Aleph5 Hummmmm

[Nelson Pass]

Originally posted by 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

Still a ground loop.

[rwagter]

Small update

I inserted the bottom of the amplifier backwards so that the trannies were on the same side als the inputs/outputs. I coorected this so that the magnetic interference is minimal and I made all the wires as short as possible.

Salas:
I found the wiring schematic that came with the pcb and connected it accordingly. The pcb does have it's own grounding but it concerns not input/output

Here's the part I'm cuurently concerned with. When connecting the aleph to the pre amp out of my sudgen amp I get an increase of humm, when I connect I to the "tape out" (which is unfortunately not controled by any means of attenuation so I cannot use it) there is no increase of hum. Where do I start seaching now.

[Salas]

Can you mask with tape the ground pin of your Sugden mains plug and see what happens?

[rwagter]

Sorry,

but it seems I'm in a mary-go-around (or whatever the correct name is)

The humm increases the I short the input, it doesn't matter if it is connected to any device. Not connected: very low 50Hzhumm, shorted RCA definite increas, higher frequency in both channnels.

Is it an idea to separate the star ground for the channels ?

[Salas]

In a vicious circle? I am not a native speaker too.

Yes you can separate and see what happens.

[rwagter]

Exactly, a visous circle.

So I seperated the common star to get a seperate ground for each seperatechannel (real dual mono). Now my left channel humms very very slightly without any input connections and when shorting the rca input it the humm completely disappearce, it so quit, it's almost eerie,. I'm a happy man with the left channel.

Now the right channel...., damn, here lies the problem. Whith no connection, slight humm, when shorting input, humm (like a andgry bug) !
I'm getting closer and closer. Because the separation of the ground there is now no connection from both stars to the mainsground, how can I connect both grounds to mains ground and still keep both ground seperate (my gutfeeling says a diodenetwork should do the trick)
Ralph

[Salas]

You need a 10-100R 10W resistor, so to break one channel ground path. You can connect 2x 5A diodes in parallel but in opposite directions. So the path to ground is broken by the resistor, but if a short occurs, the diodes open to safety ground and the resistor survives.

[woodturner-fran]

I think you need a switch to switch between the balanced and unbalanced operation. In unbalanced mode the RCA ground goes to both GND and neg input.

Fran

[rwagter]

woodturner-fran

of course with rca connected the negative pole of the xlr is connected to the gnd. If I remember correctly the largest difference is 3dB of amplification

[glaieuldeboua]

I also got a hum problem.

I put two PCB in one case (stereo...), one transformer (750KVA), one capacitor bank (12 X 22,000mfd), star ground and 5 ohm thermistor.

But I have hum! When I disconect one input cable, hum disappears...

So, would it be better to connect the two RCA grounds together and then to the star ground?

Would it help to connect the two output grounds together and then to the star ground?

But it plays wonderfully...

Thanks.