thorpej
Super Member
In my day job, computer software is my thing, and one thing that really irks me in that discipline is having to do one-offs. Even worse, a one-off that's really similar, but ever so slightly different, to the previous one-off. When that happens, I like to take the time to refactor the code and in so doing build myself an easily-adaptable, re-usable building block.
So, I was taking inventory of the projects I have on the drawing board... and all of the power amps in that queue all use the Mullard 5-20 front-end topology (favored by @kward, myself, and others) -- a gain stage direct-coupled to a long-tail pair phase-inverter/driver stage.
So, I thought to myself -- hey, perhaps I should attempt to make building block that will be flexible enough for all of these projects (no two of those front-ends were exactly the same), but will still save me a bunch of time and hassle.
And so here it is: Jason's All-Purpose Stereo 5-20 Front-End board. Features:
But I do plan to make a small run of these boards, and would be happy to offer them up to other interested AK'ers for cost + mailing (and would increase the production run, if necessary -- minimum order for the fabricator I use is 10).
Attached are a couple of CAD teaser photos.
So, I was taking inventory of the projects I have on the drawing board... and all of the power amps in that queue all use the Mullard 5-20 front-end topology (favored by @kward, myself, and others) -- a gain stage direct-coupled to a long-tail pair phase-inverter/driver stage.
So, I thought to myself -- hey, perhaps I should attempt to make building block that will be flexible enough for all of these projects (no two of those front-ends were exactly the same), but will still save me a bunch of time and hassle.
And so here it is: Jason's All-Purpose Stereo 5-20 Front-End board. Features:
- Fairly small ... as currently laid out, it measures approx. 7.25" long by 3.25".
- No tube sockets ... it just has provisions for using TE-style screw terminals or directly-soldered flying leads to make the tube connections, so tube choice and chassis layout is flexible.
- Resistor footprints are big enough for 2W resistors, if needed.
- Provision for radial electrolytic cathode bypass capacitors on the gain stage, if desired (or you can just leave them out).
- Provision for split cathode bias resistors in the gain stage, if needed by your NFB loop. If you don't need a split resistor, just solder in a jumper for the bottom leg.
- To power supply inputs -- one for the gain stage, one for the inverter/driver stage, in the event that different supply voltages are required.
- No explicit terminal connections, but soldering on flying leads for CCS modules (for the gain stage plate load or for the LTP tail) should be fairly straight-forward (in fact, I'm counting on the latter).
- Similarly, if you wanted to add a gain adjustment pot for the non-inverting triode of the LTP, that shouldn't be too difficult with flying leads.
- Large axial footprints for the the LTP output coupling caps and the LTP grid bypass caps. Polarized footprints are used to indicate correct orientation of the outside foil end of the cap for lowest noise (negative end).
But I do plan to make a small run of these boards, and would be happy to offer them up to other interested AK'ers for cost + mailing (and would increase the production run, if necessary -- minimum order for the fabricator I use is 10).
Attached are a couple of CAD teaser photos.