Amplifier Strapping

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What is amp strapping?

Strapping amplifiers is when you link two identical amplifiers for greater power output. When strapped, one amp’s preamp settings control both amps. 

You should only strap identical amplifiers with a built-in strapping function. As an example, consider the S1-2250 and the S1-2250.1. Some of their spec’s are similar. However, their built-in strapping circuitry is not designed to work together. Problems will definitely happen if they are strapped.

Strapping is not the same as gain matching. It is also not to be confused with bridging channels on a multi-channel amplifier. 

When should I decide to strap amps?

The choice to use the strapping method should happen when designing a car audio system.

It is inherently more difficult to strap amplifiers down the road than it is to purchase a larger amp from the get-go. Any change to one part of the closed system affects all other parts of the system.

More Power, More Impedance

Your coil and wiring configuration is crucial to getting full power out of strapped amps. When two amplifiers are strapped, each amp encounters half of the impedance load for the wiring configuration. If your subs are wired to a 2 ohm load, each amplifier encounters 1 ohm of resistance. So when strapping two identical 1-ohm-stable amplifiers, your subs must be wired to a 2 ohm load to reach the lowest stable impedance for each amp. 

For example, you wire two HDS3.210-D2 subs to a 2 ohm load. You’ll need about 2400 W RMS to drive the subs. Strapping two S1-1250.1 amps will yield 2520 W RMS at the 2 ohm load. 

Why would you want to strap amplifiers?

Sometimes it’s not in the budget to buy a single amp to power your system. If you already have an amp that is strappable, buying a second and strapping it might make more sense. 

Strapping your amplifiers is one way to get more power without draining your bank account.


How do I strap my amps?

Strapping Steps:

You will need:

  • two identical amplifiers
  • fuses for each amplifier
  • individual power and ground wires for each amp
  • an extra RCA cable.
  1. Set the Main amplifier’s switch to Main.
  2. Set the Strap amplifier’s switch to Strap.
  3. Connect the MAIN/STRAP RCA of the Main amplifier to the MAIN/STRAP RCA of the Strap amp with a single RCA cable
  4. Connect the (-) Negative Speaker Terminal of the Main amplifier to the (-) Negative Speaker Terminal of the Strap amp 
  5. Connect the (+) Positive Speaker Terminal of the Main amplifier to the (+) Positive Lead of your subwoofer(s)
  6. Connect the (+) Positive Speaker Terminal of the Strap amplifier to the (-) Negative Subwoofer Lead 
  7. Connect the Remote Wire to the Main amplifier with a bridge to the Strapped amplifier
  8. Connect your head unit or signal processor to the Main amp
  9. Tune the Main amplifier, it will control the Strap amplifier. Preamp settings of the Strap amp will have no effect when in Strap mode

When is strapping a bad idea?

If your HDS2.2’s have D-4 coils, you can’t wire them to a 2-ohm load. The combined power output from the amps up against 8 ohms of impedance defeats the purpose of strapping. 

On the other hand, wiring to a 1 ohm load risks blowing your amplifiers. After halving the impedance you’ll be below the recommended minimum impedance load for 1-ohm stable amps.

Many SPL competitors want to squeeze every drop of juice that they can get. Because of the combined ohm load, strapping amplifiers means you cannot wire your system as low as you’d like. 

Takeaways

  • Strapping is a choice you need to make before you build your system.
  • The two amps have to be identical and have a built in strapping function. 
  • Strapping two amps at a higher impedance configuration defeats the purpose.
  • Adding another amplifier and strapping amplifiers is difficult to do after designing and building a setup.