The Preamplifier

Through extensive research and development, we can offer one of the ultimate expressions of what is possible with a vacuum tube preamplifier.

Volume control is performed through a TVC (Transformer Volume Control). A pair of Finemet transformers and a multi-position rotary switch simply alter the input signal’s ratio of voltage to amperage. This method does not dispose of any sonic information as it attenuates the audio signal to the preferred listening level. Music does not lose any detail or energy, regardless of listening level.

The properly attenuated signal is then sent to the amplification stage using the 4P1L directly-heated vacuum tube in triode configuration. The 4P1L has a low plate resistance is ideally suited to make a low output-impedance preamplifier. The sound is clear and clean with the pleasing predominant 2nd harmonic. The tube is run in filament-bias mode, with the filament supply provided by a Coleman regulator.  This has the advantage of using a very low value resistor to bias the tube and therefore there is no need to decouple it with a capacitor. The entire gain stage is completely free of coupling or decoupling capacitors, yielding a sound uncolored. Custom made output transformers using Finemet cores complete the signal path. The Treehaus Preamplifier essentially is a SET amplifier in design philosophy.

The 4P1L produces incredible sound, however, like many vintage tubes in some instances this tube can be found to be microphonic. We have carefully engineered the preamplifier to mitigate this issue. Working closely with edenSound, we have utilized their proprietary engineered polymer TerraStone to create an isolation layer within the signal enclosure. The main signal board is mounted to a TerraStone plinth, which in turn is mounted to the chassis through isolation bushings. This eliminates any chassis vibration entering the 4P1L through the tube socket. To mitigate vibration transmitted directly into the tube from the glass, edenSound IsoDamp tube dampers provide both mechanical and EFI shielding to the tubes. Finally, we offer edenSound TerraCones footers for yet another layer of mechanical isolation. We feel the sound the 4P1L offers is worth the effort.

Like our other products, a proper power supply is critical. The preamplifier has a separate power supply enclosure to keep noise transmission to an absolute minimum. The power supply utilizes several power transformers to isolate circuits as necessary. A pair of 6CJ3 diode tubes provides high-speed DC voltage tube rectification to the audio circuit, and a CLCLC (capacitor-load-capacitor-load-capacitor) utilizes both film capacitors and a Finemet choke in the final stage for ultra-pure power.

Special care has been taken to the usability of the preamplifier as the control center of system. A front standby switch on the signal enclosure makes powering on easy. (We use a special 12VDC circuit for the power switch so that no AC wall current is in the signal enclosure, and a main power switch is on the back of the power supply). An optional remote control can operate the attenuator switch so volume adjustment from the listening position is effortless. A trigger out can also be fitted if requested.

Cardas connectors are used for the RCA inputs and outputs. Elma or Seiden rotary switches are used for input selection and volume attenuation via the TVR. MIL-spec Amphenol connectors supply power to the preamplifier via an umbilical cord. The Kinsuido design possesses hardwood veneer cases over Baltic Birch, with 5mm oxidized aluminum faceplate and patinaed brass knobs to complete the aesthetic. The A/Machines design uses vintage-looking large dials, Simpson gauges, black inset panels and hammertone cases.