Hybrid Vacuum Tube Headphones Amplifier (Part 6) Battery Powered

This month posting is full of hybrid vacuum tube amplifier.

The title said headphone amplifier is actually not quite suitable because this amplifier cannot drive high impedance headphone very well. But for sensitive and low impedance earphones like Sony MH1C, it work very well.

On the previous part about the building process of this pocket size vacuum tube amplifier is intended for the experimental project using 2 AA type batteries. This is not enough juice from those little batteries to drive the tube heater. Then the name portable will not suitable because at the end it still using external power adapter.

I keep try to find the best way to make this vacuum tube amplifier portable. This could be achieve by using the batteries. So here I am building the batteries pack for this vacuum tube headphone amplifier.

As you can see from the photo above, my previous hybrid vacuum tube headphone amplifier is now become a reliable portable amplifier. It is a bit chunky because there is additional unit for the battery pack. This makes me remember many portable audio setups around late 2010 stacking the iPod like this.

In this batteries pack build, I will using 3 pieces 18650 lithium batteries. To keep the cost down, I got the batteries from dismantled laptop batteries. Lucky for me the batteries are still in great condition. The capacity still maintain the power capacity as per specification.

The total voltage for 3 series batteries is 12,4 volt when fully charged and operating voltage is vary from 11,4 volt to 10,8 volt.

With each battery capacity rated 2100mAh, this batteries pack is sufficient enough to powering the vacuum tube headphone amplifier around 5 hours.

The casing using for the batteries pack is the same like I use in the amplifier. The same casing will make the look of each unit similar and more easy to stacking.

I also make a simple low batteries indicator using 2 transistor. The schematic about this can be search on the internet. This low battery indicator can be adjust on how the red LED will lit on certain voltage level or bellow, while the green LED is only for battery operating indicator.

I also bought battery management system module for the batteries protection during charging and discharging. This will also maintain the charging level of each batteries at the same level.

Once everything are done, now I can attach the batteries inside the tin by using the double-side tape. It really tight fitment inside the tin and I want to make sure there is no short-circuit from the batteries to the chassis.

To prevent the short-circuit, I am using the cloth tape to isolate the batteries polarity. It is not look very tidy but I think the safety is more important.

So how this batteries pack perform?

The short answer is really good. It makes the amplifier also sound better.

Why?

Because using the battery is more linear than the power adaptor. I really remember the background hiss noise when using the power adapter and it is gone now. Batteries really superior for the near zero noise level. This amplifier right now is dead quiet with no noise at all when it's idling. The other benefit is the music is now more clearer on every frequency range.

Now I can carries the whole setup on one hand and I can listen music at anywhere with this vacuum tube headphone amplifier. The charging time when the batteries low using 12 volt 3 ampere power adaptor will takes about 3 hours. This is really a reliable portable vacuum tube headphone amplifier for sure.

At last my dream to have a portable vacuum tube amplifier can be achieve now:)

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