Description
Great all tube tube linestage in very good condition. Dual mono construction with large separate power supply. This is the predecessor to the Red Rose model 3a which presently sells for $5k. The Mantissa sold for $2k, is pretty much the same as the Red Rose sonically and is rarely seen on the used market.
This particular pre-amp has had many upgrades done to the power supply new internal wiring, Cap changes All work has been done by Raptor Audio and is now upgraded to SOTA status
More info
Very impressive tube line stage unit incorporating two each 6DJ8/6922 and 12AU7/5814 tubes, one each per channel, supplied by an external power supply The preamp board is isolation mounted to the black anodized aluminum chassis with the cover dampened. The external power supply has connectors for the preamp and AC power. It provides rectified and filtered DC voltage for both high voltage and low voltages. The external supply provides 500VDC for high voltage regulators, 11VDC for filament regulators and 11VDC for aux power. The preamp takes the 500VDC and regulates it to 450VDC for the two 295VDC 12AU7 and two 145VDC 6DJ8 regulators. Additionally the 450VDC regulator utilizes the 11VDC for a low voltage reference regulator. Each tube has an independent filament regulator that provides 6.15VDC in operate and 3.5VDC in Standby from the 11VDC. The preamp has five line inputs and a switched non-buffered Tape Out. Operating modes are Standby, Mute, On and -1.5dB. The last will reduce both channels volume by 1.5dB to provide finer steps in control. Two independent 23 position stepped ladder volume controls with discreet resistors provide attenuation with 3dB steps per position. The preamp is muted for 30 seconds after power is applied or when switched out of Standby position to either the On or -1.5dB position. Mute will defeat the output or restore immediately if the 30 second power on or Standby delay has occurred. A front panel bi-color LED indicates red for Mute, green un-Muted. A rear panel switch allowed floating the chassis or connecting it to circuit/signal ground to obtain the lowest signal hum. The 6DJ8 dual section triode is operated in parallel in grounded cathode mode and provides 20dB of gain. The 12AU7 White follower buffers the output without gain but provides a low impedance drive. No global feedback is utilized and the 6DJ8 is direct coupled to the 12AU7 Will ship
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http://app.audiogon.com/listings/audio-prism-mantissa-red-rose#TxFmRElX0eu0bIp1.99
