is to be supplied a dual rail power supply and can be powered with anything from +5V -5V to +15V -15V.

A two driver configuration


In the 2 way design, only a high pass filter is used, the low pass is derived as the difference between the input and the high pass output signal. This automatically ensures a system with a flat frequency response, while eliminating of the need for expensive critically matched parts.

A three driver configuration


In the 3 way design, two non over lapping filters, a high pass, and a low pass are used. The bandpass mid range is derived as the difference between the input and the sum of both the high and low pass output signals. This automatically ensures a system with a perfectly flat frequency response while eliminating of the need for expensive critically matched parts.


RC Spreadsheet

Download the R C calculation spreadsheet here .


2 way Printed Circuit Boards


Part list

Designator Package Quantity Designation
R2,R3,R8,R9 Res_TH_0,25W 4 2k2
R4,R7 Res_TH_0,25W 2 6k8
P1 st_3_5.08 1 CONN_01X03
U1,U2 DIP-8__300 2 NE5532
D1 led3mm 1 Green
P3,P4,P5 st_2_5.08 3 CONN_01X02
C1,C3 C_Rect_L7.2mm_W3.5mm_P5.00mm_FKS2_FKP2_MKS2_MKP2 2 10nf
C7 C_Rect_L7.2mm_W5.5mm_P5.00mm_FKS2_FKP2_MKS2_MKP2 1 1uF
R11 Res_TH_0,25W 1 4k7
C5 npcap_thp_5mm 1 100nF
C6 C_Radial_D6.3_L11.2_P2.5 1 220uF35V
R12 Res_TH_0,25W 1 22k

Here are pictures of the different layers of the double sided sided through hole plated board.
silk.gif

top.gif

bottom.gif

Download

Here are PDFs for all of the layers.
2 way Silkscreen
2 way Top layer
2 way Bottom layer




3 way Printed Circuit Boards

Part list

Designator Package Quantity Designation
R6,R1Res_TH_0,25W 2 2k7
R2,R3,R5,R8,R9,R10 Res_TH_0,25W 6 2k2
R4,R7 Res_TH_0,25W 2 6k8
P1 st_3_5.08 1 CONN_01X03
U1,U2 DIP-8__300 2 NE5532
D1 led3mm 1 Green
P3,P4,P5,P2 st_2_5.08 4 CONN_01X02
C1,C3 C_Rect_L7.2mm_W3.5mm_P5.00mm_FKS2_FKP2_MKS2_MKP2 2 10nf
C7 C_Rect_L7.2mm_W5.5mm_P5.00mm_FKS2_FKP2_MKS2_MKP2 1 1uF
R11 Res_TH_0,25W 1 4k7
C5 npcap_thp_5mm 1 100nF
C6 C_Radial_D6.3_L11.2_P2.5 1 220uF 35V
R12 Res_TH_0,25W 1 22k
C2,C4 C_Rect_L7.2mm_W4.5mm_P5.00mm_FKS2_FKP2_MKS2_MKP2 2 220nF

Here are pictures of the different layers of the double sided sided through hole plated board.
silk.gif

top.gif

bottom.gif

Download

Here are PDFs for all of the layers.
3 way Silkscreen
3 way Top layer
3 way Bottom layer



Shop



2 way kits

A pair of 2 way PCBs
$20 (free shipping)
A pair of Unassembled 2 way Kits
$30 (free shipping)
A pair of Assembled 2 way boards
$40 (free shipping)



3 way kits

A pair of 3 way PCBs
$20 (free shipping)
A pair of Unassembled 3 way Kits
$31 (free shipping)
A pair of Assembled 3 way boards
$41 (free shipping)





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