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#1 Douglas Self Phono Stage

Posted: Sun Jan 01, 2023 5:23 pm
by Tony Moore
Hi All,

Well, after the Owston back in 2021 I had another hankering to build something and so I went ahead and bought the phono PCB from Mr Self. I built it back at the start of 2022 I think and then proceeded to ignore it.

It had some initial noise issues with MC input and so what with other projects on the go it got forgotten about. (Vinyl doesn't figure heavily in my normal listening!)

Since I had some time I've dragged it back out and wanted to take a look and see if I could solve the noise issues.

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Attached are a couple of photos of the build. The psu is very simple (probably way too simple!) and connected to the phono amp via an un-shielded umbilical.

I have two problems with noise, one is a very low level 50/100Hz which I guess I need to sort with either better smoothing or perhaps identifying hum loops? The other issue is a slight "rustling" which I can totally stop by putting both hands around the umbilical. However, trying a makeshift screen and grounding it does not have the same effect.

It would be nice to get this completely functional as it does sound really very nice. Any advice would be gratefully received! The power supply and the implementation are the weak links here of course (since I did them!) as I'm sure the amp itself is very well designed. However, I can always upgrade the psu.

Cheers,
Tony

#2 Re: Douglas Self Phono Stage

Posted: Sun Jan 01, 2023 5:58 pm
by Nick
Try some decoupling caps where the umbilical joins to the PCB, the noise you hear might be some HF instability. So you have a scope?

#3 Re: Douglas Self Phono Stage

Posted: Sun Jan 01, 2023 5:59 pm
by RhythMick
I would consider using good quality metal braiding around the umbilical, earthing one end - I would be inclined to ground the shield at the PSU end, effectively making the shield an extension of the (presumably metal) PSU case.

What umbilical connectors are you using? Metal or plastic?

There will I'm sure be plenty of good advice from the gurus here on shielding and grounding.

#4 Re: Douglas Self Phono Stage

Posted: Tue Jan 03, 2023 1:28 pm
by Tony Moore
Thanks for the replies guys!

The connectors are metal XLRs. I will try out the decoupling initially as that is the simplest to try. Strangely the rustling noise was not present when I tried it yesterday so I'll just have to see if it comes back and try the decoupling then.

Cheers,
Tony

#5 Re: Douglas Self Phono Stage

Posted: Thu Jan 05, 2023 3:54 pm
by Michael L
Another discussion on diy-audio relating to screening umbilical

https://www.diyaudio.com/community/thre ... st-7223990

#6 Re: Douglas Self Phono Stage

Posted: Thu Jan 05, 2023 4:23 pm
by Nick
221 pages, argh.

Edit: Ahh, its not all about shielding cables.