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Showing posts from January, 2024

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 n...

parts list

 (Note, this parts list reflects "version 2" of the amplifier, which doesn't actually exist yet: i.e., this is the newly-designed version using 4x12AX7 and a switching power supply, so no EZ81.  Schematic so far only reflects "version 1".) Mon 01 Jan 2024 10:43:02 PM PST McGrath Mini amplifier parts list jacks 3 switching (input, fx return, ext spkr) 1 non-switching (fx send) 2 non-switching stereo (footsw) iec power jack & cord fuse holder, 2a fuse relays 6 5v dpdt tubes 1 EL84 4 12AX7 tube sockets 5 9-pin switches 1 dpdt (power) 6 dpdt 3-pos (nfb, boost, coldness, drv1, drv2, fx) 2 spst footswitch LEDs 1 rgb (power) 3 orange (drv1, drv2, footsw1) 2 blue (fx, footsw2) pots 4 1M-A (gain, M-gain, bass, vol) 1 500K-B (level) 1 dual 500K-B (freq) 1 250k-A (treb) 1 25k-A (mid) resistors 1 820 4 1k 1 5.6k 1 10k 2 22k 1 33k 1 39k 2 47k 9 100k 4 470k 7 1m...