I have a Chinese Zero Zone tube PREAMPLIFIER......I have a hum in one channel. Low enough that I can't hear it over even the softest passages of music. But I know its there.
Today I dug into it a bit.
#1) It is a bit louder with the cover off the top of the preamplifier
#2) If I put my hand anywhere near the four tubes, it gets much louder
#3) There is no chassis ground from the three prong plug. There is a yellow wire (see picture) from the ground pin to the Tformer, but there is zero continuity from the plug to anywhere on the preamplifier
#4) If I touch the chassis the hum is cut nearly in half
#5) I checked every connection that could possibly be loose. All tight.
#6) The hum is there with no source connected / with source connected / with shorting plugs on the input
#7) The hum does not increase with volume turned up or down
Should I ground the chassis? Any chance of causing damage if I do this? Should I put some type of device between ground and chassis.
(Randy T has been a big help with this, I totally appreciate him helping. But I didn't want to bother him further...on a Sunday...Thanks Randy)
Today I dug into it a bit.
#1) It is a bit louder with the cover off the top of the preamplifier
#2) If I put my hand anywhere near the four tubes, it gets much louder
#3) There is no chassis ground from the three prong plug. There is a yellow wire (see picture) from the ground pin to the Tformer, but there is zero continuity from the plug to anywhere on the preamplifier
#4) If I touch the chassis the hum is cut nearly in half
#5) I checked every connection that could possibly be loose. All tight.
#6) The hum is there with no source connected / with source connected / with shorting plugs on the input
#7) The hum does not increase with volume turned up or down
Should I ground the chassis? Any chance of causing damage if I do this? Should I put some type of device between ground and chassis.
(Randy T has been a big help with this, I totally appreciate him helping. But I didn't want to bother him further...on a Sunday...Thanks Randy)
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There is not enough information in your description to diagnose the fault. The cause of the hum is indeterminate, any answer is just hit or miss and may have other undesirable ramifications even if it reduces your current issue.
To clarify: there is no connection from the power cord's PE/safety ground pin to chassis?
All good fortune,
Chris
Independent of the hum issue, this is a safety issue that needs to be resolved first. Can you determine if this is a production fault (and a frickin serious one) or something intentional? It needs to be fixed, unless the power supply is rated Class 2, etc. Certainly wouldn't trust anything enough to operate this around family or pets until resolved.
All good fortune,
Chris
All good fortune,
Chris
Thanks Chris....This is how the preamplifier is delivered. The ground goes to the main transformer, but there is no connection from there to the chassis.....Being a hoarder of vintage equipment, it is amazing that nearly 100% of this older product only have two prong plugs.....And many don't even have the large and small prongs on the plug. My concern is that I connect this ground to chassis and I damage something in the preamp......I recently built a Tubes4HiFi Dynaco clone amplifier and was surprised to see a two prong plug supplied. When I questioned this to the designer and a DIY Dynaco forum, I was told to absolutely not replace the cord with a grounded one as it would cause hum issues and was not needed...???
For safety, and probably also for legal liability, the PE/safety ground must connect to chassis (exposed conductive parts). This may or may not solve your hum issue, but safety first.
Hum issues around safety earths are trivially easy to solve (plug everything into the same power strip) and advice otherwise is amateurish nonsense. And often dangerous.
All good fortune,
Chris
Hum issues around safety earths are trivially easy to solve (plug everything into the same power strip) and advice otherwise is amateurish nonsense. And often dangerous.
All good fortune,
Chris