PSU Gnd Question - Page 1
Forum section: electronics / beginners

author: goldfinger
author_rank: Regular Contributor
timestamp: February 08, 2017, 02:07:14 am
content: Hi Guys,I have a quick question regarding grounding. I have a transformer that has 2 x 20VAC/3x12VAC secondaries with a chassis earth electrostatic shield.The IEC connector and tranny 0v shield will be taken to chassis gnd as well as gnd taps off the power supply boards.The 20VAC will be going through one full bridged cap filtered pcb board and likewise the 12VAC’s (through 2 separate boards). All supplies are single rail +/gnd power supplies. The power supply will actually be sitting in separate enclosure to the amplifier and aux that need power.. I have a suitably rated aviator/circular connector to carry the dc power (approx. foot lead)to the main unit.My question is in relation to grounding. To reduce the wiring between the two units, is it ok to tie the two (2) gnd for the 20VAC/26VDC together and only carry one ground wire through to the other enclosure (and split out again) Likewise with the 12VAC/16VDC, consolidate the 3 gnd to one?Or even consolidate all the gnd across both the 26VDC/16VDC supplies.One final question, should I also look to tie the gnd to chassis in the second box also, or is chassis grounding in the power supply enclosure suffice?Hope the above makes sense. Appreciate any feedback and thoughts.

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: February 08, 2017, 03:22:22 am
content: The others may correct me if I'm wrong but as far as I know...It is perfectly OK to tie all of the power supply grounds together in the PSU chassis. In fact, it is mandatory. Be sure to tie the grounds together at the big filter cap terminals then wire it to the interconnect connector and all of this with the biggest gauge wire you have.Unless you need two conductors to carry the current due to pin current limitations, don't use two conductors to get the ground to the amp chassis as that may (probably will) create a potential difference between those wires since they will, no doubt be carrying different amounts of current. If that potential difference were to leak into the audio signal then that would inject noise or hum to be amplified along with it and be very difficult to get rid of. If you must use two conductors for this due to current issues, then make sure they are shorted together on BOTH ends of the cable.On the amp end, establish the power connector pin as a star ground for the rest of the power currents. Try to keep this ground network separate from the signal ground network. They, of course must connect somewhere so its best to connect them between the input connectors and the power connector.

author: goldfinger
author_rank: Regular Contributor
timestamp: February 08, 2017, 06:16:13 am
content: Quote from: basinstreetdesign on February 08, 2017, 03:22:22 amHi Basin,Thanks for feedback appreciated. In total there are three psu rectifying cap boards one for the 2x 20vac taps and the other two PCB's for 3x12vac.So I'll take the 4x gnd output wires of the psu to chassis then one from chasis ground to psu panel mount which will carry over to the amplifier box.That sound correct?Ideally I suppose it might have been better to do the rectification in the amp enclosure and carry the ac from the psu box, but unfortunately space doesn't permit!

author: Ian.M
author_rank: Super Contributor
timestamp: February 08, 2017, 07:33:14 am
content: If the transformer has a grounded electrostatic shield, you don't need to ground the secondary side in the PSU at all for safety or signal integrity reasons. If any other connections to its load introduce a ground, its probably best NOT to ground the secondary side in the PSU, to avoid any risk of a ground loop. If the load is not otherwise grounded, it *MAY* be worth grounding it in the PSU.If you don't ground the secondary side, consider adding a metal oxide varistor or a gas discharge surge suppressor between 0V and ground so that any unexpected high voltage applied to the floating output doesn't compromise the transformer insulation.

author: goldfinger
author_rank: Regular Contributor
timestamp: February 08, 2017, 09:21:20 pm
content: Quote from: Ian.M on February 08, 2017, 07:33:14 amHi IanOk thanks for your feedback. Chassis grounding the psu aside is there any issues I should consider if I consolidate the gnd output of each D.C. rectified pcb into one gnd between both boxes?

author: Ian.M
author_rank: Super Contributor
timestamp: February 08, 2017, 11:31:58 pm
content: If the DC rails for the preamp are regulated in the PSU rather than in the preamp itself, and the main amp has its load returned to 0V (i.e not a bridge tied load configuration), there is a significantly higher risk of instability if you use a single 0v wire for both, due to the load return current across the 0V wire and connector resistance developing a voltage that is effectively in series with the preamp's supply rails. If you do use a common 0V wire, you should regulate the rails in the preamp and, if the load returns to 0V, have hefty decoupling caps for the positive annd negative rails right at the main amp output stage to keep the load current out of that shared 0V wire.