#MIDISID Monday 11 July - monophonic mode, honky tonks and an annoying hum

This first video is about monophonic mode. I'll be talking about the modes a lot because MIDISID works in three very different ways and it'll be good to demo them as much as possible.  In this one I talk about the honky tonk and how we might reproduce that rustic sound.

I've also been working on an annoying hum I've been experiencing since building the last revisions of the boards. Counterintuitively it seemed worse when on battery power (there's a clue).

Today I've been cutting traces and adding bodge wires. Adding capacitors and generally messing around, trying to find out where the problem lies. 

Here is the problem. The first half of this demonstrates the problem. You'll hear the chime of the SwinSID Nanos as I apply the power, and then you'll hear the hum before the music starts.  The second half is how things sounded after fixing the problem. The hum is undetectable and the sound level is better (these things are visually obvious too in the Sound Studio window.) 

To cut a long story short, thin traces carrying 0v  and 5v across the board and going near all sorts of other signals isn't ideal. That didn't help but the real culprit was my 9v supply. I was using what I thought was a new and good quality battery. Turns out that it was measuring less than 7, and supplying my board with less than 7v causes the hum. Bring that up above 7 (better still fit a new battery, or a good 9v mains adaptor) and the hum goes away.  I think this just has to do with the way that the 7805 works. I had assumed that anything above 5v would work, the excess being wasted as heat. but it seems to need a good couple of volts above the target. 

Anyhow. I wasted a lot of time on this. A good 9v supply is what's needed and the output should be very clear and noise-free. I leave this blog post for my own future reference.