TPA3116 / RuneAudio Project

[Peter]

[skrodahl]

I am a minimalist, and quite happy with reducing my system to the bare minimum.

As of now, it is RuneAudio player, an amplifier board, input selector, balance, volume and the RIAA stage. (Balance only for those LPs that aren't perfect...)

That doesn't mean I can't experiment a little. I read about Nelson Pass' , and found this little circuit that has less gain and a more readily available jfet: http://www.beavishifi.com/projects/JFET_preamplifier/

Again, a lot of other stuff to do, but I think this should be doable.

[Downunder55]

[skrodahl]

[skrodahl]

So, here it is. My little preamp, or closer to a buffer, built on the jfet transistor MPF102 in class A.

IMG_20140916_151412.jpg (230.63 KiB) Viewed 2898 times

The output from HifiBerry DAC on my RuneAudio player is just above 2.1V with my 1kHz test tone:

IMG_20140916_151451.jpg (240.62 KiB) Viewed 2898 times

Run through the preamp, and it's amplified to almost 2.9V. About 3dB voltage gain in other words:

IMG_20140916_151012.jpg (222.73 KiB) Viewed 2898 times

Spectrum analysis (a previous iteration with less gain) shows 2nd harmonic distortion.

IMG_20140916_144618.jpg (228.17 KiB) Viewed 2898 times

My scope is a Velleman EDU09 kit that I soldered together myself. I'm not at all sure of the scope's accuracy, but it gives clear indications at least.

I don't have the time to do a listening test yet. I need to rearrange components on the board to place inputs/outputs correctly, and I need to install the RIAA stage so I can see where to fit the preamp in my enclosure.

[skrodahl]

My phono stage has to go in before the little preamp.
I have now installed an isolated 12+12V power supply to feed the phono stage, and mounted it.

IMG_20140919_120847.jpg (329.43 KiB) Viewed 2876 times

A little tidying up and soldering the audio connections, and I'm ready to decide how to mount the preamp.

[Downunder55]

[skrodahl]

That's a great layout Downunder55, could you perhaps share it?

There were so few components, so I just winged it. The circuit is quite resilient in regards to layout, but I wanted to have a single strip on the stripboard reserved for ground. I get both input and output in between the two channels, so I'm quite happy with the layout. Still, you have proved that it can get considerably smaller.

The two capacitors on the top right of my board, together with a resistor that can't be seen on the picture, form a power supply filter. My PSU (a Dell switch mode charger) was horrendous on the scope, but it cleaned up nicely with that small filter.

It's quite difficult to get a good looking result from soldering on stripboard. Make sure you have no cold solder joints and verify that none of the component leads are touching each other on the top of the board, and you should be good to go.

[Peter]

Sure board has arrived, and is now set up and working great. Curse you skrodahl and Downunder55---- Now I will have to start building a preamp, after your previous encouraging photos and comments! When will the madness stop??

Every time I build something, I cut myself, and end up with blood on something, hence TBA (The Bloody Amplifier), and TBC The Bloody Cables). I suppose TBP (The Bloody Pre-amp) can't be far away.

As ACX said, maybe I should use blood as the new snake oil...I find that, rather than just ferrite beads to reduce noise, some blood smeared on the power cord reduces noise as a result of blood ferritin, just smooths the top ends.

[skrodahl]