Output stage
The output stage is based and designed around the 845 tube, and comes as standard with the excellent Elrog 845. The power supply, biasing circuit and output transformer is a development of the successful designs of our Concero 25 MK1 design.
Output is rated at 20W, via a massive output transformer with selectable 2, 4 and 8 ohm secondary winding selectors. The output transformer weighs more than many SET amplifier’s total weight, and is of the highest quality.
The output transformers massive core used in the design is mandatory for delivering true undistorted upper and lower bass, and driving any speaker through complex musical content. Some SET amplifiers exhibit distortion when driving speakers with complex music due to core saturation. Our output transformer can easily take 60W at 20Hz, so at 25W intermodulation artefacts are next to zero.
Driver Stage
Driving the output tube is a major task, and where many SET amplifiers fall short, using tubes not adequate to the task, tubes with high Rp and small current swing capabilities. For the redesigned Concero 25, we decided to use the driver stage used in our bigger models such as the Concero 65. The driver stage is designed as a small Single Ended amplifier by itself, with it’s own power supplies, transformers, bias stage and filament supplies.
Our driver stage can deliver more power if asked than most other Single Ended power amplifiers. The driver tube is the 814 Directly Heated Pentode and is transformer coupled to the grid of the output tube using a very wide-bandwidth inter-stage transformer. No RC coupling is used in any of our amplifiers to ensure ultimate sonic performance it retained.
Separate power supplies are used throughout the Concero 25, fed by 2 toroidal transformers rated at over 900VA total. Separate toroidals are used for the driver stage, output stage, filaments and bias circuits. Driver and output power supplies are ground-choke filtered and energy banks are over 4000 joules per channel.
Filament Supplies
Both the driver and output tubes are Directly Heated tubes, that is their filament power supply units is part of the signal current loop. Any noise/hum present in the filament supplies will be amplified by the gain of each stage. Filament supplies can be a major source of noise and sound degeneration in DHT SE designs.
As in all of our DHT SE amplifiers, the filaments are fed with tripled filtered DC current. Filters are triple PI CRC filters bringing noise and hum to vitually unmeasurable levels. This is one of the reasons why the Concero 25 is one of the quietest amplifiers on the market, regardless of technology.
Biasing
Both driver and output stage bias can be monitored and set/adjusted on the fly, with the use on the built in digital monitors, paired with biasing adjusting knobs. Users can adjust the bias on the fly even while music in playing! This is a highly flexible feature and the sonics can be tweaked based on the settings.
Low / Medium Gain Version
The amplifier comes as standard in the low gain version (x1 gain) as well as the medium gain version (x7).
To get the maximum performance out of the amplifier, a high gain high output preamplifier is preferred.
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