30 W Amplifier for Subwoofer

 

 

This is a subwoofer amplifier, made for a HIFI.
It is associated with two amplifiers in satellites.
The power output is 30 W effective in this case

 

Rapid analysis of the scheme:

The power supply produces a voltage symmetrical 25 V - 25 V. Feeding adder and filter is a voltage of 12 V symmetrical, - 12 V. The summation (U2: A) adds the signals from the left and right channels. The R11 can be adjusted to balance the sound level between the subwoofer and satellites.
The filter (U2: B) can pass only the frequencies basses.L amplifier (U1) provides power to suvwoofer.

Schema of the amplifier for subwoofer

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Subwoofer amplifier

Summing

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Artwork

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plot plan components

The settlement pattern is rpésenté side traditional components.

Nomenclature: Resistance Adjustable Capacitor Integrated circuit Diode Self Transformer Pimples Spacer x 3

R1, R2, R4 R3, R12 R5, R6 R7, R8 R9, R10 R11 C1, C2 C3, C5, C6, C14, C15 C4 C7 C8, C9, C13 C10 C11 C12 C16, C17 U1 U2 U3 U4 D1 L3 TR1 X1, X2, X6 X5, X0P X14, X15, X16 XF, X4 -

47 k - SMD 1206 4.7 - SMD 2512 39.2 k - 1% (or 47 k - 5%) 20 k 4.7 k 47 k - 20 laps 2200 uF / 35 V 100 nF - SMD 1206 100 pF - 1206 SMD 220 nF - SMD 1206 330 nF 47 pF 150 nF 15 nF 4.7 uF - 16V Tantalum LM12 DO 5532 with support 8-pin DIL 78L12 - TO92 Case 79L12 - TO92 Case A bridge 3 - 80 V (Fagor) 22 uH - Air 230 V - 2 x 18 V Secondary transformer Subwoofer Inputs Output Filter, Ground for tilt M3 x 16 + screws for fixing

Manufacturing:

After drilling the circuit, start with soldering the CMS. The positioning of these components is facilitated by over-sized pellets. Create a solder bridge in place of the strap located beneath the pin X6
(See layout diagram). Component side, solder the two straps.
Then solder the side preamplifier
The variable resistor R11 is provided for two different locations.
One can notice the spike "speaker output" with its location at 5.08 mm.
The photo below shows the parties and filter before summing wiring U1.

Each pin of the LM12 is protected by the shrink tubing on the thickness of the radiator. The LM12 is coated with thermal grease to improve heat transmission to the radiator.

The LM12 is mounted on the radiator.
Two slices of 3 mm will be inserted between the printed circuit and the radiator (increased area of ​​contact with air).

The assembly is fixed on the circuit board using two M3 nuts.
The nut, left side of the photo-cons and the screws are brass.
To improve the electrical contact between the negative power supply and the case of LM12, the nut is welded to the copper face.

For those who can not procure resistance of 4.7 ohms CMS, you can solder two resistors traditional flat copper side. On the photo against is a 2.2 ohm resistor is located.
The choke L3 is soldered copper side. It is isolated from the circuit with an insulation TO220 case, then glued to avoid vibration.
The last component can be soldered on the circuit.
For those who have the keen eyesight, some photos from a version of an amplifier different version.

Detailed analysis of the scheme:

The summation:

The structure is built around a NE5532 for its low noise. We can use a TL082 instead.
It's a classic summation inverter. The right lane is connected to X14, the X15 in the left lane (or vice versa).
With R5 = R6 = R, the expression of the output voltage is V OUT = - [(V + V X14 X15) x (R7 + R11)] / R
Cells and R5/C8 R6/C9 form a high pass filter with a cutoff frequency of 12 Hz at -3 dB.
The capacitor C10 improves overall stability and avoids collisions.
The variable resistor adjusts the gain of the structure. Its role will be explained later.

Filter:

It is a low pass filter of second order.
Its cutoff frequency is 144 Hz - 3dB.
Its role is to pass only low frequencies to attack the subwoofer.
Notes on component values:
C11 and C12 are wired in parallel. There are an equivalent capacitor C11 + C12 = ceques
C eq = 150 + 15 = 165 nF and hence C13 = 330 nF = 2 x C eq
R9 = R10

If you want to change the cutoff frequency of the filter, the simplest solution is to change the values ​​of the resistors.
R = R9 = R10

The amplifier is a monolithic circuit, the LM12.
The structure is a non-inverting amplifier whose amplification factor is
Av = 1 + (R1 / R2) = 2 in this case.
I use this amp for hi-fi, it is never pushed beyond 10 W.
To increase the amplification factor, increase R1.
The structure C7 / R4 is a low pass filter cutoff frequency 15 Hz - 3 dB.
The resistance R4 eliminates the offset voltage output.
Its ideal value should be the result R1 in parallel with R2.
In practice, a value of 47 k gives the best result.
The capacitor C4 limit the bandwidth of the amplifier to 33 kHz.
This value can be increased, the amplifier working on very low frequencies.
Cell R3 / C5 allows the amplifier to "see" a minimum load for high frequencies, the speaker is a highly inductive load in this area.
Cell L3 / R12 protects the amplifier against capacitive loads, if any,
(Length of connecting cable ...). R12 torpedo the quality factor of L3.
The clamping diodes have not been established, the amplifier working at low frequencies, the risk of high power output is virtually zero.

Settings:

The setup is classic. The subwoofer is central, the two satellites placed as two stereo speakers.
I placed a microphone with an oscilloscope on the spot instead of listening. The amplifiers of the housing and satellites are attacked by a generator BF.
Setting range:
The AF generator is set for a sinusoidal frequency of 2 kHz. Only the satellite speakers are concerned.
There are, then the amplitude of the signal coming out of the microphone to the oscilloscope.
The AF generator is set to obtain a frequency of 50 Hz sinusoidal (amplitude remains constant). Only the subwoofer is concerned.
R11 must be set to obtain the same amplitude of the signal to the oscilloscope as before.
The frequency response of all box / satellite is then linearized.
Setting the stage:
It sets the AF generator for a sinusoidal frequency of 144 Hz, the filter cutoff frequency (the amplitude remains constant).
One reverses the polarity of the subwoofer by examining the wave amplitude on the oscilloscope. It holds the wiring provides the highest amplitude.
Moving the subwoofer back and forth to get the maximum amplitude at the oscilloscope.
The phasing of the housing and satellites is complete.