100W Subwoofer Amplifier Circuit

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100W Subwoofer Amplifier Circuit
100W Subwoofer Amplifier Circuit

Subwoofer Amplifier Circuit Design

Audio Filter Design:
Here we designed a Sallen Key low pass filter using OPAMP LM7332. The cut off frequency was assumed to be 200Hz and the Quality factor is assumed to be 0.707.  Also assuming the number of poles to be equal to 1 and value of C1 to be equal to 0.1uF, value of C2 can be calculated to be 0.1uF.  Assuming R1 and R2 to be same, the value can be found by substituting known values in the equation
R1 = R2 = Q/(2*pi*fc*C2)
This gives a value of 5.6K for each resistor. Here we select 6K resistors as R1 and R2. Since we want a closed loop gain filter, we do not require resistors at the non inverting terminal, which is shorted to the output terminal.
Pre Amplifier Design:
The preamplifier is based on class A operation of transistor 2N222A.  Since the required output power is 100W and load resistor is 4 Ohms, here we require a supply voltage of 30V.
 Assuming the collector quiescent current to be 1mA and collector quiescent voltage to be half of supply voltage, i.e.15V, the value of load resistor is calculated to be equal to 15K.
R5 = (Vcc/2Icq)
Base current is given by, Ib = Icq/hfe
Substituting the values, hfe or AC current gain , we get the base current to be equal to 0.02mA. The bias current, Ibias is assumed to be ten times the base current, i.e. 0.2mA.
The emitter voltage is assumed to be 12% of the supply voltage, i.e. 3.6V. The base voltage, Vb is then equal to Ve +0.7, i.e. 4.3V.
Values of R3 and R4 are then calculated as given:
R3 = (Vcc – Vb)/ Ibias  and R4 = Vb/Ibias
Substituting the values, we get R3 to be equal to 130 K and R4 to be equal to 22K
The emitter resistor is calculated to be equal to 3.6K (Ve/Ie). However this resistance is shared between two resistors, R6 and R7, where R7 is used as feedback resistor to reduce the decoupling effect of C4.  Value of R7 is calculated by the values of R5 and gain and found to be equal to 300Ohms. Value of R6 is then equal to 3.2K.
Since capacitive reactance of C4 should be less than the emitter resistance, we calculate the value of C4 to be equal to 1uF.
Power Amplifier Design:
The power amplifier is designed using Darlington transistors TIP142 and TIP147 in class AB mode. The biasing diodes are selected such that their thermal properties are equal to that of the Darlington transistors. Here select 1N4007.
Since a large value of bias resistor is required for a low bias current, we select R9 to be equal to 3K.
The driver stage is used to provide a high impedance input to the power amplifier. Here we use a power transistor TIP41 in class A mode. The emitter resistor, R8 is given by the values of emitter voltage, Ve (1/2Vcc- 0.7) and emitter current, Ie (equal to collector current, i.e. 0.5A) and is found to be equal to 28.6 Ohms. Here we select a 30 Ohms resistor.
The value of bootstrap resistor R10 should be such that to be provide high impedance to the Darlington transistors. Here we select R10 to be 3K.

Subwoofer Amplifier Circuit Operation:

The audio signal is filtered by the Sallen Key low pass filter using the OPAMP such that only frequencies below and equal to 200Hz are passed and remaining filtered. This low frequency signal is given to the input of the transistor Q1 through the coupling capacitor, C3. The transistor operates in class A mode and produces a amplified version of the input signal at its output. This amplified signal is then converted into a high impedance signal by Q2 and is given to the class AB power amplifier.  The two Darlington transistors operate such that one conducts for positive half cycle and other for negative half cycle, thus producing a full cycle of output signal.  The emitter resistors R11 and R13 are used to minimize any difference between the matching transistors. The diodes are used to ensure minimal cross over distortion.  This high power output signal is then used to drive a loudspeaker or subwoofer of low impedance, about 4 Ohms. Note that here we have used an 8 Ohm resistor for testing purpose.

