Hi all, i hope i posted this in the right section.
There is a cheap tube amp on amazon which is actually quite nice if you can get over its cheap construction. Tube is soldered to the PCB, not a huge deal anyway. I will socket the opamps once I solve the hum issue.
https://www.amazon.com/dp/B01I19SBAW/ref=twister_B01I19SBGG?_encoding=UTF8&psc=1
The real problem with it is that the grounding is done poorly and it easily starts allowing thru a nasty 60hz humming. Static sound has not been a problem, just the humming.
I don't think the grounding of the amp is done well by the factory; it's a single wire going from the PCB to a tiny nut and bolt on the chassis. It uses a DC barrel plug for power so there is not an easy way to get it connected to a proper ground.
Should I try to add a ferrite core to the power supply cable? Or a 3.5mm ground loop isolator the audio input? I am also wondering if I should attempt to run a wire from the amp's chassis to an earthed metal surface near my desk.
There is a cheap tube amp on amazon which is actually quite nice if you can get over its cheap construction. Tube is soldered to the PCB, not a huge deal anyway. I will socket the opamps once I solve the hum issue.
https://www.amazon.com/dp/B01I19SBAW/ref=twister_B01I19SBGG?_encoding=UTF8&psc=1
The real problem with it is that the grounding is done poorly and it easily starts allowing thru a nasty 60hz humming. Static sound has not been a problem, just the humming.
I don't think the grounding of the amp is done well by the factory; it's a single wire going from the PCB to a tiny nut and bolt on the chassis. It uses a DC barrel plug for power so there is not an easy way to get it connected to a proper ground.
Should I try to add a ferrite core to the power supply cable? Or a 3.5mm ground loop isolator the audio input? I am also wondering if I should attempt to run a wire from the amp's chassis to an earthed metal surface near my desk.
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Can you send me a photo of the tube soldered in the circuit board? A top and bottom view of the whole board would be nice. I may have a solution but you might not like it.
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I will do this when i'm able to. (away from the device right now).
Is there any chance your advice might include running a new ground wire from the tube directly?
Until then here is a shot i found on google of the top of the board. I suspect that point marked "GND" might be of some use.
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I hate to be the bearer of bad news. The blue light made me suspicious as well as the low voltage DC power source. Tubes operate with higher DC voltages and use larger high wattage components. After seeing the board, the small SMD (surface mount device) components and blue light tell me that the tube is for show only. Some of them will even change color with the music. There would be a much larger power supply than the 5 or 6 volts printed at the plug socket. Tubes require voltages well over 200 volts usually 300 up to 600 volts. Some manufactures in audio are adding a tube that lights up blue on surround sound systems calling it tube sound and they get away with it. I doubt if other grounding suggestions will fix your problem but the wrong DC adaptor, a cheap DC adaptor, or a bad DC adaptor will definately give you 60 cycle hum. Sometimes there is a coating on the metal and a scrapping under the ground scew might help. I have worked on many of these type of fake tube products before I retired. I know what tube gear looks like and tube equipment is not cheap.I will do this when i'm able to. (away from the device right now).
Is there any chance your advice might include running a new ground wire from the tube directly?
Until then here is a shot i found on google of the top of the board. I suspect that point marked "GND" might be of some use.
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Tubes operate on DC voltages of 300 to 600 volts. Your power supply adapter is maybe 5 or 6 DC volts. Enough for the Op Amps to operate, amplify the sound, light up the tube filaments, and light up the blue LED's. Not enough for the tube to operate and amplify the sound. Sorry, the tube is fake. A bad, wrong, or cheap power adapter can give you a 60 cycle hum. Sometimes the metal has a coating and you can try scrapping under the ground screw. Also make sure the screw on the board and the two standoffs are secure. Do not over tighten and break the board. Good luck.
OK, maybe i should have made it clear earlier that i was already aware this is not a real tube amp. IT quite obviously sends the whole signal path thru op amps and i am fine with that. This amp costs under $50 new.
I still want to know how to minimize the ground hum. I am using a linear, regulated lab DC supply so i know my power supply is not bad. I have tested with 4 or 5 other 6V supplies as well.
Thanks for your writeup but i already knew it was not *true* tube gear. i will see if the coating on the metal is preventing a good contact on the ground screw.
if anyone else has any suggestions other than re-checking the chassis ground i am all ears?
