Amplifier forms the centre of every stereo system.
On the one hand, all program sources are connected and managed here, on the other hand, the amplifier must process and amplify the signals of these program sources to the extent that the connected loudspeakers can be adequately driven.
The choice of the amplifier thus plays a crucial role in the quality and usability of the entire stereo system.
Howdy SEA Fans, welcome to another tip Tuesday blog post and today we would like to give you some tips on what to pay attention to when buying a stereo amplifier.
Let’s start off with the basic concepts regarding Amplifiers,
Roughly speaking, stereo amplifiers are made up of two components:
the preamplifier and the power amplifier.
Usually, these two components are combined in one device.
One speaks then one speaks of a complete amplifier.
If the modules are housed in separate independent housings, then one speaks of a pre-stage and power amplifier or of a pre / final stage combination.
The preamplifier is the control centre.
All program sources are connected here and their signals are processed in such a way that they are in a voltage and impedance range usable for the output stages.
In addition, the preamp includes the volume control.
Since the voltage output by the preamplifier is not sufficient to drive a loudspeaker, the preamplifier must be followed by an output stage, which increases the voltage so far that the loudspeaker can be operated properly.
Nowadays many speakers have an integrated power amplifier.
These are referred to as active speakers and can be connected directly to the preamplifier.
Integrated amplifiers are a combination of pre-amplifier and power amplifier. Here you can connect the signal sources on one side. On the other hand, a power amplifier is able to drive the speakers. Since here – unlike separate Vor-Enstufen – only one device is needed and integrated amplifiers are usually cheaper than in sound and equipment comparable separate components, integrated amplifiers enjoy great popularity with the end user.
The high-level inputs
At the high-level inputs, all sources are connected, which output their signals analog.
The only exception is turntables.
The input sensitivity of the high-level inputs is 100 to 500 mV.
Make sure that your amplifier has enough high-level inputs for the program sources you are using.
High-level inputs usually have cinch sockets.
In addition to these connections, balanced XLR connections exist – predominantly in the high-end range.
The symmetrical signal transmission comes from the studio technology and is less sensitive to interference.
If the signal source also has balanced outputs, connecting via XLR makes sense, as there may be little sonic advantages.
A connection via RCA XLR adapter, however, does not make sense, because the signal is not transmitted symmetrically and therefore there are no benefits.
On older devices, it can be found sometimes even 5-pin DIN connectors.
These are phonetically equivalent to RCA plugs.
Again, it is worth using only if both source and amplifier have DIN sockets.
a) Make sure that the selected amplifier has enough high-level inputs for all the program sources that you want to operate via the analog outputs.
b) DIN or XLR inputs are only required if you have program sources that have corresponding outputs. An adaptation does not make sense.
Digital Inputs and D / A Converters
In the recent past, more and more computers or televisions serve as signal suppliers for the stereo system.
After all, many computer users have now stored their music archive on the hard drive of the computer, and the sound of the TV just better suits the big picture when played back on adult speakers.
As the sound cards of computers do not meet high demands on the sound quality in the rule, a connection of the stereo system to the home network is recommended.
Since this is a topic of its own and is also very extensive.
As an alternative to the connection to the home network offers the possibility to connect the computer (digital) via USB cable (USB in the dictionary) with the amplifier.
Also with the television sets a digital cabling is recommended, since the devices often no longer have analogue sound outputs.
Although coaxial digital connections are a little bit better than their optical counterparts, televisions, like set-top boxes, should always be connected via the optical digital inputs, as they are connected via coaxial (electrical) ) Connections can lead to ground loops.
Coaxial digital inputs, on the other hand, are used for CD drives, network players, and other digital sources that are not connected to the house antenna (whether cable, satellite or terrestrial).
In addition to optical, coaxial and USB inputs, there are still BNC, XLR and Firewire inputs, but rather have an exotic status and will not be explained in detail here.
In order to process digital signals, an amplifier – in addition to the corresponding inputs – requires a computer that can convert the digital signals into analog signals.
This calculator is called a D / A converter. Since the D / A converter has a great influence on the sound quality of the digital sources connected to the amplifier, it should be correspondingly high quality.
Although there is an increasing demand for stereo amplifiers with D / A converters and digital inputs, the offer is not very extensive.
But do not worry, just the fact that the amplifier, which has been painstakingly selected for a long-term selection process, does not have the necessary digital equipment, should not stop you from buying the desired device. The desired amplifier can then be easily combined with an external D / A converter.
While the digital signal sources can be accommodated at the corresponding inputs of the converter, the converter is connected via its analog outputs (RCA, XLR) to a high-level input of the amplifier.
a) In order to connect the computer or the TV to an amplifier, it requires digital inputs and a D / A converter.
b) If the desired amplifier does not have the necessary digital equipment, this can be compensated by purchasing an external D / A converter or a CD player with digital inputs.
c) Make sure that the converter can process the sound formats of all the audio files you have archived.
d) Since all sources that are to be digitally connected to the amplifier are strongly influenced by the quality of the D / A converter, this should be as high quality as possible.
e) Although the coaxial (electrical) connection is a bit better than the optical one, all sources connected to the house antenna (cable, satellite or terrestrial) should be connected to the amplifier via the optical inputs Grounding ground loops could form.
The connection of a Turntable
If a turntable is to be connected to the amplifier, a phono input is required.
One of the “normal” high-level inputs cannot be used for this purpose, because the signal from the turntable has a much lower level than the high-level signals and also needs to be equalized.
Note that there are two different types of pickups, each requiring different phono inputs.
