What is the role of a preamp?

[Tanoj]

Hello Friends

so basically for my Amp Akai am u33, there is inbuilt phono stage
speakers would be Acoustic Portrait MS101
do i need a phono preamp like NAD pp2 etc ?
or should i look for a preamp ?
or do i need all the three, NAD phono pp2, pre amp , and Akai u33 ??
or should i look for a power amp ?
also if i just add nad pp2 to the amp will it improve the sound quality ?

Cheers

Tanoj

 

[gobble]

Agree !



This is not possible. The best it can do is NOT to add more veils in the most important areas.

Well... I heard George's original Grounded Grid at my place do exactly that, years back. It was a magical synergy where not just the amp and preamp disappeared, but also the CDP. I was left imagining a CD spinning in thin air connected directly to the speakers.
To hear a vocalist and "see" the imagery of nothing but his vocal chords, not even his face .... It was a serendipitous match that provided astounding synergy at least in my setup.

Cheers

 

[square_wave]

Well... I heard George's original Grounded Grid at my place do exactly that, years back. It was a magical synergy where not just the amp and preamp disappeared, but also the CDP. I was left imagining a CD spinning in thin air connected directly to the speakers.
To hear a vocalist and "see" the imagery of nothing but his vocal chords, not even his face .... It was a serendipitous match that provided astounding synergy at least in my setup.

Cheers

Are you saying that a preamp can add more details than what is not there in the output from the source ? How can this be possible? Does the preamp manufacture these details?

In some cases where there is a technical problem where the source cannot drive the power amp directly, when you connect the right preamp to correct this technical problem, the details in the source can be clearly heard. Are you by any chance talking about this phenomenon ?

 

[soulforged]

In some cases where there is a technical problem where the source cannot drive the power amp directly, when you connect the right preamp to correct this technical problem, the details in the source can be clearly heard. Are you by any chance talking about this phenomenon ?

In Gobble's terms that would be like what...wonderbra???

 

[Hiten]

Iam perplexed with the role of a preamplifier in the audio setup.

Sorry if I am repeating and I am not a technical person but I guess a preamp is used to as signal attenuator (Volume control) Source selector (As different sources may have different output), Buffer (to avoid mismatched impedance) or voltage gain device (Input level decides the gain of a power amp which will drive the speakers). All this should be done without degrading the original signal. This is very important thing to have if one is required. As it will decide the sound quality.
In short all this effort is to match impedance. Impedance thing is too technical to understand but each amplification stage should show high impedance to its previous stage so as we get maximum amplification without degrading sound quality. Think of it as load put on previous stage for maximum benefit. Need to confirm this with gurus.
This may help - Preamps Explained

 

[gobble]

Are you saying that a preamp can add more details than what is not there in the output from the source ? How can this be possible? Does the preamp manufacture these details?

No. Merely that most HiFi gear does not deliver the goods when it comes to reproduction of music and I have heard for myself the preamp overcoming the deficiencies of the rest of the chain.

The fact that it made my mediocre budget power amp and CDP disappear and even feel like a cable-less system... The proof of the pudding is in (the) hearing and I definitely had a moment of revelation with that preamp. :clapping:

Anyways please await my review of my new tube gear shortly in a few hours.

--G0bble

 

[omishra]

Just stumbled across this thread!

Are you saying that a preamp can add more details than what is not there in the output from the source ? How can this be possible? Does the preamp manufacture these details?

Lot of preamp qualities are already discussed in the posts on page 1.

If your source has been good enough to reproduce all details still you are bound to loose it while connecting to power amp. It may be due to

• impedance mismatch, where noises generated, IC oscillation can happen, source's output gets loaded due to current drawn by power amp(I am talking in terms of mA and pA, Milli ampere and Pico ampere).
• Source has very low output and can not drive less sensitive power amp.
• Source output need to be controlled without degradation in quality. Good quality Volume control comes in picture.
• Source selection

Preamp is put in middle to sort out all of above problems without changing phase of input signal. Though it does not add its own coloration it helps preserving the details which could fall pray to noises by above issues and get lost in middle. This needs to be minimalistic and neutral for audio signal.

