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When theory actually works in practice.


catman

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G'day all, a bit of a surprise for me this afternoon.  Using one of my DIY kit phono stages I realized that the 'whistle' that normally comes from the switch mode power supply air conditioner unit in here was largely absent, compared to other mains powered phono stages that I use in here. 

 

Looking closely at the circuit I realised why, the preamp uses a simple RC first order low pass filter on the plus and minus DC split rail input.  Simple, but quite effective at filtering out the crud on the mains.  Most interesting!  Regards, Felix.  

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Hi Felix, have you tried a Hagerman Bugle 2 at all? It used a plugpack SMPS but has filtering on the input, it has coils involved so is LR config, does a great job of filtering the mains.

 

Regards

Steve

 

P.S. getting some Burso V5i op amps very soon (in the post) so will try them in the Bugle and Akitika, see how they go.

Edited by Batty
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G'day mate, no I don't have that phono stage....way too many already!  I was genuinely surprised by how effective this simple low pass filter network is, and the overall sound quality is particularly good too!  More things to investigate.  Regards, Felix. 

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I'm a fan of putting a passive RC filter in front of voltage regs. With a lot of the older reg ICs, their ability to block crud on the incoming DC drops rapidly with frequency, and they may be completely ineffective at switchmode PSU frequencies. An RC filter is lossy, and gives a bit of attenuation regardless of the frequency of the noise.

 

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