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Old 13th March 2018, 07:39 AM   #1061
kalinowski is offline kalinowski  France
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Join Date: Mar 2008
Yes, it's a meanwell PD-25.

Regarding ground loops: I've tested with a laptop and a phone - both produce the same result which is a quiet but still audible hum. Since neither a laptop nor my phone were connected to mains during the test I'm thinking I may have a ground loop somewhere internally then.

The amp produces quite a lot of noise when no input is connected - is it normal?

I know I may be fighting an uphill battle here with a SMPS but I'm willing to spend time to debug this one and add some more filtering if necessary.

I'll try to draw all my ground connections later today so that you guys can have a look and tell me if I'm missing something here.
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Old 13th March 2018, 08:42 AM   #1062
massimo is offline massimo  Italy
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Most probably a PD-2515, quite interesting... dual +/-15V, 0.8A, compact, not expensive (about 15$), fixed switching freq. 100kHz... it should be easy to filter.
PD-25-MEAN WELL Switching Power Supply Manufacturer
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Old 13th March 2018, 08:47 AM   #1063
aradan is offline aradan  Singapore
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Well thus actually is a grounding problem.

With floating ground

I had similar issue in another head amp. Whenever it was connected to a non grounded spruce simialr to yours there was hum.

How is your volume pot wired btw?
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Old 13th March 2018, 09:01 AM   #1064
kalinowski is offline kalinowski  France
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No volume pot for now, feeding it straight from the source. I will try to unplug some redundant ground connections and see what happens.

EDIT: I think I solved it. I wired the headphone jack in the wrong order I'm testing the amp right now with HD600s and it's super quiet. I need to wait till I go back home to test with my IEMs as they are more sensitive.

Last edited by kalinowski; 13th March 2018 at 09:24 AM.
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Old 13th March 2018, 09:24 AM   #1065
jameshillj is offline jameshillj  Australia
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It looks from your photo (a nicely detailed one too) that the 0v grounds for each channel are common together on the power supply output terminals, then go each amp (with it's own input ground/shield) and you have taken a separate ground wire output and commoned up these on the headphone socket - try removing one from the amplifier output terminal and see what happens - I use the 4 pins wiring system these days to avoid this possible complication

I remember somewhere that a resistor was sometimes inserted in the signal ground wire but can't remember if this is practical/suitable here

Check the Meanwell ground/0volt scheme - You could also make up a metal mesh cage to cover the PR2525 and fasten it to the chassis

On the Neurochrome amplifier switch-mode power supplies, Tom uses a choke and a cap on the output of the switcher supplies - I don't know the values (a proprietary design) but it illustrates that it might be worth looking at this later on.

It is worth persevering with
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Old 13th March 2018, 09:29 AM   #1066
kalinowski is offline kalinowski  France
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Thanks for the suggestion jameshillj, when I rewired the headphone jack I had to disconnect one of the ground wires from headphone jack (no soldering iron at hand) so maybe that helped as well!
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Old 13th March 2018, 10:34 AM   #1067
jameshillj is offline jameshillj  Australia
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Yeah, I missed that too

I have an idea that altho the circuit isn't totally new or unique, it'll provide no end of variations - I got a couple of the single Burson V6 ICs (still a couple available here in the FS section) to expand the chip selection and playing with different power supplies too

I didn't realise that Nisbeth had boards available and had one designed -
're-invented the wheel', so to speak - and I got some boards from china - similar layout - could have saved the trouble, damnit!

I once used a 'shorting' jack plug on a headamp - a silly mistake and caused no end of trouble
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Old 13th March 2018, 12:39 PM   #1068
kalinowski is offline kalinowski  France
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Yeah, my next step will also be to experiment with front end. I'm thinking about building an opamp from nelson's opamp article using lsk parts. Let's see if I stay motivated, for now the amp sounds pretty good!

For the boards, I don't think he was selling them, I saw his build and shot him a PM so he sent me some spares.
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Old 13th March 2018, 12:45 PM   #1069
Nisbeth is offline Nisbeth  Denmark
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New PassDIY Headphone Amp (now available)
Great to see you got the amp running Michal! (I should probably get started on my own boards soon )

@james: I only had a few spare boards from my order that I sold off and they are all gone, but if you want the files are available from here
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Old 17th March 2018, 01:39 AM   #1070
chat72 is offline chat72
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Click the image to open in full size.

Click the image to open in full size.

My own version with super regulator and the Burson classic.
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