continuing design work on v2

 The version 2 design of the McGrath Mini is advancing nicely at present.

As mentioned before, 4x12AX7, with new switchable boost stage in the input section, two stages of gain on the fx return, and several other new features.  Power amp stays same, single-ended EL84 (I'll probably also try the 6P14P), with no NFB.

I will use the Bud AC-1407 chassis box (or Hammond equiv, 1444-84515).  This causes final case dimensions to become 9.5"W x 10.5"H x 7.25"D.  I.e., slightly taller and narrower than the almost-square version 1.  I don't like the proportions as much; given in-house fab I'd go back to square (i.e., 10.5"W x 10.5"H).  But that's OK, features are good, so here form follows function.

Knobs (8) will be as in v1, though with some re-naming.

There will be four switches on the upper back panel, between the input jack and fx send: voice, scoop, brt, ~cold.  ("voice" is a 3-way DPDT.)  These switches control those functions which are not assignable to the footswitch, i.e., not associated with relays.

There will be five relay control switches in a row, plus the power switch, on the lower back panel: ~nfb, boost, aeq, M-drv, fx.  Each one has 3 positions: on, off, ftsw; the ftsw position is numbered 1 or 2.  Accordingly, each of the five switches is permanently assigned to footswitch 1 or 2.  (1 for the gain stages and ~nfb, 2 for aeq and fx.)

There will be six LEDs along the bottom edge of the front panel, in between knob positions for visibility.  Five reflect the relay switching functions: ~nfb (yellow), boost (orange), aeq (green), M-drv (orange), fx (blue).  Then there is the usual RGB power LED, as in v1.

The same two-button footswitch will be used (stereo 1/4" cable), but LED colours will be 1:orange, 2:blue.

The "voice" switch selects cathode circuits for the first two tube stages, input and boost.  "M" position gives 2k7 || .68u.  "F" position gives 1k35 || 25u (i.e., 2k7 || 2k7 || 25u).  Middle position is 2k7, no cap.

The "scoop" switch engages a fixed R-C network approximating the AB763 tonestack with treb and bass at maximum, mid at minimum.  When bypassed, a series 22n is engaged instead.

"brt" engages 120p across the 1M-A "input" pot (AB763 volume).

"~cold", as before, switches 10k into parallel with the 39k cold-clipper resistor in the M-drv section.