e-licktronic Forum

Hi
Iv done this power option to my Yocto
firstly to have a proper use of toroidal transformer which previously
I was using just one secondary output
also I didn't like "virtual ground" solution
finally installed loop breaker too,
in fact I don't have enclosure for now
(awaiting for) so for now my ground is just connected
to mains ground and later I will connect that to metal box
There is one thing Im wondering about -
when moving transformer around whole Yocto
it picks up a lot of hum from transformer
hopefully with properly grounded enclosure
it will not happen

all above Iv done also hoping to resolve my problems:
viewtopic.php?f=16&t=382
but it did not....

anyway - it is proper power solution for Yocto project
thanks jeroenbvo for your tips

Hi,

I noticed that the hum is about 10dB higher (at 50Hz and 150Hz) with the internal toroidal dual power supply than with an external single supply.


There is an RC loop breaker between shield and analog ground, with R=10ohms 5W, C=100nF polyester.
The external single supply and internal dual supply share the same rectifier diodes (half-bridge for single supply, full bridge for dual supply).

Do you have an idea of what could be the cause?

PS: Only one of the two supplies shall be and is connected to mains at the same time.
PS bis: Note that the levels in the frequency spectrum shown above are the sum of the background noise of the 11 individual instrument outputs.

Hi EchoBoy,

I don't quite understand the y-scale on your graph. If it is in dB, I would say that it is opposite. The internal PS shows +- 10dB less at 50Hz and 150Hz.

Hi jeroenbvo,

The y scale is negative dB. For instance you can see a noise peak at 50Hz in both cases.
The external power supply produces a peak of about -86dB at 50Hz.
The internal power supply produces a peak of about -75dB at 50Hz, which is about 10dB higher than the external power supply.
Similarly, there is a second noise peak at 150Hz that is quite higher (about 8dB) with the internal toroidal transformer than with a basic external ac supply.

I wonder what could be the reason for such an increase of hum using the toroidal transformer.
Could it be due to its magnetic field?

Hi EchoBoy,

I realized later that that would be the case with a negative scale. Makes sense.
You say it is the sum of the 11 individual outputs, as people are reporting hum/noise issues when they are using 2 or more individuals at the same time it might be related to that.
Can you make a comparison of the internal and external supply, but only measuring at the master output? I'm curious to see that.

On a side note, I had a noise/harmonics issue with my Tom/Congas that got solved by grounding the Yocto the way I did, not meaning all is perfect but I feel I'm going in the right direction.

Would grounding the analog section with the circuit breaker to the chassis minimize noise in the audio path?
I have a torroidial transformer with parallel 15V output, no 0v center. It introduces quite some noise when placed near the main board, especially it seems to set off the MC oscillator.

jeroenbvo wrote:Hi EchoBoy,

I realized later that that would be the case with a negative scale. Makes sense.
You say it is the sum of the 11 individual outputs, as people are reporting hum/noise issues when they are using 2 or more individuals at the same time it might be related to that.
Can you make a comparison of the internal and external supply, but only measuring at the master output? I'm curious to see that.

On a side note, I had a noise/harmonics issue with my Tom/Congas that got solved by grounding the Yocto the way I did, not meaning all is perfect but I feel I'm going in the right direction.

Yes, the analog part can be grounded like that, just make sure all references to ground should go to the same point (Star Ground)to avoid the ground loop.

I've built in the torroidal transformer (no 0V line) and added loop breaker circuit on the 0V.
I'm still getting quite noticable hum when i have my conga's on. Sounds like filtered 50hz hum. I don't have an issue with other instruments, it seems the filter frequencies of the conga's are in the hum spectrum. I can hear the sweep when i turn the conga tune pot.
Does anyone have an idea how to fix this?

@deejayraoul: Did you keep the external supply option to make a SNR comparison between external and internal supply?

I did not have time to investigate on my hum issue yet. Sorry Jeroenbvo for not having replied earlier.
In my case the hum is present on all outputs, whether instruments are played or not. This hum also exists with the external supply but >10dB quieter which makes it acceptable.
For now I suspect radiation from the toroidal transformer.

[resize=500]http://i.imgur.com/ft4EqOD.jpg[/resize]

I'm interested to do this. I don't understand, what did you connect to the upper transformer 15V output ? Nothing ?

Later you talked about powering the 7915 and 7815 separately with each 15V output.. that's not what you did, right ?

A reply from anyone who think (s)he better understands is welcome !