hum issue with Aleph P1.7

[Stefanoo]

Hello guys.

As i posted on another 3d here on this forum, i have an issue with noise on the woofer of the loudspeaker with the preamplifier Aleph P1.7.
The preamplifier sounds fine even with very bad capacitors on the signal path and let me think that after have changed a couple of components it will sound very nice.
But before to buy pricy parts i would like to make sure that the pre doesn't have that problem.

To ensure that the power supply wouldn't inject any noise on the preamplifier, a commercial, dead silent, integrated amplifier's power supply was used.

I have a common audio and power ground.
The gound plane is a mask that goes around the two layers ad passes by the nets of the circuit ensuring a shilding.
I always thought that that way of routing a board would guarantee a low hum noise...but i am probabily worng.


Any good suggestion?

Since the power supply is inside the box of the integrated amplifier i don't know how to wire the two of them.
i'm actually souring the ground from the groound star of the integrated amplifier...that goes then....on the main ...unique...ground of the preamplifier board.


Any suggestion is welcome and if you guys have any doubts of my arrangement please ask me and i will try to ppost some pics if they can help or answer to any question.


thanks a lot for the attention.


Stefano

[JC Fardo]

Originally posted by Stefanoo

To ensure that the power supply wouldn't inject any noise on the preamplifier, a commercial, dead silent, integrated amplifier's power supply was used.

I have a common audio and power ground.
The gound plane is a mask that goes around the two layers ad passes by the nets of the circuit ensuring a shilding.
I always thought that that way of routing a board would guarantee a low hum noise...but i am probabily worng.


Any good suggestion?

Since the power supply is inside the box of the integrated amplifier i don't know how to wire the two of them.
i'm actually souring the ground from the groound star of the integrated amplifier...that goes then....on the main ...unique...ground of the preamplifier board.


Any suggestion is welcome and if you guys have any doubts of my arrangement please ask me and i will try to ppost some pics if they can help or answer to any question.


thanks a lot for the attention.


Stefano

Ciao Stefanoo

What´s wrong with the original PS ????
I would keep it simple as is, otherwise you are making an unwanted closed ground loop with that shielding around and stuff.

Happy new year

[Stefanoo]

thanks JC....i just don't get why i would make a ground loop with that?

[analog_sa]

Originally posted by Stefanoo

Any good suggestion?

Get a scope. Quote figures for the hum in mV and Hz instead of colourful decriptions. Forget about groundplanes for such a simple circuit. Have a look at working, hum-free P1.7 boards. Copy them.

Build a power supply that doesn't blow.

Now, i know this is in the realms of the wishful thinking, but is it not possible to keep all your misadventures with the Aleph in one thread instead of starting several daily. A great place would be here

[Stefanoo]

i don't think i have used coloured expression as you said...i have just wrote what my problem is.
If you than say that a pic with the noise would help...then....unfortunately i don't know if i am able to do that since my scope has a little problem that doesn't allow me to measure low level noise.
Another thing that i do not agree with is about daily post but i will take your suggestion on keeping the subject on few posts.

[analog_sa]

Originally posted by Stefanoo
i don't think i have used coloured expression as you said...i

What would call this?

I have ...indeed....still.....an issue with the hum (i think it is hum....it is a little noise JUST on the woofer of the loudspeaker...dont' really know difference with buzz).

The importance of measurements in this case cannot be underestimated. How would one know if the "little noise" which may or may not be "buzz" is actually hum?

Unless you have taken actual measurements from the output of the preamp (preferably preceding the pot) we are all left guessing whether:

- the hum is external to the preamp (connecting cables, power amp grounding issues, etc)

- the hum is not hum at all but the preamp is oscillating at a high frequency

- your power amp/speakers have above average gain/sensitivity

- your ears are ultrasensitive

To resolve a ground loop will only be possible if we can see a picture/drawing of the pcb artwork together with connections to the power supply.

[Stefanoo]

ok....i understand.
i'll try to see what i can do with my scope and measure this noise.
I would defintely exlude from the ultimate options that i got from you....the ultrasensitive ears ...eheheh.

Anyways....i'll try to post some pics in the next days.

thanks anyways for the answer.

[Stefanoo]

today i'll try to make some measurements with the scope that i have post 'em here.


just a couple updates.
i am currently using the pre as a single ended.
Till now i had shorted the - IN and source the output from the - and + (connecting the - to ground and the + to the out signal).
I realized that it is wrong and so i sourced the output from + to ground.
The hum in this way went down a lot.

If i touch one of the 3 mosfets, thought, on the + side i can hear la noise on the output that increases if i keep my hand there
(if i'd source the output from - , the things are reversed and the mosfets that causes noise are the 3 on the - side) .

Is it normal?
If not i can i fix it?
I'm using 240ohm as a gate stop resistor.


thanks in advance.

[analog_sa]

This sounds too much like oscillation. The scope is again your friend. Raise grid stoppers to 1k.

[Stefanoo]

ok...i'll try and i'll post the results...