Built: August 2020
After spending some time reading the various posts on the forums I decided it was time for another project to build. I came across Wayne’s BA2018 Linestage a few months ago and when I discovered it could be configured and built as a headphone amp with pre-out I wanted to build this so I could compare it to the Whammy which is also another design by Wayne Colburn.
Firstly I had to solder the tiny SMD JFET’s to the board before moving on to the other components. To get each of the JFET’s soldered to the board as straight and neatly as possible, I used a small blob of Blu-Tack to hold the component in place while I soldered the first contact. Once I had done this I removed the Blu-Tack and then soldered the remaining contacts and the result is in the images below.
Primarily this project is a linestage but after reading on the diyAudio forum I discovered that with a few changes you can in fact make it powerful enough to drive headphones. To do this you change Q8/Q20 from KSC1845 to KSC2690 and Q10/Q25 from KSA992 to KSA1220. These changes are to implement more powerful output transistors capable of driving most headphones. The other changes that need to be made are to change R11/R12 and R32/R33 to 1/2 Watt resistors to handle the extra power and increase the bias by changing their values from 27R to 15R which is recommended when using the higher output transistors. R23/C4 and R46/C9 should be left open and finally C1/C7 should be changed from 10pF to 5pF. You can then use this as a headphone amp as well as a pre amp. The notes for the changes are included on the schematic below.
I ordered two sets of the BA2018 PCB along with components for both configurations. One set I have put away as a spare or one day I might just build it anyway. Now I have sorted out the components for the build as a headphone amplifier it’s now time to start soldering the rest of the components. I soldered the resistors first followed by the capacitors and then the trimpots.
Next I soldered the LED’s and the terminal blocks onto the PCB. Thinking about it, I should have soldered the transistors before the terminal blocks but it doesn’t really matter that much.
Finally I soldered all the transistors into place taking extra care of the orientation as I went with there being so many. Once I had done this the board was finished and I cleaned the underside with 99% IPA and a toothbrush which cleaned the board up a treat! Now it’s time to sort out a power supply for this project.
Okay so next we need a power supply. The BA2018 accepts a bi-polar input of (+/-) 15V to 24V. User 6L6 on the diyAudio forums recommends a power supply output of 18V as the sweet spot for this build. I also remember reading somewhere that Wayne recommends 20V so its all down to preference and what sounds best to you.
I wanted to build my own power supply for the Linestage based along the lines of the one that powers the Whammy as its simple, clean and dead silent. I went ahead with my design, got the boards back and built one up for testing with the intention of using it with this project in the same type of Hammond 1455T2201 enclosure as I used for the Whammy as its a decent size to hold everything while still being neat and compact.
At this point I powered up the board to test and saw the red LED’s lit which was a relief to see, I then proceeded to measure and test the DC offset on the audio outputs with my multimeter and then use the onboard trimpots to zero the values out. Once this was done it was time to start building into my enclosure.
As you can see in the image above, I had to go with a different power supply as the original one I designed did not allow enough width to accomodate the Linestage board. This was the second power supply I designed only this time I upgraded the regulators and designed it as an adjustable power supply to make it more useful for future projects. The end result is a slightly more sophisticated looking power supply utilising the same CRCRC filter as before but with an overall reduced footprint.
The hardest part of the build and also the most tedious is measuring, cutting out and then eventually wiring up the end panels. I am always glad once this task is done and out the way. It is important to note as we are playing with mains voltage in places, its a very good idea to ensure you earth your chassis/enclosure to protect you from high voltage if a fault was to develop. I cannot stress this enough. Also notice the capacitor on the rear panel in the image above right. This is to prevent ground loops and is connected in series from the RCA ground to the earth connection. This will prevent any hums, buzz or hiss through the headphones when no music is playing.
Panels are test fitted into place while the rest of the wiring takes place. This is to ensure the cable is cut to the right length but not too long as to allow the removal of panels for future maintenance. You may notice this build has 2 power switches. The rear switch is to power the whole amp including the transformer and the front switch is connected to the power supply regulators ‘Enable’ or ‘ON/OFF’ function which allows the amp to be powered on and off while leaving the transformer and power supply filter powered.
The build is finally finished and although it took much longer than my last two amp builds it was worth it in the end. The biggest hold up was having to design a new power supply for this build. Although I could have gone and purchased one that would have done the job just as well I thought as this is DIY, I would make my own because it’s the best feeling ever when you use something you have built yourself. You appreciate it more. Also you get the added benefit of having the layout exactly as you want it.
This was a fun build and I am really pleased with the end result. It sounds really clean and analytical and I personally think it sounds slightly better than the Whammy in comparison but my brother disagrees. This is why we say sound is always subjective. We all have different thoughts and opinions but both the Whammy and the Linestage certainly have their own place and I don’t think I will be parting with either of them any time soon!