You are right, more technical insight would have helped in the beginning as references to it being a tube device and tube related issues threw me off. Even with a nice supply, have you checked for any supply ripple with a scope or traced with a scope starting at the input chip? This would help confirm a grounding problem or signal related issue. Sorry I could not be any help. Good luck.
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Many misconceptions here. There are tubes that operates at MUCH lower voltage (one among them http://www.diyforums.org/data/12AE6A-ge.pdf), and the fact that the power supply is low voltage, does not prevent a DC-DC boost regulator to bump it up considerably.
Now, on that board, at least on the up side, I do not see neither the appropriate sized capacitors (for the diode+caps boost regulators), nor the inductors (for the ones based on them) which typically characterize boost regulators.
They might be on the bottom side though.
It is quite possible they use the tube as VAS, and the opamps as current buffers.
As was as the noise, unfortunately, this is an issue with many El Cheepo Chinese electronics.
Without schematic and some reverse engineering it is hard to fix.
Could be the cost (in time and $$) to fix it, would be better spent in some higher quality component.
Now, on that board, at least on the up side, I do not see neither the appropriate sized capacitors (for the diode+caps boost regulators), nor the inductors (for the ones based on them) which typically characterize boost regulators.
They might be on the bottom side though.
It is quite possible they use the tube as VAS, and the opamps as current buffers.
As was as the noise, unfortunately, this is an issue with many El Cheepo Chinese electronics.
Without schematic and some reverse engineering it is hard to fix.
Could be the cost (in time and $$) to fix it, would be better spent in some higher quality component.
Thanks for the great info. I never did work on any tube car audio. Nice little tube. But at $50 and SMD's I doubt that the tube is operating. I just don't think a real tube unit would go to the trouble of adding blue LED's. And like you said, China. Why design the unit using a 6 volt power source when a 12 volt power source would have done the job without boosting. Just doesn't add up.
Do you know if this tube or similar has been used to produce real tube audiophile quality headphone amps?
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For what it is worth. I built two low voltage tube (12AU7) headphone amps and also experienced grounding or ground loop noise. So this is what I found: If my amp power supply and the music source was both earthed (that third wire going to the wall socket) – no noise. If neither was earthed – no noise.
In your case, you use a laptop brick type power supply that is not earthed, so you might experience less/no noise when using a music source like a MP3 player or cellphone. When using a USB DAC connected to a Desktop computer (which is earthed) – you pick up noise via the USB. If this is the case, then you can get USB devices that clean out the noise. HiFimeDIY has one: https://hifimediy.com/usb-isolator
Worth giving it a try – but there is no simple solution here, but i hope you find one to enjoy your amp!
In your case, you use a laptop brick type power supply that is not earthed, so you might experience less/no noise when using a music source like a MP3 player or cellphone. When using a USB DAC connected to a Desktop computer (which is earthed) – you pick up noise via the USB. If this is the case, then you can get USB devices that clean out the noise. HiFimeDIY has one: https://hifimediy.com/usb-isolator
Worth giving it a try – but there is no simple solution here, but i hope you find one to enjoy your amp!
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when you see tube stuff, but without HV circuit (or voltage multipliers) (at least 100V) it´s probably fake.
Exceptions, >30vdc with some nuvistors, could be ok. Or tubes made for 12v car radios...
non tech people are happy when heater is lit, they do not understand how it works
It was cheap anyway
Exceptions, >30vdc with some nuvistors, could be ok. Or tubes made for 12v car radios...
non tech people are happy when heater is lit, they do not understand how it works
It was cheap anywayA blue or changing color tube has always been a dead giveaway with fake tube stuff. Real tube stuff will usually not go to that extreme to prove they use actual operational tubes. But they might let you see the filaments glow. The first I worked on was home theater surroundbars or heads and cheap DVD players all from the Koreans.when you see tube stuff, but without HV circuit (or voltage multipliers) (at least 100V) it´s probably fake.
Exceptions, >30vdc with some nuvistors, could be ok. Or tubes made for 12v car radios...
non tech people are happy when heater is lit, they do not understand how it works
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https://www.tubeclockdb.com/non-clocks/333-new-line-amp-from-nixiekitseu.html
hybrid tube phono preamplifier---65v anode voltage.
i´m afraid, chinese kits are not even close
hybrid tube phono preamplifier---65v anode voltage.
i´m afraid, chinese kits are not even close
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