Novice's blog Objective 2 headphone amp

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Hi all. I couldn't find a build blog for this headphone amp, despite having had some good info from NealJ, Mooly and Aefewulf, and all the others who've contributed to my build so far, including the designer himself (who might be a Rocket Scientist)



So I've decided to share my novice's work in the hopes that it helps others too.
I've built an ACA, and I was hoping for this headphone amp to double as it was intended and as a preamp for the ACA (initially I was looking for some gain, largely because of the "on paper" low output of 8watts.


At line level though, first tests proved it to be ample loud enough.
To that end, the kit that I bought from Head'n'Hifi which did not include the enclosure (my choice), had included SIP sockets to enable the user to hot-plug the gain resistors.
These look fiddly and are to a degree, but I found a way to fit them.
The resistors plug in fairly snugly so initial worries I had about them falling should prove to be unfounded.


The reason I didn't buy the enclosure is because I wanted a larger enclosure to be able to add a selector switch to vary from cd to tuner inputs on the RCA's, also use a better 10k pot and change the small input (3.5mm) jack to a 1/4" jack.


I add a photo to show my method of holding the SIP pins in place-sticking tape!
Once taped down, I simply turned the pcb over to solder the pins.


ADDED LATER: You'll see further down that I had trouble with the resistors, and will look at another method of hot-plugging them onto the SIP sockets
 

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Ok, sorry for the delay, I wanted to finish the burr walnut covering of the ACA (photos of which I posted on that forum).
This one will have even more burr walnut on it if I'm successful.
So I bought an enclosure similar in size to the ACA unit from Modushop, but this one is their Maggiato range.
I did this because of the extra space I wanted and to make it look like an accompaniment to the ACA as I was primarily using it as a preamp to it.
As you can see, I mounted it on standoffs about 20mm up from base, largely for symmetrical spacing of the buttons and wiring access.
TBH I'm spoilt for room here.
Next up will be the wiring in of components.
The sheet you see to the side is a 2mm aluminium sheet that will take the place of the 3mm front plate provided with the chassis as the Objective2 kit requires only 2mm front plate.
 

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Now you see the layout.
Standoffs were placed around 25 mm off the floor of the chassis so any cables like power could be re-routed away from signal cables.
the pcb was offered up to the new aluminium 2mm front plate, and the holes to be drilled marked on the inside.
(This was only done like this because the headphone sockets that come with the kit can be used only with max 2mm panel).
The two holes in the middle are the pcb-mounted S1 & S2 switches, above two are for a selector switch and Alps 27mm potentiometer, and far left and right are input and output headphone sockets (both 1/4" for symmetry).
It's intended to have cd and tuner inputs hence selector switch.
The extra power switch on the back is to relieve stress on S1, as you'll see later the buttons for which are quite heavy on my amp
 

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I attach a photo of the pcb with the pot and selector switch, you'll notice that R6 is missing cos I cocked up the soldering of that and had to pull it out-it subsequently broke necessitating me to wire it underneath the pcb.
Also, you'll see the SIP sockets, now they were a nightmare to get the resistors to stay in as firstly, they're close to S2, and they are so close together.
In the end I got so frustrated with trying to get them in and out, I ended up soldering the stock value resistors INTO the top of the SIP sockets.
Perhaps what I should've done is to try to get one SIP to slip into a SIP on the board (with its own resistor pre-soldered onto two SIP contacts, piggyback style) perhaps then, they could be swapped out to represent different gains.
 

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Next up is cladding in burr walnut.
Now it's working ok, I'm going to leave only the bottom and rear panels in black, the rest will have the walnut.
I'll post back here once I've done that, in the meantime, if anyone has any questions feel free to ask. I'm a complete noob but still managed to get it working despite all my best efforts to scupper it with rubbish soldering.
 
FYI - you're supposed to push the component flush against the pcb and cut of the excess wire on the back, it makes for a much tidier result. Something to consider next time!

Congrats on finishing the build :)


Thanks for your input there Cal42. You're quite right of course.


There are two reasons that I mount the components a bit aways from the board, firstly it's a novice thing, I've never had much luck in desoldering faulty components from the board and pulling them off, my braid wire doesn't seem to suck up anything and my desolder syringe works but only takes up the main blob and there always seem to be enough left to hold the component on, so I figure if I leave long tails coming up, at a pinch, I could solder the new component to them, messy, but it works.


Secondly, all the years I've repaired dry joints on boiler pcb's I've noticed that the components have not had enough air around them to keep them cool, especially highish power resistors (leaving a brown mark on the pcb).
So I thought that keeping them away from the board might help in cooling.
Her's a closer pic of the board, don't all laugh please!
 

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