Dragon Inspire QMB-25 Mono Block Amplifiers are a Single-ended, Class A, parallel quad connected design by the legendary, Dennis Had.
Sold as Pair
We are pleased and excited with this 25 watt design featuring the 6V6 Beam Power Vacuum Tube Mono Amplifiers. Inspired by music of the 6V6 vacuum tube amplifier of Dennis's youth, this design might be the best he has heard in 57 years since listening to his father's string quartet practice on Friday nights. Can you just imagine the sweetness of one of the world famous 6V6 vacuum tube in a quad set producing 25 watts? Just about any home listening room loudspeaker can be driven with ease with the QMB-25 mono-blocks.
Each amplifier is hand-built with point to point wiring by Dennis Had himself. Each amplifier is hand signed by him on the botom plate. Dennis considers this his form of art. Each amp is like a newly sculpted masterpiece. He personally listens to each amplifier, both in the shop listening room and his home listening room, before it is shipped out. This is a passion he has held for over 59 years now ever since he built his first single-ended 6V6G hi-fi amplifier for the 7th grade science fair. He never dreamed that retirement was going to be so much fun!
The QMB-25 utilizes 4x 6V6 per amp. The 6V6 is a tube that can be operated well beyond it's published specifications. It works effortlessly in this design but with authority and control. Granted it is not going to be able to drive a huge pair of low-efficiency electrostatic speakers to peak demands. With regular to efficient sensitivity speakers, it will provide an amazing musical and warm sound. It is more on the neutral to warm side rather than laid-back lush sounding. Most of Dennis's designs over the years have had this tonality. The amplifier runs in Class A configuration. Class A offers a shorter simpler circuit to provide less signal deterioration. No Tube biassing is required.
The driver tube is a 6SN7. A very reliable and well regarded tube. It is arguably the best general purpose triode tube around. What we like to call a fun tube. Lots of choices (manufacturers) to tube role with providing a different tonality. Drew's personal favorite is the Sylvania Green Label 1950's 6SN7 GTB with a chrome dome.
The amplifier utilizes a 5AR4 for tube rectification. This tube essentially changes AC to DC for the power tubes to do their business. Like the 6SN7 this tube can have a good bit of difference in the tonality of the amplifier even though it is not in the signal path. Essentially it controls internal impedances when there are peak demands. It helps the amp clamp down on the speaker driver and provides the control of the sound. It affects attack, compression, dynamics and the sensitivity of the amp. It is an often a forgotten about piece of the puzzle. All tubes in the circuit essentially lend to the end result. The better the tubes the better the sound.
Dennis Had recently developed a new circuit to prevent power supply distortions caused by the output tubes pushed into high and even higher non-linear levels of output power. These distortions show up as parasitic modulation products even on the smallest forms of the power supply. The actual sonic audible indications are sharp high-frequency lisps on vocals and instruments becoming strident and for a better word ear piercing. Dennis normally lets his ear be the design chain but in this case, he went to the test equipment spectrum displays for analysis of the power supply waveform along with the output waveform and harmonic content. His goal was to limit odd order products in the output signal and in turn, discovered the source of many overload distortions. He discovered that when an output device, in this case a vacuum tube, became non-linear it produced various spurious distortion products back fed into the power supply. In the case of a basic power supply supplying both the output devices, along with the driving front gain sections, he was able to detect these modulated parasitic products in the driver stage compounding the problem of output distortion of the final product.
He was surprised to find the nasties invading even the regulated power supply circuit used for the input driver tube and output tube screen grids. His thought process, (dangerous!), took time to figure out a high impedance decoupling device for the power supply between the output and input devices with a shared power source. Well, since he has lots of free time these days to think about circuits and not banks and employees … bingo … the lights went on. How about the good ole two-element vacuum rectifier vacuum tube. Yea, like good ole 5U4, 5R4, 5AR4 etc and variants …. use the vacuum between the elements and to transfer the positive DC voltage from the high B+ output tube potential to the lower (+250 VDC) regulated driver and screen grid supply. With some additional parts and old man soldering, it worked well. It can now drive the heck out of a single-ended amplifier and create a listenable signal even in complete overload with the 2nd order harmonic masking the third and fifth order nasties. How does it sound …. smooth, with honey flowing from the loudspeakers. Observing the amplifier operating on the spectrum analyzer with the new power supply circuit shows that no matter how hard we drove the new revised ” Inspire, the second harmonic remained predominate at full clipping. Oh, and the DC bias current did not budge with this new power supply circuit.
5-year limited warranty on amps, 30-day on tubes