F6 Illustrated Build Guide

[2 picoDumbs]

2 But I am seriously wondering if the input decoupling caps are not shielded enough. When i touch them the hum gets louder.
!

It is a good idea to isolate the capacitors from the chassis with some foam rubber or something similar.
This can also happen when things aren't grounded properly too.

Isolate the caps first.

 

[2 picoDumbs]

Touching the caps and the hum increasing is a positive verification that you DO have a grounding issue.

I agree.
This is a very common effect to a grounding issue.

 

[2 picoDumbs]

Yaho

Measure resistance from 0V on Meanwell psu to chassis.

 

[Yaho]

Measure resistance from 0V on Meanwell psu to chassis.

no reading discontinued

Touching the caps and the hum increasing is a positive verification that you DO have a grounding issue.

should i resolder everything on the board, especially the caps?

 

[2 picoDumbs]

Do you mean open circuit?

 

[Yaho]

yes, open circuit

 

[2 picoDumbs]

In my regular B1 (the original), the chassis and psu 0V are intended to be connected.
You should measure 0 Ohms (or near it due to some contact resistance of your probes) here, not open circuit.

 

[2 picoDumbs]

Are you using metal standoffs on your pcb?

In the original B1 pcb this electrical connection was made from the pcb through the pcb standoffs

 

[2 picoDumbs]

I will check my Firstwatt B5 active crossover, and confirm how that is connected also.

 

[2 picoDumbs]

Yes it should be definitely connected.

It measures 5 Ohms, this is just a combination of contact resistance of the probes and anodizing on aluminium.
It is directly connected.

 

[2 picoDumbs]

You need to fix this connection.

The earth wire should only be connected to meanwell chassis which needs to be completely isolated from every thing else. Leave it disconnected temporarily

 

[WKCox]

@Yaho: What about the stepped attenuator relay board and its power supply? (From your post in the B1 Korg thread.) How is this connected?

A wiring diagram and some pics would certainly help 2 picoDumbs and others to help you.

 

[2 picoDumbs]

no reading discontinued



should i resolder everything on the board, especially the caps?

Hope you got the information above.

Try fixing this

 

[Yaho]

Sorry about the delay. My basement AC drainage pump was spitting water all over the place. It took me a while to wipe the water from the floor. So I am here.

Are you using metal standoffs on your pcb?

yes.

Measure resistance from 0V on Meanwell psu to chassis

correction...O ohm

 

[2 picoDumbs]

Instead of shorting the -ve rca inputs on the pcb.
Try running twisted pairs or coax for each input.

 

[2 picoDumbs]

Also how is the Meanwell psu 0V connected to chassis?
Maybe it is a bad connection.
It should be as low impedance as possible.

Do you have paint or anodizing?

Make the connection as tight and perfect as possible.

This is very important

 

[Yaho]

Also how is the Meanwell psu 0V connected to chassis?

I did not connect PSU 0V to the chassis. Should I? Just to be sure, 0V is the negative side of PSU?

I just did a chemo-therapy on B1, resoldering, rewiring, and did everything you suggested. The hum is reduced! I touch the caps, no noise. But the faint hum is still there. Faint but I hear it, even from a few feet away. May be I am CDO!

It's demonic! I can't get rid of the hum.

 

[2 picoDumbs]

Yeah negative side of supply.
Just temporarily make a direct connection between PSU 0V and the chassis of the preamp (not chassis of supply).

Usually this connection is made via the standoffs or possibly the volume pot. TIGHTEN EVERYTHING nice and tight.
If you make these connections super tight you can break through the oxides on the surface of the aluminium. Otherwise get sandpaper and sand the chassis around these areas?
A starwasher can also be useful to bite through oxides.

 

[2 picoDumbs]

Just the other day, I fixed someone's PA rig.
They had an annoying hum problem.

It was due to the pots not making a solid electrical connection to the chassis.
I had to TIGHTEN the volume pots nice and BLOODY tight, and the hum completely disappeared

So try the things mentioned earlier regarding making sure you remove oxides and paint.
AND just cause you can't see oxide doesn't mean you don't have it. YOU HAVE IT

 

[Yaho]

TIGHTEN EVERYTHING nice and tight

Got it. I will definitely do that. Thanks for all your help.