Amplifier Voltage Gain Explained – Matching Amp to Preamp (2022)

Most everyone that has ever purchased an external amplifier is at least familiar with the term voltage gain. Simply, it is the degree to which an amplifier actually amplifies the input from the preamplifier/processor. Often overlooked by those unaware of its importance, this one parameter can have significant implications on actual performance when an amplifier is introduced into an AV system. Understanding the impact that different levels of voltage gain can have in your system can very well be the difference between poor sound and getting the most out of an external amplifier.

So…what is voltage gain exactly?

When you think about it, an amplifier has a pretty straightforward job: to take an incoming voltage signal from a pre/pro and make it bigger. The amount by which the incoming signal is amplified is given in decibels (dB). Every 6dB of gain equates to a doubling of voltage; as such, a hypothetical amplifier with a voltage gain of 30dB will increase voltage by 2^5, or by a factor of 32. For unbalanced inputs, the THX standard gain level is 29dB; utilizing balanced inputs decreases this to 23dB, though naturally the output of the preamp is boosted by 6dB under this scenario (i.e. voltage output of the preamp is doubled). For example, in the Audioholics review of the Integra RDC-7.1, the unbalanced outputs were measured to deliver 7Vrms; via the balanced outputs, the Integra delivered 15Vrms!

Sounds easy enough, but why does it matter?

Naturally too much or too little of anything can present a problem, and the ideal amount of voltage gain can vary depending on a few factors. Utilizing a receiver with poorly implemented preamplifier outputs for example can be a problem when coupled to a high powered amplifier with relatively low voltage gain and consequently a high input sensitivity, which is the amount of voltage needed from the preamp to drive the amplifier to full unclipped power. Suppose you have a receiver that can deliver 1 volt RMS from its preamplifier outputs before clipping; if you pair this receiver with a high powered amplifier expecting a huge boost in headroom, you might be sorely disappointed if its voltage gain is a below average 27dB.

Fig. 1: Unclipped sine wave versus a clipped sine wave.

A gain of 27dB equates to a ~22.6x increase in voltage, meaning our amplifier will be putting out 22.6 volts RMS, or a whopping 64 watts into an 8 ohm load before our AVR’s pre-outs run out of gas. Even if the amplifier is rated to deliver 1,000 watts, all you’re going to do when you push harder is get garbage as your AVR clips the signal to the amplifier or potentially trip its protection circuits. Long story short: if you want to add power to a lower end receiver with pre-outs, you probably want something with a better than average amount and a low input sensitivity.

Fig. 2: QSC GX Series Amplifier Datasheet

Above is the voltage gain and input sensitivity specification for the QSC GX series professional power amplifiers. For those mathematically inclined, you can verify the numbers with the equation:

Voltage Gain (Av) = 20 * Log (Vout/Vin)

(Video) Preamp specs to match a power amplifier

Plugging in 48.99V for Vout (300W into 8 ohms) and 1.2V for Vin, you arrive at QSC’s 32.2dB figure for voltage gain.

OK, so barring the manufacturer of an amplifier being kind enough to provide input sensitivity, how do you calculate how much voltage is required from a preamplifier to drive an amplifier to full rated output?

First we take the power in watts that an amplifier can deliver into an 8 ohm load and convert that to voltage with the formula:

Power = Voltage^2/Load Resistance

For example an amplifier that is rated to deliver 50 watts RMS into an 8 ohm load would be 50=Voltage^2/8 or 400=Voltage^2. Solving the equation, we find that 50 watts into an 8 ohm load means our amplifier is delivering 20 volts at full power. Now we simply divide by the amount of gain that the amplifier is providing.

Going back to the earlier equation Av = 20 * Log (Vout/Vin) we can perform a bit of mathematical manipulation and say 10^(Av/20)=Vout/Vin. So if our amplifier has a gain of 28dB, we find that our amplifier is boosting the input from the preamplifier by a factor of 10^(28/20) or ~25.1. So if our amplifier rated to delivering 20 volts RMS and is amplifying the input signal by a factor of 25.1, we can know say that our preamplifier needs to deliver no less than: (20/25.1) = 0.797V RMS to drive our amplifier to full power. Isn’t math fun?

So if too little gain is a problem, we should flock to amplifiers with higher than average gain, right?

Not so fast! A very high level of gain leads to its own problem, namely noise. It makes sense when you think about it: in the previous scenario, our AVR was being asked to put out a lot of output, whereas now it is being asked to deliver relatively little voltage. As the voltage from our preamplifier output goes down, our signal will get ever closer to the noise floor of the system. Get too close, which is more likely with a higher sensitivity speaker, given that they need less output from the amplifier to begin with, and you’ll quickly learn the meaning of the saying “garbage in = garbage out”.

Besides noise configuration, an increase in amplifier gain will decrease in the bandwidth (BW) of the circuit, meaning some valuable data may get eliminated from the input signal (the amplifier works as a filter). Additionally, having a high gain amplifier may introduce DC offset at the output. In an amplifier with high input impedance, increasing the gain will introduce a DC offset which affects the operating point of the circuit (changes the balance of the amplifier).

Reading the above, it may seem that those who seek the additional output of an external amplifier are caught in a vicious catch 22. Certainly if you happen to have a combination of an AVR with a poor preamplifier output section combined with ultra-high sensitivity loudspeakers, you may want to reconsider some of your hardware choices; beyond that, careful selection can help ensure that you get the most out of your equipment. Further, it should be noted that while some low end receivers may not be the ideal starting point for adding separate amplifiers, some AVRs can do quite well; a Yamaha RX-A1010 Aventage was recently benched tested by Audioholics to deliver 2.8 volts RMS from its pre-outs, which is adequate to drive any external amplifier within reason. Meanwhile in the distant past of 2010, a Marantz SR6004 was able to deliver 7 volts pk-pk (2.49Vrms) from its pre-outs. The preamp section of this receiver should have no problems driving any external power amplification to its full output capability.

(Video) How To Calculate The Voltage Gain of a Transistor Amplifier

Fig. 3: Marantz SR6004 Preamp FFT Distortion Analysis.

As part of our receiver measurement suite, we test the pre-outs to ensure they are capable of driving a wide range of amplifiers to full power.

Load Impedance

At this point, we’ve discussed voltage gain and input sensitivity, but there are a couple more potential caveats to be aware of. First is the load for which a preamp’s output voltage is rated for. There is naturally a big difference between rating voltage output on an open circuit, i.e. no load, versus 600 ohms, which is likely to be a considerably tougher task than most amplifiers you’re likely to meet, which have input impedances on the order of tens of thousands of ohms. Rating open circuit doesn’t take into account potential current limits which could bring on preamp clipping much sooner than you might expect once you introduce real world conditions such as esoteric amplifier designs with low input impedances. In addition, some esoteric high capacitance connecting cables can cause premature high frequency roll-off.

Of course, there is also the matter of the loudspeaker load. This is old hat if you’ve read the Audioholics article on impedance. As noted prior, adequate voltage output drive from the preamplifier to allow the power amplifier to reach full power is critical. The amplifier still needs a sufficiently stout current stage to deal with the loudspeakers complex load impedance, lest you run into voltage sag/clipping on the amplifier side. Ideally of course, an amplifier would act as a voltage source, maintaining output regardless of the load (i.e. it would “double down” into 4 ohms, and “double down” again into 2 ohms). However, few amplifiers are capable of accomplishing this feat at high drive levels.

Conclusion

Are you interested in purchasing a separate amplifier? If you’ve paid attention to this article, then you’re probably also interested in its voltage gain as well. It’s hard to imagine one little number that often times gets overlooked having such a big impact on overall performance. However, this little detail can be the difference between a truckload of distortion or noise and nice clean sound. Take care in your selection, and you’ll avoid the problems outlined above. Happy listening!

Bpadilla96 posts on January 29, 2020 08:22

(Video) RCA Voltage explained RCA and Gains

Ok guys! Thanks so much for your input. I was able to connect RCA to RCA. And had an instant 6db gain! The other cables RCA to XLR was the cause of my problems. I noticed it instantly on my initial set up. READ INSTRUCTIONS FIRST! Clearly stated not to use that kind of cables in AMP! I guess is a guy thing . Install then read. THANKS

PENG posts on January 22, 2020 17:41

Bpadilla96, post: 1364410, member: 90636
The speakers are set for 4 ohms that is the reason I got the amp. What do you mean on switching back to 8 ohm

What did you mean by “the speakers are set for 4 ohms…”? From what I could see on their website the M100 is rated 4 Ohms, no mentioning of any “setting” to change that.

