What’s the Difference Between a Preamp and Power Amp?

You’ve probably heard about preamps and power amps but still need clarification, especially when working your guitar rig.

Which is why you are here reading this article. Preamps and power amps, for those who don’t know, have a way of affecting the overall sound of your guitar. They’re responsible for shaping and pushing your sound.

While both affect your guitar sound, they do have differences to note, especially when looking to get a particular effect from your instrument. 

What’s the difference between a preamp and a power amp?

A preamp is a section in an amp that handles the tone shaping of your guitar or any other audio source. A power amp is an actual amplifier that drives your signal to a louder output that can drive passive speaker systems. Both are essential in an amp and are needed to deliver superior sound.

Both sections in an amplifier bump up your signal; however, they have different approaches.

The preamp is the section responsible for how much of the EQ frequency will be present in a signal and bumps it up to line level. At the same time, a power amp handles how loud the overall signal will be when it hits the speakers by increasing the signal’s power further.

What is a preamp?

A preamp in an amplifier gives your guitar, or any other instrument or device, its tonal characteristics. Using EQ controls lets you tweak how your sound will come out of the amp’s speakers. Unless you have outboard effects, a preamp is the first thing your signal interacts with.

Without a preamp, a guitar will sound flat and dry. While flat is not a bad thing at all, you will want to bump up frequencies to get the perfect sound, and using a preamp addresses this situation by providing your sound source with tone-shaping tools that will also put more body in your sound.

A preamp is also found before the amplifier section, hence the “pre” prefix. You should note that the preamp is not the actual amp but the phase in the signal chain that processes the sound before it hits the amplifier. Sometimes, a preamp raises the signal to line levels for compatibility with a power amp.

In some cases, preamps add a small amount of compression, often with valve amplifiers that employ vacuum tubes. In the case of guitars, these tubes also help induce breakup sounds, which creates an overdriven or distorted sound.

A preamp also has the advantage of being able to connect to other devices, such as mixers or other effects units. However, you cannot use it to connect directly to a speaker cabinet. 

What is preamp distortion?

Particularly with guitar amps, preamp distortion is the effect of breaking up when the gain or volume control is increased. Preamp distortion varies for each amp. Some amps have more compression, typical for amps with high gain.

Now distortion at the preamp section tends to vary. Sometimes it’s caused by the preamp itself, and other times by diming or setting the volume control at maximum. If you want to know if the distortion is caused by the preamp or the volume control, set your master volume at a lower level, then increase the gain. If it distorts, it’s the preamp section.

What is a power amp?

A power amp is the actual amplifier, which gives your signal enough power to drive passive speakers. It’s often the last stage in the signal path, which also helps shape your overall sound. Some power amps give you the ability to shape the tone further with EQ controls.

Power amps also determine the wattage. This wattage is your reference on what speakers you can attach to the amp. Often, you can only go lower if the speaker output on the amp has a starve control that lets you play at lower wattages.

Many power amps use tubes, just like preamps. These tubes play a crucial role in the tone that comes out of the speakers. Some amplifier brands prefer specific tubes due to the type of break up it induces, while others use tubes that introduce higher headroom and more volume without distorting.

A power amp is essential when connecting to a passive cabinet speaker. However, you can only link to other equipment, such as mixers or active powered speakers, if you have a line-out option or an attenuator to convert the signal to line levels. 

What is Power Amp Distortion

Power amp distortion is produced when the master volume of the amp is cranked. It often has more mid-range and tends to be more open, which is good if you like playing around with your pick attack and dynamics.

The amount of distortion you get with a preamp depends significantly on the tubes you use in your amp. Tubes like the EL84 and EL34 tend to distort the power amp at lower volumes, as they have less headroom, while amps that use 6L6 and 6V6 tubes have higher headroom and take a while to reach breakup tones.

Getting power amp distortion is easy and results from cranking the master volume while keeping the gain or channel volume control down.

What is an effects loop?

An effects loop is the section between a guitar setup’s preamp and power amp. As some effects, such as modulation and time-based effects, sound better after the preamp section, the effects loop allows you to insert effects into the signal chain after the preamp section and before the preamp.

Now, not all amps have an effects loop section. To know if your amp has an effects loop, look for a pair of jacks, usually denoted as “FX Loop” or Send and Return.

• To add an effect to the FX loop, plug one cable into the Send jack, then plug the other end into the input of the effects.
• Take another cable, plug it at the end of the effects chain for the loop, and then plug the other end into the return jack.

