Nat audio are a very interesting company who manufacture high quality valve based amplification from their base in Serbia. Their amplifier topologies are predominantly single ended Class A with several innovative use of triode types of valves. Triodes are known as the most linear of all amplification devices but are also known for typically low output power. Nat audio’s relentless innovation has come up with solutions to this problem in utilising specialist high powered triode valves such as the GM 70 which is featured in the Single HPS amplifier.
The audiophile world still holds single ended triode amplifiers in such high regard, however users have been put off using SET amplifiers due to their low power and lack of damping factor which results in poor control over the bass drivers. The Nat audio approach retains all the magic and simplicity of a single ended class A triode and at the same time provides high power and a low enough output impedance to maintain control over a wider range of loudspeakers.
Personally I am a huge fan of the magical sound of single ended class A valve amplification. Output devices running in single ended mode don’t suffer from the effects of crossover distortion associated with push pull equivalents, which results in a very natural engaging sound.
My desert island amplifier would definitely be single ended class A valve type.
Please see below for details:
Single HPS operates in single-ended, zero global feedback, pure class A manner. Power output is set to 50W into 8 ohms. Best quality of amplification will be with moderate sensitivity loudspeaker with stable impedance from 4 ohms to 16 ohms.
Driver stage in Single HPS form E88CC (or equivalent) tube, capable to act as low distortion stage, made by military standard, indicate as N.O.S. (new old stock) grade of the highest quality.
Output stage form military grade direct heated triode (D.H.T.) GM70, high performance tube capable to dissipate up to 125W. Single HPS represent a truly single-ended design without parallel connection of tubes with high 50W of power output.
Hand coiled and assembled wide bandwidth output transformer (custom designed for NAT ) is used.
Single HP’s bandwidth from 10Hz – 60.000Hz has exceptional good flatness for single-ended zero feedback type.
By specific connection of the output transformer with power tube, amplifier may drive almost any type of loudspeaker with damping factor that is few times higher than normal.
Filament soft start improve reliability of entire integrated amplifier by avoiding voltage stress during turn-on procedure. Standby function additionally improve reliability of non analog section.
No any adjustment from time to time of output tubes is necessary. Single HPS has automatically adjust current capability for GM70 tube no matter of tube duration – constant current in time domain – from the brand new to the end point of tube lifespan.
To avoid unnecessary heat Single HPS has possibility to be selected to low mode – 30W of output power with significantly reducing of power consumption!
Power supply section participate in sound quality almost as amplifiers main circuit. Silent power unit of 400W is designed for double power than Single HPS consume.
Over 500J of energy storage is used in form of high quality multi-capacitors bank!
Separate power supply (conditioner) unit additionally improve sound quality by removing magnetic leakage flux inside the main chassis!
For the highest “purity” of power supply voltage a special designed and selected passive components are used. Tonal quality is totally independent from line voltage instability.
Attenuation network as one of the most important part of any integrated amplifier is realized in Single HPS as 56 high reliability silver contact silent relays network. Only one resistor of high quality at any volume setting is on the signal path (shunt type) ! Volume control linearity is at high level – from DC to over 1MHz!
Single HPS is equipped with multi function remote control unit made from solid block of aluminium. Front panel is made from solid block of aluminium as well! Indication of all amplifiers function is shown by blue led’s on universal function display.
Quality of electronic components that is used inside Single HPS are at high level – military grade and N.O.S. tubes, Teflon and “in-oil” military grade capacitors, Caddock and Vishay 5ppm resistor, Ohmite Alumina HV type resistor, many electrolytic capacitors for 105C of operating temperature, last generation J-FET semiconductors, laboratory grade speaker connectors, Hammond mechanics, teflon isolated silver-ofc military grade wiring…
Single HPS works properly at world wide AC line voltage from 100 – 250 VAC, 50-60Hz (different voltages set in factory only).
ADDITIONAL INFO: Single HPS is equipped with pre. out connection for subwoofer amp. or similar biamplification purposes. There is possibility for connecton of external preamplifier (line stage) to drive Single HPS as stereo power amplifier.
NOTE:
–Standard version use pseudo-balanced input
-First step of upgrade : pure-balanced input realised with hand coiled nano-crystalline core transformer
-Premium step of upgrade : pure-balanced input realised with hand coiled silver-ofc wired nano-crystalline core transformer
| Technical Specification | |
| Name | Value |
| Type | Single Ended Tube Base Zero Global Feedback |
| Power | Up to 50 W @ 8 ohms |
| Frequency Response | 10 to 60 kHz, -3 dB; 20Hz to 20kHz, +/-0,5dB |
| Noise | 90 dB IHF reference to 1W |
| Sensitivity & Gain | 0.4V for full power, 34 dB (X 50) |
| THD & N | < 0.15 % @ 5W output, < 1 % @ 40W output < 5 % @ 52W output |
| Input Impedance | >15 kohms |
| Output Impedance | <0.8 ohms (damping factor >10 reference to 8ohms load @ zero global feedback) |
| Stereo Separation | >95 dB |
| Tube Complement | 2 x 6N23P (E88CC) & 2 x GM70 per unit |
| Power Requirements | 100VAC to 240VAC (50 to 60 Hz), max. 390 VA |
| Dimensions | 19″ (483 mm) wide ´ 15.7″ (400 mm) deep ´ 10.2″ (260 mm) high |
| NET Weight | approx. 74 lb. (33.5 kg)/unit + 16.5 lb. (7.5 kg)/power supply |
| TOTAL Weight | approx. 114.6 lb. ( 52kg) packed in polypropylene crate |
Design Features
– single-ended type – integrated amplifier
– zero global feedback design
– triode direct-heated (D.H.T.) output type
– short signal path
– full dual mono construction
– 50W of pure class A
– output section – GM70 tube by military grade and N.O.S.
– driver section – 6N23P (E88CC) tubes by military grade and N.O.S.
– hand coiled balanced output transformer (custom designed for NAT)
– separate transformer-conditioner power supply unit
– regulated power supply for all stages (including the output)
– universal (12 leds) display
– filament soft start operate to improve entire reliability
– remote control made from solid block of aluminum
– automatic bias current control with long term stability
– standby function
– relay (silent type) attenuation network
– hand assembled all modulated chassis
– high mass Schutzinger laboratory grade output connectors
– gold plated PTFE insulated RCA input connector custom ordered from NAT
– extensively used computer numeric control machines (CNC)
– 5/8″ (15mm) thick aluminium front panel
– cover cage (optional)
