1590B · 1 knob
Merlins Glassblower V1.5
Based on the Merlin Blencowe Glassblower
From the vendor
Merlin Blencowe's GlassBlower — a clean, hi-fi guitar booster that delivers up to 28 dB of boost and a clean 12 V p-p output swing from a single 9 V supply, using a Class-G rail-bootstrapping technique that lets the supply rails follow the signal. The GlassBlower is a high-headroom buffer / booster designed by Merlin Blencowe — purpose-built for slamming the front of a valve amp without running out of clean headroom. It produces no tone-shaping and no clipping; it's purely clean amplification with the kind of swing usually only available from charge-pumped supplies. This V1.5 board is a revision of the original PCB — the noisy VU meter implementation from earlier revisions has been removed f
Schematic
The schematic is in the vendor's build document. Open the build document. No KiCad fragment has been drawn for this circuit yet.
Parts list 18 rows
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| Ref | Value | Normalized | Type | Notes |
|---|---|---|---|---|
| Resistors 11 | ||||
| R1 | 10M | 10M | Input pull-down to ground (anti-pop). 6M2 if 10M unobtainable — gives a slightly higher input HP corner, still well below audio. | |
| R2 | 22k | 22k | Bias divider top — sets IC1A non-inverting input reference. | |
| R3 | 27k | 27k | Bias divider bottom — together with R2 sets bias ≈ 4.96 V. | |
| R4 | 20k | 20k | Series resistor between IC1A output and bootstrap stage. | |
| R5 | 1M | 1M | Bias feed from divider node into IC1A non-inverting input. | |
| R6 | 2k2 | 2.2k | Lower leg of GAIN feedback network — sets minimum gain. | |
| R7 | 4k7 | 4.7k | Series with GAIN pot — sets minimum gain limit (≈ 9.9 dB). | |
| R8 | 220R | 220 | Bootstrap drive resistor — Q1 (NPN) collector to V+ supply pin. | |
| R9 | 220R | 220 | Bootstrap drive resistor — Q2 (PNP) collector to V− supply pin. | |
| R10 | 20k | 20k | Output pull-down to ground — sets output impedance, anti-pop. | |
| R11 | 20k | 20k | Output series resistor — DC isolation, current limiting. | |
| Capacitors 2 | ||||
| C1 | 100n | 100n | Box film — input DC-blocking / coupling capacitor. | |
| C4 | 100p | 100p | Ceramic — feedback stability / RFI rejection across GAIN network. | |
| Diodes 1 | ||||
| D1 | 1N4001 | 1N4001 | Reverse polarity protection — observe polarity, band toward circuit. | |
| Transistors 2 | ||||
| Q1 | BC337 | BC337 | NPN — bootstrap stage upper rail. TO-92 pinout (flat side facing you, leads down): C–B–E. BC547 is pin-compatible. 2N3904 has reverse pinout (E–B–C) — insert rotated 180°. | |
| Q2 | BC327 | BC327 | PNP — bootstrap stage lower rail. TO-92 pinout (flat side facing you, leads down): C–B–E. BC557 is pin-compatible. 2N3906 has reverse pinout (E–B–C) — insert rotated 180°. | |
| ICs 1 | ||||
| IC1 | TL072 | TL072 | Dual op-amp, DIP-8. Use a socket. JRC4580D OPA2134 TLC2272 | |
| Potentiometers 1 | ||||
| GAIN | B50k | B50k | B taper — sets boost amount from minimum (≈ 9.9 dB) to maximum (≈ 28 dB). | |