My journey into Photography, Horology, and Audiophilia
I have a pair of General Electric 12B4A given to me by a friend and I was planning to use these for a "spud" amp. I have seen the use of the 12B4 as a pre amp in Yeo's website at DIY Paradise but not until I saw this long thread about the 12B4 besting a grounded grid pre amp (which I also lusted to make) that I decided to make one.
Here's the crappy prototype of the 12B4 in pre amplifier duties.
And here's the underside of the prototype.
The prototype was based on this schematic which I came up with
Frank De Grove of the DIY Audio forum suggested this modification in the forum thread I mentioned above.
This pre amp sounds so good and I know it bested my Foreplay so I decided to give it a nice chassis :)
I salvaged a data switcher from the dumps and turned it into this:
Cool don't you think? I just need good looking knobs and this will be playing for a good while!
Here's the back view with the two (2) inputs (A/B) and one (1) output. Notice that there's no power switch :)
Just like the Foreplay I built, I did not use any botique parts for this project. In fact, I downgraded to an Electrocube from an Auricap for the coupling caps. I still use ALPS blue for the volume control as I can get these relatively cheap. The power supply needs to be solid state based to keep the footprint down. From the power supply secondary, I configured four FR107 in bridge configuration and used CRCRC for the filter.
My star grounding is perfect again, no noise whatsoever, even at full volume with shorted inputs. Just make sure that the ALPS potentiometer is properly grounded and we can rock and roll!