Vermes
Advanced Member level 4
It is a construction of headphone amplifier – system based on popular transistors BD139 and BD140. Tube buffer used in this project consists of duotriodes ECC88, but you can use their substitutes as well or PCC88 version (when you switch glow in the power supply from 6,3V to 7V). Anode voltage is approximately 140V DC.
Button on front panel is used for the selection of operation mode (switching system consists of chip 4017). You can select from:
- headphone amplifier (operational amplifier and transistors)
- preamplifier ECC88
- headphone amplifier + preamplifier ECC88
That features make it a universal system, which can be used for both headphones and as source stengthening the signal before the final stage of tubes and transistors.
The device is divided into separate PCBs:
- power supply + driver
- audio
Power supply:
Power supply provides to the amplifier: +/-15V, stabilized, precisely set by multiturn potentiometers (under load), anode voltage +140W (together with 30 seconds delay system) about 6,3V or 7V to glowing of electrone tubes (user can set the needed voltage himself). In addition, you can get 5V from the transformer. Power supply provides voltage to only those components, which are currently used, so for example tubes are not in use in transistor mode.
Housing:
Front of the housing was made of sanded aluminum, protected with transparent spray.
Elements of the housing:
- mains switch backlit by an orange ring
- button for changing the operation mode
- three LEDs for current operation mode of the amplifier
- 6,3 jack input for headphones
- volume potentiometer
Sides were made of wood. Top and bottom were made of perforated metal sheet to provide ventilation. Top is not screwed so that the use can easily reach the tubes or operational amplifier. Sound can be modified at any time. Top is connected to the rest of the housing as shielding.
In the back (from the left), you have: two RCA plugs, right, left input channel, RCA right, left channel, preamplifier, output, fuse and input for mains votlage about 230V.
The amplifier stands on spikes with bases in gold color.
Link to original thread - Wzmacniacz Słuchawkowy z buforem ECC88
Last edited:
