Hey All,
So, I have rebuilt my preamp (seen in 12B4A Linestage thread) in new enclosures and I now have some hefty hummmmmmm.
I've looked over my grounding scheme, and it looks fine. I think the problem may exist from the PS chassis, and the chokes being places too near each other.
So, time to ask the experts...
First things first. When I look at the ripple, I measure 5.0 and 4.1 mV on the L and R channel output. I can trace this back to the plate. What is more interesting is the ripple at the last filter cap before the ccs which loads the plate. It dances around at values between 8 and 14 mV, and is not steady. After the CCS, it is staedy at the 5.0 and 4.1 mV values.
Any thoughts?
So, I have rebuilt my preamp (seen in 12B4A Linestage thread) in new enclosures and I now have some hefty hummmmmmm.
I've looked over my grounding scheme, and it looks fine. I think the problem may exist from the PS chassis, and the chokes being places too near each other.
So, time to ask the experts...
First things first. When I look at the ripple, I measure 5.0 and 4.1 mV on the L and R channel output. I can trace this back to the plate. What is more interesting is the ripple at the last filter cap before the ccs which loads the plate. It dances around at values between 8 and 14 mV, and is not steady. After the CCS, it is staedy at the 5.0 and 4.1 mV values.
Any thoughts?
Aluminum.
To clarify (or complicate matters) there are two chassis. PS and Audio. Both are built on aluminum top plates which sit on wood chassis. Both top plates are grounded.
Interesting enough, I just pulled the regulator tubes (thus eliminating B+ from the valves) and I still have the hummmm. Would this lead one to believe the humm is coming from the heater circuit? I'll poke around there and see if I can uncover anything....
To clarify (or complicate matters) there are two chassis. PS and Audio. Both are built on aluminum top plates which sit on wood chassis. Both top plates are grounded.
Interesting enough, I just pulled the regulator tubes (thus eliminating B+ from the valves) and I still have the hummmm. Would this lead one to believe the humm is coming from the heater circuit? I'll poke around there and see if I can uncover anything....
AC heaters are very unlikely to induce that much hum. Almost all valves cope very well with AC heaters.
Its much more likely to be induced hum from poor layout. My last Valve headphone amp had real issues with hum, which all turned out to be induced and ground loops. I just completed a valve phone amp and absolutely no hum first time.
Its really a matter of search the net for guidance on eliminating earth loop hums and trying everything systamatically one at a time.
Shoog
Its much more likely to be induced hum from poor layout. My last Valve headphone amp had real issues with hum, which all turned out to be induced and ground loops. I just completed a valve phone amp and absolutely no hum first time.
Its really a matter of search the net for guidance on eliminating earth loop hums and trying everything systamatically one at a time.
Shoog
This is in fact true. I realized this error last evening after I typed the reply, but could not find the "edit" tab on the webpage...
I'm going to tweak with the wiring layouts and tripple check my grounding. It must be something simple that I am overlooking.
I'll report back my findings after I finish poking around.
Thanks,
Bryan
I'm going to tweak with the wiring layouts and tripple check my grounding. It must be something simple that I am overlooking.
I'll report back my findings after I finish poking around.
Thanks,
Bryan
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