Distortion and hum with Pearl

[neil_kaye]

Just finished my Pass Pearl built from Promitheus boards and there is a background hum, but worse there appears to be disortion generated from high notes.
I tested all the volatges at the indicated points on the boards and they all check out, at least within 5%-7%.
I though that it may be something else in the system but i ran my turntables signal through a cheap pro-ject phonobox and it is dead quite. What could possibly be causing this weird distrtion and hum from the Pearl?
I have attached images of the boards.
Again, as always, help would be greatly appreciated.
Cheers
Neil

[neil_kaye]

image 1

[Dr. ODD]

Did you try to keep the Trafo away from the Boards ?

[lykkedk]

neil_kaye :

Actually i tried to place torrid close to mainpcb, back when i was making my pearl, and anything near < 20cm, was giving me noise and stuff like that. I never tried to attach a metalplate between torrid and pcb through, i simply plugged the psu in another cabinet.

[neil_kaye]

Hi,
Having read through some other threads i suspect it may be a grounding problem. The way i have ground the project is as follows:
1. From the central ground point on each board (arrow on board which says connect grounds here) i have run a wire to a chassis star ground- see two red wires in photo.
2. From this point there is a direct ground wire to the AC earth / ground

I think the distortion might be from cross talk, would someone please let me know how they succesfully wire their Pearl or please comment on my wiring stradegy.

All my internal wires are shielded.
I have tested the board with different cartridges the the problem of distrortion and hum persist.
The chassis itself is 1/4" aluminum plate so no chance of components picking up interefance through that and the trafo is seperated from the boards with a 1/4" plate .

Thanks for the help

[neil_kaye]

I have tested the votlages and this is waht i get. Both channels are identical:
DC In: 49.7V
R8: 28.3V (29V = 2.5% deviation)
Q3: 23.9V (24.6V = 3% deviation)
Q4: 13.2V (13.8V = 4.5% deviation)
Q5: 10.9V (11.7V = 7% deviation)

These numbers seem pretty good but still the hum persists and there is also a high pitch whine. Ughhh

[Magura]

Originally posted by neil_kaye

The chassis itself is 1/4" aluminum plate so no chance of components picking up interefance through that and the trafo is seperated from the boards with a 1/4" plate .

Thanks for the help

1/4" aluminum is not neseccerely enough to keep the trafo from interfering with the circuit. You have also got your in and out running past the trafo, which is sure not a good idea.

Try moving the trafo a couple of feet away from the circuit and see if that helps.

Magura

[Magura]

Originally posted by neil_kaye
I have tested the votlages and this is waht i get. Both channels are identical:

Your post crossed mine.....

If the hum is also identical on both channels, you can be sure it's either a ground issue, which I see no reson you should have in your setup, or its the trafo being too close to something.


Magura

[neil_kaye]

At this point i am certain you are correct. Before i dis-assemble everything i was wondering if you know of an off the shelf product that would shield the transformer in its current posistion?

[Magura]

Originally posted by neil_kaye
At this point i am certain you are correct. Before i dis-assemble everything i was wondering if you know of an off the shelf product that would shield the transformer in its current posistion?

Not really, depending how big the problem is you could maybe get away with a thick box of aluminum, but when I say thick I mean like 1"

Keep in mind that it must be a box covering the entire trafo to really work.

My recommendation would be in direction of making a seperate PSU like most other Pearl builders have done.


Magura