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What are a 6H30PI, 6C45, and a T-100?

They are vacuum tubes.  The 6H30 and the 6C45 are small signal triodes built by Sovtek for voltage amplification.  The T-100 is designed and built for audio use by KR Audio in the heart of Bohemia, Prague.  The  T-100 is the master work of the late tube wizard Dr Riccardo Kron, founder of KR Audio in Czech Republic.  It is similar to an 845 in many aspects, but is dramatically improved for audio quality.  Sadly, he did not live long enough to see an amplifier ever built with this tube. Luckily, his wife (also Dr. Kron) has taken over the business and continued the tradition with an incredible passion.

The T-100 is undoubtedly one of the finest low frequency audio tubes ever built. Like all KR Tubes, it is built with Pyrex glass and is completely hand assembled and tested in very small batches. The KR Audio lead engineer, Mr. Marek Gencev does engineering control to ensure consistency. This means that each KR tube is precisely matched to specifications. These tubes have an lifespan of 10000 hours.

What are Class A, Single Ended, and Push Pull?

Class A and Single Ended/Push Pull describe the architecture of the amplifier. Class A amplifiers are the least efficient  because the electronics are always working their little hearts out.  Class A amps produce the least distorted most true sounds available. Single ended amplifiers use tubes to drive the transformer.  Most electronics produce sound in a single ended mode (on the RCA output jack).  This is a perfect input for a single ended amplifier.  For an example of single ended amplifiers, go to

Push-Pull amplifiers work like a slinky. The transformer is energized by two tubes operating exactly out of phase. To minimize componentry, push-pull amplifiers frequently synthetically generate the out of phase signal, with additional circuitry.  In the case of Opus, it uses balanced inputs directly from the equipment. While a less common signal format, it is  the least distorted push pull architecture available.  Courtesy of the extreme care in materials and workmanship, the Renaissance Audio Opus 2 has a power bandwidth that extends from 20Hz to over 100000Hz. 

Why tubes? Why Transistors?

These questions are enough to make the hair stand up on the back of any audiophile's neck! It is a debate that continues on with a theological zeal. Technically, there are only two ways to amplify signals. Voltage swing can be increased or Current swing can be increased. There is a mechanical analogy. When you run water through the kitchen sink and shut it off quickly, the pipes bang with the inertia of the water passing through them. The force of the water is dramatically changed through this process. This is much like current flowing through a wire. Voltage swing is like having the same water in the pipe, but having a balloon at one end and a piston at the other. Very little movement of the water will make large size changes in the balloon. Tubes work like the piston and the balloon. Transistors work like the kitchen sink. In truth, each has their strengths and weaknesses. We opted for tubes in the output stages because, in general, there are significantly fewer components required to make a tube amplifier work well. As such, the possibility of the sound being altered by a component is reduced.

What is Negative Feedback?

Negative feeback is a method of circulating a small piece of the output signal back through the circuitry to gain better control of the natural hysteresis of the output transformer. Negative feedback can also be used to flatten the frequency response of a given circuit.

The reality is that it can slow the response of the amplifier and dull the sound of the finished product.

We are proud to print that due to our extensive materials selection and engineering development process, Opus 2  requires no feedback of any kind to alter the signal.

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