“Shiny Eyes” PSE 300B
A few month ago I had long phone conversations with my audiophile friend from New Jersey who wanted to buy a 300B amp for his new field coil speakers. He looked at the Audio Note PSE 300B, but had an itch for Monolith Magnetics transformers. I offered to help him design and build a PSE 300B.
And here is the final product, result of a few month of talk, design, breadboard, wooden enclosures ( I made them myself…my grandfather was a skilled carpenter and I learned few basic things from him) and final assembly…and now enjoy listening for a while at least…
This amp was designed in same manner like my PSE 4P1L: separate enclosure for PSU, top plate ( CNCed at Front Panel Express) will hold all parts and sub-assemblies, generous slots for heat management, symmetry across the board for a nice “stereo” look, very attentive to detail regarding the optimum placement of all components.
This is my first amp designed using 300Bs and I can say that I am very happy with the sound result. It has the power reserve that PSE 4P1L lacks of.
Few design strategies: self biased final stage ( as my friend asked to have a free of adjustments amp), driver and first stage with minimum 6dB overhead, all DHTs amp, all Monolith Magnetics power and audio transformers, all high quality components.
Few words to describe the schematics:
- Final stage parallel 2x300Bs Princess Sophia B/c with separate self biased provided by equivalent 1Kohm 36W ( 3x3K MRA 12) resistor parallel with 220uF/100V Cerafine capacitor.
- Driver 4P1L loaded on the interstage Monolith IT-01 gaped for 30mA, self biased using equivalent 0f 3.75Kohms/ 24W ( 2×7.5k MRA12) parallel with Cerafine 220uF 200V ( 4x 220uF/100V series/parallel)
- First stage CX-301A loaded on Ale’s Gen II gyrator Mu output DC coupled to 4P1L. 01A is filament biased on 20 ohms MRA12 resistor
- 8x Coleman filament regulators provide supply at constant current for all DHTs
- SSHV1 is used to provide supply for the driver-input stage
- PSu is providing unregulated, well filtered DC high voltage. The circuit uses 6CJ3 tube rectifiers and CLCLC filtering. Because of the high cost of the audio transformers, I provided a HT fuse.
- There are 8 raw supplies, one for each Coleman regulator. The schematics of the raw supply is according to Rod’s documentation, providing low enough ripple.
- two 11 wires flexible umbilical cords carry all the LV and HV, and Ground from the PSU to the Main.
I used my minimal equipment to make some measurements ( I am using a scope, an interface and Audiophile 192 sound card, ARTA software).
Here are few results:
- FR : 10Hz-20kHz =/- 0.5dB
- Input sensitivity for 16W on 8ohms output: 0.8Vrms
- THD at 12W on 8Ohms output : 3%
- Driver THD at 16W output: 0.2%
Here are some more pictures:
Coleman regulators on 300x75mm heat sinks
More from design stage and woodwork
Inside the belly of the beast ( each enclosure weights around 80 lbs.
Some temperature measurements:
And finally schematics and top plates:
I want to give thanks to Ale Moglia for his awesome gyrator , Rod Coleman for his great regulators and his advises and Yves at Monolith Magnetics for his permanent support.
I also want to gives thanks to my friend who gave me the opportunity to build such an expensive amp.
Facts: Weights total of 160 lbs and draws about 500 W.