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Valve amplifiers or tube amps

We say Valve Amplifiers, they say Tube amps but we're talking about the same thing!



When technology changed from valve to solid-state, it was noticed that solid-state amplifiers lacked warmth and bass performance and had to be twice as powerful as valve amplifiers, to sound as loud.



Valve amplifiers behave in �Current Drive�. This represents an open circuit across the speaker without over damping, allowing maximum response and efficiency.



Sensitivity: Valve amplifiers (current drive) are sensitive to crossover resonances and speaker impedance variations. Quality speaker systems often used passive crossovers that were second-order, constant impedance, and critically aligned to avoid resonant effects. Some quality speakers had copper caped pole pieces, which helped damp impedance variations.



Note:- With solid-state amps in voltage drive, power decreases as the speaker impedance rises. With valve amps in current drive, power increases as the speaker impedance rises.



Therefore a flat speaker impedance is synonymous with a flat frequency response.

Modulating Offset:



The output of solid-state amplifiers is directly connected to 2 DC power supplies through the output transistors. The instantaneous non-symmetry within the music waveform (particularly from the bass notes) is averaged as a modulating DC offset. This modulating offset is small, but it varies the efficiency of the speaker, introducing inter-modulation distortion, amplitude modulating the music.



This problem is mostly eliminated by the trend to use an active sub-bass.



In valve amplifiers the output transformer isolates the speaker from the amplifier electronics. No modulating offset can be produced.

Open Loop Gain: Feedback



Solid-state amplifiers are inherently nonlinear.

They have a very large �open loop gain� approx 20,000. The amplifier output is (feedback) to the comparator input to reduce the gain to approx 50. Therefore 99.9% of this feedback corrects all instability and non-non-linearity of the amplifier, as explained in amplifiers.



The speaker also acts as a large microphone. All non-linear movements and vibrations within the speaker cone, (caused by reflected nodes, chaotic resonances etc) of which there are many, are regenerated back into electricity by the voice coil.

This re-generated signal from the voice coil is inadvertanetly fed-back to the solid-state amps comparator input, and re-amplified back to the speaker as recycled distortion.

Re-amplified Distortion:



This re-amplified distortion is audible by comparison, when switching between a solid-state and valve amplifier in real time. By paying close attention, it is heard as a fine spurious inter-cluttering within the music. This is clearly noticeable with efficient speakers but not with inefficient speakers.

Valve amplifiers are inherently linear.



Their natural gain is small and therefore require minimal or no negative feedback.

Their designs do not require them to have comparator inputs as with solid-state amps. The small amount of negative feedback in valve amps is only required to provide damping to the speaker.

Valve Amplifier Design



From physics we know certain things must be a particular order and size to be efficient and this is acutely so with valve amps.



That's why you'll love the valve sound especially with vinyl.

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