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PostPosted: 04 Jun 2014, 22:08 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
ewharff wrote:
I am building another one of these amps. I am going to put it into a case and I want a volume control on the case. What pots are you using? I cannot seem to locate a decent 1M stereo pot anywhere. Thanks for the help.


You can use lower value pots e.g. 250K. In the past I have used miniature cct. brd. pots. I can get them in 1M (I think its been a while)

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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PostPosted: 13 Mar 2017, 05:55 
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It's been a while since we have had a post here. My daughter has been studying for uni so I'm on the phones these days. I'm using a Pi2/HDMI audio extractor as my source and DAC and an original K272A as the driver HP amp for my Sennhieser 700s. Originaly my K272A didn't have a volume control so I was using Volumio's software volume control. It sounded really good. I then upload Rune to the same Pi but the software vol. control is rubbish. Volumio's is much better.

To remedy this I have now added a 50K micro PCB pot to my HP amp. The musical is back and I have disabled the software vol. control in Rune. I line my ABS encsloures with bituamised heavy Al foil but not earthed them. As a result when my hand got near the HP amp it hummed. Now earthed and dead quiet.

While doing the above I noticed I had modded the K272A to run 18V on the tubes. Also I noticed I used three-nines 0.7mm pure silver wire as hookup wire. Also I saw all the resistors are carbon film. I haven't looked inside this HP amps for many years. This K272A sounds absolutely fab and I was wondering why. No I know. It is an absolute gem and plays all my 24/192 files from the Pi2B and 2T drive with guts and glory. I hope my daughter never finishes Uni - lol.
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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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