Discrete

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A discrete amplifier is an amplifier made of individual parts. Usually it defines an amplifier with solid state components even though tubes also are discrete parts. Components like resistors, capacitors, inductors, regulators, transistors, FET’s, MOSFET’s e.t.c are considered discrete parts.

Regulators are actually not single components as aren’t operational amplifiers (Op-amps) as they are complex designs with lots of components but are all tucked away in one ‘housing’.

In audio forums it is often stated Discrete amplifiers are better than the ones with op-amps in the signal path and also are technically better than tube(valve) amps.

Most discrete amplifiers consist of an input stage (that has a certain amount of amplification) and a secondary amplification stage followed by ’emitter follower’ stages that have no voltage amplification like the first 2 stages do but only amplify the current capabilities so the load (headphone in this case) can draw the needed current when the amplifier supplies the voltage.

amp principle

The overall voltage gain is higher than needed and for this feedback is needed. Feedback can be local (per amplification stage) and/or overall, meaning the output voltage is returned to the input stage in a fixed attenuation. This attenuation determines the total gain of the amplifier.

There are also designs that only use local feedback or no feedback at all and some people claim they can hear this. There is, however, no technical basis that supports this claim. In most cases these designs have higher amounts of distortion because of this topology. The question remains how high distortion can be before it becomes audible and how GOOD the transducers need to be to make these distortions audible and HOW these distortion signals IMPROVE the perceived sound quality.

Most designs are based on lots of gain and overall feedback. This feedback extends the frequency response, lowers the distortion and lowers the output resistance of the amplifier circuit and is essential in these designs for it to function properly.

TX amp insideThere are LOTS of discrete circuit designs out there and a few designs can be found in the DIY amplifier section amongst them a not so standard design called TX gain amplifier (shown above) which  uses a transformer as voltage gain stage and the ‘standard’ schematic of the well known ‘Panda’ amplifier.

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back to solid state amplifiers

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