Valkyrie 20w valve amplifier
Here is our 20W valve power amplifier, this is a Sound Aid design, aimed to fulfil the demand for the clean sound of an SE amplifier circuit, but with the strong drive capabilities of a push-pull amplifier using feedback. Quite a lot to ask for you might think, and after a year of development, we have it!
To take advantage of the professional balanced outputs now fitted to the majority of good quality DACs and preamps, this amplifier has a genuine balanced input as standard. A phono input version is also available.
The voltage amplifier stage is based on the ECC83, one of the best sounding high gain signal valves ever made. The output stage is built around a pair of K5881 beam tetrodes, biased in class AB, and using the ultra linear configuration. These are automatically biased, using a variation of the cathode bias principal.
The output transformers used on this amplifier are very special indeed. They are a precision wound double C core type, and when used with a nominal 8 ohm load will give a perfect impedance match to the output valves.
21dBs of overall feedback have been applied to the amplifier, and together with the unique circuit configuration provides an extremely clean sound, free from the colourations which characterize the majority of push pull amplifiers.
Careful design and quality components combine to deliver this hard to achieve result. The mains transformer is custom made to our specifications in the UK and feeds an oversized silicon rectifier. High voltage smoothing is via an audio grade reservoir capacitor made by Jensen in Denmark. All the resistors are audio grade, and the signal coupling capacitors are high quality Mundorfs. Point to point wiring is used throughout with silver plated copper wire having a rating of 9amps….
Loudspeaker connection is provided via tough 4mm banana posts which accept bare wire and spades. There are two pairs per channel to allow easy connection of bi-wired speaker cables.
Although this is a 20W power amplifier, each channel has its own volume control, using Alps blue potentiometers. The polished stainless steel top plate is 1.5mm thick and is braced to the 4mm thick base plate using solid brass supports to eliminate any vibrations. These plates are housed in a recycled solid afromosia teak surround.
This amplifier delivers on strong expectations, offering the benefits that valves promise, but without the typical coloured sound of push pull operation. The first ten watts are provided in class A, and the 20W output rating means that loudspeakers with a medium efficiency can be driven fully.
Obviously, all these high quality parts greatly increase the costs in making this amplifier, but the rewards are more than worth the extra expense.
We are delighted with this amplifier, very much welcome all enquiries to demonstrate this unique sound.