Ground PI with power?

[theundeadelvis]

I know a lot of amps run a ground buss and ground everything to it. I know some also ground the preamp and power sections separately. When doing this, do you ground the phase inverter with the power side or the preamp side? Is there really any advantage to separating the grounds in this manner? Thanks guys!

[RicharD]

A lot of folks around here swear by Doug's grounding scheme.  I've used it several times and it has never let me down.
http://www.el34world.com/charts/grounds.htm

Lately I've been using the "galactic" grounding scheme.  That's where you ground each tube or each DC voltage node separately.  A common component between the 2 is keeping your power tubes grounded separately from everything else.  This seems to be very important.  One of my early builds squealed like a pig and it had a common grounding bus. Separating the power tubes from everything else fixed it.  It is also good practice to put the line power cord ground to it's own point on the chassis, usually to a PT mounting bolt.  Regardless of which scheme you use, the most important aspect of grounding is secure & solid connections.  Many older circuits used all chassis grounding which is fine as long as the connections to the chassis are sound.  Many of these older amps relied on rivets for connections.  Over time these become loose and the amps become problematic.  This can usually be repaired by soldering over the rivet.

[JayB]

I know a lot of amps run a ground buss and ground everything to it. I know some also ground the preamp and power sections separately. When doing this, do you ground the phase inverter with the power side or the preamp side? Is there really any advantage to separating the grounds in this manner? Thanks guys!

Helps keep the hum out. I run a buss for all my pots that runs down to the input jack where that is tied to the grounds for all the preamp cathodes and any grid leak resistors (they get their own buss too) at the input side of the chassis. All my filter caps including the bias caps get tied together and bolted to a power transformer bolt. I run a separate ground for my phase inverter which is grounded with the output transformer ground and that is located where my presence pot is. There is some high voltage on the phase inverter cathodes that could leak down into your preamp inputs if you tied the phase inverter grounds to the preamp buss. Doing this I have found it's less hum if any. You have to think of the grounds just like any other electrical circuit. The filter caps filter out the ripple and that can get injected at 120hz back into your preamp if you tie those together.

I did a lot of experimenting by untying the grounds and using alligator clip leads and switching everything around to find the quietest setup. That was the best way of doing it which is pretty much what Hoffman has a grounding scheme on his website. Not a scientific explanation, I'll leave that to P.R., but I hope it helps.

[PRR]

> phase inverter with the power side or the preamp side?

Not real important. Levels are high and some PIs are push-pull.

The NFB return may be important. Since the OT secondary can be flaoted, the OT and the NFB may return to the end (not middle or front) of the preamp bus.

The important thing is to keep the rectifier and power tube cathode current jolts OFF the preamp bus. Rectifier crap will buzz no matter how good your B+ filter is, and power tube crap will thump the whole preamp in unexpected ways.

Hoffman has preamp bus to chassis at input jack, PT CT (rectifier ground) to chassis at PT. The return is made through chassis. This is a very common plan and does work. As JayB suggests, flowing the high-level PI return "forward" past all your preampery to chassis to PT can be a little like running your sewer past your well. In this plan it may be better to take the PI to the PT bolt, not the long way around the input jack.

[FYL]

It is also good practice to put the line power cord ground to it's own point on the chassis, usually to a PT mounting bolt.

If you want to follow really good practices you should *never* use mounting bolts for ground or earth connections. Use dedicated points using suitable idiot user-proof hardware, with earth as close as possible to the mains inlet.

[theundeadelvis]

Thanks for the input guys! This forum is great!