Bottlehead Kits > S.E.X. Kit

S.E.X. on glass

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Bourney:
After a little back and forth over my gerber files my PCB for the power supply supply has arrived.

I remembered to put a radius on the corners this time.

This board has the same specifications as the amp board, with the exception that this one is immersion gold (enig) with 2U" thickness gold, versus the amp board which is HASL with lead. As far as production quality goes they both appear to be of the same standard.

Below pictures are self explanatory. Mounting position copied from the Mainline.

I'm waiting on the custom front panel to arrive before I can go any further. Should be here next week.

Bourney:
I completed the build and everything tested OK, but I have some hum/static.
I was suspicious of the 'balancing' resistors to ground on the XLR so I cut them. They weren't the problem.
I removed the components from the C4S section and installed the 150k resistors. Things improved. The static dropped away and left just a very low level hum in the left channel, silence in the right channel.
When I play music, even at low volume the hum is not audible, until there is silence in the piece, or between tracks. Not the end of the world, but not ideal either.
The hum exists with nothing connected to the inputs, but disappears when the tubes are removed.
When I locate my Mainline, Crack, Crackatwoa in the same location they have no noise, so it is not a noisy location, or perhaps the other amps are less susceptible.
I'll try the earth tab/diode mod next with some UF4007.
In any case I'll redo the amplifier board , move some components, reroute some traces and reduce the trace size on the C4S section because (a) I'd like the C4S and (b) the layout of my first design really made it a nightmare to wire up - a trap for the inexperienced.

On the positive side my CAD drawing for the plynth worked out nicely.

Paul Birkeland:
Did you test for hum pickup when you moved the plate chokes and output transformers?

Bourney:
No I didn't test, I took a chance, but it does seem that the cause is not external.

Any suggestions for the test method - moving and rotating and see what occurs?

Paul Birkeland:
With the tubes removed and one of the high voltage AC wires disconnected from that PC board, you can turn the amp on to energize the power transformer and it will radiate its 60Hz magnetic field.  Set your DVM to read AC millivolts and probe between terminals 5 and 10 on each output transformer to see how much 60Hz noise is picked up. 

It might also help to look at how your ground traces are laid out on your power supply PC board, as that can cause some weird noise problems in ways that aren't always intuitive.

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