Metal casing always PE except for actual products sold in stores... Almost all consumer audio gear has 2 prong power cords... At least in USA/Canada...
Here is the back of a modern Onkyo receiver: No PE (ground) in sight except for the phono ground screw..
I agree it's best practice, but double insulated devices exist, too.
Here is the back of a modern Onkyo receiver: No PE (ground) in sight except for the phono ground screw..
I agree it's best practice, but double insulated devices exist, too.
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For clarity, see: https://www.chromausa.com/product-faq/what-are-the-different-types-of-insulation-class-i-ii-iii/
- CLASS I indicates anti-shock protection of product not only depends on basic insulation but also includes grounding method.
- CLASS II indicates anti-shock protection of product not only depends on basic insulation but also includes additional precaution. For example double or reinforce insulation but without grounding or installation condition for relying precaution.
- CLASS III indicates anti-shock protection of product depends on power voltage is safety extra-low voltage (SELV) and it don’t generate danger voltage.
DIY is always class I. So metal casing to PE, always. We could discuss medical electronics, SELV etc. and all possible exceptions but this is about a DIY device with a safety error and a hum problem.
Or do we like to go against forum rules and plain electrical craftsmanship and advise stupidly wrong/unsafe methods to DIYers? Very thin ice.
Or do we like to go against forum rules and plain electrical craftsmanship and advise stupidly wrong/unsafe methods to DIYers? Very thin ice.
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There is reversing the cap in channels and reversing the cap in a channel in "polarity". Non native speaker here but I could not make up what was meant. Just suppose the "defective" capacitor was used in the other channel exactly the way it was in the previous channel 🙂 A long time ago I had this a few times and then, at last, I got the outer foil thingie. Especially in high gain and phono stuff this was/is an issue with caps.
@Rbertalotto: for complete and adequate analysis also please measure all resistors in that input stage. I see carbon composition resistors. Compare values of each resistor with that one of the other channel and the values in the schematic. Just to make sure we don't overlook anything.
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Some here do use wood or other non-conductive chassis. Also some commercial units do not have a metal chassis.
There's an English guy with a small company (don't remember his name) who has been doing that for some time.
My aunt smoked 2 packs a day and died when she was 102.
What is is with the tube section? Why avoiding the facts? This is a metal casing and it is a DIY device with a hum problem which can be explained easily. Maybe no one notices but it is the same issues over and over again as the average tube DIYer does not know jack of grounding and safety. Attention goes to creating devices with tons of useless GAIN! which makes it worse. As a result they get rewarded with hum and then they ask here for help. So if someone tries to help out by starting with the very basics why do fellow tube guys step on the brakes and try to soften plain incorrect methods?
Elektor magazine had this basic information covered in every single monthly issue!
What is is with the tube section? Why avoiding the facts? This is a metal casing and it is a DIY device with a hum problem which can be explained easily. Maybe no one notices but it is the same issues over and over again as the average tube DIYer does not know jack of grounding and safety. Attention goes to creating devices with tons of useless GAIN! which makes it worse. As a result they get rewarded with hum and then they ask here for help. So if someone tries to help out by starting with the very basics why do fellow tube guys step on the brakes and try to soften plain incorrect methods?
Elektor magazine had this basic information covered in every single monthly issue!
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I had no idea how microphonic a capacitor could get. Just barely touching it with a screw driver makes a clicking sound in the left speaker. DSame as if you wee tapping on a microphone.
As far as chassis ground....What about the million stereo components built during the 50s, 60s, 70s, and even through the 80s and early 90s that had metal chassis and two prong plugs. I have a few Dynaco pieces that have two prong plug and it isn't even a polarized plug. And in over 50 years being in the business I've never heard of anyone being gravely injured or killed by a piece of ungrounded stereo equipment. Shocked...Sure. Certainly I've heard of musicians being killed but as far as I know, usually outdoors in the rain! I'm not saying these devices shouldn't be grounded.....I did ground this Chinese preamplifier and recently replaced the two conductor power cord on my VTA ST120 Dynaco Tube clone with a three wire IEC socket and cord.
Later production Dynaco amps were labeled on their chassis as "Class II" insulation,
for both their tube and solid state units.
But being even slightly shocked can trigger another involuntary action, which then could
cause severe injury or death. If this has not yet happened to you, consider yourself lucky.
