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Old 31st January 2011, 02:36 PM   #591
norture is offline norture  Indonesia
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Quote:
Originally Posted by pinkmouse View Post
Because it's many times more work to build a good switching PSU than it is to use iron...
Good point! Of course it takes a LOT of time and work to build an SMPS. Then it all comes down to our liking. I for one am would rather buy the PSU because it is cheaper here. Then I'd make a home-made amplifier for it.
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Old 31st January 2011, 05:42 PM   #592
AndrewT is offline AndrewT  Scotland
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Originally Posted by norture View Post
and that is going through properly made LC filter there'll be hardly no noise at its output, right?

Any transient demands will be served nicely if we add a couple more caps at its output, right?
I disagree on both counts.
I know that an LC filter cannot be a brick wall filter. It let's through noise.
I know that if you modify the SMPS filter by adding more capacitors, that you are out on your own and that you admit the extra filtering must be removing some of the noise that you claim is not there.
Finally, decoupling at the amplifier to meet the Fast Transient demands of the speaker and the filter at the SMPS to meet the Slow and Medium term demands of the speaker are not perfect. They attenuate the sag (glitches and spikes) occurring on the supply rails, they do not eliminate it.
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Old 17th February 2011, 06:10 AM   #593
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Originally Posted by porthillsbomber View Post
Ok thanks guys I'll give it a go and see how it goes, can someone direct me to the currently recommended snubberized PSU design
Click the image to open in full size.


Well I've made one channel of my first amp. I just copied the PS schem in the brianGT chipamp manual because that's what I had parts for. It gets mildly warm around the chip on the copper plate, that is to be expected right? Also with my ear within a ft of the speaker I can hear a very quiet hum, is that alright?

I haven't isolated the chip yet but will do so.

Can anyone see any reason why I shouldn't go ahead and build the other channel the same?
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Old 17th February 2011, 05:55 PM   #594
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Originally Posted by porthillsbomber View Post
with my ear within a ft of the speaker I can hear a very quiet hum, is that alright?
That is your decision. If the hum does not annoy you, it is OK. If it annoys you, it is not OK. It is hard to detect on the photo, but apparently you have one ground wire to the speaker and one common to the amp. You could try to split the amp's ground wire into seperate signal and power ground and take separate leads from there to the star-point.

What is the purpose of the big resistor across the speaker terminals?
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Old 17th February 2011, 07:54 PM   #595
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Well it's not audible from my listening position so it shouldn't matter then I guess. There is one wire from the star ground in the supply to the star ground on the chip and one wire from the star ground in the supply to the negative binding post, should I do it differently?

That resistor is part of the zobel network, it's overspec power wise but that's all I could get. It's a wirewound resistor does that matter? should it be metal film or something?
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Old 18th February 2011, 04:30 PM   #596
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If the hum does not annoy you, leave the grounding as it is. Never touch a running system.

The Zobel resistor should have low inductance. Wirewounds have a small inductance, but you would need an oscilloscope to find out, if it does any harm. Metal film is fine there, in case you want to replace the resistor.
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Old 19th February 2011, 09:47 PM   #597
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Ok I'll probably change that resistor at some stage. I found out that there is no hum at all with something connected to the inputs and also when I touch the input ground with my finger it hums loudly. What could have I done wrong?
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Old 20th February 2011, 05:36 AM   #598
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Nothing. When you touch the input you create a ground loop through your body.
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Old 23rd February 2011, 04:54 PM   #599
grakka is offline grakka  Sweden
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I am currently building my first amp, a lm3886 dual mono gainclone from chipamp, and there is one thing that I am not sure about. I am not sure about the different cables on the trafo. The text/spec on the trafo says "primary 230V 50/60Hz ye-ye" and "secondary 2x22V 150VA gr-re/br-bu". There is two yellow cables on the trafo and one green, red, brown and blue. By thinking logically i think that the primary cables cant be wrong since both use same color (it would be weird to use same color if there is a difference) and should be the yellow cables due to the "ye-ye" text. There by, one of the yellow cable should go to the "N" on my appliance inlet and the other yellow should go to "L". Am I right about this?

I am even more concerned about the secondary. I am about to solder the secondary cables to the pcb (image) and they should be connected to the AC1 AC1| and AC2 AC2| but i don't know which of the secondary cables that should go where. Should i keep the green and red (gr-re) as a pair and the brown and blue (br-bu) as another pair? And then just pick one of the pairs for AC1 and the other for AC2? Whats the difference between eg. "AC1" and "AC1|"?

I don't require a answer for all my questions. I just wanna understand 110% correctly where to put which cable. This is my first amp build ever and i have BIG respect for electricity and I don't wanna fail on this part. It's not the end of the world if I do fail but It's unnecessary to take a chance on a thing like this.

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Old 23rd February 2011, 08:04 PM   #600
grakka is offline grakka  Sweden
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My bad, I happened to post a little too fast. After I red all the 60 pages in this thread i found the answer to my question regarding the secondary.

A new question regarding the appliance inlet. I guess that the N is Neutral and L is Line due to this image Power Supply for Power Amplifiers . My inlet only have 1 switch. Does it matter if N or L go via the switch? Any of them need to be unswitched.
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