On the one hand, there are the MM (moving magnet) systems with a comparatively high level. On the other side are the much quieter MC (moving coil) systems.
Depending on the pickup system used, the input sensitivity values are different (2 to 5 mV at the MM input or 0.1 to 0.5 mV at the MC input) and accordingly an MM phono input or an MC phono input is required.
In the analog domain, cables are known to have a particularly strong range of sound quality.
Since the voltage at a phono input can be up to 5,000 times (0.1 mV to 500 mV) lower than at a “normal” high-level input, it makes sense to make these connections with a special phono cable.
A few MC cartridges – so-called high-output MC – have enough levels to operate on an MM input.
Almost every phono input is suitable for MM systems. In contrast, MC systems can only be operated on a part of the phono inputs.
If the desired amplifier can only manage high-level signals, it is necessary to purchase an external phono preamplifier.
This too must be suitable for the type of pickup you are using.
Numerous turntables – especially in the entry level – have a built-in phono preamp and can be connected to any high-level input.
a) Turntables cannot be operated on high-level inputs, but require a special phono input. An exception are turntables with integrated phono preamplifier.
b) Make sure that the phono input is also suitable for the pickup system you are using (MM or MC).
c) If the amplifier has no phono input, it can be supplemented by an external phono preamplifier.
How expensive should an amplifier be?
The purchase price of the amplifier should be based on the speaker.
There are different opinions on how the weighting of the budget of a hi-fi system on speakers and amplifiers should ideally be distributed.
The most commonly read is that about 60-70 per cent of the budget (for speakers and amplifiers) can account for speakers.
The remaining 30-40 per cent remain for the amplifier.
Overall, the best sound result for the amount of money used should be achieved.
If you intend to purchase small high-end speakers, it may be useful to shift the weight slightly more towards the amplifier.
Even loudspeakers with high electrical demands on the amplifier – whether due to their extremely low efficiency or due to an impedance curve that approaches the short circuit – require powerful and therefore expensive amplifiers.
Again, the amplifier may be slightly more expensive in relation to the speakers.
a) The amplifier should cost about half as much as the connected speakers.
b) When operating electrically demanding speakers should be slightly more invested in the amplifier.
What should be the power of the amplifier?
The performance of the amplifier is in the eyes of many end users a crucial criterion for its quality.
But does a 100 watt amp really sound better than its colleague who only has 50 watts under the hood?
This question can be answered with no.
How much power an amplifier needs is ultimately dependent on the connected speaker.
And here, too, there is a big misunderstanding.
Often the load limit of the speaker is seen as a measure of the required amplifier power.
But this has little to do with reality.
But how should you proceed with the purchase of the amplifier to find out how much power is needed?
The amplifier should be about half the price of the speakers to which it is connected.
Now they are already halfway on the safe side.
In addition, the key criteria for which the power required by the amplifier is the efficiency of the connected speaker, as well as its impedance characteristics.
The efficiency indicates how loud the sound pressure of the loudspeaker is at a distance of 1 meter when the loudspeaker is powered with a power of 1 watt.
Most speakers on the market today range around 85 dB.
If this is also the case with your speakers, you do not have to worry about the power of your amplifier, because almost every transistor amplifier is capable of driving the loudspeaker.
If the efficiency is lower, the amplifier needs more power.
Inquire whether the desired amplifier provides enough power for your speakers.
In particular, so-called Class A amplifiers often do not have enough power to properly drive low-efficiency speakers.
Tube amplifiers have – as far as the performance is concerned – a special position.
Especially with single-ended triode amplifiers, an efficiency of 85 dB is not enough. Inquire also here which efficiency your desire amplifier needs.
The impedance (measured in ohms with the Greek letter O) is frequency-dependent and varies more or less with most speakers.
The deciding factor is the lowest impedance value that the loudspeaker achieves over the entire frequency spectrum that it can reproduce.
This value is referred to below as the lower limit impedance.
The higher the lower limit impedance, the less critical it is to drive the speaker for the amplifier.
Here, values of 4 O are not critical for the vast majority of stereo amplifiers.
It becomes problematic only with a lower limit impedance of 2 O or less, in which only the fewest amplifiers remain really stable or load-stable.
When selecting the amplifier, the following applies.
At a lower limit impedance of more than 4 O, the operation of the speaker for virtually any stereo amplifier (even for tube amplifier) is not a problem.
With a lower limit impedance of less than 4 O, tube amplifiers will fail, and if less than 3 O, then you should also ask transistor amplifiers to see if the amplifier can drive your speaker properly.
a) The key factors for the power required by the amplifier are the loudspeaker’s efficiency and lower limit impedance. If both are in the common range (> 85 dB,> 4 O), practically every transistor amplifier is able to supply the loudspeakers with sufficient voltage.
b) If the efficiency and lower limit impedance are lower, it must be clarified in particular for Class A amplifiers whether the power of the amplifier is sufficient for the existing loudspeakers.
c) Depending on the circuit principle, tube amplifiers require a much higher degree of efficiency once again.
The above statements are primarily aimed at beginners.
In order to provide this target group with a high level of practical use, we absolutely wanted to avoid killing our readers with a wealth of technical expertise. Therefore, we deliberately tried to make the connections as simple as possible and to limit ourselves to essential information – just tricks and tips.
We ask you to consider this, if you, dear reader, belong to the group of “high-end audiophile specialists” and miss the necessary depth in this article you are welcome to share your tips and updates to this article as a comment below
Happy Sound Engineering