F6 Illustrated Build Guide

[2 picoDumbs]

1) When you turn the pre on what do you now measure at the speaker outputs?

2) What do you measure across the outputs of the pre when it is not connected to F6?

I really am sleeping now.

 

[6L6]

It might not be the pre, (Hopefully it is, but...) it could be a ground loop that’s finding itself through the input connections.

Drive the F6 directly from a phone, see if there’s hum.

 

[2 picoDumbs]

Yes..

The measurement should hopefully confirm this.

That's the intended the reason for requesting it.

 

[Yaho]

It might not be the pre, (Hopefully it is, but...)

It is pre. I've tried to limit ground loop as much as i can.

2 picoDumbs, I hope you were able to sleep a little. If you are working, ignore this. But I am transferring this conversation over to the B1 with Korg Triode thread. Hopefully, you will join us there.

Thanks

 

[2 picoDumbs]

I am back.

Hahahaha

 

[2 picoDumbs]

Take measurement across pre outputs when not connected to F6.
What do you get?

Is your Korg pre powered by a switch mode supply?

 

[Yaho]

0v. nada!

Is your Korg pre powered by a switch mode supply

Yes, it is a switching power supply.

RS-25-MEAN WELL Switching Power Supply Manufacturer

 

[2 picoDumbs]

Ok

It's pointing towards a ground loop.
Are you using a thermistor in your F6 to break 0V from Chassis earth?

Still thinking to be sure

 

[Yaho]

Are you using a thermistor in your F6 to break 0V from Chassis earth?

Yes.

I am using bridge rect for the pre to break the ground loop as well.

BTW, when i touch the input caps (10uf), it the hum becomes louder. May be the caps are not well insulated?

 

[2 picoDumbs]

Ok

1) Turn off your F6
2) Disconnect from pre

3) Take a resistance measurement from 0V on the psu to the chassis?
What do you get?

Do this measurement for both F6 and your Pre separately

 

[Yaho]

Take a resistance measurement form 0V on the psu to the chassis?
What do you get?

from the B1 or the F6

 

[2 picoDumbs]

Both

 

[Yaho]

F6 008.8
B1 000.2

Perhaps I am not lifting the ground on pre properly

 

[2 picoDumbs]

Now connect F6 and Korg together via RCA (but not power cords connected) and measure from the F6 0V psu to Korg Chassis

 

[Yaho]

0 ohm

 

[2 picoDumbs]

Then have both rca and power cords connected to the wall (not turned on) and repeat the measurement.

 

[2 picoDumbs]

0 ohm

It should be still 8.8 Ohms

You have a problem somewhere

 

[Yaho]

0 ohm

 

[2 picoDumbs]

As noted above the first measurement should have been 8.8 Ohms F6 0V to Korg Pre Chassis (RCAs connected)

Find out what is causing this issue and you will most likely fix your hum

 

[Yaho]

Got it. Any primary suspects...or hints?