SWIN,
was that earth a real earth? Your photo just shows (bottom right by the yellow shrouded cable) what purports to be an earth for the right channel. This connected to zero. You can't see this unless you remove the volume PCB. As I said in a previous post I created an earth from the input PCB to the chassis. When I discovered that the right channel had no real earth I cut the wire just before the 1K R/C resistor and used this earthing point and the hum was so minimal and didn't change with volume.
You can see the yellow/green earth cable sticking out just close to the blue disc capacitors - the yellow/green goes from the mains earth input straight to that point.
And that is the main earth point of this circuit, and everything is earthed to the earth pin on the mains socket.
Yes it is a bit of a mixed mess, but generally works, please note than only two cables goes to the phones socket, both channels are earthed thru the chassis, no separate earth lead.
It is a major engineering mistake to just dump the 50 Hz / 6,9 V heater straight at the left channel earth.
And then tell customers that it is a defective tube that causes the loud left channel hum at zero volume.
But still it is sold in huge numbers, and people accept it anyhow - there is a huge market for this type op OTL headphone amp, and a really silly mistake made by the Chinese engineers, this type of referencing the heaters to ground has been around since the 1950´s.
Just tested my circuit coupled to a Pioneer CD player, thru a Beyer-dynamic DT 990 Pro 250 Ohm phone, and it is dead quiet up to say 3 a clock PM on the volume control.
And the phones are quite loud at 9 a clock AM, and whats more, dead quiet at zero volume, when this thing just buzzed loudly in the left channel before I modded it.
Please, I thought I checked the volume control for any anomalies, but could find none - I read your post, but I could not find any error in the volume control circuit - all connections are there, I think, and everything checks out?
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