Vermes
Advanced Member level 4
It is a construction of headphone amplifier – classic design of a tube system, simple and stylish device.
It is a module construction, which consists of two audio boards and a power supply. It can be closed in a small housing. Design uses 1% resistors and good quality capacitors and components of audio circuit.
Audio part:
Preamplifier was carried out on TESLA ECC88 tubes operating in WK/KA. Glow current is approximately 300mA. Anode voltage in the power supply turns on after about 1,5 minute, what prolongs the life of tubes. ECC88 have 3mm orange LEDs in plinths, which looks nice in the evening. Switch on the front is the same color.
Gain stage is implemented on transistors HEX-FET IRF540, 2 pieces per channel. All those were insulated from each other using mica pads and insulating spacers. Board with them were placed under the grid.
Power supply:
Power supply board is a typical universal board for tube constructions, which consists of:
- anode power supply +150V
- +15V power supply for transistors
- 6,3V power supply (voltage and current rise slowly)
- delayed switching anode voltage
Housing:
Housing was made of adapted housing of a computer power supply. Unnecessary holes were filled. Then it was covered with a base and black acryllic matt. Sides were finished with varnished oak wood about 1cm thick.
The amplifier is passively cooled. Final stages – transistors, are placed on heat sinks from PC power supply (one per channel). Hot air passes through the top ventilation grid, so there is no problem with heat dissipation. Rear heat sink dissipated heat from voltage stabilizers of the power supply.
Transformer:
Transformer was placed in a separate housing on a long detachable cable to eliminate interferences in the system. Housing of the transformer is made of plastic and it is eqquipped with fuse and mains switch. The transformer is shielded and toroid.
The inside of the device:
Link to original thread - Hybrydowy wzmacniacz słuchawkowy w klasie A, ECC88