If the transformer was tried outside maybe the AC wires are to close to that shield . And that shield is very good for coupling magnetic field like mumetal is 
The component mods on the board are for improving the sound quality , nothing to do with hum . Cutting the plus and minus traces is for using separate wires , plus and ground , from each channel to filter cap , as we discused before about star ground
The component mods on the board are for improving the sound quality , nothing to do with hum . Cutting the plus and minus traces is for using separate wires , plus and ground , from each channel to filter cap , as we discused before about star ground
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Since I am a novice, unfortunately, and are a little afraid to do something wrong and fry parts, could you be specific on where on the board I safely can connect to signal ground (or if it's on the inputs or something else)? I know it sounds like I shouldn't mess with this stuff and that's probably correct.
Just to be clear, do I bypass this resistor with a wire? Do I need to do it on both channels at the same time?
Hello ,
i build this preamp also and had no problems with hum . The aluminium case is from Douk Audio and all parts of the case are grounded . I have a ground lift switch only for the pcb . I have a small toroidal transformer for the power supply . Ground are the green/yellow wires , a must in Germany .
Kind regards , Alexander .
i build this preamp also and had no problems with hum . The aluminium case is from Douk Audio and all parts of the case are grounded . I have a ground lift switch only for the pcb . I have a small toroidal transformer for the power supply . Ground are the green/yellow wires , a must in Germany
.Kind regards , Alexander .
You can disconnect the wire/track going from the filament Graetz to the common pont of the divider (200k + 20k), and connect F9 to the signal GND. This is just for a test.Since I am a novice, unfortunately, and are a little afraid to do something wrong and fry parts, could you be specific on where on the board I safely can connect to signal ground (or if it's on the inputs or something else)? I know it sounds like I shouldn't mess with this stuff and that's probably correct.
Second option: connect the divider to the F4/5 instead of the Graetz.
Sorry Icsaszar, but you lost me at Graetz haha. Is that the rectifier? I am way to much of a novice to follow your instructions.
Jessica on the Lencoheaven forum wrote this about grounding the heater supply (she's one of the persons behind these popular mods):
"Be careful connecting the Heater supply to ground, designs like the 834 require a lift on the heater of about 45V to counter the V3 cathode being over 100V above ground. There has to be a reference to gnd and this is DC referenced as part of the potential divider used to produce the lift (you should be able to measure a resistance to gnd), for AC ie the hum, there should be a large value cap 10uf or above between the heater- and ground, this grounds the AC and removes the hum. If you already have a cap and still have hum, try increasing the value or using a polypropylene cap, though I do not get hum using a 10uf poly."
This was in response to a guy who had run a ground wire from heater supply to get rid of hum.
Jessica on the Lencoheaven forum wrote this about grounding the heater supply (she's one of the persons behind these popular mods):
"Be careful connecting the Heater supply to ground, designs like the 834 require a lift on the heater of about 45V to counter the V3 cathode being over 100V above ground. There has to be a reference to gnd and this is DC referenced as part of the potential divider used to produce the lift (you should be able to measure a resistance to gnd), for AC ie the hum, there should be a large value cap 10uf or above between the heater- and ground, this grounds the AC and removes the hum. If you already have a cap and still have hum, try increasing the value or using a polypropylene cap, though I do not get hum using a 10uf poly."
This was in response to a guy who had run a ground wire from heater supply to get rid of hum.
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In my experience with the version of the board I use, the black ones made by Zhili audio and I think the zerozone ones are the same (which may be the douk board?), they sound great built as designed with no mods. At this point, I have no way of knowing if all these mods are the problem or what it would sound like. I've even built them with the super cheapo China electrolytic caps and they sound good.
The only thing I can agree with here is you don't need the 68K resistor if you aren't using an attenuator.
I have not heard this board without the mods but it's sounds really good with these mods too. The mods are basically just bypass caps for the electrolytics and minor adjudtments for the riaa curve.
The sound quality is great, it's just that it is annoying that I cannot get it hum free.
I use the same board as you use in your videos.
The sound quality is great, it's just that it is annoying that I cannot get it hum free.
I use the same board as you use in your videos.
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Bypassing the 2M resistor by the second valve did make the hum go away. Dead silent! So what does this mean?
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When I short 47k input resistor there is still hum.
I might add that my SUT is permanently installed in this build. I did remove it earlier to see if it was the cause of the hum but it made no difference so I put it back in. However, that was before I made all of the shielding. I should probably remove it again. It might bee the cause of this hum.
I might add that my SUT is permanently installed in this build. I did remove it earlier to see if it was the cause of the hum but it made no difference so I put it back in. However, that was before I made all of the shielding. I should probably remove it again. It might bee the cause of this hum.