If you meant the AVR was set for 4 Ohm speakers, @everettT suggested you change it back to the default setting of 8 Ohms, if I understood his post#79 correctly.

You should just use RCA to RCA and you will be fine if the amp in fact has a gain of 29 dB.

Bpadilla96 posts on January 22, 2020 11:32

everettT, post: 1364312, member: 78951
As TLS mentioned, the xlr inputs are probably a different sensitivity. You should use the RCA. Also did you re-run Audyessey? Also you should switch back to the 8ohm setting.

Thanks i am on a trip now when I get home I will switch the cable and re run odyssey. The speakers are set for 4 ohms that is the reason I got the amp. What do you mean on switching back to 8 ohm setting.? I don’t think I have that option on the denon 4200. Thanks for the reply. I will keep you guys updated.

(Video) Power amps matching to pre amps, what to know before you buy

TLS Guy posts on January 22, 2020 08:41

Bpadilla96, post: 1364305, member: 90636
I forgot to mention that the amp came with rca connection option. something I have not tried. I would let you know. Thanks again. .

I would try going RCA to RCA. However the amp does not specify a different sensitivity for the RCA and XLR. If you have the same problem going RCA to RCA then you will need two of the devices I linked you to. From the spec sheet I suspect you will need two domestic to professional line level converters.

everettT posts on January 22, 2020 03:59

Bpadilla96, post: 1364305, member: 90636
I forgot to mention that the amp came with rca connection option. something I have not tried. I would let you know. Thanks again. .

As TLS mentioned, the xlr inputs are probably a different sensitivity. You should use the RCA. Also did you re-run Audyessey? Also you should switch back to the 8ohm setting.

FAQs

How do you match a preamp to an amp? ›

You always want to go from a low impedance to a high impedance. So you want your power amp to be at

How much gain should a preamp have? ›

Most digital sources will be 2 volts or higher and often high gain preamps are`nt needed, 10 db of gain should be plenty. With too much gain in a system your useful range on the volume control will be quite limited i.e. 7-9 oclock, as above that level the sound becomes to loud, and fine tuning is very difficult.

What is amplifier voltage gain? ›

Gain is basically a measure of how much an amplifier “amplifies” the input signal. For example, if we have an input signal of 1 volt and an output of 50 volts, then the gain of the amplifier would be “50”. In other words, the input signal has been increased by a factor of 50. This increase is called Gain.

How do you increase the voltage gain of an amplifier? ›

In order to increase the gain, β must be reduced. This can be done by increasing the ratio of R2/R1. However, there is no way to lower the feedback to the inverting input for a fixed-gain difference amplifier since this would require either a larger feedback resistor or a smaller input resistor.

What is more important preamp or power amp? ›

Power output could be a big concern with power amps depending on your speakers and environment. Power output is never a concern with preamps, though gain might be. The poweramp is typically going to be a bigger safety concern for your speakers than the preamp.

What happens if the impedance matching is not done in an amplifier explain? ›

The low impedances in the load side draw excessive power from the active devices to meet load requirements. Apart from power loss, improper impedance matching affects the performance, gain, and efficiency of multistage amplifiers.

What does gain do on preamp? ›

Your gain setting determines how hard you're driving the preamp section of your amp. Setting the gain control sets the level of distortion in your tone, regardless of how loud the final volume is set.

What is preamp output voltage? ›

Manufacturers specify how much voltage their source units can produce on these preamp outputs. Most radios offer at least 2 volts of signal, but some offer 4 volt, 5 volt or even 8 volts.

What level should I gain stage? ›

So maintaining the same concept of optimal gain staging that you use during recording is your best bet: -18dBFS is a good average level to aim for. Keeping it conservative will help you maintain proper gain structure throughout your mix.

How do you test a preamp output? ›

You can quickly test if the preamplifier is receiving power by plugging any household electrical equipment into the same outlet as your amplifier and turning it on. If the electrical equipment is working properly, there is a power issue with your preamplifier.

How many volts do amplifiers need? ›

Usually the range is somewhere between 10.5-16.5 volts.

