The output transformers sit directly under the power transformer, inside the chassis, picking up the magnetic field from it. Lifting the power transformer as shown reduces the hum by noticeably. If you have space, you can also try rotating, or start adding magnetic shields.
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Hi, I have wired an earth direct to chassis with 1.00mm earth where the transformer mounts, I assume this would be large enough cross sectional area?
Tom
Tom
1 square mm cross sectional area is OK for the internal earth connection (it is the area used in the UK for 15amp domestic mains wiring). Strictly speaking the earth connection to the chassis should not be shared with any other component - it should have its own point of connection to the chassis. This is so that removing that component, or any movement of that component, cannot disturb the earth. Personally, if the connection is clean (metal to metal, no paint in the way) and secure, then I would go with it.
hi, earth been done to bare metalwork, as said with 1mm earth, hum still there though,vey low level though,gonna leave it me thinks???
thanks all,
tom.
thanks all,
tom.
Yes, I agree 🙂
The interesting thing is, the manufacturer was apparently trying to resolve the 'hum' issue, as a newer version of the little 'Headphone SE amp' (I bought it off ebay as 'A-308 EL34 headphone amp' trying to set up a 'reference/unmodified' amp to compare against the hacked/modified version I was working on) had a choke added to the HV under the chassis. Of course the hum was still there 😉
The amp pictured evolved into my 'pet' bedroom amp a few years ago, the guts are basically Mr Padilla's EL34 SE circuit (the page seems to be removed from Angela Instruments, but it may be available in the 'web time machine'), and in fact the amp sounds pretty good to me. The amp measures around 6.5mV hum cold (with the power transformer raised, as pictured, as far as the leads would allow it).
In contrast to this, my 'Meng X3' (after all the mods I mentioned) measures around 2.5mV on the speaker warmed up, 0.0mV cold, so there does not appear to be significant magnetic coupling between the cores.
I was just trying to reassure the OP that, IMHO, a few mV hum on the speaker is not too bad (there are more important things to focus on) and that fiddling with valve amps (after the safety issues have been dealt with) is good fun 🙂
ouch
regarding trafo mounting, it seems like I made poor effort to be 'ironic', in light of the noise issue described....my bad, sorry
actually, I dont know whether its a good or bad idea to 'clamp' power and output tranny together, on top of each other like that
usually this takes great care, with proper orientation etc
but I would expect it have been tested properly
or it could have been changed without doing the test
convenient and practical ? seems so
vibrations ? well, either they damp each other, due to the weight, or one will transfer vibrations to the other
magneticly problematic ? not sure
but you alread said that
Quote
The output transformers sit directly under the power transformer, inside the chassis, picking up the magnetic field from it. Lifting the power transformer as shown reduces the hum by noticeably. If you have space, you can also try rotating, or .........start adding magnetic shields.
adding 'shields' goes for signal cabling too, I guess
regarding trafo mounting, it seems like I made poor effort to be 'ironic', in light of the noise issue described....my bad, sorry
actually, I dont know whether its a good or bad idea to 'clamp' power and output tranny together, on top of each other like that
usually this takes great care, with proper orientation etc
but I would expect it have been tested properly
or it could have been changed without doing the test
convenient and practical ? seems so
vibrations ? well, either they damp each other, due to the weight, or one will transfer vibrations to the other
magneticly problematic ? not sure
but you alread said that
Quote
The output transformers sit directly under the power transformer, inside the chassis, picking up the magnetic field from it. Lifting the power transformer as shown reduces the hum by noticeably. If you have space, you can also try rotating, or .........start adding magnetic shields.
adding 'shields' goes for signal cabling too, I guess
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