HIFI/HOME THEATRE & PORTABLE AUDIO

Cayin HA-300MK2 Direct Heated SET Class A Balanced Driven Vacuum Tube Headphone Amplifier

COMING SOON. The Cayin HA-300MK2. Like it predecessor, the HA-300MK2 is a Class A Transformer-coupled headphone and speaker Single-ended Triode Amplifier (SETA). It use a matched pair 300B Direct Heated Triode as output tube and a matched pair of 6SN7 as driver tube. The tube amplification circuit is operated in Single-ended, that’s why it is referred as SETA, and then feed to a pair of output transformer for single-ended headphone, XLR-4 and 4.4mm balanced headphone output and one set of speaker terminal.

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1. The irresistible 300B Direct Heated Triode

A lot of tube enthusiasts consider the Directed Heated Triode (DHT) as the holy grail of vacuum tube for audio application. DHT refers to Triode tubes that use the cathode as the filament and will heat up the cathode directly during operation. These can be considered as the minimal approach to amplification and have a huge following, especially among Japanese and Chinese audiophile communities. There is a long list of vacuum tubes belongs to this family, but for modern audio application, the more commonly used DHT are 45, 2A3, 300B, 845 and 211, and 300B is probably the most well-known and sought after DHT in audiophile community.

The 300B offers an attractive tonal characteristic that is very close to the dream of audiophiles. It has a prominent full-body midrange, harmonically rich with unforced details that bring out the best of acoustic instrument, and the holographic presence that how the singer (or the band) appeared to be directly there in front of you. Technically, 300B offers very high linearity during amplification. This probably accounts for the natural presentation and excellent low-level details that re-created the presence that bring us closer to our music.

Cayin adopts a matched pair of Gold Lion Genelex PX300B as output tube for HA-300MK2. This is a low-noise audio triode that offers very decent frequency extension with a natural, sensible and realistic sound signature. This tube is considered to be an excellent upgrade tube by many 300B users and has been called the best “Common Man” 300B tubes.

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2. SETA, a Purist’s One-way Ticket

Single-ended Triode Amplifier (SETA) is a vacuum tube-based design that uses a single-triode tube per channel to produce output without splitting the musical signal’s plus/minus parts in each channel. In contrast, a push/pull amplifier, which uses a pair (or more) of tubes, splits the plus/minus of the music signal, then it has to put them back together to form the complete musical wave in each channel. ……The perceived high sonic quality is mainly attributed to the simplicity and minimalist approach of the circuits involved, as well as the triode vacuum tubes that are typically used. One SET aficionado describes it as “a Zen simplicity to reproduce the complexity of music. Less is more.”

Cayin recognized the beauty of SETA and has devoted a lot of resource to develop dozens of SETAs in our history. HA-300 and HA-300MK2 employs the same 2-stage single-ended amplification with 6SN7 as driver tube. It will boost the input signal to the appropriate level so that the 300B output tube will perform its second stage amplification at a very linear condition. In simple terms, driver tube amplifies signal voltage while output tubes amplify current.

Cayin always use 6SN7 as driver tube when we use 300B as output tube. Chris Marten called this combination “legendary in audiophile circles” in his HA-300 review (HiFi+ July 2018, issue 161, page 69-72). For the HA-300MK2 implementation, Cayin uses a matched pair of Tung-Sol 6SN7GTB as driver tube for almost the same reason as Genalex Gold Lion PX300B. This is a super linear, low noise high performance, highly reliable and natural sounding driver tube for SET amplification.

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3. Transformer Coupled Balanced Driven

HA-300MK2 is a transformer coupled SETA. The output from the 300B output tube will drive a pair of proprietary output transformers which support both headphone and speaker outputs. If the 300B triode tubes are the spirit of the HA-300MK2, the output transformers are the flesh and blood of the amplifier. Cayin believes in this design. While there are different types of vacuum tube amplifiers in the market, we stick with transformer couple whenever possible, and that means literally all our desktop tube amplifiers are transformer coupled.

We understand the preference towards balanced headphones in Personal Audio hobby. For transformer coupled design, it is fairly straight forward to support both single-ended and balanced driven in the same circuit because our amplifiers are transformer coupled. Since balanced headphone amplification is feeding opposing polarity signals to the left and right ear-cup of your headphone (in regardless of whether there is a dynamic driver or a planar inside). We can achieve this through a specific method to wind the transformer so that the positive polarity (aka “hot”) and negative polarity (aka “cold”) are driven in opposite directions, hence deliver a fully balanced output from a single-ended tube amplification circuit. In other word, both single-ended and balanced headphone output are “original” output from the transformers, we don’t take the single-end output and then convert it into balanced through wiring. .

HA-300MK2 offers two balanced headphone outputs: 4.4mm and XLR4 and we have optimize these two headphone outputs separately. The XLR4 output is a full-fetched output from output transformer while the 4.4mm winding is a level-matched, lower noise, lower power output with the same audio performance, making it more suitable for portable headphones.

