Click on schematic for full size
Click on schematic for full size
A DHT Dynamically Balanced Amplifier + preamplifier
by Lynn Olson from Aloha Audio, USA.
April 2000
The AMITY amplifier is based on the AVTT mesh tube AV8B, and The AV300B, but can be easily adapted, using other tubes, like the AV20, or 2A3, 32B, 520B, or the AD100. As an the output tube, several tubes can be choosen from. For exact data see the table in the schematic.
Click on schematic for full size
Click on schematic for full size
As a preamplifier, the RAVEN was designed to match
the power amplifier. This preamp uses finest Japanese resistors
from Shinko and Kiwame. As transformers the high qaulity Lundahl and
Electra Print products were choosen. ( See AVVTCLUB page for
manufacturers addresses)
Click on schematic for full size
Click on schematic for full size
The distortion measurements show what this balanced amplifer is really capable of. The spectrogram from the HP 8535A shows a 1kHz fundamental tone (measured at 1.6 watts into a 4 ohm load) and the harmonic distortion the amplifier generates. If the amplifier were distortionless, all you would see would be that single 1kHz tone extending to the top of the display, and the "grass" or noise floor at the bottom of the display.
The next little bump to the right of that is about 6.5 intervals down
from the top of the display, so that's 65dB below the fundamental, or
about 0.05% or so. That's the 3rd harmonic. A little bit of 5th is
peeking out from the noise, and it's around 8.2 intervals down from
the top, which is -82dB down, or about 0.008%. The rest appears to be
noise at the -92 to -95dB level ... this is the limit of the measuring
system, not necessarily amplifier noise.
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Author: Lynn Olson from Aloha Audio.
Aloha Audio is now called Nutshell
High Fidelity