How do you calculate voltage gain? ›

How To Calculate The Voltage Gain of a Transistor Amplifier - YouTube

Which feedback is used to increase voltage gain of amplifier? ›

Positive feedback increases gain of the amplifier also increases distortion, noise and instability. Because of these disadvantages, positive feedback is seldom employed in amplifiers. But the positive feedback is used in oscillators.

How do you calculate the gain of an amplifier? ›

You find the voltage gain of an amplifier by taking the output voltage and dividing it by the input voltage. This calculates the ratio of the output voltage to the input voltage.

What is the voltage gain in a common emitter amplifier? ›

The power gain of a common emitter amplifier of voltage gain 50 and input impedance 100 ohm is 1250.

Do preamps enhance sound quality? ›

Conclusion. The sound contribution of preamps is not so much in its frequency response but in the texture it imparts on the sound. However, a preamp shapes the sound to a much lesser degree than one would think. Usually, its sound character only becomes obvious at high gain settings or when you drive it into distortion ...

Does a preamp boost volume? ›

Preamp volume is the process that makes the sounds being captured by a microphone become audible. It is measured in dB, and generally, a preamp adds up to 60dB of volume to the signal. The correct amount of volume to be added depends on the microphone, the instrument, and the preamp itself.

Can you use a preamp without an amp? ›

No. Even if you have the best mic preamp, there is no way to use it without an amp. A preamplifier is a supplementary device, while an amplifier plays a critical role and cannot be excluded from the system.

How do you improve impedance matching? ›

Techniques to Improve Impedance Matching

One such technique is to insert a matched attenuator in front of a mismatched load impedance. The mismatch observed at the input of the attenuator is improved by an amount equal to twice the value of the attenuator.

Is impedance matching necessary? ›

Whether you are working with digital or analog signals, you'll most likely need to match impedances between a source, transmission line, and load. The reason impedance matching is important in transmission lines is to ensure that a 5 V signal sent down the line is seen as a 5 V signal at the receiver.

What happens if you dont match impedance? ›

If the impedances aren't matched, maximum power will not be delivered. In addition, standing waves will develop along the line. This means the load doesn't absorb all of the power sent down the line.

What happens if gain is too high? ›

If the gain is too high at the input stage, your audio will reach the point of distortion or clipping. This can be a good or bad thing depending on what you are going for, as you might want to get some distortion with an amplifier, though you might want a clean tone for digital audio.

What happens if your amp gain is too high? ›

Amp gains work the same way – too low, and the background noise, or “hiss” takes over Too high, and music becomes distorted even at a normal volume level.

What happens if gain is too low? ›

If you have your gain set too low, your amplifier will not be able to reach full power, which could allow the source unit to clip which in turn will result in a distorted signal being delivered to your speakers. This is especially relevant with low voltage sources (lower than 2.5 Volts - typically OEM units).

How many preamp outputs do I need? ›

If you have less than 3 pairs of pre-outs on your deck, and you are not satisfied with these conditions, you will need a processor between your HU and amp to handle that. Since you have the rare condition of single pairs of pre-outs, the signal might have to be split twice per channel.

How does gain affect voltage? ›

Gain in Voltage

The voltage gain of an amplifier is the ratio of the output voltage to the input voltage. For example, if an amplifier has a voltage gain of two, then the output voltage will be twice the input voltage. If the gain is three, then the output voltage will be three times the input voltage.

How do I increase my RCA voltage? ›

A line driver will boost the voltage of an RCA signal before the amp. I understand that you're worried about adding more components to the signal chain, but your options are either live with the noise, buy a head unit with higher output voltage, or buy a line driver.

How do you set a proper gain structure? ›

To establish proper gain structure, the primary element and first concern is input gain. Each system input provides adjustable Gain In or trim level, with an associated Peak indicator. For best performance, increase the gain on a given input until the Peak indicator just begins to flash on normal signal content.

How do you optimize gain? ›

Gain Optimization for Microplate Readers - YouTube

Does gain increase noise? ›

To recap, volume is a control of the loudness at the output of a sound system and has no affect on quality, while gain lets you increase the loudness inside of an audio system, which absolutely determines the quality of the sound or recording.

How do I choose a preamp? ›

Choose your phono preamp according to the sound quality required. Depending on the type of music you play and naturally the sound quality you are looking for, you will have to consider different phono stages. Sound quality will differ depending on the components used by the manufacturers, and the technological bias.