It has certainly happened to me, and to many others as well.
for both their tube and solid state units.
But being even slightly shocked can trigger another involuntary action, which then could
cause severe injury or death. If this has not yet happened to you, consider yourself lucky.
It has certainly happened to me, and to many others as well.
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OK now I reverse it. What we have here is a Zerozone PRT05A 12AX7 SRPP device with Duelund paper in oil capacitors blah blah. It has a partly steel, partly aluminium casing and an r-core transformer. The r-core transformer has a static screen. We look at the IEC connector and see only the screen connected to PE. The preamp has a gain of 30 dB and when a fly walks on the PCB you can hear it. It sounds perfect.
There are no safety measures taken as the designer only focussed on sound quality. The hum is a feature.
Problem solved.
There are no safety measures taken as the designer only focussed on sound quality. The hum is a feature.
Problem solved.
If both channels had the hum, I would agree, but since it has the hum on only one channel, something else is afoot.
Agreed, the hum is or could be a feature, as I mentioned earlier, in post #8.
With a design defect like this floating chassis, one cannot perfectly predict the consequences.
And they may vary with the environment.
With a design defect like this floating chassis, one cannot perfectly predict the consequences.
And they may vary with the environment.
Some PRT05A seem to have IEC connectors with direct connection to chassis. Anyhow, this is a combination of factors. One tiny mishap may be aggravated by another omission.
It would be strange if that cap is the cause. I think I would measure all resistors, PCB tracks and caps at that section. Or measure the resistors and simply replace just that 2 caps for normal good quality film caps to avoid PCB tracks peeling off. When both caps are replaced and the hum is gone that would be the fastest way too.
But ....the hum we hear is clear and where does it come from? How would a hum hunter go to his pray? How would he fight the hum animal? Yes he will try to find what feeds the hum animal.
It would be strange if that cap is the cause. I think I would measure all resistors, PCB tracks and caps at that section. Or measure the resistors and simply replace just that 2 caps for normal good quality film caps to avoid PCB tracks peeling off. When both caps are replaced and the hum is gone that would be the fastest way too.
But ....the hum we hear is clear and where does it come from? How would a hum hunter go to his pray? How would he fight the hum animal? Yes he will try to find what feeds the hum animal.
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If it's nothing ground related, which it very well could be... You could always swap parts until the hum moves to the other channel.
When you post questions like this it is a good idea to post the schematic along with extensive pics or video. There's a lot of helpful people here, but if they have to chase the basic, they mostly move on. 😉
When you post questions like this it is a good idea to post the schematic along with extensive pics or video. There's a lot of helpful people here, but if they have to chase the basic, they mostly move on. 😉
There is nothing ground related. There, you have it. And on that metal non ground related metal casing there are 2 transformers buzzing along. What would that cause?
If you read a few posts above , that is exactly what I did. Moving that one capacitor, moved the hum to the other channel. Therefore, it certainly seems like that cap is the issue. I've ordered a pair to replace both of them. There is no schematic available. This is a Chinese copy of a Conrad Johnson preamplifier...It is not DIY. Others report these preamplifiers are stone cold quiet. The other channel on this preamp is dead quiet........
A. Did you reverse that cap in the channel it came from? Change "polarity" so turning it around and resolder it in the same channel?
B. Since you are sure it is defective you could cut the lead wires directly at the cap and solder anything resembling the ratings* to the wires. Just for testing as the new caps are on their way.
C. Did you measure resistors, PCB tracks, connections?
*What if ... it still hums with another cap?
Chinese knockoffs that are built unsafe are same category as DIY and should be treated like that. I am very sure this device wouldn't pass regulations/tests.
B. Since you are sure it is defective you could cut the lead wires directly at the cap and solder anything resembling the ratings* to the wires. Just for testing as the new caps are on their way.
C. Did you measure resistors, PCB tracks, connections?
*What if ... it still hums with another cap?
Chinese knockoffs that are built unsafe are same category as DIY and should be treated like that. I am very sure this device wouldn't pass regulations/tests.
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Reversing it made no difference according to what he wrote in #22...
https://www.diyaudio.com/community/threads/strange-tube-preamp-hum-issue-help.383073/post-6941977
https://www.diyaudio.com/community/threads/strange-tube-preamp-hum-issue-help.383073/post-6941977