Tube-based Buffer amplifier

Posted on Feb 5, 2014

The solid-state, unity-gain power buffer is easy to imagine, as many already exist. But what about corresponding tube equivalents Have they been made Could one be made Actually, super cathode followers (complex-and-augmented cathode followers with a gain of 0. 99) have a long history, with many interesting designs appearing in the 1940s and 1950

Tube-based Buffer amplifier
Click here to download the full size of the above Circuit.

s. But a tube power buffer robust enough to drive directly loudspeakers is rare, and with good reason: the impedance mismatch can only be easily addressed with an output transformer. Because of the transformer`s phase shifts, however, the amount of feedback that can be wrapped around a tube amplifier and its output is limited. And all buffers use some form of feedback to deliver low distortion and output impedance. Couldn`t an OTL tube-based power buffer be created that would allow much greater amounts of feedback to be used Sure; but it, like all tube OTL amplifiers, will be a beast. In the schematic above, we see a power pentode configured in a simple single-ended topology, with the only interesting twist being the pentode`s cathode direct connection to the transformer`s secondary. This connection eliminates the pentode functioning as an amplifier, as the cathode follows the grid, thus providing 100% degenerative feedback. This short feedback loop gives the pentode`s output stage a low impedance output that it would otherwise be altogether lacking. It also lowers the distortion, improves the PSRR, and extends the bandwidth. Actually, the PSRR is fairly good in a pentode-based single ended amplifier, even without the feedback loop, as the pentode`s high rp, unlike the triode`s low rp, makes a poor voltage divider against the output transformer`s primary impedance. In the schematic below, we can see the noise relationships...

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    10000Vdc Supply
    Self Retriggering Timed Generator Circuit
    87C51 Selling Leads
    RGB LED Strip Circuit with Arduino
    2x60 Watt Stereo Audio Amplifier LM4780
    raspberry pi vu meter
    high voltage 555 audio modulated flyback
    rgb color sensor on arduino
    switching loads with MOSFETs
    usb powered mobile phone battery
    simplest led flasher
    fm generation using 555 timer
    Wiring up to the AN2131
    Low Voltage Preamplifier