So details are not manufactured in preamp but its loss is prevented. "your chain is as strong as weakest link in the chain" So final delivery of details still depends further in the chain.

Still if you don't have above issues then no need of any preamp. Having good preamp (with possible practical pros and cons) does not hurt. I don't find any place for equalizer/bass-treble controls on the preamp panel. Still they are there in some preamp.

 

[square_wave]

So details are not manufactured in preamp but its loss is prevented.

I guess we both agree about this point

 

[marsilians]

Just catching up with the discussion here...

For starters, there are 2 types of pre-amps active and passive. At a simplistic level, the passive ones pretty much offer volume control and source switching. The ones that are being discussed in this thread are the active ones.

primarily, this has to perform 3 primary functions.

1. Signal processing - Allowing to control the sources and also enhance and subdue certain frequencies (this is the reason people think that a pre-amp "adds" more details). In an AVR this is the DSP function.

2. Impedence matching - it should provide a high impedence to match the source and a low impedence to the amp.

3. Amplification - this boosts the input signal as a voltage gain so that the power amp then can provide higher current gain to drive the speakers.

The most critical factor of a preamp apart from switching is the amplification it provides typically measured as signal to noise ratio.

preamp + power amp = integrated amp
preamp + power amp + freq tuner = AVR
preamp, power amp, sources = separates.

@omisra - the preamp does not solve any problems as such. its got a function as any other component in the audio setup.

 

[omishra]

@omisra - the preamp does not solve any problems as such. its got a function as any other component in the audio setup.

I did not understand this. Please elaborate.

 

[jls001]

The most critical factor of a preamp apart from switching is the amplification it provides typically measured as signal to noise ratio.

@marsilians: amplification is measured with respect to the input signal, in decibells. One can also use linear scale and simply say that the amplitude of the output of an amplifier under test is X times the amplitude of the input signal.

Assuming the input signal is higher than the noise floor, if one were to measure the gain with respect to the noise floor, then the gain thus calculated would be higher than the real gain.

 

[BLASTO]

So details are not manufactured in preamp but its loss is prevented.

If it is true, that summarizes all.

 

[marsilians]

I did not understand this. Please elaborate.

YOu had mentioned the following in your note.

Preamp is put in middle to sort out all of above problems without changing phase of input signal.

I am just saying they dont necessarily solve the problems thats all.

 

[BLASTO]

One related question. I ask because it is related to volume control whch is one of the things the preamp does.

In budget gear, When we increase the volume above normal listening levels, the details come out much cleaner and wider as what we would expect.

But once the volume is decreased to listening/below listening levels, we do not perceive that all the details are present.

What is the root cause of the phenomenon? What is the first equipment in the chain that needs to be changes when we need details lower and lower in volume levels. Should the whole chan be changed?

 

[marsilians]

@marsilians: amplification is measured with respect to the input signal, in decibells. One can also use linear scale and simply say that the amplitude of the output of an amplifier under test is X times the amplitude of the input signal.

Assuming the input signal is higher than the noise floor, if one were to measure the gain with respect to the noise floor, then the gain thus calculated would be higher than the real gain.

I agree with most of what you are saying conceptually. the only thing I dont is that dB scale is logarthmic so you cant use a linear comparitive. On retrospect I could have used the term 'gain' vs. 'amplification' in my note as I refer to the voltage gain, which is the ratio of output vs. input values.

Regarding the quality, what I was getting at is the defining characteristic of a pre-amp which is typically indicated by S/N ratio, also measured in decibels.

 

[Kannan]

A good preamp is like Lingerie. It makes the content and playback more revealing, allowing the man a deeper insight into the source material, and paints a vivid seductive picture of the artists original intent, and keeps him thirsting for more ... A good preamp titillates the listeners senses hyeah:

I hope this post explains things as it really matters, in a format more understandable to the lay audience than all the previous needlessly technical and geeky explanations

--G0bble

lol....this would be one of the best marketing explanation for preamps....
THE END I SAY.....

