The amp is still humming, about the same as before, but now it’s the same in both channels. The amp now shuts down with a quiet thump as it should. I fiddled a bit with the wires from the power supply board to amp boards, and I can change the volume of the hum by moving them around. The volume goes up the closer that the wires feeding power to the boards get to the rectifier blocks. What steps do you think I should take next? The ground lift mod?
Last edited:
Live is also fused. The schematic and build guides indicate that ground should also be fused.
It may be just me, but two of those three connections look as if they were made with an iron that wasn't man enough (or hot enough?) for the job.
GND in particular.
GND in particular.
Having a fuse in-line with your mains gnd is unsafe. If it should blow, and a short happens you’ll be in some deep ‘doo-doo’ when you touch the chassis.
Also, twist them tightly, and consider rearranging the bridges further from the amp boards, as said before. Since it increases and decreases when moving wires around, this indicates that some - or a lot - of what you are hearing is AC ripple from the wires to and from the rectifiers, inducing small currents in the clean dc power cables, and that is then amplified by the Aleph J gain stage(s).
And yes, there must be no fuse in the ground plane. For your own safety, please remove immediately.
Last edited:
You are correct. I misread. It is supposed to be live and neutral that is fused. I will take the fuse off ground and put it on the neutral leg.
The chassis is a bit tight from side to side, and it isn’t very deep either. It’s mostly just tall. It seems that it may be best to move the power supply to a different chassis. Do you think that given the space available, I can re-wire and twist wires and have it result in a silent amp?
Well, it is difficult to say, it may or may not. Remember, moving the psu out creates issues of it’s own, and dangers. You really need to know what you are doing.
I would recommend you try and see how good you can get it with the psu inside the amp chassis.
But first: Is Boky happy? Saw you had some discussions earlier, but seems it was solved.
1: First off, follow bokys advice on the hum breaking resistor. 10-20 ohms should do it.
2: Just twist them wires, and route them close to the chassis floor, as far away as possible from the bridges and transformer.
3: Consider collecting the psu gnd’s on one side of the psu boards.
4: how does it sound after those steps?
Quiet aleph on 104db sens is a challenge, but you can do it 🙂
PS: just mount the transformer vertically, and you will have loooooads of space 🙂
Attachments
Thanks for your help with this. I am familiar with the use of umbilicals and separate chassis for circuit and power supply, as I have done it with a couple of my tube based projects. What sort of issues are created by separating power supply and signal chassis? My plan was to add a couple of big capacitors in the signal chassis and have the umbilical act as the R to the final C in the chassis. That sad, I will definitely try to make it work in one chassis first.
Boky pointed out an error in the wiring of the input jacks on the two boards. When I fixed that, the loud noises at shutdown stopped, and that plus some fiddling with the power wires to the boards indicated that the left over hum was indeed a grounding and/or lead dress issue.
I will do the things you suggest in 1-3 tonight. With respect to 4, the amp sounds fantastic as it is, but I’ll let you know if it changes after my work on it. I’m very impressed!
As Andy mentioned, twisting of wires to minimize loop area is beneficial. To each channel, the V+, V-, and Gnd should be tightly twisted together. The Gnd should follow the V+ and V- wires to their connection points on the board, and then the Gnd goes to its connection point.
Rotating the transformer to find the quietest orientation is also beneficial. If your transformer is an Antek, I have found that they "leak", and the quietest orientation is with the location of the AC in and out of the toroid pointing towards the front and back of the case.
How much capacitance do you have in your power supply? In my experience with my 103dB speakers, a 44mF - 0.1R - 44mF CRC filter will still have a very low level of hum that is audible with my ear against the speaker. This is after taking care minimizing loop areas and EMF emissions.
To further minimize ground loops, all components of the sound system should be plugged into the same wall AC receptacle. Use a power bar if necessary.
Rotating the transformer to find the quietest orientation is also beneficial. If your transformer is an Antek, I have found that they "leak", and the quietest orientation is with the location of the AC in and out of the toroid pointing towards the front and back of the case.
How much capacitance do you have in your power supply? In my experience with my 103dB speakers, a 44mF - 0.1R - 44mF CRC filter will still have a very low level of hum that is audible with my ear against the speaker. This is after taking care minimizing loop areas and EMF emissions.
To further minimize ground loops, all components of the sound system should be plugged into the same wall AC receptacle. Use a power bar if necessary.
Last edited:
If your product only has one fuse on the primary side, it must be installed on the Live side, not neutral.