Harmonia v4 45/2A3/300B

2025 Harmonia v4 - The Harmonia v4 will continue on only as a DHT output stage for source components. A volume control will no longer be supplied with the V4.

2025 Production pictures posted soon.

Notice: The Harmonia is not a "buffer stage". It is a true DHT output stage. The Harmonia products DO NOT use a cathode follower circuit like other buffer stages on the market where you do not benefit from the full potential of the DHT tube. With the Harmonia you are hearing the full 45/2A3/300B sound. 

The industry's one and only DHT vacuum tube output stage

The Harmonia is meticulously designed to elevate audio systems with the distinct sonic richness that single-ended triode tubes provide.  

 Key Features: 

 1. The DHT tube serves as the core component, delivering the hallmark SET sound.     

2. A relay-based input selector facilitates connection of up to four source components. In the balanced configuration, all inputs and outputs are transformer coupled for optimal performance.     

3. Dual DC regulated power supplies ensure clean DC voltage is delivered to the tube filaments.  

The Harmonia represents a singular advancement in DHT vacuum tube output stage design, focusing on the most revered SET tubes: the 45/2A3 and 300B. 

Over the years, Musica Bella has been dedicated to refining this innovative design, ensuring an unparalleled listening experience.

OVERVIEW
The Harmonia stands as the world’s first audiophile-grade output stage, meticulously engineered around a Directly Heated Triode (DHT) tube. This innovative design remains unparalleled, providing a DHT vacuum tube output stage worthy of integration into even the most sophisticated audio and video systems. It serves as a standalone DHT output stage, enriching your listening experience with the sonic depth and warmth characteristic of the 45/2A3 or 300B tubes.  

For those who have yearned for the Single-Ended Triode (SET) sound but encountered limitations in traditional amplifiers—particularly with today’s more demanding speaker loads—the Harmonia offers a solution. Featuring a high-quality relay-based input selector, it allows for the rich characteristics of a SET output stage to be accessed by up to four source components, seamlessly integrating into high-powered solid-state systems.  

 Within the chassis of the Harmonia, Response Audio upholds its commitment to exceptional quality, utilizing only the finest components. Consistent with our standards, you will find only point-to-point wired circuit boards, as the design primarily employs independent dual DC regulated power supplies for the tube heaters. Both the power supply and analog circuits are crafted using 100% point-to-point wiring, ensuring optimal performance and reliability.

For the V4 series, we have introduced a new regulated DC filament supply that maintains a stable 2.5V or 5V, accommodating tubes that require high filament currents. 

Each main B+ and filament supply is driven by separate high-current transformers. The B+ supply for the tubes employs a CLCRC topology with a choke-loaded anode for each tube. This design choice means that a choke replaces the capacitor or resistor as the feeding element to the plate. 

The Harmonia seamlessly integrates with any source component, such as tape loops, integrated amplifiers, and receivers. When positioned after a high-quality CD player, DAC, or phono stage—regardless of whether they are tube or solid-state—the Harmonia imparts a richness, smoothness, and organic quality reminiscent of Single-Ended Triode (SET) systems, all while maintaining the high standards expected from premium audio equipment. 

 This device has the ability to elevate a dry, fatiguing home theater into a listening experience that guests may mistake for being powered by SET tubes. However, it's important to note that the Harmonia cannot transform inferior components into exceptional systems; its role is to enhance and reveal the full potential of your existing setup.  

For those who enjoy experimenting with tubes, we encourage you to explore the use of your favorite Directly Heated Triode (DHT) tube to maximize performance.

 Integrating the Harmonia into any audio system is as straightforward as connecting any standard source component.  The benefits of the Harmonia are as follows:  - Restores proper frequency balance through superior impedance matching attributed to its exceptionally low output impedance. - Enhances tone and weight without introducing unwanted bloom. - Adds DHT smoothness, richness, and organic characteristics to otherwise sterile or dry solid-state and tube source components. - Improves the dynamics of source components that lack effective impedance matching. - Increases detail, resolution, and transparency. - Reduces listener fatigue. - Enhances the three-dimensional soundstage of higher-grade electronics and recordings.

Design Features

Signal Stage

- High quality tube sockets 

- Neutrik RCA & XLR connectors insure low connector loss and high signal transfer 

-  Balanced input and/or output transformers (balanced version only)

- Transformer coupling of both balanced and RCA single ended inputs and outputs (balanced version only)

- Quality output coupling capacitors for smooth, full bodied sound while maintaining air, extension and detail. 

- Tube cathode bypass capacitors bypassed with high quality film capacitors 

- XLR/RCA ground switch on balanced version allows for best grounding plan for your application

- Equipped with 2 pieces Sovtek 2A3 tubes

Power Supply (5AR4 Tube Power Supply Available On Request)

- High current toroidal transformers.

- Regulated DC tube filament supplies running off separate transformer taps for exact voltage. One for each DHT tube

- Choke filtered

- UF diodes used for rectifying stage

- Each DHT tube is choke loaded on the anode

Applications:

-DHT Source selector between sources and preamplifier (recommended), integrated amplifier, solid state receiver, tape loop

- Use between preamp and amplifier to get that DHT emotional sound.

Current In-Stock Chassis
- Aluminum

-1/4" Thick Acrylic Faceplate. You choose the color

-Custom Charcoal Powder Coat Chassis

- Laser Engraved Front Panel

-Heavy damping material applied

Specifications

- Output gain: <3dB
- Output impedance: 180 ohms balanced
                                              150 ohms single ended- Gain: <1dB
- Tubes: 2x 45, 2A3 or 300B
- 16" W x 16" D x 4.5" H with feet
                          9.5" H with tubes

Price: $4,500 Single Ended

$5,500 Balanced

Footnotes:

(*) - Please note that the Harmonia with volume control is used as a preamplifier or used between a preamplifier and amplifier, there is a slight potential for noise depending on your system configuration.