This is another EL84 amplifier that I built as a variation on the previous “Matariki” design. Home-built, as are all of my amps. It is simplified in that it has no tone controls, no phono stage, and no remote control. Being built in the same size chassis as the Matariki, this means there’s a lot of empty space inside.
The person it’s been built for has a Langcaster electric guitar with pickups and a little battery powered preamp built in, so the guitar input on the front is just a line-level input with both channels tied together. There are no distortion or non-linear effects added to the guitar input.
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Insides and construction
|Topology|| Line-level amplifier, grounded cathode gain stage, DC-coupled|
cathodyne phase inverter, push-pull EL84 output in class AB using fixed-bias ultralinear topology, global negative feedback. 330V Plate Voltage.
|Valve complement|| Gain stage: 1 X 6N2|
Phase Inverter: 1 X 6N1
Output: 4 X EL84 / 6P14P
|Power Output (measured)||15W RMS both channels driven, 1kHz continuous, resistive load|
|Distortion (measured)||1.5% THD at rated power, 1kHz, resistive load|
|Output Impedance||4Ohm 8Ohm|
|Input Impedance||100 KOhms|
|Input Sensitivity||1.2v p-p for rated power (0.4v RMS)|
|Frequency Response||6Hz – 22kHz ±3dB|
|Power consumption||230v 50Hz 90w nominal|
The sound from this one is clean, detailed and very pleasing. The main amp stage is based on the well-regarded Fisher X100, with the appropriate modifications for the Russian triodes in use.
The output stage is EL84 in fixed bias ultralinear, biased to 8.4W quiescent dissipation (70% of rated maximum)