It seems this is coming down to Martin's preamp pcb and Jim's EQ pcb. You guys have already done much of the work, so it just is a matter of the best way to finish out the project. At the risk of being a possible 'downer' I am convinced that unless these are INTENDED to work seamlessly together then you're inviting headaches for many within the group, no doubt. Redundant components on both boards (preamp and output stages) is asking for confusion, IMO. These two pcb's, two separate and complete projects, mind you, mashed together, doesn't really represent an elegant solution to the original request at the top of this thread. True, an experienced DIY'er should be able to take two such boards and, with a little modification and effort, put together a finished, functioning 1084 circuit, but for the less experienced it is destined to become another 1081 project.
Besides the redundancy of circuits the other significant problem is how to arrange the gain switch for a graft of the two pcb's. Both mic and line inputs on a 1084 were functions of a single gain switch, a rather complex switch that 1) routes signals from various transformer secondaries to active stages, 2) selects/routes the total number of gain stages involved, 3) incorporates switched pad networks at various points throughout, and 4) controls actual active gain from one of the 'NV' sections. All with one 3x24 switch. The EZ1290 gain switch handles these functions for the mic gains only. Adding a second, line-input only version (is yours just unity gain or multiple gains, Jim?) means adding a separate gain control (particularly if you want more than just a unity gain input), yielding a different final circuit than the 1084. Despite best intentions, and regardless of how fabulous the final circuit sounds, this will confuse some folks and disappoint others, since it's a different final circuit.
Perhaps the bottom line is that either way, I think you're limiting the final number of folks who will want to climb aboard an otherwise desirable project.
If I may be so bold, Martin and Jim, why don't you guys work together, modifying the designs of your boards to make a project that fits together seamlessly, without redundancy? I know you don't like this idea of an eq-section-only pcb, Jim, but follow me for a moment: Martin, you could simply alter the design of your existing EZ1290 pcb to omit the Grayhill gain switch and all the associated resistors, and instead provide clear markings for connections to be made from a properly populated Elma 3x24 mic/line gain switch (using the classic Neve arrangment for both mic and line inputs). Add the right pair of input transformers and the proper output transformer, and you've got all the input and gain arrangements used in a 1084 (and 1064, 1066, 1067, 1073, etc.).
You can also offer the EZ1290 platform, as is, for folks who only want a mic pre with eq.
Jim, you can then focus solely on the eq section. Not only would this simplify the design but it would shrink the size (and cost) of the final pcb. I don't believe the lack of gain stages will diminish interest in your EQ boards. On the contrary, I think it would significantly increase the scope of interest.
Think about it. How many people here (and on other forums) have already built Neve class-A preamps, or have purchased BA283 boards, hot rod 1272 boards, Seventh Circle kits, etched their own pcb's, etc, and would LOVE a simple solution for adding proper Neve eq to those circuits that they already have? It doesn't matter what flavor of 2 or 3-stage class-A Neve preamp they have, your pcb would work with ALL OF THEM! They'd even be useful to folks who own commercially-built Neve preamp-only clones (Vintech 72's, Averill 1272's, etc.). After all, it simply fits between the output of the last preamp stage and the input of the output stage. ANY class-A Neve preamp project could use your EQ pcb, and the lack of redundant components makes it more desirable for people who either already have some Neve's or already have the parts to build them. People then have the freedom to choose the type of preamp they want to use with your EQ board. They can decide if it will be a line-line-level only device, unity gain or gain options, both mic/line inputs, 2-stage, 3-stage, whatever, and still have a simple solution for the proper EQ.
And an incredibly detailed set of instructions on how to implement it within a class-A Neve circuit would even be a cinch to produce. Neve EQ. Simple, elegant, authentic, and useful for just about everyone!
I have several 1272's that I'd love to add eq to for drum tracking, as do many friends of mine. I would happily snag 8 or 12 of your EQ-only pcb's if you decided to go that route. That's really all we need to turn our past, current, and future Neve preamp builds into full-blown channel amps!
If you do this, I'm in for a stack of them!
Lastly, you and Martin could offer a package with the two cards together along with directions on how to build them out depending on what you want the final project to be (any of the various 1272 types mic pre's, the 1084/1290-type mic pre, or a line-level only device). The clarity of this arrangement will make the total project far more accurate and also accessible, to even novice builders.
And you, Jim, would have totally new, and large additional market for your pcb's.
Win/win.
JC
PS - I do hope you will forgive the long-assed nature of this post. ;D
