Which advantages do balanced input signals offer
Why are discrete signal paths important
Twin op-amps are the most common design for operational amplifiers, i.e. two amplifier circuits are integrated in one device. If left- and right-channel signals are processed simultaneously by such a device, interaction between both cannot be excluded. This interaction is admittedly diminutive, but should be avoided whenever a different design offers the possibility.
Why are op-amps ideal for low-level signal processing
But an op-amp consists of tranistors as well...
Also ageing issues play a much less important role.
Due to the large number of op-amps types offered, it is possible to pick an optimum type for any specific application.
Why does frequency bandwidth limiting make sense
The elder the listener, the less he will hear high frequencies in particular.
In order to transmit these frequencies at optimum quality, the frequency response of an amplifier should be as wide and as "flat" as possible.
At the low end of the scale, this limit is represented by DC, as there is no frequency lower than zero.
In upward direction, the limit can be set to practically any frequency, but the higher, the more susceptible the device becomes concerning electro-magnetic interference.
This is not audible in the first place, but may interfere with the useful signal and then become evident.
Therefore, unrestricted frequency response attests thoughtlessness rather than remarkable engineering skill.
Why is a good volume pot essential
Digital Audio Converters
About digital volume control...
A Vinyl record has its limits at 60 d, a tape recorder without noise reduction systems will not be better.
People who are doing real world recordings can tell, that it is nearly impossible to record more than 60 dB dynamic range with a microphone - although microphone makers claim dynamic ranges from their mics to be more that 130 dB. This may be true when recording a cricket near a starting F-14 Tomcat. But - who needs that. Also, sitting in you living room, it is hard to follow dynamic ranges of more that 20 – 30 dB unattanuated without having trouble with your neighbourhood afterwards.
Today´s pop music´s dynamic range is reduced during recording to 2 – 3 dB … Please also note that harmonic distortion inside the signal cannot be smaller than the dynamic range.
It is not possible to have 100 dB THD (0,001%) with 90 dB dynamic range,
but it is possible to have 110 dB THD (0,0003%) with 120 dB dynamic range !
The best today AD converters offer dynamic ranges from 120 dB with distortion figures about –110 dB THD. The limits of physics are not far away. Lots of losses have to be faced during recording, editing, mixing … so the CD as a final storage and play-back media is a totally sufficient solution. You cann´t figure much more with senseful efforts.
Digital attenuation is done by shifting the signal from MSB (Most-Significant-Bit) in direction LSB (Least-Significant-Bit). Shifting a complete bit in LSB direction (and replacing it with a 0) means 6 dB attenuation.
We learned from the above ( the "real-world" A/D converter) that also a real 24 bit signal carries a maximum of 20 “senseful” bits - in practice there are no more than 18 bits. So, also a 24 bit signal may be attenuated by a minimum of 6 dB x 4 Bit = 24 dB = factor 35:1 WITHOUT doing any harm to the original data. For a 32 bit converter the calculation is 6 dB x 12 bit = 72 dB = factor 4.000:1.
About the analog output level...
Professional broadcast facilities in Germany - i.e. radio and TV stations - understand 0 dBFs as equivalent to 15 dBu analog level. In other countries this may be handled differently.
Why it makes sense to make such huge efforts
Why does an active feed-through make sense
Why does PRE-GAIN make sense
The (pre-)amplifier provides 4V output voltage, whereas the headphone requires only 2V for 100dB sound pressure level.
The (pre-)amplifier provides 1V, whereas the headphone requires 20V to release 100dB of sound pressure.
Why are high supply voltages essential
A headphone doesn't really require high power, but from the equation P = U2 / R we can see that the square of the supply voltage determines the power into a given load resistance.
The higher the headphone's impedance, the more voltage will be needed.
But this deals with the achievable loudness to a limited extent only:
Technically spoken, music lives on fast transients which put high demands on signal processing.
And thus a fast transient can easily push an average amplifier with +/-15 volts supply to its limits.
Due to VIOLECTRIC´s high supply voltage you will benefit from doubled output swing capability.
Why is a low output impedance = high damping factor essential
When the voice coil of a headphone has been displaced by the signal, an (error)-current will be induced when it swings back to its initial position.
This current must be suppressed as far as possible, which is effected best if the amplifier's output impedance is the lowest possible.
The damping factor describes nothing but the ratio between output impedance of an amplifier and a given load.
This results in an output impedance of <0.06 ohms in case of the HPA V200.
Why does a relay make sense when switching power
Amplifiers generate unwanted output signals when applying or removing power, which can damage the connected headphones.
The relay breaks the connection between amplifier and headphone and thus protects the latter until electrical conditions have stabilized.
Why turntables are susceptible to hum
Unfortunately indeed, since a balanced connection would be hum-free in practice and much more advisable in technical terms.
Common pickup systems usually represent a perfect dipole, and thus the advantages of balanced signal connection could easily be made use of.
During playback, the equalizing preamplifier inverts this process, thus enhancing not only the low frequency range, but also any hum interference to the signal lead.
Why did we choose instrumentation amplifiers for PPA V600
Like mentioned earlier, the balanced signals are fed to special instrumentation amplifiers with differential inputs, which were originally intended for the use with microphones.
Those instrumentation amplifiers are made to make lots of gain with only very small portions of noise - as low as no op-amp or a combination of op-amps could offer !
However, the difference between dynamic microphones and pickup systems isn't as big as one might assume:
By means of wire coils and magnetism, they both deliver very low signal voltage at quite similar impedance.
During design, we discovered that this breed of instrumentation amplifiers is ideally suited for turntable pickups as well.
Why an easily accessible gain control is useful
Furthermore, gain control can be achieved without any significant change in bandwidth, as faced with (multi-stage) operational amplifiers.
Thus, bandwidth still exceeds 200kHz at a gain setting of remarkable 60dB, equalling a level ratio of 1:1000 !
At the same time, precision resistors ensure perfect stereo matching at maximum 0.25 dB tolerance.
Why an easily accessible balance control is important
This value represents the loudness difference between channels, resulting to a shifted stereo image - or centre position - during playback.
The fine-resolution balance control of PPA V600 allows shifting of the perceived centre position to where it actually should be, of course with a detented neutral position.
The advantages of a variable input impedance
The PPA V600 provides eight different impedance settings, while the ninth (47k) is the standard setting for moving-magnet (MM) systems.
The setting is situated inside PPA V600.
The advantages of a variable input capacitance
Moving-magnet (MM) pickups with their typically high output impedance are much subject to influence by the amplifier's input capacitance.
For this purpose, the PPA V600 offers 16 individual input capacitance settings.
The optimum setting is to be read from the pickup's specification sheet in the first place, but may also be refined by further recommendations or listening tests.
The input capacitance setting is situated inside PPA V600.
What makes selectable equalization curves practical
During playback, the preamplifier must invert this equalization in order to obtain the original frequency response of the contents.
Quite a number of equalization curves were used over the decades, however, among which the 'RIAA' curve became the most widespread - named after the Recording Industry Association of America.
Other relativly popular equalization curves one may encounter are 'NAB' (National Association of Broadcasters) or 'BBC' (British Broadcasting Corporation), which can also be properly handled by the PPA V600 when set accordingly.