Enclosure not stated · 2 knobs
Shin-ei OB-28 Octave BoxVerified
Based on the Shin-ei OB-28 Octave Box· 1 other board clones it
- Category
- Octave / Pitch
- Controls
- Sensitivity · Octave Vol
- Build
- Vero· 27×24· 35 cuts, 13 links
- Layout
- Verified · Dirtbox Layouts marks it as built and working
- Tags
- Octave, Shin Ei
From the post
Here is an old odd cat. This is an all discrete clean monophonic octave down effect made by Shin Ei back in the early 70s. Initially I though this was a Maestro OB-1 clone but the schematics revealed that's not the case. See the notes below the layout for components that needs matching for best result. And I must admit the switching is a bit confusing but I think I got it right. Also worth mentiong is that reducing the horizontal cap right to Q11 will give a more aggressive and louder octave down signal.
It was sold under several brand names like Pax, Rands and Sekova. Colorsound also made their own version called Octivider but it had a quite few value changes so that one deserves an own post. *Update 240120* Verified by JRuss with a small correction. Pinout of Q77 altered to match the schematic.
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 40 rows
Report a wrong parseGot parts in a drawer? See what you can build with them.
Check before you build · 1 value the reader of this layout was not sure of
- 250pF x3 (column 27 row I-J, columns 20 and 23 rows R-S): printed clearly, unusual value
| Ref | Value | Normalized | Type | Notes |
|---|---|---|---|---|
| Resistors 13 | ||||
| ×10 | 100K | 100k | read from the layout by eye | |
| ×7 | 10K | 10k | read from the layout by eye | |
| ×5 | 470K | 470k | read from the layout by eye | |
| ×4 | 6.8K | 6.8k | read from the layout by eye | |
| ×4 | 3.3K | 3.3k | read from the layout by eye | |
| ×3 | 47K | 47k | read from the layout by eye | |
| ×2 | 1K | 1k | read from the layout by eye | |
| ×2 | 150Ω | 150 | read from the layout by eye | |
| ×1 | 33K | 33k | read from the layout by eye | |
| ×1 | 22K | 22k | read from the layout by eye | |
| ×1 | 2.2M | 2.2M | read from the layout by eye | |
| ×1 | 2.2K | 2.2k | read from the layout by eye | |
| ×1 | 220K | 220k | read from the layout by eye | |
| Capacitors 8 | ||||
| ×9 | 100nF | 100n | read from the layout by eye | |
| ×3 | 6.8nF | 6.8n | read from the layout by eye | |
| ×2 | 220nF | 220n | read from the layout by eye | |
| ×2 | 1nF | 1n | read from the layout by eye | |
| ×1 | 10nF | 10n | read from the layout by eye | |
| ×3 | 250pF | 250p | read from the layout by eye | |
| ×1 | 22uF | 22u | electrolytic; read from the layout by eye | |
| ×1 | 100uF | 100u | electrolytic; read from the layout by eye | |
| Diodes 4 | ||||
| D1 | SH-1 | SH-1 | silicon rectifier diode, Try 1N400X; match with D2; read from the layout by eye | |
| D2 | SH-1 | SH-1 | silicon rectifier diode, Try 1N400X; match with D1; read from the layout by eye | |
| D3 | SH-1 | SH-1 | silicon rectifier diode, Try 1N400X; read from the layout by eye | |
| D4 | 1N5817 | 1N5817 | read from the layout by eye | |
| Transistors 11 | ||||
| Q1 | BC549C | BC549C | BC549C, 2N5088 etc. (2SC644 in original); read from the layout by eye | |
| Q2 | BC549C | BC549C | BC549C, 2N5088 etc. (2SC644 in original); read from the layout by eye | |
| Q3 | BC549C | BC549C | BC549C, 2N5088 etc. (2SC644 in original); read from the layout by eye | |
| Q4 | BC559C | BC559C | BC559C, 2N5087 etc. (2SA666 in original); read from the layout by eye | |
| Q5 | BC549C | BC549C | BC549C, 2N5088 etc. (2SC644 in original); read from the layout by eye | |
| Q6 | BC549C | BC549C | BC549C, 2N5088 etc. (2SC644 in original); read from the layout by eye | |
| Q7 | BC549C | BC549C | BC549C, 2N5088 etc. (2SC644 in original); read from the layout by eye | |
| Q8 | BC549C | BC549C | BC549C, 2N5088 etc. (2SC644 in original); read from the layout by eye | |
| Q9 | BC549C | BC549C | BC549C, 2N5088 etc. (2SC644 in original); match with Q10; read from the layout by eye | |
| Q10 | BC549C | BC549C | BC549C, 2N5088 etc. (2SC644 in original); match with Q9; read from the layout by eye | |
| Q11 | BC549C | BC549C | BC549C, 2N5088 etc. (2SC644 in original); read from the layout by eye | |
| Potentiometers 2 | ||||
| Sensitivity | A100K | A100k | Potentiometer | read from the layout by eye |
| Octave Vol | A100K | A100k | Potentiometer | read from the layout by eye |
| Switches 2 | ||||
| Octave Sw | DPDT on/on | DPDT ON/ON | read from the layout by eye | |
| Normal Sw | DPDT on/on | DPDT ON/ON | read from the layout by eye | |
Other boards based on the Shin-ei OB-28 Octave Box
- Shin Ei OB-28 Octave Box Effects Layouts (blog)