Aleph5 Hummmmm

[rwagter]

So after two years I rebuild my aleph5 with a new psu and more easy to access layout, see my earlier problems at:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=52936

The amp is working fine but now I have a humm problem.

When all inputs are empty there is nearly no audible hum. If I connect a shorted inputcable to the right channel (or left) the hum starts (no preamp just cable). When I attach my preamp to 1 channel it gets louder, it doesn't mather if the preamp is turned on.
Please help me to find the ground problem

Groundschematic, chassis is not grounded since it is glued together

The pcb's are the origanal ones I bought about 5 years ago: http://www.kk-pcb.com/aleph-4.html, the fets are hard wired.

[sandstorm33]

From your diagram it would appear that both balanced inputs are grounded. Try grounding the neg input only.

[rwagter]

only the negative input is grounded (with a jumper). The rca groud goes to the XLR ground which goes to the PCB.

[GRollins]

Assuming that I'm reading your diagram correctly and that it accurately reflects what you have in your circuit, you'll need to make sure that the inputs (both RCA & XLR) attach to ground in some manner. Also, why are the RCA jacks connected to both the XLR and the circuit board? One or the other I can understand, but not both.
Depending on how close your amp is to other things that might induce hum, you might need a chassis that shields the circuit. I've got some Aleph 2s that function just fine naked, but you may have something nearby that's causing problems.
As far as support for the kk boards, I would suggest that you contact the fellow who sold you the boards. I've never seen a set and have no idea how they're laid out. He should support his boards.

Grey

[Nelson Pass]

You want to have a star ground which brings together all the input,
0utput, chassis and AC grounds together and then attach that via a
single fat wire to the main power supply ground. Also, you should
allow for isolation of earth (AC) ground to the wall through a
power thermistor or resistor to help break ground loops.

[Salas]

Originally posted by rwagter
only the negative input is grounded (with a jumper). The rca groud goes to the XLR ground which goes to the PCB.

Hello! From what I see, your pcb asks for balanced GND and Unbalanced GND to go separately to their respective points. I would test without the bridge from RCA cold to XLR GND to PCB. I would go XLR 2+3-1GND, RCA hot U, cold GND PCB left.

[sandstorm33]

Originally posted by Nelson Pass
You want to have a star ground which brings together all the input,
0utput, chassis and AC grounds together and then attach that via a
single fat wire to the main power supply ground. Also, you should
allow for isolation of earth (AC) ground to the wall through a
power thermistor or resistor to help break ground loops.

THE BASIC "PLUMBING" !!!

[rwagter]

My quickly drawn schematic was, as it seems, not very clear. But after some changes I wilt try to describe the fenomenon a little bit in more detail for 1 channel (the other one acts the same.)

Input:
XLR + --> pcb+
XLR - --> pcb-
rca + --> pcb unbalanced
rca ground and XLR ground --> star ground

Output:
speaker - -->star ground

Other:
pcb ground --> star ground
psu ground --> star ground
star ground --> ntc --> ac ground
chassis --> not grounded (corners are glued and have
no baremetalconnections between each other)

these are all single wires. But here it comes. After turning the amp on dc offset goes to about 13mV when connecting the preamp and the humm gets louder dc offset doesn't gets higher and my multimeter tells me that is exactly 100Hz.

PSUschematic:

bridge+ ----------------------------------V+
                  |              |
              C 68Mf       MKP 4,7uF
                  |              |
bridge- -----------------------------------
                                       |
                                       |----star ground
                                       |
bridge+ ----------------------------------
                  |              |
              C 68Mf       MKP 4,7uF
                  |              |
bridge- -----------------------------------V-

[Salas]

The PCBs must be incorporating some grounding scheme. I would test the possibility of connecting the inputs as I described in my previous post, and just connect each channel PCB central GND to star with one wire per PCB. See what that will do, its simple.

[rwagter]

What I just found out today is not a groundloop although it seemed one but parasitic hum (the 100Hz give it away) from the trannies. When moving the wires around I could make the noise nearly go away but since I used some lang wires I'm going to rewire the amp first and move all wires away from the magnateic field of the trannies

Ralph