Raffle Amp Main Board

I've been quiet, but busy -- with now just a few weeks until the raffle, construction of the raffle amplifier is now well underway.

Here's a link to the current schematic.  There are a few component values that still remain to be tweaked, especially in the reverb/dry mix and tremolo sections, but it's close enough to the final that I've been using it as my working document.

I thought it might be useful to document my build process a little bit.

As usual, the starting schematic is drawn in LTSpice, a great freeware simulation package.  Although I typically don't bother trying to simulate an entire amp of this complexity all at once, I do also make heavy use of LTSpice to simulate many of the individual subsections of the amplifier.

Once I have a schematic in-hand that is sufficiently fleshed out, I begin the process of laying out the design.  I do this mainly with the excellent shareware DIY layout creator (DIYLC) software by Bancika, proprietor of the DIY-fever blog.

I use DIYLC to layout the individual boards, but also to get a good-enough idea of where all of the chassis-mounted components such as the transformers, tube sockets, and pots will go.  The boards are fabricated more-or-less directly from images exported from DIYLC, but I typically will draw final drill plans for the chassis itself in another vector drawing program that is more purpose-built for that sort of thing.

Here's my overall rough layout in DIYLC as it stands right now:

I started with fabrication of the mainboard.  To do this, I export a PNG image from DIYLC of the whole layout, then import it into a graphics program, then crop and scale the image to the actual size I want.  I then print out this out (taping together pieces if it's larger than will fit on an 8.5"x11" paper), and tape the overlay onto G10 garolite that I have cut to size.
  
 Here's what the main board (which is an impressive 20.5"x3.5") looked like prior to drilling:

 I then go ahead and drill the holes suitable for the rivet-like turrets that I prefer:

Note that there are some slight (but inconsequential) irregularities in the edges and spacing.  I'm typically just using hand tools for this, I don't have (or really need) a fancy setup!  Anyway, after banging home all the turrets, the board looks like this:

Note the two large empty areas.  If you look back at the original DIYLC layout picture, you'll see that these correspond to area where I intend to mount a couple of small PCBs right onto the turret board.  The design calls for a few things like transistors, a relay, and a small chip-amp for the reverb driver that will be more happily accommodated on a PCB.  So this is a hybrid approach that should allow me to take advantage of PCB where it will be best, but stick mostly with rugged, familiar, and easier-to-tweak point-to-point construction methods.  The first PCB largely corresponds to components for channel switching and the reverb driver, while the second board is entirely dedicated to the solid-state low-frequency oscillator and other circuitry dedicated to the tremolo circuit.  I will show later how these PCB can be hand-fabricated using the press-n'-peel method.


Here's a few shots of the (mostly) populated board:

Close-up of the input section:

Close-up of the overdrive section:

Close-up of the power section:

More soon, next up will be the boards providing the bias supply and the area around the power tubes....