Author Topic: DIY tube amp Simple?  (Read 2361 times)

Ruptor

DIY tube amp Simple?
« on: January 09, 2018, 05:21:10 PM »
This isn't about a stompbox directly but I wanted a small amp, preferably valve based, for headphones to plug my guitar in to to test stompboxes and this seemed like a neat way of getting one with little design input. Unfortunately it wasn't as simple as it looked and became a catalogue of hoop I had to jump through to get what I wanted. I saw this valve amplifier that at a quick glance looked like it would do what I wanted so I bought it
https://www.ebay.co.uk/itm/AC-12V-6J1-Valve-Pre-amp-Tube-PreAmplifier-Board-Headphone-Amplifier-Buffer/391911476838?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
The first problem was it was a kit but no problem I built it and it worked perfectly with a very wide band of over 100 KHz although I left off the stupid blue LEDs under the valves. After sticking it in a box with a 12VA toroidal transformer at the bottom I plugged my headphones in and the sound was not loud enough so I thought the guitar level needed more amplification and stuck a 400 uF cap across the cathode resistor to increase the gain. On the scope it looked great but when the headphones were plugged in the signal disappeared. :icon_rolleyes: Looking at the output it is clear it is a preamp not a headphone amp as advertised. After a few choice words and a beer to calm the nerves and stop me chucking the amp at the wall I decided it would be very easy to add another amp to drive the headphones especially now since the gain of the valve part had been increased so I stuck a 100W single chip board I had lying around and that happened to work off the same supply voltage of 12V AC like this.
https://www.ebay.co.uk/itm/TDA7293-AC12V-32V-100W-Digital-Audio-Amplifier-Mono-Single-Channel-AMP-Board/272335220177?epid=2134837205&hash=item3f6871add1:g:6SkAAOSw-itXqBqT
It only runs a Watt or less so no need for a heat sink but it is too large and doesn't fit in the box and it is mono so I have ordered one of these that is less than an inch and stereo. :)
https://www.ebay.co.uk/itm/PAM8610-Digital-Audio-Amplifier-Board-2-15W-Dual-Channel-Stereo-AMP-Class-D/291416872526?epid=1288740610&hash=item43d9cc964e:g:8iMAAOSw~gRV29ty
We will see if it works out as easy as it looks but there will probably be more hoops to jump through before this is done. The front end pot of 50K on the valve preamp could do with being made higher resistance possibly but that can come later.
I have ordered one of these so the box has stereo capability
It won't use the 15W capability since the transformer is only 12W but 1W or 2W is good enough for headphones. Total cost for this off the shelf mini amp is about 10 with small transformer and a few bits of wood & screws. It measures 3"x3"x5" so is quite dinky making it handy.
« Last Edit: January 10, 2018, 05:25:20 AM by Ruptor »

bamslam69

Re: DIY tube amp Simple?
« Reply #1 on: March 12, 2018, 09:31:51 PM »
Lol, I just made the Beavis Audio noisy cricket.
Worked really well, and had enough power to run a 12" speaker.
Rhythym in jump, dancing close to you