Applications of Subwoofer Amplifier Circuit:

  1. This circuit can be used at home theatre systems to drive subwoofers to produce a high quality, high bass music.
  2. This circuit can also be used as a power amplifier for low frequency signals.
Limitations of the Circuit:
  1. The filter circuit tends to increase the DC level of the audio signal, causing a disruption in the biasing.
  2. The use of linear devices causes power dissipation, thus reducing the efficiency of the circuit.
  3. It is a theoretical circuit and output contains distortion.
  4. The circuit doesn’t provide any provision to remove noise signal and thus the output may contain noisy disturbance.
Circuit Components:
300 Ohms
30 Ohms
R9, R10
3 K
C1, C2
0.1uF, electrolyte
10uF, electrolyte
1uF, electrolyte
D1, D2
Dual Supply

How to match subwoofers and amplifiers

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How to match subwoofers and amplifiers

The secret to great bass is making sure your subwoofers and amp are evenly matched and will properly work together. And this article will help you figure out how to do just that — match amplifiers and subwoofers. We cover the important basics of power-matching, impedance, and planning for the number of subs you want, and we approach the situation from both sides of the system:
  • Part A: You have the subs, which amp should you get?
  • Part B: You have the amp, which subs should you get?
Start with either part you want, but they're both worth a read.

Part A
You have the subs, which amp should you get?

The subs need to be the same
Multiple subs wired together must be the same coil type and impedance. If they’re not, the power won’t divide evenly between them, and some subs would probably be over-powered while others get under-powered. If you want to run different types of subs in a system, each type needs to have its own separate amp.

Step 1: How much power? Find out the “watts RMS” rating of the sub

Then, multiply the number of subs you have by the RMS rating of each, to get their total RMS rating. You want to make sure the amp you choose is capable of supplying from 75% to 150% of the sub system’s total RMS rating.

Step 2: What impedance? The results of combining coils and subs

Figure out the possible total impedance(s) that the subs can be wired together to form.
(SVC = single voice coil, 1 pair of terminals; DVC = dual voice coil, 2 pairs of terminals.)
  • 1 SVC 2-ohms can only have 2 ohms of impedance
  • 1 SVC 4-ohms can only have 4 ohms of impedance
  • 1 DVC 2-ohms can have 1 ohm or 4 ohms of impedance
  • 1 DVC 4-ohms can have 2 ohms or 8 ohms of impedance
  • 2 SVC 2-ohms can have 1 ohm or 4 ohms of impedance
  • 2 SVC 4-ohms can have 2 ohms or 8 ohms of impedance
  • 2 DVC 2-ohms can have 2 ohms or 8 ohms of impedance
  • 2 DVC 4-ohms can have 1 ohm or 4 ohms of impedance
  • 3 SVC 2-ohms can have 6 ohms of impedance
  • 3 SVC 4-ohms can have 1.3 ohms of impedance
  • 3 DVC 2-ohms can have 1.3 ohms or 3 ohms of impedance
  • 3 DVC 4-ohms can have 2.7 ohms or 6 ohms of impedance
  • 4 SVC 2-ohms can have 2 ohms or 8 ohms of impedance
  • 4 SVC 4-ohms can have 1 ohm or 4 ohms of impedance
  • 4 DVC 2-ohms can have 1 ohm or 4 ohms of impedance
  • 4 DVC 4-ohms can have 2 ohms or 8 ohms of impedance
 For more combinations of subs and their impedances, see Subwoofer Wiring Diagrams.

Step 3: Pick an amp that can do both — X watts at Y ohms

Look for an amplifier that can put out power within the RMS wattage range you’ve figured in Step 1, at an impedance load the subs can be wired to form, from Step 2.
Estimating amp power at the odd impedance values:
  • 8 ohms — figure on the amp putting out half the power it would at 4 ohms
  • 6 ohms — figure on the amp putting out three-quarters of the power it would at 4 ohms
  • 3 ohms — figure on the amp putting out the average of what it would at 2 ohms and at 4 ohms
  • 2.7 ohms — figure the same as for 3 ohms, and add a few watts
  • 1.3 ohms — use the 1-ohm spec and take away a few watts
Alpine Type R SWR-843D

You have two Alpine Type R SWR-8D4 8" subwoofers and you want the right amp for them.

They are DVC 4-ohm subs rated at 350 watts RMS each.
Two 350 watts RMS subs together need a total of 700 watts RMS, but an amp putting out from 525 to 1050 watts RMS will do. (75% of 700 is 525; 150% of 700 is 1050.)
Using the chart in Step 2, 2 DVC 4-ohm subs can be wired together to form a 1-ohm, a 4-ohm, or a 16-ohm load.
The last is too high a load to be practical, so you’ll look for an amp that can put out from 525 to 1050 watts RMS into either a 4-ohm load, or a 1-ohm impedance load:
  • (525-1050) watts RMS x 1 at 4 ohms, or
  • (525-1050) watts RMS x 1 at 1 ohm
Among Crutchfield’s selection of amplifiers you’ll find:
Any one of these high-quality amplifiers would work well with those subs. It doesn’t matter which impedance an amp plays through — 600 watts RMS through a 4-ohm load produces the same volume as 600 watts RMS through a 1-ohm load.  Notice that the Rockford Fosgate Power T1000-1bdCP can play that pair of subs at 700 watts RMS or 1,000 watts RMS, if you want it louder, just by wiring them together differently.
Rockford Fosgate T1000-1bdCP
Rockford Fosgate T1000-1bdCP subwoofer amplifier
The last two amps listed above, the Focal 2300RX and the Rockford Fosgate Power T600-2, are 2-channel amps that happen to work with these two subs when bridged in 1-channel mode. But multi-channel amps are typically lower-powered than mono subwoofer amps, and usually can’t drive loads lower than 4 ohms when bridged.

Kicker DXA1000.1
Kicker DXA1000.1 subwoofer amplifier

Part B
You have the amp, which subs should you get?

Step 1: What can the amp do? Find the RMS ratings of the amp at different loads

Find the amp’s power, expressed in “watts RMS”, at 4 ohms, at 2 ohms, and, if it can, at 1 ohm. Pick the power you’d like to achieve. The load impedance (ohms) of that rating will be what you want your subs’ total impedance to be.

Step 2: How many subs do you want?

Divide the power you picked in Step 1 by the number of subs you want. This number is the target RMS rating for each of the subs you’ll choose.
  • Divide that target number by 1.5. This is the lowest RMS rating per sub that will work.
  • Divide that target number by 0.75 for the highest RMS rating per sub.

Step 3: What impedance does each sub need to be and how many voice coils?

Using the impedance you picked in Step 1 and the number of subs from Step 2, cross-reference the possible coil configurations that you can use: 
1 subDVC 2-ohmsSVC 2-ohms
DVC 4 ohms
SVC 4-ohms
DVC 2-ohms
2 subsSVC 2-ohms
DVC 4-ohms
SVC 4-ohms
DVC 2-ohms
SVC 2-ohms
DVC 4-ohms
3 subs(1.3 ohms)*
SVC 4-ohms
DVC 2-ohms
(3 or 2.7 ohms)*
DVC 2-ohms
DVC 4-ohms
(6 ohms)*
SVC 2-ohms
DVC 4-ohms
4 subsSVC 4-ohms
DVC 2-ohms
SVC 2-ohms
DVC 4 ohms
SVC 4-ohms
DVC 2-ohms
* Estimate amp power at the odd impedance values like in Part A, Step 3, above.

Step 4: Pick a sub that works for both — (SVC or DVC) X-ohms, Y watts RMS)

Look for subs that are rated within the wattage range you figured in Step 2, and are configured as you found in Step 3. This might sound confusing, so let's walk through an example and it'll make sense.
Kenwood Excelon X500-1
Kenwood Excelon X500-1 subwoofer amplifier

You have a Kenwood Excelon X500-1 amplifier and you want it to drive two subwoofers

The amp is capable of 300 watts RMS x 1 at 4 ohms and 500 watts RMS x 1 at 2 ohms.
Let’s say you choose to maximize the amp’s potential and want the system to put out 500 watts RMS. This means your subs have to be wired to form a total impedance of 2 ohms.
Two subs on a 500 watts RMS amp will want about 250 watts RMS each.
250 divided by 1.5 is 167; 250 divided by 0.75 is 333. So you’ll look for subs each rated between 167 and 333 watts RMS.
Using the chart in Step 3, for two subwoofers, a final 2-ohm load can be achieved with either two SVC 4-ohm subs or two DVC 2-ohm subs.
So, you’ll look for two subs that are either SVC 4-ohms or DVC 2-ohms, rated between 167 and 333 watts RMS each:
  • 2 SVC 4-ohms, (167-333) watts RMS, or
  • 2 DVC 2-ohms, (167-333) watts RMS
Among Crutchfield’s selection of subwoofers you’ll find:
Kicker CompD 10"
Kicker CompD 10" component subwoofer
All these subwoofers will sound their best when amplified with the proper amount of power. Differences in size have more to do with tonal qualities and frequency response than with power performance. And optimizing performance is the point of matching subs and amps together.