static noise and hum

Hello,

I have build an Aleph 2, which is working better and better. However I have a difference between the channels in noise and hum.

In channel 1 I have a little bit of hum in the woofer but no noise in the tweeter at all.

In channel 2 I have a little bit of static 50hz 'ticking' noise in the tweeter but NO hum in the woofer at all.

So channel 1 of the opposit of channel 2... Very funny. The levels are very low (so a it is not an earth loop I think) you really need to put your ear in front of the speakers. The hum in the woofer of channel 1 is a bit higher of level than the noise in the tweeter.

When I checked the output with a scope; channel 1 shows a kind of 50hz saw form (the hum). Channel 2 does not show this saw but has a thicker line (the noise?!).

I have about 0.02V DC offset in both channels.

My questions;

1) What is the single most important part for hum cancelation in the circuit, as channel 2 does this better than channel 1.

2) What is the single most important part for noise pickup. As channel 2 is more prone to pick up...

I drive them single ended, but I am going to pickup a balanced cable tomorrow to test this.

Both channels have there own 1000VA power supply and currently I am running them as mono blocks on a piece of MDF wood. No connection of grounds whatsoever between them. They only share the 220V inlet. The ripple of the powersupply is about 200mV top-top.

Thanks,

Edwin


[IMGDEAD]http://www.xs4all.nl/~edwind/e.jpg[/IMGDEAD]

P.S. As I type this, I thought of swapping the power supplies between the boards... I am going to try this now.
 
Bill Fitzpatrick said:
Have you checked the inputs? I have not built one of these and don't even have a schematic but assume that the red and black leads coming from the bottom of the photo are the inputs. They ought to be twisted together or shielded, don't you think? The right side of the photo shows and extra black lead. What is that?

Thanks,

the black and red are the speaker cables. The 'extra' black cable on the right is a shielded input cable.

Edwin
 
If I were trouble shooting this I'd look at the output with a scope and with a pair of wooden tongs a move some of the wires around a bit to see the effects, if any - particularly around the input cable which might also be suspect of marginal shielding.

It's hard to tell but it looks like the wiring from the supplies is going to the main board rather than the output boards and that the output devices get their power from the main board. I would have done it the other way around.

As an aside, I'm wondering if the wiring from the supplies isn't a little on the skimpy side.

Before I started looking for problems on the main boards, I'd eliminate all other possibilities.
 
Bill Fitzpatrick said:
If I were trouble shooting this I'd look at the output with a scope and with a pair of wooden tongs a move some of the wires around a bit to see the effects, if any - particularly around the input cable which might also be suspect of marginal shielding.

It's hard to tell but it looks like the wiring from the supplies is going to the main board rather than the output boards and that the output devices get their power from the main board. I would have done it the other way around.

As an aside, I'm wondering if the wiring from the supplies isn't a little on the skimpy side.

Before I started looking for problems on the main boards, I'd eliminate all other possibilities.

The power supply wires are 2.5mm^2 for the blue and brown ones, and 1.5mm^2 for the temporary white ones. The white ones will be removed when the amp gets in the alu case.

Edwin
 
Hey Edwin!!!!!

Your power supply rails are way,way to long....!!!!!!.....
Suppose the pick up lot of noise,for 50 or 100 Hz don't run a cable near capacitors,cross everything at right angle and shorten to MAXIMUM all voltage rails.
Perhaps a pi filter would give you less noise,and use a balanced signal to drive the amp

Regards;)
 
Nelson Pass said:
The Aleph design is quite stable without bypass
caps, even with some length on the supply lines,
and so I am inclined to presume that your caps
are fine, but that you have another problem.

Those lead lengths do look a bit long, tho.

Thanks,

does power supply lines are that long, for flexibility reasons, this way I can move the heatsinks, turn, flip, lay them on their back etc. When I am going to build them in a case I will remove most of them, and put the shortest path between the powercaps and the boards!

I will shorten them just to see what happens!

Edwin
 
I know it's a dumb question but, while you are testing this thing do you have anything plugged into the input or have the input shorted to signal ground? If you don't have anything plugged into it or have it the input shorted it will hum. I'm not out to be insulting but I always look for the simple things first as they're the ones that throw the hardest curves.:)
 
Vince:
That should have read "and not have the input shorted". Thanks for catching that. You should not have an open input when testing, naturally when it is in use something will be plugged in, but when you are testing you must give the circuit a point of reference in order to adjust it, it keeps the noise down as well. Everything I have tried has hummed with an open input. If you have an o-scope it should be easy to find. Start looking back towards the power supply. Phono stages are high gain and more prone to these problems. I have a problem with a borbely phono stage that I recently built and it turns out it was coming from the turntable. Simply plugging in some shorting plugs showed me that without any tools or meters. You can also use a meter on the output to see if it is dc offset. You should read under .050 millivolts dc. Most stuff will go down to under.010 + or -. If the pearl has a servo circuit it will be around.002 or zero, I hav'nt looked at the pearl very well yet but I am sure it is an excellent preamp. Good Luck and thanks again.

:rolleyes:
 
PassFan said:
I know it's a dumb question but, while you are testing this thing do you have anything plugged into the input or have the input shorted to signal ground? If you don't have anything plugged into it or have it the input shorted it will hum. I'm not out to be insulting but I always look for the simple things first as they're the ones that throw the hardest curves.:)

Hello,

it will hum a bit (I should stress the bit part, it is not a 300mV ground loop hum, I know when they hit me ;-) however one channels hums less than the other. So I know it is possible to get the hum down with these wires, power supply etc. When I swap boards or swap powersupply, the hum always stays with the board!

So this why I asked for parts more prone to hum, or parts which suppress hum on the boards, so I could swap a few. I read somewhere that the 220uf C8 does something like this, so I will buy 2 new ones and try them...

The inputs are shorted, or connected to my Pass Aleph P (a real one, not a DIY, which I could buy for a good price second handed) .

Edwin