US Amps AX owner manual Why Tubes?, Tube In, Tube Out VTCSD Vacuum Tube Current Sync Drive

Why Tubes?

You may know that a transistor is a modern, efficient, less expensive version of a vacuum tube, which is the device that made sound recording and reproduction possible in the first place. Now, the electronics industry has been

trying for many years to equal the sound quality available from tubes. They have been able to make transistor amps louder, cooler, more abusable, and less expen- sive than tubes, but to this day, they’ve been unable to make any solid state amp sound as good as a tube amp.

So, our engineer got to wondering, “What if I combined the sonic character of a vacuum tube with the drive capabilities of solid state?”

Well, the result is the U.S.Amps’ VTCSD hybrid amps. Using the signal path directly out of the tubes as a “steering” signal and the following drive signal wave from the transistors as the “motor,” with absolutely no negative feedback as a corrective to the transistor’s waveform, we achieved the most detailed, pleasing, articulated sound available in mobile audio today.

Tube In, Tube Out

VTCSD (Vacuum Tube Current Sync Drive)

Hybrid Tube/Transistor Amps

				Uneven Clipping
		Solid State Amplifier		Odd-order Harmonics
Solid State Input	Preamp Signal
Low Voltage	Smooth, Low
		Negative Feedback		Listening Fatigue
Low Current	Tube Voltage
		Transistor Switching		Compression
			Noise	and Coloration

Classic Vacuum Tube Amps w/Output Transformer

	High Voltage/Low Current
	Signal from Output Tube is	Output
		Transformer
Tube Input		converts
		Voltage
		Energy
Low Voltage	fed into Output	into
Low Current	Transformer	Current

The resultant signal is soothing and pleasing

Yet lacks much of the tubes’ original dynamic range

Vacuum Tube Current Sync Drive

	Positive Current Sync
Direct Input
Input signal is fed
DIRECTLY into the tube.		The original high voltage tube signal is joined by
There are no solid state	Negative Current Sync
gain stages or processors		a null-gain current following circuit that is pulled
in the signal path.		to the voltage rails by an opposing pair of
		current syncs, providing a sort of amplifier
		“power steering” to deliver speaker-driving

power without taxing the character of the original tube voltage content.

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