SOHA: Power supply
The SOHA's power supply is quite simple. It's quite clever how it obtains the ~40 volt B+ for the tube - it basically stacks two full-bridge rectifiers, decoupling them with big caps. To make case layout and circuit debugging easier, I decided to put the power supply on its own board and use various salvaged connectors to hook up to the main amp board. The only mod I made to the original SOHA circuit was use a bigger transformer (1000 mA) to power some eye candy (and put a bigger heatsink on VR3 to handle the extra power). Oh, I also removed the power LED (I've got other plans). I much prefer surface-mount assembly to through-hole (no drilling a thousand little frickin' holes), so I found equivalent SMT parts to the recommended through-hole parts. Here are the part numbers I used for the power supply (refer to figure 4 on the HeadWize page here). Note the connectors are absent from this list - I have no idea what I used. A few years back, some jerk broke our dorm TV. Silver lining: it contained lots of sweet surface mount connectors!
| Reference | Description | Mouser Part |
|---|---|---|
| R9 | 2k2 1/8W | 71-SMM02040C2201FB30 |
| R10 | 1k3 1/8W | 71-SMM02040C2000FB30 |
| R11 | 11k 1/8W | 71-SMM02040C1801FB30 |
| C3-C6 | 100u 100V | 5985-AFK100V100-F |
| C7, C8, C11 | 47u 16V | 667-EEE-HDV470XAP |
| C9, C10, C12 | 470u 35V | 667-EEE-TKV471UAQ |
| BR1, BR2 | 100V 1A Bridge Rect. | 625-DF02S-E3 |
| VR1 | 12V 0.1A Positive | 511-L78L12ACU |
| VR2 | 12V 0.1A Negative | 511-L79L12ACU-TR |
| VR3 | 1.5A Neg Adj Vol Reg | 512-LM337T |
| D3, D4 | 1N4002 1A 100V GP | 583-FM4002 |
| T1 | 30.0V CT @ 0.83A | 553-VPT30-830 |
Laying this thing out was a bit of a pain due to those large caps. Also, the kicad library archive didn't have modules for most of these parts. Oh well. Here's what I came up with:
SOHA power supply board. About 3.5" by 2".
Attached are some pics from the build. PCB made via toner transfer via laminator.
I've uploaded a KiCad project containing a schematic and the board layout.