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4. Impedance Matched Headphone Outputs

One of the very useful feature of Cayin vacuum tube amplifier is the impedance matched headphone output. HA-300 provides three headphone impedance settings, and the amplifier will optimized its output to handle the headphone loading according to the specified headphone impedance. Each impedance matched output is an independent secondary winding from the output transformers. The impedance settings are:

Recommended for​Target Impedance (XLR4 and 4.4mm)​
Low (L):8Ω~64Ω​32Ω​
Medium (M):65Ω-250Ω​64Ω​
High (H) :251Ω~600Ω​300Ω​

Matching headphone impedance should produce a natural sound with well-defined bass reproduction. This is our recommended starting point but not necessarily your preferred sound signature, so you can start with the nearest setting to your headphone and then experiment with other settings.

Back to Transformer

To summarize, the output transformers of HA-300B are extremely complicated because we need a pair of Multiple Winding Output Transformers that takes cares of three headphone outputs (6.35mm, 4.4mm, XLR4) at primary winding, and supports three impedance matched headphone outputs, plus one set of speaker output, at secondary winding.

Transformer plays a vital role in transformer coupled vacuum tube amplifier. The design and implementation of transformers become an important part of our product tuning. The choice of transformer core, specification of copper wire in different parts of winding, and the winding instruction will affect the performance and sound signature of our product. This is a critical core competence that will maximize our product development capability, extend our product life cycle and enhance our operate efficiency.

Given Cayin’s scale of operation and devotion to build high quality tube amplifiers for our customers, Cayin bite the bullet and incorporated a small transformer plant in our facilities. We design and wind all the power supply and output transformers of our tube amplifiers in-house. This will allow the R&D department to have total freedom in specifying the winding instructions for our products, and we have total control on the material and craftsmanship on the transformer of our tube amplifiers.

5. Tube Regulated Outboard Power Supply

The power supply for HA-300MK2 uses a custom-build toroidal power transformer. This is a special circuit to supply different gain stages, and we have used 4 pieces of NOS RCA 22DE4 rectifier tubes to convert incoming power source to DC current for cleanest power with minimum interference for the amplification circuit. These are one of the best version of 22DE4 tube and when used as rectifier tube in HA-300MK2, they can easily last heavy usage of 5 to 10 years. The four 22DE4 are supposed to work independently from each other. When we replace a 22DE4 rectifier tube, we can do that per piece without any matching process. Please check back later for more detail about the outboard power supply of HA-300MK2.

Design and Features

  • Single-ended Direct-Heated Triode design, brings out the charm of the tubes with natural and realistic music playback.
  • Driver Tube: matched pair of Tung-Sol 6SN7GTB
  • Output Tube: matched pair of Genalex PX300B
  • Rectifier Tube: 4 pieces of NOS RCA 22DE4
  • Support Balanced (XLR) and single-ended (RCA) input, balanced input will transform to single-ended through a pair of input transformer.
  • The output from 300B will feed into a pair of custom design in-house manufactured high quality EI output transformer for speaker, single-ended (6.35mm) or balanced (4-pins XLR and 4.4mm) headphone output.
  • Choice of three impedance matched headphone outputs (L, M and H) to make sure HA-300MK2 can handle vast variety of headphones satisfactory.
  • Powerful headphone output, handle demanding headphones with ample headroom.
  • Custom make silica gel shock absorber as anti-shock buffer between critical tube components, chassis mainframe and tube socket, remove microphonic of 300B DHT effectively and provide quiet and realistic playback from sensitive headphones.
  • Minimize interference by reinforcing shielding of transformers, effective circuit layout and optimized circuit design
  • 60sec startup delay circuit to enhance circuit protection and minimize pop noise when startup.
  • One set of speaker terminal as alternative output, can be used as an integrated speaker amplifier with 8 watt per channel Class A output.
  • Outboard power supply provides pure and steady power for the amplification circuit with minimum interference.
  • Custom design in-house manufactured high quality toroidal power transformer and EI output transformers.
  • High voltage power rectification with set of four NOS RCA 22DE4 tubes.
  • Two-boxes design with multi-stage tube regulated power supply reduce interference to signal amplification effectively through independently regulated power supply for voltage amplification circuit. Optimize power provision to all circuit and enhance audio performance significantly.
  • Point-to-point Wielding to ensure shortest signal path and enhance the transparency and refinement of audio performance
  • High-Precision JRC MUSES72320V electronic volume controller with 41-steps ALPS balanced potentiometer to provide low noise and accurate volume control.
  • Premium grade MultiCap coupling capacitor improves resolving capability and soundstage.
  • High quality shielded silver-plated cable for internal wiring, minimize interference during internal transmission.
  • Beautifully design and crafted VU meter
  • Lock On quick-release aviation grade copper connectors with silver plated Teflon umbilical cable for outboard power supply connection.
  • Detachable vacuum tube shielding cage, easy to detach and install.
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