HE One

2.0 zostava zosilňovač + reproduktory


About time to create something proper, so I decided to build a 2.0 set. At first I was thinking about active two-way bookshelves, but for technical reasons I changed my mind and started a work on a set with a separate amplifier. That will mean less difficulties with sealing the enclosures, which will be a bit more compact and everything will be a bit more universal


The heart of the amp will be JPA100SE by zosilnovace.eu. According to its creators, output power is 100W/4ohm, so something around 50W into 8 ohms, which is enough for this purpose. Frequency range is 15Hz - 230kHz, which is obviously more than enough for even the best tweeters; distortion should be 0,059% THD and 0,064% at full power. Slew rate 33V/μs. High end parameters.
Kit arrived excessively packed in many many bags, one for each value of resistance, another for capacitors, transistors, connectors and the other stuff. And of course PCB, aluminium bracket and printed instructions of how it works and how to assemble it. Bad thing was I found out that I could order components necessary for overheat protection from zosilnovace.eu as well from this instructions after the order, not from the webpage before it.

Assembling the amp was not that complicated, PCB was pre-drilled, so I could only place components and solder. There were a few packed resistors which were extra, which was kinda cool, but one of the resistors had a totally different value than it stated on the bag (and as it was needed), and I also missed one nut, which could have been my fault. Nothing I couldn't solve from my home resources. After soldering, which took quite some time, I tested if everything works correctly, all according to provided instructions. And it looked like it did, except for a strange behaviour on the output. But, as I later found out, it was because my test transformer did not provide enough voltage for the protection relay to switch. So this process will continue with a proper transformer.

Another step was to order components necessary for power supply and a few other things - I ordered 300VA transformer with 2x30VAC output, fast diodes, 4 10mF/80V SNAP-IN capacitors, ALPS potentiometer and cinch connectors from REAN (cheaper Neutrik brand). Power supply also has AC outputs necessary for amplifier protect circuitry.

To have something to put the amp into, I ordered 2U rack chassis with heatsinks from modushop.cz, together with aluminium stands and base board. After my attempt to assemble it I was disappointed. Material quality is on a great quality level and so is the finish, but the way it's getting assembled is terrible. I'm pretty sure engineers who designed this did not spend more than 15 minutes on it. Individual pieces do not fit to each other in some exact way, you'll need to assemble it a few times before you'll know how to do it in a correct way. For some reasons there were no washers, not even for the metric screws holding everything together, top and bottom are held by tapper screw. Printed picture acting as a how-to was not helpfull at all, I could not mount the bottom piece by metric screws, holes in the brackets were too small. Also aluminium stands had completely different screw holes than the plastic ones, so I used double-sided tape to put them on the bottom plate. Not really worth the money.

As it turned out, it was a great thing to order a base board, which provided a really easy way to mount the transformer and stands for PCBs.
What I was afraid the most, was how would I make a hole in the back panel for the AC connector. It's not that easy to make a sqare hole in a steel plate that thick. But a small drill-bit and a flat rasp did it - it doesn't look bad and it holds the connector securely. Holes for cinches were not a problem, the only small issue were holes for the speaker terminal - it needed 12mm holes and I only had 10mm drill bit, but even this was not an unsolvable problem.

Wiring was relatively easy, just a bit tedious. All the connections are throuhg fast-ons, or by wire-to-board, only the speaker cables have forks on one of their ends. Everything should be disassemblable, but also well dimensioned.

Now I wait for audioswitch and somewhere in the future I will also add a relay input switch.