Tube Preamp mismatch

Hi,
Could someone pls let me know where has it gone wrong with this connection. I have just bought this little tube preamp FX-Audio Tube-01J (suppose to be very popular in Japan) on Ebay to be connected to my Rotel power amp and cd player. Very disappointed that only a very loud humming noise is produced. The vibration of the speaker cones moved air in front of the ports. I have no problem when using a similar cheaper product from China. Pls help, tq Rgds, Leo

Hi Leo,

There are possibility that your tube were damaged during transportation. If you have working spare tubes you can just replaced them to ensure not tube problem.

If you do not have working spare tubes, you will need a multimeter for further checking.
From information I found from web, below are circuit diagrams for your Tube-01J.


I hope the circuit diagram above is correct represent the circuit of you Tube-01J.

1. First thing to check: measure the voltage of your 12V DC power adaptor to make sure you get around 12V DC output.

2. After that please check the voltage up converter circuit for +/- 29.5V DC. From the picture found from web, I guess should be the two capacitors which I mark with red arrow below. When you measure the voltage of these two capacitors, you should get around +29.5V and -29.5V DC.



After check above 2 steps and found the voltage to be correct, then there are high possibility that your tube already damaged. Get them replaced and you should be able to enjoy music with your new Tube-01J.

If you are not familiar with voltage measurement, get some help from friends familiar with electronics measurement.

Good luck !!

Mr Lim thank you for your info much appreciated.

Mr Lim,
I was using the other similar tubeamp from China without any problem. Also the tubes are small and well packed. I think the chance of both tubes are faulty is slim. I'm trying to get someone to test it with his power amp. I'll let you know the final result. Tq Leo

Hi Leo,

I have heard stories about batches of tubes when arrived here, some quantity already damaged due to filament inside broken, although the tubes looks perfectly fine in terms of cosmetic, probability due to rough handling during transportation. If you know the filament pin number of the tube, you can also measure the resistance using multimeter. If you do not get any reading, that means the filament inside already broken.

Since you use another similar tube amp without issue, I think your Tube-01J is not functioning. If you want to try using another power amp, I would suggest try using with integrated amp, reason is you can adjust volume control and less chance to damaged the speakers or power amp. Remember that power amp will amplified anything you feed to it without any attenuation, quite risky to do so when you suspect your Tube-01J may be in fault.

Regards,
cslim

Hi Lim, A friend has came to point out where the problem was. It's the power supply, I was using the 12vdc transformer for the cheap preamp. This one is operated on 12vac power. I have overlooked the tiny ac n dc next to the 12v. Tq for your reply