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In Reply to: RE: 4P1L line stage posted by Brinkman on April 22, 2014 at 11:58:37
Here is a photo of the second prototype. Across the front you can see the filament supply components. The large heat sink accommodates the Coleman current regulators for the filaments. The raw power supply sits just to the right, one channel's supply stacked on the other, and a pair of rigged PC mount filament transformers in the right front corner. The high voltage supply is fed by an R-core transformer and Triad choke (choke loading), raw supply and time delay, then shunt regulator. The 4P1Ls are each on a PC board with integral socket (using Mill-Max pin sockets) and the 13R cathode resistor (with filament current passing through it) on the heat sink. This board is not mechanically decoupled, but could easily be arranged that way with EAR-type stand-offs to minimize chassis-borne microphonics. Finally, the plate load transformers, which are Lundahl LL1692A/18mA.
This layout is probably not optimum, but it does illustrate the real estate necessary to get the job done at this level of performance. In the near future I will be be redesigning the raw filament supply and getting some beta boards for the circuitry together for a few of you to try.
Kevin Carter
K&K Audio
www.kandkaudio.com
Follow Ups:
This looks wonderful.
I am curious how you intend to incorporate the Rod Coleman filament supplies into this offering. Are you considering importing a small batch for resale?
Also, what are the dimensions of the chassis shown?
I am happy to still have already ordered a few of the standalone modules for this kit. Despite having a pair of your regulator boards, I really want to try out VR tubes. I would like to know if you have managed to coax satisfactory performance out of any of the family of VR tubes.
I have approached Rod about reselling them and he is OK with it.
The pictured chassis is 17 inches wide, 11 inches deep, and 3.15 inches internal height.
I have had no recent experience with VR tubes, so I can't say what they will do in this design. If you observe the restrictions regarding capacitive bypassing, they certainly work well enough, but how they would affect the sound would require trying them.
Kevin Carter
K&K Audio
www.kandkaudio.com
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