Audio Blues Valve Amp

I have wanted a valve amp to add to my collection for some time but the cost of buying a good quality one has always stopped me. I have read a few books on building a valve amp over the past few years and after a lot research into different designs I finally made the decision to build one. My choice in design was Peter Millets DCPP Engineers amp (Web Link). This is a modern designed amp using MOSFETs for the power regulation and compactron TV sweep tubes for the output stage. These tubes are cheap in the USA but not available in the UK so I had to get these imported. Peter deigned a PCB for this amp which could be purchased through ebay which at the time of publishing this blog is still listed here for $50.00 + $27.00 postage which works out to approximately £54.00. So, I ordered the PCB and started looking for the other components.

For the valves I ordered 6JN6 and 6CB6 and valve sockets for each from Vacuum tubes online which is a USA company so the valves had to be shipped to the UK. The cost of the valves and sockets was $67 which converted to £47.0 but due to import tax and handling fees through Royal mail total cost was £78 so if I build this again I would like to get the parts from Europe or UK. For the electronics I ordered it through Mouser Electronics which cost £74.00 with postage. For the transformers I wanted to go with Edcor but was not happy to buy through the USA due to import taxes, luckily after some searching on the net I found a Europe company which supplies the Edcor transformers Don Audio total cost with postage was £270.00. All I needed now was an aluminium plate and some speaker terminal post, audio input connectors cables etc which cost approximately £30. The wooden box was free as I already had an old piece of hard wood from an old desk.

The basic build of the PCB was easy to follow and the metal plate was drilled out using normal metal cutters on my pillar drill. This was then deburred and polished up and the PCB was held into place using brass pillars. The box was mitre jointed and routed out for the plate and for a bottom piece of plywood. I also routed out the front to have a metal grill with LED lighting for a cosmetic effect. For the LED lighting I used Neopixels controlled by a nano Arduino. The power on/off switch and audio connections come out of the plate so the amp can sit close to the wall without cables coming out the back.

My second video blog shows how the amp has progressed to be tested. Both output stages need to be balanced which is nicely explained on Peters web site. I used an oscilloscope connected to both test points to get the voltage levels correct and balanced. The amp powered up nice with no problems and had a good sound.

I have finally finished the amp with the LED lighting and name plate now fitted. The lighting is provided by neopixels which are controlled by a nano arduino. Program is a very basic color swipe which looks great at night. Power supply for the lighting had to be made using a 12v transformer and two LM317 regulators to give me 12v regulated supply for the arduino and main on/off switch LED and a 5V supply for the neopixels. 

The name plate was routed out by hand and once vanished glued on with hot glue gun. Amp was tested and had an initial hum from the PC audio connection which I believe is caused by a ground loop. I have now connected the audio via Bluetooth dongles which stops the hum and gives the amp an added Bluetooth advantage.

For now its working really well and the sound quality is excellent. I am still running the volume control by the PC and only have one input. My next challenge will be to design and build an arduino controlled attenuator for the volume control and input switching control to have the ability to switch between more than one audio device. This will also have an LCD display for volume and input selection.

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