Mantissa and Model 3

AudioPrism Mantissa and Red Rose Music Model 3

 The Mantissa Preamplifier was designed by Victor Tiscareno. It was produced by AudioPrism and sold under that label until 1999 when Red Rose Music purchased the company. Upgrades were performed on the preamp and it was then sold as the Red Rose Model 3 Line Preamplifier. AudioPrism had an Issaquah and later a Redmond, Washington address. Manufacturing, Sales and Service continued in Redmond after the sale to Red Rose Music until the location was closed and tube electronics discontinued.

 General Description

 All configurations were a 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.

Later Mantissa and all Red Rose Model 3 tubes were JAN/Philips 6DJ8 and 5814. These tubes were treated with a proprietary method. Tubes were selected for low microphonics, noise, distortion and 0.1dB  balance between channels. The rejection rate from the selection process for the 6DJ8 was very high while the 5814 was much better. The 6DJ8 higher fallout rate was due to the stringent requirements imposed on the gain tubes for greater then 90dB Signal to Noise un-weighted and very low microphonics.

The external power supply was painted black and configurable for 100, 120 and 230 volts with transformer wiring changes. A detachable IEC power cord is utilized with the AC inlet providing a fuse within a pull-out drawer. The supply has a 9 pin connector for the umbilical cord from the preamp to connect. The Mantissa Silver Signature Reference and the Red Rose Model 3 Silver Signature used a larger inductive capacitive supply with a 19 pin connector and larger umbilical cord from the preamp.

Mantissa

.The Mantissa was supplied in an anodized Champagne color with black front panel and white rear lettering. It was also optionally available in Silver with black lettering or Black with champagne lettering.

  Also available was the Mantissa Silver Signature with standard supply and the Mantissa Silver Signature Reference. with a larger power supply that had additional transformers and inductors for the high voltage. The Reference had a 19 pin while the others had a 9 pin connector.

 The Silver Signature units had upgraded Kimber RCA connectors and KCAG silver signal wiring, silver contact volume attenuators with HALCO resistors, Multicap PPFX-S capacitors and Caddock resistors. Additional dampening was added to the chassis and the front panel thickness was increased. The Reference provided more independent supplies for the high and low voltage reference supplies and thicker umbilical cord for additional connections.

  The MFM-1000 was optionally available as an upgraded external supply with a larger inductive capacitive supply for the Mantissa and as a MFM-1000R to upgrade the Silver Signature to the Reference.

 Running changes were made to all units. There was no designation change as the upgrade were incorporated. Units returned for service had some updates done automatically while upgrades were an option. Upgrading from a Mantissa to a Silver Signature or Reference was a complete rebuild. Adding the MFM-1000R to the Silver Signature required returning to make internal changes and add the larger umbilical cord.

 Upgrades and repairs were preformed to the Mantissa by the Redmond Red Rose Music

Red Rose Model 3 and Model 3a

 When purchased by Red Rose Music, the preamp standard color changed from Champagne to Silver as the obvious external change. Internal changes occurred as well; coupling capacitors changed from ASC to Multicap, some resistors changed and the 6DJ8 grounding was revised. The Model 3 Silver Signature was derived from the Reference with circuit and external power supply changes.

 The Model 3a was the last change to the preamplifier. The output of the main regulated 450VDC supply feeding both left and right channel 295VDC and 145DC regulators were split with RC networks.  This improved isolation between channels. Also the external supply incorporated an additional transformer for the filament supply, un-burdening the HV transformer

 The Model 3a Silver Signature added an additional board providing active regulation to separate the left and right channel 450VDC supply and a change of the resistors for the 295VDC and 145VDC regulators. The external supply added another inductor with a new circuit board and some other changes.