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Sony Vfet Illustrated build guide
Sony Vfet Illustrated build guide
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Old 24th September 2018, 06:22 PM   #651
Ben Mah is offline Ben Mah  Canada
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Some good information on minimizing noise:

http://hifisonix.com/wordpress/wp-co...mplifier_3.pdf

There is some practical advice near the end of the article.
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Old 24th September 2018, 07:17 PM   #652
dcbingaman is offline dcbingaman  United States
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If you have hum, try connecting the signal grounds (ALL of them) to the chassis ground via a CL60 thermistor. Usually eliminates hum or buzz problems.
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Old 25th September 2018, 01:13 PM   #653
protos is offline protos  Greece
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Thanks for the suggestions. I will post a pic soon but to my eyes the build does not seem to have any differences to what I have seen posted here or even classic Firstwatt pictures and connections which are very similar.
Though to be sincere the only difference is that I did not connect PS Ground to chassis with any method (ie diodes or thermistors). Only AC ground is connected to chassis for security. So this connection should not be an issue in a ground loop. I see First watt amps are quoted with noise usually around 50 to 100uV.
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Old 25th September 2018, 01:18 PM   #654
Botte is offline Botte  United States
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I chased this for a bit and the solution i found was to go old school. Look back to the A75 where Nelson used two diodes with a resistor across them to chassis ground. This made my units silent where with the CL60 i still had a buzz.

My two cents.
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Old 26th September 2018, 06:36 AM   #655
carsten.witt is offline carsten.witt  Germany
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This worked like charm. ;-)

Click the image to open in full size.

Thanks to Dragan.
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Last edited by carsten.witt; 26th September 2018 at 06:38 AM.
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Old 26th September 2018, 09:39 AM   #656
Zen Mod is offline Zen Mod  Serbia
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Sony Vfet Illustrated build guide
to be nitpicky , diodes must be stronger than mains fuse
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Old 26th September 2018, 10:13 AM   #657
carsten.witt is offline carsten.witt  Germany
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@ZM,
yes your right ... that should be only a possibility (in my case was ist 300mA main fuse).
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Old 27th September 2018, 10:53 AM   #658
protos is offline protos  Greece
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vfet.jpg
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Old 27th September 2018, 11:32 AM   #659
Rodeodave is offline Rodeodave  Austria
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This is why we asked for pictures. The transformer is right inside the loop formed by the inputs' ground wires and the ground wires of the PSU (the loop is closed when you connect a source). The mains going to the primary of the transformer are way too close to the audio circuitry, it looks like they're running directly underneath the frontend portion of the pcb. I'm surprised you're not picking up more hum.

I would redo the AC wiring. Turning the bottom plate 180 should give you the correct arrangement of the transformer and the PSU pcb. That way the transformer will be outside of any ground loop. See pictures of First Watt amps for reference.
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Old 27th September 2018, 11:51 AM   #660
protos is offline protos  Greece
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So you are saying this is an EMF issue acting on the input wires and PSU wires. The funny thing is that I removed the input wires completely and there was no discernible difference in the hum. I also disconnected one channel to check if there was some kind of two channel loop area, as you say, and again no real gains. However your suggestion is easy to implement. In fact I can just distance the whole PSU with some cables and see if EMF is the issue.
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Last edited by protos; 27th September 2018 at 11:54 AM.
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