[Folsom]

I have been using this power supply because I got it for free...

http://www.newark.com/jsp/search/productdetail.jsp?SKU=38C3146&CMP=AFC-OP

However the transformer is ridiculously noisy so I want to replace it with a torodial. The problem is I am not sure how to, without tearing it apart while I still use it, figure out what voltage and VA transofrmer I need... Here is the schematic.

http://www.spctechnology.com/prodinfo/specs/ta-485.pdf

I will probably replace the caps with some FM's or something too.

[JoshK]

5V @ 9A is 45VA.  Your toroid is going to be at least that because of the watts burned by the regulator.  Measure the secondary of the transformer under load before the bridge and you'll get the loaded secondary voltage, unloaded will be say 6-8% higher.  This is just a general fudge factor for 6-8% regulation which is probably reasonable for a toroid.  Others with more experience can give better estimates but this will get you close.  Add a few watts extra for good measure and you'll be fine.

[Folsom]

Awesome, thanks for the help! Down with the hum!

[BradJudy]

Is it humming because of DC on the main lines?  If so, you might be better off to make a DC filter for the line instead of switching transformers.  There are some schematics here for one. 

[Folsom]

I guess I never thought about that. How would I know for sure which one it is? The power supply seems to make the sound even when the SB is not plugged in.

[Steve]

Hi Destroyer,

Is the transformer itself physically humming? Is the tranny vibrating the case? If so can you isolate the transformer from the case by installing rubber isolation between the transformer and the case? On the cheap, one could purchase a rubber mat, cut a section out and drill holes through the rubber, or maybe a variation of the above. Then place it between the case and the tranny.

Just a suggestion I have seen work. Take care and hope this helps.
Steve

[Folsom]

My case has rubber feet but it seems to be a joke compared to the hum. I think it might be a little bit more than rubber can handle. You could probably still hear it even if it was suspended in air.

[JoshK]

My case has rubber feet but it seems to be a joke compared to the hum. I think it might be a little bit more than rubber can handle. You could probably still hear it even if it was suspended in air.

There is a bit of a difference between rubber feet under the unit and what Steve was suggesting though.  If the transformer is unbalanced causing it to physically vibrate it might be turning the PSU chassis into a drum for amplifying its vibration.  That is what he was talking about.  Is the noise coming from the unit itself, as in physically?  Putting some sort of standoff between the transformer and the chassis is cheap and worth a shot, although it might not cure your ailes. 

If you have a fancy-schmancy voltmeter you can sometimes measure the DC on an AC line.  Also a scope can be used to measure the DC by the amount of offset to center the wave.  Otherwise you have to suck it and see (don't put your tongue in the power supply, that is a figure of speech ). 

[art]

It probably hums because it  does not have enough copper on the primary. (Translation: it is an "inexpensive", brute force linear supply. Call it cheap, if you will.)

If the problem is DC on the line, the toroid will makes tons more noise.

Lastly, if you replace it with a 5 V AC transformer, it won't work! Some of you guys shouldn't be giving advice that you are not qualified in.

I just looked at the data sheet.............any chance that you are on the 100 V AC input tap??

Pat

[JoshK]

Who said anything about a 5V AC transformer?

[art]

He asked about size and voltage rating. You said this:

"5V @ 9A is 45VA."

Might look like 5 V AC to a lot of people. If it doesn't, then you didn't really answer his question, did you?

Pat

[JDUBS]

He asked about size and voltage rating. You said this:

"5V @ 9A is 45VA."

Might look like 5 V AC to a lot of people. If it doesn't, then you didn't really answer his question, did you?

Pat

Why would the 5v be confused for AC when the Squeezebox takes 5v DC?   

[art]

Because the gizmo that he has is a linear regulator. It needs a certain voltage above its 5 V DC output to actually put out 5 V DC. He needs to measure it to know exactly what it is.

You need to concentrate on the current draw of the SB3, instead. It is only around 500-600 mA. That tells more about the VA requirements than the stamped value on the side of the gizmo. Of course, it may very well sound better with a larger than required transformer than the actual needed VA. There are reasons for that.

Knowing the secondary voltage required is more important than sizing its VA requirements. Since there is no way the SB3 takes 9 A.

And when you do size the VA requirements, you do it based on the secondary voltage. Not the actual output voltage.

None of this addresses why the damn thing makes so much noise. Changing transformers may not be needed.

Pat

[JoshK]

Because the gizmo that he has is a linear regulator. It needs a certain voltage above its 5 V DC output to actually put out 5 V DC. He needs to measure it to know exactly what it is.
....
And when you do size the VA requirements, you do it based on the secondary voltage. Not the actual output voltage.

If you reread my first post, I told him how to measure the secondary voltage.  Which is why I was confused about your response.

[art]

Yes, now that I am only slightly less sleep-deprived, I see your point. However, the proper answer for both questions can only be given if you know that it is either a full-wave bridge or a full-wave centre-tap. The answer is different for either.

He would be better looking at a transformer manufacturer's site.............someone like, say.......Signal Transformer. They probably have (somewhere) a detailed explanation on how to size transformers. You will find that the proper VA rating is indeed much higher than you first imagined. Even higher for a centre-tapped version.

Pat

[Folsom]

Thanks for the help so far guys. I might even consider scrapping this for a better switching power supply. It is an improvement over the original PSU for sure though.

[kyrill]

if you really NEED the SB3 to be a high end source you need two voltages into the SB3 5V and 3.3V
as Pat suggested some time ago the internal switcher of the SB3 to produce 3,3V is very noisy and KILLS high end sound
So the SB3 needs to be modded ( by Wayne for instance) to accept two voltage inputs.

Then you need an as good as you can get pws. a standard analogue "nice" pws will not do at all
I have heard a modded Elpac analogue pws and the Hynes on my same unit and the difference made the SB3 3 layers more transparent and 3D in favour of the Hynes

I would recommend http://www.paulhynesdesign.com/page7.html because he has DIY modules
the top of the line from Wayne is an alternative
http://www.boldercables.com/servlet/Detail?no=377

[Folsom]

if you really NEED the SB3 to be a high end source you need two voltages into the SB3 5V and 3.3V
as Pat suggested some time ago the internal switcher of the SB3 to produce 3,3V is very noisy and KILLS high end sound
So the SB3 needs to be modded ( by Wayne for instance) to accept two voltage inputs.

Then you need an as good as you can get pws. a standard analogue "nice" pws will not do at all
I have heard a modded Elpac analogue pws and the Hynes on my same unit and the difference made the SB3 3 layers more transparent and 3D in favour of the Hynes

I would recommend http://www.paulhynesdesign.com/page7.html because he has DIY modules
the top of the line from Wayne is an alternative
http://www.boldercables.com/servlet/Detail?no=377

Unfortunately that stuff is a little out of my price range at the moment. I am a full time student, with a part time job. Perhaps one day I will have the top of the line everything, but for now I am going to have to work with what I have or can get easy. If the modification to have the 3.3v and the 5v coming in was not too expensive I could probably get a PWS for each, but they would not be anything to blow your mind.