Concero 25 Monoblock Tube Amplifiers

 

The new redesigned Concero 25 is our flagship of our smaller Prestige Series, a Direct Heated Tube Single Ended Monoblock amplifier.

The new design is designed using a blend of technologies used in our previous Concero 25 and Concero 65 amplifiers, modified to use the 845 tube.

As always we again endeavoured to produce a design that has all the sonic virtues of only the best of the best Single Ended amplifiers, but with absolutely none of their shortcomings.

Output stage

The output stage is based and designed around the 845 tube. The power supply,biasing circuit and output transformer is based on the tried and successful designs of the previous Concero 25 design.

 Output is rated @ 20W, via a massive output transformer, with selectable 2, 4 and 8 ohm secondary winding selector.

The output transformer weighs more than many SET amplifier's total weight. The highest quality massive core of the output transformer used in the design, is mandatory for delivering true undistorted higher and lower bass, and driving any speaker through complex musical content. Many SET amplifiers get distortion when driving speakers with complex music,because of core saturation.Our output transformer can easily take 60W at 20Hz ,so at 25W intermodulation aftifacts are next to zero.

Driver stage

Driving the output tube, is a major task, which almost all SET amplifiers fell short, using tubes not adequate to the task. Tubes with high Rp and small current swing capabilities. For the redesigned Concero 25,we went ahead and used the driver stage used in our bigger models like the Concero 65.The driver stage is designed as a small SE amplifier by itself,with it's own power supplies,transformers,bias stage and filament supplies.The driver stage can deliver more power if asked than most SE power amplifiers.

The driver tube is the 814 DHP 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.

 

Separate power supplies are used throughout our design, using 2 toroidal transformers rated at over 900VA total.Separate toroidals are used for driver stage,output stage,filaments and bias circuits.

 

Driver and output power supplies are ground-choke filtered and energy banks are over 4000 joule per channel.

Filament supplies

Both the driver and output tubes are Direct Heated tubes,that is their filament psu is part of the signal current loop. Any noise/hum present in the filament supplies will be amplified by the gain of each stage. Filment suppies is a major source of noise and sound degeneration in DHT SE designes.

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 at almost unmeasurable levels. This is one of the factors that 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 on-line digital current monitors,paired with biasing adjusting knobs.User can adjust the bias on the fly even while music in on!

Low/medium gain version

The amplifier comes 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.