Spasticteapot
100+ Head-Fier
- Joined
- Oct 16, 2006
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After a marathon session in EaglePCB, I finally finished a PCB design for an amplifier, which I've chosen to call the Mjolnir. This is my first time designing a PCB both this small and this complicated, and I'd appreciate any thoughts you might have on the PCB or design.
What's in it:
It's an implementation of the headphone amplifier from the LME49600 (National's equivalent to the BUF634) datasheet, though using a single quad instead of four dual op-amps and a much smaller PCB. The amplifier contains an op-amp gain stage with a buffer in the feedback loop for more current, and a DC servo so you don't need to use an input capacitor (which suck.)
http://www.national.com/an/AN/AN-1768.pdf
What parts does it use:
I based it around the LME49600 buffer and LME49740 op-amp. Both of these are excellent components and not too expensive. However, just about any quad op-amp should work.
The resistors are a fairly standard 2.8 x 6.4mm size - I'm using 1% metal film resistors. I chose to use multilayer ceramic capacitors in the power supply due to extremely low ESR, but there's enough room for WIMA polypropylene capacitors to be used instead.
All the parts used are through hole for easy soldering, with one exception - the zener-based static discharge protection diodes at the input and output. Fitting eight more diodes on the board simply wasn't practical, and the IC is of a fairly large and easy-to-solder size - and it's optional anyway.
How well does it work:
As you can see from the datasheet, distortion is very, very low. Despite the amplifier's tiny size, it's good for up to 250mA at +/-15V at the outputs - enough to drive just about anything.
Why is the PCB so ludicrously small:
Seeed Studio does 2" x 2" PCBs at the low price of 5 for $16 if you give them all the documentation for your project.
Why the name:
I could lie and tell you it's due to the impressive power output - not many headphone amps can do more than 3WPC. However, I'd be lying. It actually refers to my design philosophy - "All problems can be solved with a hammer - so long as you use a sufficiently big one." If you'll look at the PCB, there's a very literal interpretation of a star grounding scheme; after spending rather a lot of time mucking about with ground planes, I found it was almost impossible to use big, through-hole components without mincing the ground plane into tiny little pieces.
What's in it:
It's an implementation of the headphone amplifier from the LME49600 (National's equivalent to the BUF634) datasheet, though using a single quad instead of four dual op-amps and a much smaller PCB. The amplifier contains an op-amp gain stage with a buffer in the feedback loop for more current, and a DC servo so you don't need to use an input capacitor (which suck.)
http://www.national.com/an/AN/AN-1768.pdf
What parts does it use:
I based it around the LME49600 buffer and LME49740 op-amp. Both of these are excellent components and not too expensive. However, just about any quad op-amp should work.
The resistors are a fairly standard 2.8 x 6.4mm size - I'm using 1% metal film resistors. I chose to use multilayer ceramic capacitors in the power supply due to extremely low ESR, but there's enough room for WIMA polypropylene capacitors to be used instead.
All the parts used are through hole for easy soldering, with one exception - the zener-based static discharge protection diodes at the input and output. Fitting eight more diodes on the board simply wasn't practical, and the IC is of a fairly large and easy-to-solder size - and it's optional anyway.
How well does it work:
As you can see from the datasheet, distortion is very, very low. Despite the amplifier's tiny size, it's good for up to 250mA at +/-15V at the outputs - enough to drive just about anything.
Why is the PCB so ludicrously small:
Seeed Studio does 2" x 2" PCBs at the low price of 5 for $16 if you give them all the documentation for your project.
Why the name:
I could lie and tell you it's due to the impressive power output - not many headphone amps can do more than 3WPC. However, I'd be lying. It actually refers to my design philosophy - "All problems can be solved with a hammer - so long as you use a sufficiently big one." If you'll look at the PCB, there's a very literal interpretation of a star grounding scheme; after spending rather a lot of time mucking about with ground planes, I found it was almost impossible to use big, through-hole components without mincing the ground plane into tiny little pieces.
