Purity Audio Design

Balanced 300B Tube Source
​Buffer Stage

Experience the sound of adding a 300B output stage to any source component.

NOTE: As of January 2020, the new Harmonia v2.0 2A3/300B DHT buffer/preamplifier will replace this product.

Please see Purity Harmonia v2.0

Update: New enhancements are coming with the introduction of the Harmonia MK2 buffer/preamplifier. The MK2 will mean a price increase. But dont worry, we are keeping the original Harmonia as well at a reduced price for a limited time If you are interested in the Harmonia at the price indicated below, we will be offering this price till the end August 2019.

There are many challenges in designing high end audio components. First and foremost, a properly design circuit from the power supply to the final output. With Purity, the next step is to come up with something that has never been done before. Leave it to Purity Audio Design to pursue these challenges. Purity has become known for developing true audiophile grade tube buffers providing balanced connection. Now we have continued this tradition with an audiophile grade buffer using 300B tubes.

The Harmonia Buffer stage has been designed for the truly passionate music lover. It is not a preamp. It is not a gain stage. It is a unique vacuum tube output stage designed around the infamous 300B DHT. Over the past several years, Purity Audio Design has been working on developing this 300B tube buffer stage. We now have what we believe is the passionate music lovers dream come true.


The Harmonia buffer is the worlds first audiophile grade buffer stage designed around the 300B DHT tube. This Harmonia is the first 300B balanced vacuum tube buffer that is designed to a level that is at home in even the most exotic audio and video systems. It is designed as a stand-alone tube buffer to bring you closer to your music by introducing the sonic richness of the 300B tube. We have all lusted for the 300B sound but found amplifiers using this tube offered limited dynamic control over many of today's heavy load speakers. Now you can have the richness of a 300B output stage of your source component in even the most powerful of solid state systems.

Found on the balance version is one set XLR balanced and two RCA single ended outputs as well as one set each for the inputs. All inputs and outputs, including single ended RCA are transformer coupled. The Harmonia uses a low output impedance 300B tube stage feeding high quality balanced transformers that have been custom made for Purity for this application. The Harmonia will enhance any line level source device.

Inside the Harmonia chassis you will find that Purity Audio Design continues it's tradition of using only the best parts including first rate input and output balanced transformers, Top grade capacitors and solid core Copper/Teflon wiring. Like our other products, you will not find a circuit board in sight other than the independent dual DC regulated power supplies for the 300B's heaters.  Both the power supply and analog circuit utilize 100% point to point wiring.

The all important circuit contains what we have found to be the best combination of passive components to bring the Harmonia alive. High quality DynamiCap capacitors provide sonic richness as well as maintained extension and detail.

Like all Purity Audio Design products, the Harmonia utilizes a hearty power supply. Starting with the high current toroidal transformer to the fully regulated DC filament supplies for each of the tube filaments, the Harmonia's power supply is designed to perform. The main B+, filament supplies are all each powered by separate, high current transformer taps. The B+ feeding the 300B tubes utilizes a CLC topology with a choke loaded anode for each 300B tube. What does this mean? Rather than feeding the tube from a capacitor or resistor, a choke is used in it's place. Purity Audio Design is known for providing some of the quietest components available. The Harmonia has an extremely low noise floor resulting in a jet black background.

The Harmonia finds it's happiness between any source component and preamplifier. Placing the Harmonia after any high quality CD player, DAC or phono stage, tube or solid state, brings a sense of 300B richness, smoothness and organic quality to any system without sacrificing any of the quality traits one would come to expect from a high end audio product.

The Harmonia can transform your dry, fatiguing home theater into a system your guest will think is driven by SET tubes. One thing the 300B Buffer cannot do is transform inferior components into giant killers. The 300B buffer can only enhance and bring forth more of the potential your system has to offer.

As can be seen in the photos above, the 300B tubes protrude from the top panel of the unit making placement more versatile while also allowing for tube rolling ease. Not to mention what will be considered one of the sexiest looking components in your system.

For the tube rollers out there, we highly recommend some experimentation with your favorite 300B tubes.

The Chassis is constructed of aircraft quality aluminum with CNC machined front and rear panels. Herbies Audio Labs Tenderfeet are located under the chassis in a 4 point configuration.

The Harmonia is available in either a fully balanced or all single ended version.

Please note there is no LED power indicator on the Harmonia buffer.

Installing the Harmonia into any system is as easy as installing any source component.

The sonic results are as follows:

Restores proper frequency balance through better impedance matching due to its extremely low output impedance.
Improves tone and weight without adding bloom
Adds 300B smoothness, richness and organic qualities to sterile or dry solid state and tube source components
Improves dynamics of source components that do not employ proper impedance matching,
Enhances detail, resolution and transparency.
Reduces listener fatigue.
Enhances the 3D soundstaging of better electronics and recordings.

Design Features

Signal Stage

- All inner signal wire uses Teflon solid core copper wiring to provide optimum performance'
- Teflon tube sockets 
- All silver Teflon RCA jacks insure low connector loss and high signal transfer 
- Custom, designed for Purity Audio Design balanced output transformers (balanced version only)
- Transformer coupling of both balanced and RCA single ended inputs and outputs (balanced version only)
- Neutrix gold plated XLR connectors
- DynamiCap output coupling capacitors for smooth, full bodied sound while maintaining air, extension and detail. 
- 300B cathode bypass capacitors bypassed with high quality film capacitors 
- XLR/RCA ground switch allows for best grounding plan for your application
- Equipped with 2 pieces EH300B Gold Grid tubes

Power Supply

- High current toroidal transformer.
- Bybee Musica Rails found in the balanced version.
- Regulated DC tube filament supplies running off separate transformer taps for exact voltage. One for each 300B tube
- Choke filtered
- Stealth diodes used for rectifying stage
- Each 300B tube is choke loaded on the anode
- Aluminum shield protects the output stage from power supply interference


- Black anodized aluminum chassis
- CNC engraved panels
- 1/8" 6061 aluminum throughout
- Herbies Tenderfeet for optimum isolation
- Heavy damping material applied throughout


- Output impedance: 180 ohms balanced
                                  150 ohms single ended
- Gain: <1dB
- Tubes: 1x 300B per channel
- 15" W x 12" D x 4.5" H with feet
                          9.5" H with tubes

Retail Price:
​Selling price

Balanced $6,200

Current Selling Price $5,995

Single Ended $5,500

Current Selling Price $5,100

Extreme Version:

​Includes StealthCap capacitors. V-Cap CUTF 300B Cathode Bypass Capacitors and full array of Bybee Purifiers at both the input and output stages.