My potentially lethal DIY amps


I have built now five Leach Amps into sheet metal boxes. What bothers me is that...

I first used too small screw connector strips for 230V AC and nothing between them and the sheet metal. Nothing bad happened and I was told about this, so I switched to bigger screw connector strips and put 2mm of oversised top quality rubber sheets between the s.c.s. and sheet metal.

to get an idea. Sorry, all text is in Finnish. All links are to pictures.

I have a power switch in every amplifier. I have first tied and then soldered the leads that come to these switches, but someone told me that the only right way to do it is to use an Abiko connector (a thing that has the lead tightly squeezed in one end and the other end is pushed to the switch's terminal).

Is it safe to use mains voltage on a plastic prototype board?

How big clearance is needed between mains voltage and grounded or low-voltage parts on the same board? I have tried to have 5mm or more always.

Or if using the same board for mains voltage and low voltage is allowed at all?

My ground bolt is correctly made. The lead that goes from chassis to mains connector is lowest in the stack, and separately fastened, and with tooth washers on both sides.

Worst thing I did was in two amplifiers that I am not using now, and wonfer if I should somehow fix or disassemble them. I used a relay with it's associated components to switch mains to the big 545VA transformer and placed the relay on a piece of prototype board I glued to the inside of the sheet metal front panel.

for details

-Kimmo Sundqvist
That plastic prototype board is called veroboard, it's okay to feed line voltage through it as far as I know. I've used it for radio projects needing voltages in excess of 500 volts, you just have to be careful how you arrange things. Also, veroboard isn't very great for sonics in audio, you've got some really nice trannies in that amp with the power relay and I think they deserve some point to point wiring or a real board;)
Yes, another good point... Signal lines should be kept well away from power lines and output lines to keep the signal clean. Also, try to keep the power wires close to the chassie and the signal wires away from it as steel and aluminum can cause inductive unlinearities in interconnect wire. This is also why it's good to suspend interconnects from the floor away from everything. Cleaner wiring makes repair and reverse engineering much much easier in the long run, also, some people say that an aesthetically clean and symmetrical amplifier usually sounds better, but hey, it's probably just liek the placebo effect, but there's nothing wrong with that here!;)