Ground problem w/ PAT-4

I thought I was just about done with the rewire on the PAT-4.

Tonight I rewired the phono inputs, added ground lugs to the new I/O board, and wired the CD and AUX inputs across the Unused Loudness Switch.

Some problems developed.

1- The PAT-4 is quiet - NO HUM - across the TUNER, TAPE, and SPARE Inputs.

2- I now have a 60hz hum (low) on the PHONO.

I used shielded cable for the PHONO inputs. I connected the shielding to the ground terminal on the selector switch and the ground terminal on the RCA Jack.
Since the ground of the Phono RCA Jack on the I/O strip was not connected to the other grounds I added a ground lug and connected the Phono Grounds to this new Chassis ground. I also added a ground lug to the other end of the I/O strip since they did not appear to have a connection to the chassis ground.
Did I inadvertantly create a Ground Loop? If so which connection would be the best to disconnect? If it helps the I/O board is the one from Roy Mottram.

3- My idea for switching the extra input through the Loudness Switch does not appear to have been a good one. I now have a bit of cross-talk between the CD and Aux (one input connected to the bottom of the switch and the other to the top, with the selector switch to the middle contacts. I will probably remove the connection and drop one input, connecting the AUX directly back to the selector switch. Unless someone has an idea to eliminate it.

Thanks in advance for any ideas

most likely you have created a ground loop, there is a reason the phono ground was separate on the new I-O board, as phono ground should NOT be connected anywhere except to the phono board itself.
If you still have trouble, send me an email directly.
Roy info@tubes4hifi.com

tubes4hifi wrote:most likely you have created a ground loop, there is a reason the phono ground was separate on the new I-O board, as phono ground should NOT be connected anywhere except to the phono board itself.
If you still have trouble, send me an email directly.
Roy info@tubes4hifi.com

Thank you Roy, my apologies if I was out of line on the forum.

However the GROUND problem appears to be resolved.
I'm posting it here because it might be of interest to others.

The hum problem appears to have not been the result of my wiring.
After going back in rechecking my wiring, and redoing the chassis grounds the hum was still there.

I swapped out the Phono RCA cable ( a brand new one, go figure)and the hum disappeared.
all of the inputs are now silent.

Next time I think I'll do the RCA swap first. What a waste of time!!!!!!!

I thought the hum problem was resolved. At low levels it was.

I discovered that with NO Signal at very high levels the hum was present on the unused AUX input and the PHONO input. Otherwise the PAT-4 was dead silent.

I finally resolved the Hum problem.

For those who may be interested in the solution.

I wired the PAT-4 to an external ground. This cut the hum but did not eliminate it.

AUX Input - I am using a shorted RCA plugs on the unused input. It is now silent.

PHONO Input - I unplugged (AC not RCA) the turntable (Technics) and the hum disappeared. Tried a different outlet, reversed the plug it came back. Unplugged it again and the hum disappeared. I decided to try my Thorens which I had rewired and knew was grounded properly. This did the trick.

The PAT-4 is now quiet.
I hope this helps someone else. Persistance and logic paid off
Next to check the wiring on the Technics TT

You do not say what cartridge is in your Technics. If it is like a Stanton or Pickering where the mu-metal case of the cartridge is being electrically connected to the tonearm headshell and thus is grounded; and the ground strap between the mu-metal case of the cartridge and one of the ground pins is still intact, you have created a ground loop. When mounting such cartridges such that the metal case is connected to tonearm ground, that ground strap should be removed.

GP49 wrote:You do not say what cartridge is in your Technics. If it is like a Stanton or Pickering where the mu-metal case of the cartridge is being electrically connected to the tonearm headshell and thus is grounded; and the ground strap between the mu-metal case of the cartridge and one of the ground pins is still intact, you have created a ground loop. When mounting such cartridges such that the metal case is connected to tonearm ground, that ground strap should be removed.

The Turntable is a Technics SLBD26
Cartridge Audio Technica AT92E

The case appears to be plastic and I don't see a ground strap on it, just the 4 pins.

I started w/ this TT as it was a spare and the Thorens was in another system. I wanted to make sure everything was working before moving the Thorens - 160C w/ a Shure V15III