NO need to fit that jumper as is for no transformer out so the -out as a 0v reference. When using a output transformer -out is not used as all as the transformer connects between +out and 0v.tazwolf wrote:On the groupdiy mega thread there was this posting by Dirk666.
Do you fit a jumper across amp BA PCB pins (4-7) when using a hybrid for the baby animal with the jlm 1:1:1 output tran?
Do you mean 50/100Hz (60/120Hz USA) so hum and buzz? At 500Hz is an unusually low frequency for a oscillation in a pre?Joe said on page 25;
‘WHEN USING HYBRID WITH BA PCB, LEAVE OFF the 47uF cap which is on the opposite side of the PCB to the LED. As this can override the power supply filtering and let noise into the pre.’
I could not find the answer to these questions so I was wondering if someone here could help.
I am getting buzz/oscillation at 500hz on mine and am wondering if these could be the cause.
Definitely leave off the 47uF cap mentioned on a Hybrid to stop high frequency noise from the SMPS getting in.
If the hum/buzz changes when you move the mic pre around then it is being picked up by the input transformer and will be worse if no mic is plugged in.
Check the metal case around the mic pre has 0v connected to it.
If using a DC connector it is best to wire from the 0v on the DC connector to a bolt on the back of the case to make sure 0v is connected properly.
A lot of cases that are powder coated need to have the powdercoating removed under the screw heads to make sure all panels are connected to 0v.
On our rack cases we do this already and use silver screws in the bottom panel to make sure all panels are shorted together properly
Make sure gain pot wiring is tightly twisted together and short and same for impedance pot wiring. Keep impedance pot wiring, gain wiring and in and out wiring away from each other.
Otherwise feel free to send me some photos of the wiring and top and bottom of the PCB and a small sound file of the noise you mention to see if I can spot anything.