After an incredibly long journey I’m glad to say that is nearly over. The Starlight CD transport (I2S output and 4x oversampling) with its discrete DAC sounds absolutely amazing. Getting back to play my CDs is what I was cherishing for a long time. I will be bringing my +500 CD collection from my previous home soon so that would be perfect timing.
I promise to write up a proper blog entry with a full description of the learning experience. For now, I will just sit down and relax. Listen to many CDs and enjoy!
All the acknowledgements and thanks go to Tom Browne for this fantastic design and all the help provided throughout this journey. I think this is the Starlight number 20 or so built so far. Not sure if there are other ones being built anyway. Also my thanks go to Jon Finlayson for his help on the DAC boards, Richard for the UI stuff and to Tony for inspiring me to give it a go…
A friend in DIYAudio came up with a great idea of using the 4P1L in a different way for a pre-amp/line stage. Given availability of IT and its gapped current, he suggested connecting the 4P1L differently. Instead of using the anode as the anode element, the screen is used as anode. The 4P1L screen has a maximum current of 10mA and dissipation should be within the 1.5W.
The 4P1L curves in this mode
Let’s look at an initial transfer curve with Uak=100V:
I wired the 4P1L in the following way to allow tracing with the uTracer:
The connection is slightly different as the one suggested by Indra. If you are looking to implement filament bias, you will have to rearrange the anode and suppressor grid connection and expect a slight shift on the curves given the change in bias. Filaments are in series here, however is preferred to wire them in parallel when using this valve in filament bias as a smaller filament resistor will be required given there is twice the filament current when filaments are connected in parallel. This will help to keep the output resistance lower as the size of this resistor is smaller (remember it is reflected multiplied by μ+1 times.