Mana and Model 1
AudioPrism Mana and Red Rose Music Model 1
The Mana amplifier initial design was by Victor Tiscareno with additional work in collaboration with Brian Hawkins. It was produced by AudioPrism and sold under that label until 1999 when Red Rose Music purchased the company. Upgrades were performed on the amp and it was then sold as the Red Rose Model 1. 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.
All configurations were a tube mono amplifier incorporating one 5842, four 6SN7 and eight 6L6GC tubes. The chassis is aluminum with dampened top and side panels and an attached front panel. The transformer cover was removable. A detachable 20A IEC power cord was provided. The line fuse is contained in a rear panel receptacle.
The amp has one line input, selectable between single ended or balanced. Operating modes are Off, Standby, On and Auto-Mute. A delay of 60 seconds was incorporated between Off and On to allow the tubes to warm up and reduce turn-on surge due to the large capacitors. A front panel bi-color LED indicates red for Standby, yellow during warm-up and green for On. A rear panel switch allowed floating the signal ground or connecting it to chassis ground to obtain the lowest signal hum.
The power transformer provided multiple windings for the various rectified and regulated supplies.. Two high voltage windings for the HV and HV reference generated a rectified 500VDC that was regulated to 450VDC for the output tubes and the regulated 400VDC supply. The 400VDC fed separate regulators for each gain tube section, the single-end input phase splitter and the driver tubes. Separate filament windings were provided for the regulators of the output tubes and the input/gain/drive tubes.. The bias supply winding were separate and regulated. An additional transformer supplied the control circuit board while power was off and for switching, mute, delay and the Auto function. The amp could be rewired for 90-240VAC operation.
The circuitry was configured as a balanced amplifier with the addition of a 417A/5842 phase-splitter at the input for single-ended operation. 6SN7 tubes were used for gain and driver tubes. Each phase was independent up to the output transformer. Separate feedback windings were provided for each phase to the 6SN7 input tube cathode providing 6dB of global feedback. The dual section 6SN7 gain triodes are operated providing gain as a grounded cathode amp feeding the other section. An AC balance control adjusts the signal level on one of the input tubes to compensate for gain differences between phases. The 6SN7 driver tube is used as a white follower, capacitor coupled driving the 6L6GC output tubes. The output tubes are operated with fixed, individually adjustable bias. Switching is provided for Triode and Ultra Linear mode. Cathode fuses were provided for each tube.
The Auto-Mute mode monitored the signal into the amp and if there was none for an hour, reduced the output tubes current by applying more negative bias and muting the amp. This would extend the tube life by reducing the current from 45mA to about 2mA per tube. When a signal was detected, the bias regulator voltage would return to normal, tube current would increase back to normal operation and the amp would un-mute. A control for each phase driver set the DC voltage level on the output coupling caps the same as provided in un-mute condition.
The 6SN7 tubes were JAN/Philips, Sovtek and then Electro-Harmonix 6SN7EH. The 5842 was Raytheon or optionally a WE 417A. Outputs had been 5881, 6L6WXT then Ruby 6L6GCMSTR. Tubes used were selected for low microphonics, noise, distortion and 0.25dB balance between amplifier pairs. The 5881 and 6L6WXT were purchased in bulk, operated in a burn-in rack and selected to match gain, bias and current.
The Ruby tubes were purchased as a matched set of 18 providing two spares per amplifier pair. In evaluation and subsequent QC testing, they had been run in the burn-in rack, tested for gain, current and bias and found to be extremely consistent. Consequently they were used with the normal 72 hour amplifier burn-in.
.The Mana was supplied in an anodized Champagne color with a black powder coat chassis, side panels and bottom cover. It was also optionally available with black or silver. The transformer cover was removable.
Running changes were made to all units. There was no designation change as the improvements were incorporated.. Units returned for service had some updates done automatically while upgrades were an option. Partial and full upgrades to a Model 1 was performed by Redmond Red Rose Music
Red Rose Model 1
When purchased by Red Rose Music, the amplifier standard color changed from Champagne to Silver. New output transformers increased power to 140 watts with 6L6WXT tubes. Input and feedback wires change to Red Rose Silver, resistors changed to Caddock and the driver tube bias changed.
Later the fuses for the output cathodes were moved the the top of the amp for convenience and Micro fuses were used. A change was made to the high voltage 450VDC regulator circuit improving full power sub-sonic demands.