Sadly but true, I don't know why this Schiit Magni unit comes with hum noise after several minute operate. This happen even with the volume knob fully down and no input present. More over, if the gain switch set to the high position, the humm noise become more audible. Fortunately I already get this problem solved. Let's take a look.
Latter I know this wall adapter is AC output instead of DC. Schiit using only a transformer without any rectifier or capacitor to feed into this Modi 3 amp.
I got two option, one is my typical hard wiring from the adapter to the unit. Second, I clean it first with contact cleaner. Then I choose the second option:)
I also put filter capacitor across the power socket. This will much helping this humm noise problem cause from a defect power connector. Using 0.1uF is sufficient, larger is better but I should consider the free space at the bottom of the board. Then I using 0.33uF which is perfectly fit to the chassis. This method should cure the hum problems right away!
You can stop the process here. And the amp will noise free after following this steps. But I am not stopping here. There much more thing should be check and hopefully could impact to the sound improvement as well.
I am too excited for this progress even I am not posting on how I open this unit.
Rewinding the process, opening this unit is straight forward. Find the four silver bolt on the top. open them all. Then there is two black screw above the connector at the back side and two silver bolt at the bottom.
At this step, I can disassembly the board completely.
I check the power supply section which in line with the power socket that I mention earlier is actually dual rail power supply. The input is single AC, then using only two diode and voltage divider, it is now become the dual rail voltage.
This section could be improve a lot with building proper dual rail power supply as external power supply rather than internally. But right now, my goal is make this Schiit Magni amp looks as original as it gets.
Testing the voltage divider after the regulator IC is +/- 16.9 volt and 17.2 volt. This is not quite balance and adjusting the resistor at the regulator can make the voltage output at the same voltage. I saved this PSU upgrade for future project.
More further inspection, I saw the trace from the PSU to the unknown op-amp IC each channel is very far. No capacitors present nearby the op-amp and this will cause high ripple issue at the op-amp.
This is what I am using for the testing purpose. I put two capacitor, each Elna Silmic 22uF 25 volt for the every voltage input pin (the plus and minus) and connect the others lead to the ground.
I re-check the lead is correctly connected to the desired polarity at the power supply to the op-amp IC.
I test this upgrade and the humm noise completely disappear. I only hear the music, very natural and detail. This upgrade is success!
Now it is time to tidy up the capacitor. I covered the open lead with heat tube shrink for avoid any short-circuit.
The op-amp IC pin number 4 is for negative voltage and pin number 7 is for positive voltage. This will lead on how you put the capacitor polarity.
The others side of capacitor lead is connect to the ground. I find it the green ALPS potentiometer holder is become a perfect ground spot.
I continue to the other op-amp IC with the same method above.
Then put it back together to the case is an easy job. No need further explanation.
Disclaimer: Any statement and photos in this article are not allowed to copy or publish without written permission from the writer. Any injury or loss from following tips in this article is not under writer responsibility.
Hello there,
ReplyDeleteI have the same issue on my magni3 and i really want to do this upgrade but i don't have to much knowledge on electronics. Would you be so kind on making a how to for dummies? there's a lot of people out there with this issue.
I try my best to guide you here.
ReplyDeleteIf you had the same problem with the Schiit unit I mention above, than doing the first 3 picture above will definitely cure it.
The fourth picture is by adding non-polar capacitor inside the unit. This is to avoid any power jack contact instability. It also give the further improvement for the electrical stability.
The rest of the picture is for improve the ripple rejection near the op-amp IC. This is quite difficult to follow and not recommended for a beginner. Thus, avoiding this step will also not make any difference for curing the hum problem as mentioned above.
Hello Orronoco, i follow your instructions and install a capacitor as show on the fourth picture. I can't find the exact same capcitor you're using but someone recommed me to use this instead: https://www.amazon.com/Pics-033uf-100v-Capacitors-Guitar/dp/B00P6SB3JI , but the problem still persist, i'm using the wrong piece?
DeleteHalo, sorry for my late reply. The cap you mentioned above can be use for this application. But if the problem still occur, you should double check on whrer the point you solder the cap. Also make sure the DC connector is firmly attach.
DeleteHi, i followed step by step this guide, first i soldered a 100nf on the input but still humming like it always did. Then y added nichicon's fine gold on both op, nothing about the humm changed. So, i did a simple try playing soft music, where i can hear the humming and without turning off the magni i unplugged it, so the music still sound untill there is residual energy into the unit but unplugged from the wall... NO HUM doing that, it magically dissapeared. My temporal conclusion is that the PSU is a shit, no Schiit. Some day i will try finding an AC psu with the requiered 14v... Any with more quality maybe.
ReplyDeleteAt last, i might say that my psu is australian type plug, 230/240v 50hz input // output 14VAC 1500ma. 21VA. is made in china by xing yuan electronics; it came with my magni. Im from argentina / here we use 220v-50hz.
Great to hear that. Building a linear power supply using toroidal transformer and regulator LT1084CP is a nice option tho. Then hard wire directly to the DC input socket would be a hassle free for a life time.
ReplyDeleteI had similar issue with a Mani 1 and fixed my issue with no soldering. First, measure your incoming AC voltage. Chances are it is near 125V, like mine. If so, get a 14V AC adapter.
ReplyDeleteBasically what is happening is that the regulators take the incoming voltage and double if not triple it and if you have too much incoming voltage it distorts the circuit because those regulators were never meant to go beyond the voltages they are outputting.
If you had a variac, you can also plug in your 16V AC adapter and lower the voltage and hear the hum go away as you get closer to 120V power.
The other fix is to actually change the voltage of the regulators to reduce them a little, but that requires some SMD soldering and some math to get the right voltage and what not. Easier to just to buy a 14V 1A AC wall wart and this still keeps things in good regulated voltages for the amp.