What is the difference between a preamp and an amplifier? ›

A preamp boosts a weaker signal, bringing it to line level, and a power amp boosts the line level signal before it goes to the speakers. In other words, a preamp increases signal strength to an acceptable level to transmit to the equipment in your chain.

What does a preamp do for home audio? ›

(PREAMPlifier) Meaning "before the amp," the preamp is the primary control unit in a stereo or home theater system. It switches low-level signals from audio and video sources to the audio amplifiers, which boost the preamp output sufficiently to drive the speakers. The preamp always includes the volume control.

How do you hook up a preamp to a receiver? ›

Steps for Connecting a Preamp to a Receiver
  1. Turn Everything Off. ...
  2. Plug Your Audio Device(s) into Your Preamp. ...
  3. Plug Your Preamp into the Receiver. ...
  4. Turn Your Preamp On and Lower the Volume All the Way Down. ...
  5. Turn on the Receiver and Adjust the Preamp's Volume. ...
  6. Adjust the Preamp's Gain.
24 Feb 2022

Does preamp improve sound? ›

The sound contribution of preamps is not so much in its frequency response but in the texture it imparts on the sound. However, a preamp shapes the sound to a much lesser degree than one would think. Usually, its sound character only becomes obvious at high gain settings or when you drive it into distortion.

How do I know if I need a preamp? ›

To check if a receiver has a built-in preamp, check if the receiver has a PHONO input. A receiver with a PHONO input definitely has a built-in preamp. If your receiver has a PHONO input, you can connect a turntable without a phono preamp to that input. This way, you will use the preamp that is built into the receiver.

How important is a good pre amp? ›

In a home theatre system, the pre-amplifier performs two main functions: it handles switching between different line level sources and boosts the signal before sending it to the amplifier. A weak electrical signal becomes strong enough for additional processing, preventing noise and offering cleaner output.

Do I need a pre amp or integrated amp? ›

A preamp is a signal-boosting device that takes the audio signal from the music-playing device and amplifies it. An integrated amp contains a built-in preamp and a power amp. A separate preamp produces better, high-fidelity sounds, while an integrated amp is cheaper and more convenient.

Does a preamp make a difference? ›

A high quality microphone preamp, however, will do much more than just make your mic level louder. It will deliver a cleaner, more accurate signal, with higher gain, lower noise, less distortion, and more headroom.

Can I use an integrated amp as a preamp? ›

Short answer, Yes. A preamp can be used with an integrated amp. Ideally, you must connect the preamp's output to the Main Input of the integrated amp.

How many channels should my amp have? ›

In general, you need one channel for each speaker that you want to amplify. If you're adding a subwoofer to an existing system, then a single channel amplifier will get the job done.

What is another word for preamp? ›

In this page you can discover 12 synonyms, antonyms, idiomatic expressions, and related words for preamplifier, like: power-amplifier, pre-amplifier, pre-amp, amplifier, preamp, compressor-limiter, pre-amps, , , subwoofer and de-esser.

How do you match speakers to amps? ›

Amplifier to Speaker Matching Tutorial | UniqueSquared.com - YouTube

How do you connect an amplifier to a receiver without pre outs? ›

To do so, you'll connect an HDMI cable to the extractor's input port and the other end to the receiver's HDMI output port. The audio extractor device will extract the digital audio stream and convert it to analog outputs you can connect directly to your power amp or AV amp.

Do you need a preamp if you have a receiver? ›

You do not need a phono preamp if your receiver has a phono input. The same goes if your record player has an internal preamp. But that does not mean you shouldn't get one. In most cases, the phono preamplifiers included in receivers or turntables are low quality.

Can I use pre outs and speaker terminals at the same time? ›

Yes, you can use the pre-outs for your front three speakers using a separate amp, and use the built in amps for your surround speakers.

Videos

1. What does a High preamp Voltage do for you
(Dean and Fernando's Car Stereo Clips)
2. Setting RCA voltage
(Jerry Aintloud)
3. PERFECT AMP GAIN SETTING COMPLETELY FREE!!!
(Adam Francis)
4. How to match amps to speakers
(PS Audio)
5. The difference between preamps and power amps
(PS Audio)
6. Difference between line out and preamp out
(PS Audio)

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