Hybrid Opamp Self Etch

So here's another little project i've made in eagle. It's a single sided PCB of a Class-A only, no servo version of the JLM Audio Hybrid Opamp.

I decided to make my own board, because that's what DIY is all about! I hate having to buy boards for circuits when you can just as easily roll your own. Designing and making boards is a great way to explore a circuit and to understand them better than when you just bought a board/kit and stuffed it. It has you making relavent decisions about what comes where and why. And you can make boards work with what components are available to you.

First off, let's take a look at the original schematic from the JLM Audio website on which i based my schematic/board. Do have a look around at their site if you're not familiar with them, there's a lot info available for Pro Audio DIY and their kits do look the bizz. Anyway, here's the schematic:

http://www.jlmaudio.com/JLM%20Hybrid%20Opamp%20circuit.pdf

on the website they list these specs for this circuit:
Specifications

• 1.1" x 1.1" PCB
• THD = 0.008%
• Min Load = 50ohm
• Maximum power rails = +/-24vdc
• Idle Current in class A/B = 10to 12mA
• Idle Current in class A = 25mA to 30mA

As we can see it's a great simple little circuit that'll drop just right in to almost any circuit requiring a Discrete OpAmp. The circuit can be run on power supply rails ranging from as low as +/-4.5Vdc to as high as +/-24Vdc, the latter giving it great headroom (+/-15Vdc minimum recommended for any serious audio circuits). The circuit can easily drive a step-up transformer on the output and still maintain a low distortion output. Heck you could even drive a pair of headphones with 2 of these. On top of that, it's easily changable from class a to a/b for some different sonic flavor. Pretty good for an opamp, some resistors/capacitors, pair of transistors, 2 diodes and a led.


Now on to my version. There were a few features of the JLM hybrid that i didn't need, like the servo for instance. Most of the circuits i want to use it with, already have DC blocking capacitors installed, so there isn't any need for a servo. The class switching is very nice, but once you've settled on one or the other you just leave the jumper alone, Right?. Since it's just as easy to solder in two diodes as it is to solder in a led i also did not implement it in my version. here's my schematic, layout and pcb:

SCHEMATIC
LAYOUT
PCB

notes on the PCB: i made most of the holes 0.5 mm to make it easier to drill the holes in the middle. C1 and C2 can be ommited if there are already power supply decoupling caps installed in the circuit you're gonna use the Hybrid with. And finally R1 and R2 should be 1/2 watt resistors to ensure they won't burn up when shorting the output.

ok signing of for now.

greetings,

Thomas


Note: Tested and confirmed working with a ne5534 opamp. The opa627 was found oscillating in the fivefish opamp test jig. will investigate and do some listening tests when i'm back from a well deserved holiday!