New project that at first was suppose to be a tube amp with mp3 and bluetooth player made out off the shelf parts and stock Aliexpress modules.
First prototype was suppose to work as a USB music sound card with these nice valve tube UV meters called Magic Eye.
But I had to skip both devices due to no room in this nice aluminum case I had, with TPU 3D printed feet’s.
We need to drill some holes for the tubes and rotary switch on the top.
On th bottom we need mounting holes for the preamp PCB and rubber feet’s. Also we need some bigger venting holes for the tubes because they are heating up. There is also a inspection hole for easy positioning of elements.
But let’s get back to the circuit. Since 6J2 valve tube preamp needs 1A 15V AC/AC adapter to work, we need some bridge rectifier with step down converter to get some steady 5V DC to Bluetooth module.
Bluetooth module is XY-BT-MINI and need’s to be connected to the Preamp IN so I had to desolder all RCA IN and OUT sockets. The module has convenient solder pads for power and audio.
I also replaced all cheap 35V 470uF Chinese caps for better quality ones, those are Japan NICHICON caps.
I have also 3D printed pot shaft extender since we need IN and OUT audio socket in front of the enclosure.
We have some more space on the back so I decided to add even more inputs to connect multiple synths. Since we had only one preamp stereo input we need some four channel rotary switch to select which audio input should be preamped. Overall we have 3 inputs and blueetooth audio stereo source.
I also decided to send mixed audio from 3 inputs to preamp, but for that we need some passive mixer based on 1k resistors.
Now for the best part, we need overdrive/distortion effect, to do that we need 2-pole or double throw toggle switch. Idea for this effect is to send one of the stereo channel output to the input of the other. For example left vacuum tube channel to the right vacuum tube channel. This will give us double amplified mono distorted audio signal from two valves.
Time to put everything in to the enclosure, on front we have stereo OUT 6,3mm jack, stereo/mono(distort) switch, volume pot, mono/stereo IN 6,3mm jack.
On the back we have mono IN 6,3mm jack, mono IN 3,5mm jack, power ON/OF flip switch, AC 15V connector.
Let’s add some labels and done 🙂
Here are the parts used: