I was really happy with the result of the prototype PCBs when they arrived, nicely made, awesome silkscreen colour. So it was time to populate the board and see if it was going to work, fingers crossed. Here is a block diagram of the system, pretty self evident from the diagram of how it is meant to work (you can click on the images to see them larger). When I was designing the PCB, I wanted to label the board so I realized I did not have a name other than turntable motor controller, so giving it some thought I decided to call it the Bi-Onda TT Motor Controller. Since this is a dual sine wave generator and 'wave' in Italian is onda, I named it Bi-Onda, which if you know Italian, bionda means blonde, as is my darling wife. Sounds ok too.
|Test Bed for the Bi-Onda|
However, it did not keep the frustration totally at bay. I first populated the PCB with all the parts up to, but not including, the output op-amp stages. This way I would be able to test the power supply, the signal generator and low pass filters. This worked like a charm, while the supply rail voltages were a bit higher than I liked, it worked fine and I could get two very nice sine waves at the output of the filters. The LCD looked good and the debounce components worked well for the tactile buttons I chose. So I thought, ok, lets put in the power op-amps.
|Back to the |
So after a bunch of trial and error, here is what I found to be the problems with the system fully put together as per the initial design:
- Power supply capacitors need to be of much larger value.
- Additional bypass capacitors have to be installed on both inverting and non-inverting inputs of the op-amps to stabilize the signals.
- Some minor component value changes and circuit improvements.
Next, hook up both output transformers and try driving the turntable motor!
That will do it for now, 'til next time.