[vern316]

I just finished the optimized Morgan Jones headphone amp from the Headwize site and have a small amount of hum present. Nothing I do can get rid of it: the power supply is seperate from the amp (in a different case), 6.3VDC filament voltage, carefull with parts placement. Am I doing something else wrong or what? The thing sounds great, just enough hum to be a pain. Also, what is the purpose of the internal shield (pin 9 I think) of the 6DJ8? Thanks.

 

[Budgie]

A couple hints:

The wire for the ac feeding the filaments should be twisted pairs.

The ground wire for the input jacks can be a source of hum. Try grounding them in different locations and see if that helps.

The hum could be coming from the source. Does it hum when using any source?

 

[ringtheorist]

The 'internal shield' on the 6DJ8 should be grounded to provide some isoluation between each triode in the tube.

As far as the hum issue goes, this has been discussed on headwize as well. I'm not sure what the resolution was -- it might just be that the optimized circuit is more prone to hum if certain precautions are not taken. Just be sure to use star grounding (or clustered star grounding with heavy gauge wires connecting the centers of the stars). I built the original MJ and had a lot of hum. When I tore out the insides and properly grounded everything, it disappeared (despite having a fairly noisy supply!)

-b

 

[vern316]

Thanks for the info on the internal shield. I used star grounding and 6 volts DC on the filaments. I built the MJ as per the schematic and had a of of hum. I changed the filter caps on the power supply to 2400uf instead of 220uf and got rid of most of the hum. If grounding the internal shield doesn't help, I'm going to raise the filter cap values to 4800uf and see what happens.