If you have a pedal or preamp that you want to use over the built-in preamp section of an amp, an effects loop lets you bypass this preamp. You plug your signal chain’s output into the return input jack of the effects. I’ve been practicing this every time I use a backline amp with an effects loop since I use a preamp pedal. 

Can you get standalone preamps or power amps?

You can buy a separate preamp or power amp to get a more customized sound for your guitar rig. Many music stores sell preamp pedals, rackmount-sized and pedal-sized power amps that you can pair with any preamp. You can mix and match these devices to get a customized tone, or even use microphone preamps.

Examples of preamp pedals you can buy include the Sansamp by Tech 21, Strymon Iridium, and the various multi-effects processors in the market today, such as the Line 6 HX stomp, which feature amp modeling. For power amps, popular choices include the Harley Benton Thunder 99, Electro-Harmonix Magnum 44, and the Seymour Duncan Power Stage.

One notable advantage of having a separate power amp is preventing heat from affecting your preamp section. Power amps can be notorious for their heat emissions due to the transformer size inside these amps. By separating them, you can prevent any noise interference and overheating from these devices. 

Connecting Preamps and Power Amps

Connecting to preamps and power amps doesn’t need much tinkering, as they are straightforward devices that go from one output to the following input. However, knowing how they connect will help you maximize your amp’s potential. In any case, you only need an instrument cable to connect these devices.

How do you connect to a preamp?

Connecting your guitar to the amplifier’s preamp section entails you plugging into the input jack of the preamp.

• Use an instrument cable to plug your guitar on one end, and the other is plugged into the input of the guitar amp, which is the preamp section.
• If you are using effects, plug the instrument cable at the end of your effects signal chain and plug the other end into the amplifier’s input jack.
• While there are no rules on what effects you can plug into a preamp, many recommend plugging into a preamp all filters, pitch shifting, overdrive, fuzz, and distortion pedals. In contrast, effects, such as modulation, delay, and reverb, are best placed in the effects loop. You can still plug these effects into the preamp if there’s no effects loop available. 

How do you connect to a power amp?

There are plenty of ways to connect to a power amp, all of which will help you sculpt your tone, even when using an internal power section on an amp.

• In guitar amps, the preamp section and the power amp section are already connected, with some amps offering effects loops to create versatility. You don’t need to take action in connecting the preamp section and power amp, as internal switches connect or switch to the effects loop.
• If you have an external preamp, such as the Sansamp, you can connect it to a power amp’s input or through the effects loop’s return jack.
• You can connect the two with an instrument or effects patch cable for separate preamps and power amps. You also have the option to put effects in between the preamp and power amp, just like an effects loop.

Once you’ve connected the power amp, you can then connect the power amp to the speaker using a speaker cable. Note that speaker cables are different from instrument cables. Speaker cables are often thicker than instrument cables, which is necessary to handle the load from the power amp. 

How do you use the “four-cable” method with preamps and power amps?

The four-cable method allows users to use external and internal preamps of their amps while switching between the main preamp and an external amp modeling system. For this wiring technique, you need an amp with a dedicated effects loop and an amp modeling system with an effects loop.

• To do the four-cable method, plug the output of your guitar or effects that won’t be affected by the loop into the input of your effects processor.
• Plug another cable into the send jack and connect it to the input of your guitar amp.
• Plug a cable from the send output of your amp and connect it to the return jack of the effects processor.
• Plug your effects processor’s output jack into the amp’s return jack.

This method will allow you to switch between your amp’s main preamp or your effects processor’s amp modeler. You must assign your amp to the effects loop block and plot it anywhere in your signal chain. 

How do you use an auxiliary input?

An auxiliary input allows you to insert line-level devices like smartphones, tablets, and laptops into your amplifier. The auxiliary input connects directly to a power amp and often lacks volume control. You will have to control the volume from the audio source.

Conclusion

Knowing the difference between a preamp and a power amp can help you customize your sound on your recording or in a live gig. You know what to tinker with when looking for a particular kind of sound, given how each section behaves in an amp setup. You will also know where to troubleshoot when things go wrong.

If you prefer a different preamp voicing, you can easily swap out the preamp with your choice and plug straight into the power amp section via the effects loop. And if you think the power amp doesn’t have enough headroom, then you can take the preamp output and use your preferred power amp and speaker combination.

But if you know what you want in an amp setup, you can buy a separate preamps and power amps. That way, you can create a guitar rig that matches your music.