 

[jls001]

I agree with most of what you are saying conceptually. the only thing I dont is that dB scale is logarthmic so you cant use a linear comparitive. On retrospect I could have used the term 'gain' vs. 'amplification' in my note as I refer to the voltage gain, which is the ratio of output vs. input values.

Regarding the quality, what I was getting at is the defining characteristic of a pre-amp which is typically indicated by S/N ratio, also measured in decibels.

Log and Linear are simply two different ways of expressing the same thing. The voltage of the input signal is measured in linear Volt scale. The output signal is also measured in the same linear scale. Volt is an absolute scale and needs no reference. The ratio of these two numbers is a linear number. Gain is nothing but 20 x log(Output Voltage/Input Voltage). dB is a relative scale, and must be formally expressed as dBW (with reference to 1 Watt), dBmW (with reference to 1 milliwatt), etc.

Why use log scale? First, when a set of measurements involve a large range, log is helpful to compress that range to manageable numbers. In our example, output voltage is very large compared to the input voltage. Second, our ears hear in logarithmic fashion. Hence audio loudness, gain, etc are expressed in log scale.

Signal to noise ratio of an amplifier is a measure of the noise floor of an amp as a whole. If an amp has a low noise floor, it will be more sensitive to lower level input signal, and hence will be considered more resolving of details. By extension, it will give the amp a higher dynamic range (allows the signal to swing from very quiet passages to very loud passages, without obliterating the low passages). Again, S to N ratio can very well be expressed in linear scale (amplitude of desired signal/amplitude of noise) but the more conventional expression is to express it in logs.

 

[omishra]

One related question. I ask because it is related to volume control whch is one of the things the preamp does.

In budget gear, When we increase the volume above normal listening levels, the details come out much cleaner and wider as what we would expect.

But once the volume is decreased to listening/below listening levels, we do not perceive that all the details are present.

What is the root cause of the phenomenon? What is the first equipment in the chain that needs to be changes when we need details lower and lower in volume levels. Should the whole chan be changed?

There are two reasons for this -

1. Human listening capability v/s frequency: When we listen at low volumes our brains could feel presence of mid range more dominantly against low and high counterparts. To overcome this some preamp has loudness feature with changes the equalization curve like shape of 'U'. This is also not implemented well in cheap preamp. This equalization must be changed wrt specific volume level. This kicks in below certain low threshold of volume level and flat at normal listening level. (ref Tandberg 3002 manual)

2. Some power amp has nonlinear sensitivity at the edges of audio band at low volumes. If volume control directly connected to amp input w/o buffer then there are lot of reasons to expect noise overtaking signal.

If somebody has more information please share.

 

[square_wave]

If it is true, that summarizes all.

If a technically correct match can be achieved between the source and power amp, there are many other solutions other than active preamps which can pretty much do the same thing. ie: prevent loss of details.

 

[odyssey]

Good question !!

This is not very straightforward to nail down but some of the reasons are as follows
1. Impedance matching/drive between pre to power, or lack off at lower volumes. The volume control POT is typically at the highest impedance wrt to the amp and hence the lowest impedance ratio between the pre and the power (ideally input imp of amp / output imp of pre should be as high as possible). At this position of the POT, the balance across all freq tends to be missing (theoretically).
2. Speaker driveability. Some speakers require more voltage to make them sing, at low volumes they just don't sound as balanced (across the spectrum), in this case, a good pre/power wont help.

One related question. I ask because it is related to volume control whch is one of the things the preamp does.

In budget gear, When we increase the volume above normal listening levels, the details come out much cleaner and wider as what we would expect.

But once the volume is decreased to listening/below listening levels, we do not perceive that all the details are present.

What is the root cause of the phenomenon? What is the first equipment in the chain that needs to be changes when we need details lower and lower in volume levels. Should the whole chan be changed?