Hum.....Huming Aleph 4 ... Help!

[Prince134]

Hi,

I am here seeking help on my Aleph 4 with 47Kohm impedence copied from Aleph60. I did not use that R1,R8 and R0 to avoid mod works on the mainboard, where originally were not considered to. The symptom is that it keep huming whenever there is a RCA connected. Without input RCA connected, no hum at all (or hardly can I hear it!). The hum level is stable regardless volume control. Here is my machine:

1500VA toroidal*1 C-L-C PSU +-50V on loading
Rifa 22000uf 63V*4
Using PA5II stasis case for stereo operation (a little too small I know)
IRFP240 X10 per channel (reduced one pair considering heat dissepation)

Tried different ground connections and failed after all.

1. Should I seriously consider R0, R1 and R8?
2. Toroidal hum or not? given no hum before RCA connection.
3. Anybody has the same problem and solved?

Your generous help is appreciated.


Regards,

Bill

[Netlist]

The negative input must be grounded when used unbalanced.
Whether you use R0 or not, the node R4/R5/Z2/Z4 should be grounded as well.
R8 are there for output DC stability, R1 perhaps also.

/Hugo

[wuffwaff]

Hi Bill,

1. No
2. No
3. Yes, in some way or another everybody had this problem. Sound like a typical groundloop to me. Check all the earth connections, it may be neccesary to use the lift resistor (R0). I use a piece of wire for R0 in my Aleph5 (also with Aleph60 input configuration)

William

[Prince134]

Thanks William,

But it still hums after I used the R0 with 3ohm 3w lift resister. I tried the rectifier between earth and the -0- and get no difference. Later I found if I operate one channel the hum is gone. While with stereo operation the hum is back. Again only when RCA connected with preamp can I hear the hum.

1.Is the problem from the toraidal due to insufficient power (currently 1500VA)?
2.Insufficient capacitance in PSU(RIfa 22000uf*4)?
3.will one Bridg rectifier with center tap ground be better than the current two bridge rectifiers?
4.due to ground loop between 2 RCAs?

Regards,

Bill

[Steve Fay]

Hi Bill,
William is correct it sounds like a typical ground loop Humm. Although they'er not always easy to find (speaking from experience here)
1.your toraidal is fine
2. 4x22000uf is plenty
3. the two bridge rectifiers should be fine
In my recent thread about my aleph 1.2 Nick and Killowattski helped me fine my ground loop. Problem fixed. I wish I knew how to send you the link,but just look under my name for posts and follow thier advise, sometimes when you're building a project you get to close to the project and need some one else to talk you through some ideas or to recomfirm your own.

Good Luck
Steve

[Prince134]

Hi,

I want to thank all that generously helped me in solving the humming Aleph 4. It's really a problem that related with PSU and the ground although it looks weird (one RCA is heaven and two RCA is hell ). I conquered the humming by using serial ground instead star ground topology, in which ground (not earth) for each channel is connected in series(or bus connection since it starts at PSU and ends at speaker protector without loop). I connected PSU ground->left PCB ground->left speaker ground->right speaker ground->right pcb ground->speaker protector ground. I also did some rework on PSU to have a neat looking but I think the serial grounding solved my problem.

The toroidal, capacitance and the earth ground are not related with my humm.

Thanks every one,


Bill

[arold19]

Hello, I just finish my Aleph30 and I have the same problem as Prince134!
When the 2 RCA is connected, I have a hum and when I connect only one, I don't have noise.
This is a ground loop problem but I don'T know how to resolve it.
Please, I need help !

[arold19]

I use a thermistor between the earth and the ground, it is better to use a retifier bridge like the ZenV4 ????

[Mark_zh]

Arold19
Try to find the closed loops of any ground wires, no one is acceptable for quality low noise sound. I think. May be you have big loop between two channels around all amplifier. Check for ground loop across metal box of amlifier.

[Nelson Pass]

My comment from another post today:

The usual solutions:

a) rotate the transformer to minimize the hum

b) attach a solid wire between the RCA grounds and use
it's center point as the star ground for the input and output
grounds of both channels , and send only 1 wire back to the
power supply ground.

also, it's very useful to ground the chassis well to the AC outlet
ground and then attach the circuit ground to the chassis through
a power thermistor like a CL60 or through diodes to give some
loop isolation while retaining a safety connection.