Anybody who looks into building their own headphone amplifier will come across the Objective 2 at some point. It was designed by the anonymous electrical engineer known as NwAvGuy as an experiment in high quality, well designed and engineered equipment, but crucially at low cost.
All of the schematics, PCB files, panel cutouts for the enclosure and BOM are readily available, along with a host of information on the design process, measurements and guidance for building. I’d been looking at this for a while but decided to wait until I had a bit more experience. I was intending to get the PCB printed and case made up myself but then came across a website, HeadnHifi, which supplies all of this cheaper than I could source it.
I decided to build the desktop mod; this moves the power input to the back, has a 6.3mm headphone jack on the front and includes RCA inputs and outputs, also at the back, whilst retaining the 3.5mm input at the front.
Dealing with HeadnHiFi was straightforward. I had a couple of questions and these were answered quickly and I was even given information on how to order what I needed more cheaply. The parts were shipped quickly and were well packed. Nothing was missing from the package.
Before attempting this build, I printed out the schematic, PCB layout and BOM. I then read all of the documentation again on the NWAVGuy website and made some notes on the printouts. There is also a download from HeadnHiFI with details of the modification to make this a desktop amp. It’s not the most elegant solution, but the terms of the copyright on this amplifier forbid changes to PCB layout and parts for distribution.
The board itself is really well made. It’s a thing of beauty in itself and appears to be very high quality. All of the through holes are tight and it really is a joy to build.
The next step is connecting all of the panel components. The desktop mod includes RCA inputs and outputs and moves the power jack to the rear. Again, the quality of the case is excellent with neat component cutouts and lettering. A thin piece of wire is soldered to the input jack ground for connection to the chassis, I used one of the spare gain resistors supplied by Head’n’HiFi in the kit and this can be seen in a couple of the photos below.
Once the amp gets to this stage, there is an extensive test procedure outlined by NWAVGuy. Here I had a problem….nothing happened after plugging in the AC-AC adaptor. A check with the multimeter confirmed the adaptor was faulty. Stefan at Head’n’HiFi responded to my email by sending out another adaptor straight away and this worked with no problems.
All that was left to do was to slide the pcb in from the rear, attach the headphone jack to the front panel, screw the panels in and attach the volume knob. Once done I tested again and had a problem with distorted sound. Opening up the enclosure revealed the problem, the headphone jack was lifting the IC out of its socket. Although I had bent up the jack’s lower solder tag according to the instructions provided by Stefan, it wasn’t enough. It took a bit of fiddling with, but eventually it was done.
So, what about the sound? Well it sounds great to my old ears, I can’t hear any hum or noise, just a clean amplified signal from my phone, a Samsung Galaxy S7. I’ve tried it with Sennheiser HD569 and HD650 headphones and SoundMagic E10 IEMs. I’ve used the front input with a standard 3.5mm cable and I’ve connected the phone to the rear RCA inputs via a QED Profile cable. I haven’t connected an external DAC yet but I will see what it’s like with my Modi and Dragonfly. I’ve read that the O2 makes an excellent preamplifer for the DIY Audio Amp Camp Amplifier which I have ordered.
My thanks to NWAVGuy for designing this and providing so much detail and insight into the design of an amplifier, and to Stefan at Head’n’HiFi for making these kits available at an attractive price.
