Hartke 3500 Output Jacks

[misterc57]

This is a sanity check. I have a Hartke 3500 whose output jacks need to be replaced. The current jacks are board mounted plastic body and thread, and no longer stay snug.

I have removed the two jacks from the output board and want to install panel mount Switchcraft # 11 jacks and run a parallel wire from the jacks to the output jack board. Then I started to over think about the #11 jacks will now be panel grounded also.
The output jack board has two wires H and G. The G has continuity to chassis ground so I am assuming that it is okay to use the #11 jacks which will also be panel grounded?

Thank you

hartke_ha3500_power_amplifier_sch.pdf

[Helmholtz]

Using chassis grounded output jacks will result double grounding (ground loop).
Might cause hum.

[Jon Snell]

If you use panel mounted jacks that ground the shield, that will cause R351 to become short circuit and introduce instability and hum to the amplifier.
R351 is placed in that position to reduce any earth loop issues between the power supply, output stage and input stages. Isolated jacks are prefered.

[g1]

You can put insulating washers on the switchcrafts. Shoulder type fiber on the inside, flat fiber on the outside.

[The Dude]

Here's the full schematic (see below). It looks to me like the jack sleeve connects directly to chassis ground (follow to power supply). I don't think it would be a problem to ground the jacks. It may or may not cause hum, but you could try it. That said, why not just replace the jacks with original parts?

Ha3500.pdf

[misterc57]

Where possible I prefer to use full metal Switchcraft jacks for durability, reliability and availability.

Now that you mention to follow the connection to the PS I see the chassis ground. I ended up installing Neutrik plastic jacks so did not get a chance to try the Switchcraft.

Thank you everyone.

[Jon Snell]

Neutrik are excellent quality.

[misterc57]

I could not get the Neutrik jacks to stay snug so I ended up installing the Switchcraft jacks, all is now well. Thank you

[misterc57]

Have my eye on another 3500. Has anyone ever replaced a NJM072D which is obsolete with current substitutes (preference to lowest prices)? Available options are in screenshot below.

Thank you

[g1]

Have my eye on another 3500. Has anyone ever replaced a NJM072D which is obsolete with current substitutes (preference to lowest prices)? Available options are in screenshot below.

Looks like you reversed 072 to 027. 072 is a standard op amp, TL072 is readily available.