| PedroPO |
Hi all.
My aleph 5 is at is "final production" stage.
yesterday night I tested it with all the chasis assembled and i noticed some minor buzzing sound coming from the tweeters.
I realized that the connections between the boards (from kristijan) and the PSU were very important.
Example:
I first wired the minus input to the ground(unbalaced operation) of the PSU at the capacitor - result lots of hum. then I connect it to the ground at the input RCA and the hum significantly reduced.
Kristijan by mistake posted this picture.
should the overall wiring be like this? |
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| Mad_K |
| where is the AC ground connection? |
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| JasonL |
humm was the humm there befor man..
id be interested too because im at the stage of building mine into my chassis now..
just a quick question im substuting irfp140's insted of 144's is there any problems..?
Jason |
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| Mad_K |
no problemo with irfp140 instead of irf/p144.
The way I have connected my Aleph, is with AC ground -> NTC -> chassis. All grounds is taken from this point in the chassis (star grounding). Absolutely no hum. |
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| mefinnis |
| quote: | Originally posted by Mad_K
All grounds is taken from this point in the chassis (star grounding). Absolutely no hum. |
Someone correct me but I thought the reason for using the NTC in the earth line was to raise the circuit ground several ohms above the chassis/mains ground. That is the mains should earth to the chassis, then the circuit earth should connect to this point via the NTC .... ??
My description of this comes from the construction notes for the Balanced Line Stage| quote: | | Earth ground from the AC cord is attached to the chassis for safety, and is connected to the circuit ground through a power thermistor (bright idea from Frank DeLuca). This gives some resistive isolation for prevention of ground loops but goes to small values of resistance in case of catastrophic connection to the live AC line. |
cheers,
mark |
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| Peter Daniel |
| quote: | Originally posted by mefinnis
Someone correct me but I thought the reason for using the NTC in the earth line was to raise the circuit ground several ohms above the chassis/mains ground. That is the mains should earth to the chassis, then the circuit earth should connect to this point via the NTC .... ??
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No need to correct, that's the way I did it too, but I have hum as well.:confused: |
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| trigon |
What about the XLR jumper in between G & - .
Or having ground point (star) after NTC that comes from AC ground, if you reed carefully Mad_K note, not on the Capacitors board it is a big no no. :-)
| quote: | | The way I have connected my Aleph, is with AC ground -> NTC -> chassis. All grounds is taken from this point in the chassis (star grounding). Absolutely no hum. |
That is exactly what I am going to do.
Trigon.;) |
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| protos |
| My impression is that the circuit and LS ground is on the 0 point on the caps then you ground that point to the chassis thru a thermistor where the AC ground is. |
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| PedroPO |
Hi all!
I kinda solved my humm problem.
In fact the humm is gone, but the problem is STILL in my head:(
I said that I connected the minus input to the PSU ground.
That is true.
My PSU ground is in between two caps wich are connected witha Y cable connected to the bridge rectifier.
I have also a ground wire that comes from the board and is on one of the capacitors, so electrically connected to the other via the Y cable.
IF I CONNECT this wire to the cap with the ground wire, all is fine.
If I CONNECt the wire to the other cap (that is electrically connected) a good humm appears..
WHY????
This appened in both channels. |
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| PedroPO |
LET ME PUT IT IN SIMPLE WORDS
The blue solid line is the no humm config.
The blue dashed line is the hum config.
IF anyone knows why, please tell me. I believe in magic now! |
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| protos |
| Seems to me that your grounding the minus input that way is unnecessary. Why don't you just connect them on the board.Too many grounding lines are not recommended. |
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| PedroPO |
You are true, but now I have all m wires soldered and the boards mounted.
I feel a little lazzy, and now the humm as gone...2xlazzy
But my question still on. Why the hell does this happens? |
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| Peter Daniel |
Pedro,
If in hum connection, both blue and dot blue wires are connected, you are creating a loop and that's wre the hum is coming from. |
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| PedroPO |
Peter Daniel,
No. Its one or other.
the dasshed config is the buzzing one.
neverteless, you say that if a loop (circle is created) hum appears?
if you have a twin separate conductor that is joined at both edges that is a loop?
why is that? |
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| Mad_K |
The folling text/image is taken from "EMC for product designers" SE by Tim Williams
The figure shows the concept of single point grounding, disregarding for now the safety earth. |
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| Mad_K |
The following text/image is also taken from "EMC for product designers" SE by Tim Williams
Regarding safety earth and the NTC in series with this earth, which is in paralell with the chassis earth connection. See also Passlabs Aleph 3 service manual, page 6 (schematic). |
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| eLarson |
| quote: | Originally posted by PedroPO
Peter Daniel,
No. Its one or other.
the dasshed config is the buzzing one.
neverteless, you say that if a loop (circle is created) hum appears?
if you have a twin separate conductor that is joined at both edges that is a loop?
why is that? |
Yes, whenever you have a loop, you have the potential (:Ouch: sorry) for picking up interference.
One source of interference is the ringing produced by your rectifiers switching on and off. The ringing freq. can act as a carrier to bring your power line harmonics over to your loop. Hence the hum. Resistor-capacitor snubbers can greatly damp this ringing right at the source, too.
Speaking of a piece of twin lead with both conductors connected at both ends, you would, technically have a loop, it would just have a very small loop-area thanks to the close spacing.
Check out Noise Reduction Techniques in Electronic Systems, 2nd Edition by Henry Ott. It has an excellent discussion of different connection techniques (twisted pairs, coaxial cables, shielded twisted pairs, etc.) and the amount of interference rejection of each config. The chapter on Grounding is also outstanding.
Erik |
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| Tube_Dude |
Olá PedroPo
The hum and busing that you have when you connect the blue dotted wire is because you have a diference of potencial between the +and- of the electrolitics...they are connected together but in their conection is passing a very strong current of riplle..the current that charge the condensers with a very high armónics content.
When you conected the blue to the - side of the electrolitc you are conecting together the grounding of the PCB and the input . In this case the voltage betwen the + and - side of the power supply don't metter.
Cumprimentos!
Jorge Santos |
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| PedroPO |
Jorge Santos,
So you say the connection beetwen the two capacitors must be much larger, like a copper plate?
If so say something. Maybe i'll change the wiring with a solid copper bar that I have. |
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| PedroPO |
Erik,
thanks.
I ordered the book second hand from amazon.com - $12.
let's see if it is good. |
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| Tube_Dude |
Pedro PO
You can put the connection much larger...it help...but it will be allways a diference of potencial betwen this two points.
It wil be better to conect the blue wire to the ground of the PCB and not to the supply ground...don't forget that in the PCB must be the signal ground and you are conecting to the dirty power supply ground.
Jorge Santos |
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