Okay, so you were intrigued by my claim that you can build a CMoy pocket amp for US$20, but then disappointed when you saw that the parts can easily crest $40. What’s the deal? It’s pretty simple: in the main part of this article, I’m in a position to recommend parts, which means I have to like the parts and I have to think you’ll like them, too. That leads me to be conservative.
However, if you really wanted to skimp, here’s how you could get the cost down to around $20:
| Description | Qty | ID | Price | Where to Get It, Comments |
|---|---|---|---|---|
| 220 µF/25 V electrolytic capacitor, radial leads | 2 | C1 | $1.00 | Any electronics store will have these |
| 0.1 µF metallized polypropylene caps | 2 | C2 | $0.68 | Digi-Key E1104-ND |
| Metal film resistors | 11 | R* | $1.21 | Anywhere. 1/4 W metal film resistors average 11 cents each. |
| LED | 1 | LED | $0.10 | Any electronics store will have these |
| OPA2134PA | 1 | IC1 | $2.63 | Digi-Key |
| Chunk of protoboard | 1 | BOARD | $1.50 | many places |
| 1/8" jacks | 2 | IN/OUT | $2.00 | Digi-Key, Mouser, or Newark |
| Power and level switches | 2 | SW | $5.00 | Mouser for cheap but good. The NKK ones at Digi-Key are nice, but expensive. |
| Basic enclosure (PacTec HML) | 1 | BOX | $6.00 | Newark, Mouser |
| Total: | $20.12 | |||
In the above part list, I include the same enclosure Chu Moy used for his original amp. It’s not actually a very popular enclosure, however; personally, I find it rather ugly. Mint tins are more popular, partly because they save you several bucks, and many think they look good.
Counterbalancing this are many things that can inflate the cost:
Taxes and shipping
Basic supplies like wire, shrink tubing, and electrical tape.
When mail ordering, there are various incentives to order more than just the exact parts you need for a single project. You might want additional resistors for gain or LED brightness tweaking. You might want a few different op-amp types to “roll,” so you can find the ones you prefer. Your parts distributor of choice might have certain order minimums you must observe.
The parts set above configures the amp for its original conception, with a level switch instead of the more popular later version with a volume control (potentiometer) and its associated knob.
The parts list doesn’t include sockets, but I consider it a must for a first time DIYer, and strongly advised in any case.