Enclosure not stated · 2 knobs
Death by Audio Germanium FilterVerified
Based on the Death By Audio Germanium Filter· 1 other board clones it
From the post
A while ago. Chris Stelloh sent me a Death by Audio germanium Filter to trace. The trace went pretty smootly and I sent the schematic to Chris and he made a vero layout out of it. However, this circuit requires some transistor and diode picking to work as intended. See Chris's notes below...
My notes + warnings from my build attempts: PROCEED WITH CAUTION.
1) The transistors: DBA used MP10b NPN germanium transistors which have a common hfe range of 20-50. The lowest gain transistors I have on hand are MP35's around 40 hfe. And none of these worked properly. At lower settings, the gain was sputtery and sounded misbiased. I was able to get the circuit to work properly with some NPN Fairchild silicon dots from Small Bear that measure at 25 hfe.
2) The unknown silicon diodes on the mosfet gate: 1n4001-4007 worked quite well. I had my best sounding results with 8.2v Zener diodes. the 9v supply will cause any Zeners with lower than that rating to heat up and pop.
And here is layout with trimpots for the collectors solve the gating issue when the Gain control is turned counter clockwise. I also ditched the internal trimpot in favour for an external volume control.
Schematic
This is a board layout, a drawing of where each part goes, and the post may link the schematic it was drawn from. Open the layout at Dirtbox Layouts. No KiCad fragment has been drawn for this circuit yet.
Parts list 27 rows
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Check before you build · 2 values the reader of this layout was not sure of
- 392Ω (two, at columns 11 and 14): printed clearly, unusual value
- D2-D3 are 'unknown silicon' in the legend; 1N400x is its first suggestion, not a known part
| Ref | Value | Normalized | Type | Notes |
|---|---|---|---|---|
| Resistors 12 | ||||
| ×3 | 1k5 | 1.5k | read from the layout by eye | |
| ×1 | 220k | 220k | read from the layout by eye | |
| ×2 | 470k | 470k | read from the layout by eye | |
| ×1 | 68k | 68k | read from the layout by eye | |
| ×2 | 33k | 33k | read from the layout by eye | |
| ×2 | 392Ω | 392 | read from the layout by eye | |
| ×1 | 2m7 | 2.7M | read from the layout by eye | |
| ×3 | 1m | 1M | read from the layout by eye | |
| ×1 | 47k | 47k | read from the layout by eye | |
| ×1 | 82k | 82k | read from the layout by eye | |
| ×1 | 100k | 100k | read from the layout by eye | |
| ×1 | ? | ? | LED resistor, value not given; read from the layout by eye | |
| Capacitors 8 | ||||
| ×1 | 680pF | 680p | read from the layout by eye | |
| ×1 | 1nF | 1n | read from the layout by eye | |
| ×1 | 2n2 | 2.2n | read from the layout by eye | |
| ×1 | 47nF | 47n | read from the layout by eye | |
| ×5 | 100nF | 100n | read from the layout by eye | |
| ×1 | 330nF | 330n | read from the layout by eye | |
| ×1 | 2u2 | 2.2u | electrolytic; read from the layout by eye | |
| ×1 | 100uF | 100u | electrolytic; read from the layout by eye | |
| Diodes 2 | ||||
| D1 | 1N4001 | 1N4001 | read from the layout by eye | |
| ×2 | 1N400x | 1N400X | D2, D3; unknown silicon (try 1n400x or zener, minimum 8.2v); read from the layout by eye | |
| Transistors 2 | ||||
| Q1 | BS170 | BS170 | MOSFET; read from the layout by eye | |
| ×2 | MP10b | MP10B | Q2, Q3; NPN germanium, low leakage, hfe 20-30; read from the layout by eye | |
| Potentiometers 2 | ||||
| Gain | B50K | B50k | Potentiometer | read from the layout by eye |
| Filter | A500K | A500k | Potentiometer | read from the layout by eye |
| Trimmers 1 | ||||
| Volume | 100k | 100k | trimpot; can be replaced with an external A100K volume pot; read from the layout by eye | |
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