Preamp Flavours
walters said:
Which Preamps give Colours and Flavors ??
There are many things to consider when trying to ascertain the 'colour' or 'flavour' of a preamplification stage. Read on.
walters said:
What causes a Preamp to have different Colours and Flavors??
We shall start with a 'signal' of a defined impedance entering into the preamplifier via the connector. The preamplifier stage ideally has 5 to 10 times the input circuit impedance than the output circuit impedance from the previous stage. Also, one must take care not to saturate the input stage of the preamplifier to distortion or cutoff ranges by matching the handleable voltage and impedance charactaristics from the output source into the preamp. One can measure, calculate, and estimate the compatibility of a preamplifier stage to a particular source by comparing the range of voltages, DBv, or DBu that the preamplifier stage may handle to the voltage, DBv, or DBu of the source using (in the example of DBv which is referenced to 1V - Assuming 'X' is your signal voltage) 20*Log (X/1)
From the input, the 'signal' can be handled in many ways. A differential bipolar transistorized input device will often have a low noise level and great frequency response, but will lack the saturation and isolation of a tranformer debalanced input. One may also use a pair of opamps to debalance the signal, often at the expense of a higher noise floor and perhaps artifacts from the inexact matching of the two devices. A transormer isolated input may not be necessary if the impedance of the input stage matches the inpedance of the input bipolar device, tube, or opamp. However, this most likely means that the interface should be coupled with a high-quality DC blocking capacitor, which often imparts its own subtle charactaristic tonal modulation to the input signal.
A transformerized input will not only isolate the output from the input of the preamplifier, it will also impart its own characteristics into an audio signal. Some of these modulations include the tendency to oscillate or 'ring' at higher frequencies, which can be measured by passing square waves of differing frequencies through the impedance reflection loaded transformer and visually ascertaining whether or not the transformer is causing said frequencies to resonate, often using the analysis of a digital waveform capture or oscillascope. This can also be caused by the physical charactaristics of the transformer itself, as the transformer will act like a reverse transducer and vibrate at the resonant frequency of which it was physically constructed to. A transformer also imparts the modulation of 'saturation' and 'inductance, capacitance, & resistance' upon the signal while passing through the electromagnetically charged coils, through a speciallized laminated conductive core, and re-instated into a differing ratio of coils. Output impedance converting or direct coupling (1:1) transformers can also be used.
walters said:
Some Preamps are clean and transparent but i want preamps that have Alot of colour and Flavors to add to the sound what causes this effect?
Each method of amplification and device coupling imparts its own sonic characteristics into the signal.
Bipolar or Field-Effect devices are usually linear, but are often capacitance coupled, which can reduce the lower end of the audible response due to phase shift filtering. One must also take into consideration the delay, Miller Capacitance, and phase shifting effect of the reverse diode within the bipolar amplification device, often due to the depletion layer of a reverse-biased or field-effected PN or NP junction.
Vacuum tube amplification utilizes much higher voltages, and is not often practical in a location where an ample supply of electricity is not available. Often a vacuum tube configuration is also transformer or capacitance coupled; in the former case one often has to utilize a low-pass filter below RF to minimize 'ringing' entering the initial preamplifier stage, and in the latter case the high-pass filtering often occurs. Even order harmonics are often incurred here, and the vacuum tube amplification stage has often been referred to as 'controlled harmonic distortion' or transconductive amplification.
