I recently purchased a Velleman 4040 already professionally assembled. It sounds fantastic except for one issue. With no material playing, I get a BZZZZZ sound from the left channel (you have to be withing a few inches of the speaker but its pretty annoying). The right channel is clear…bit of a hisss as if gain was turned up but not noticable at all.
what can I do to research this bzzzzz? It is heard even with no inputs connected, I have rebiased the tubes (currently running russian 6P3S-E / 6L6 / 6L6GS / 5881 ) tubes new. I have tried turning the transformer like the guide says (that appears to be for a hum though) and no effect.
Also, should I hear a HUM from the transformer itself…think its the power transformer…that one I hear 3 ft away.
Appreciate any help as I love the amp…but the bzzzz is killing my joy…please note, I an electirical novice so speak slowly…lol
First a fact: tube amps are never as silent as transistor/FET amps.
Without exact figures obtained by measurements, we cannot determine if the hum is excessive or not.
Due to the layout and the positions of the tubes, it is possible that the left channel is a little more susceptible to hum than the right, but this is purely theoretical.
It also depends on the speaker sensitivity. If yours are over 90dB, which means very sensitive, then it is almost normal to hear every little bit of hum. If you remove the tube from the first stage, is it gone? Did you try replacing this tube?
Keep us informed.
Thank you for the response. I do understand about tubes amps vs SS however; the sound is a bit excessive in that channel. And also, turly it is not a hum but an electronic bzzz. The sound you hear standing under a power transformer on a road at night…bzzzzzzzz
I have been working (remotely) with some experts and have totally isolated that its coming from the amp. Swapping speakers themselves (left to right, right to left) still causes the buzz in the left speaker while the right remains buzz free.
Wanting to be sure it was not dirty power or uneven source voltage, I added an ADC power regulator/conditioner because my home current was reading a bit high. No change so its not a house voltage issue.
When you say pull the tube on the first stage, you mean the input tube (12AX7)? I can try that. I have switched those tubes so I know its not a tube issue. What will pulling the tube determine for me, what should I listen for ?
Can I rule out a bad RCA ground since it does this even with no input plugged in ?
Finally, I have read its rare for a transformer to go bad but I have also read of these types having buzz issues with age due to defects in build lot.
Sorry for the long email, but 1) Its really bugging me and 2) Worried it will just get worse.
What is the sensitivity of your speakers?
Did you remove the first stage tube? Was the noise gone when you did?
At this time, we do not if there is a problem and what could be causing it.
You state that the amp was assembled, so we assume it has been assembled by a third party?
If this is the case, there could be an assembly problem.
Thank you for the reply.
Sensitivity on the speakers is 90db
Pulling the first stage tube makes the noise go away (its not the tube as various have been tried)
Yes assembled by a third party of some renown
It does not appear to be an assembly problem but rather a design flaw that CAN arise sporadically. Several people have arrived at the following conclusion independently:
Researcher #1 Just a long shot, but am looking at jumper J11 in the center of the overall picture. This is in the trace connecting the left channel to the front end tube. It connects C9 to it’s left from the juncture of pin 6 on the front tube socket and resistor R59. This signal trace runs right under/near a couple of the large power supply capacitors and is a high impedance point in the circuit. It makes me wonder whether it might be picking up some power supply noise. The right channel signal routing avoids the proximity of the power supply.
Just wondering out loud. To test it would require disconnecting the audio circuit from the trace at both ends and running a wire above to reconnect the two ends of the circuit.
Researcher #2 (Ironradio) who actually fixed this issue similarly) I discovered that the slight hum I was picking up in the left channel was mitigated by running the V11 pin 6 to C9 through coax. After removing J11 and J15, I ran RGS-316 between the hole for J15 over to the left hole for J11 and attached the shield end to J12
In short, it seems the path from the right leading to the left channel is subject to picking up noise. Now before I let anyone go hacking at my amp, I have a team that is going to go over the amp this weekend (osciliscopes, etc) to really hone it on the root cause. Can you check independently that this path could produce teh situation ? It would be helpful to me and to others and perhaps you could have a technical bulletin that describes the symptom and a manufacturer suggest fix ?
Thanks…anxious to hear back from you
90dB is quite sensitive, so the speakers will reveal more than average.
The amp kit has been available ‘as-is’ since 1997. In these 15 years we do not have any records of similar problems.
I repeat, due to the layout and the positions of the tubes, it is possible that the left channel is a little more susceptible to hum than the right, but this is purely theoretical. At this time, we are unable to simulate the problem. Maybe your team will come up with something that gives a closer insight into the nature of the problem. Keep us informed.
Really need your help. At least to narrow things down.
I did successfully eliminate the BUZZ in the left channel by using the recommended process in the manual (Increases R65 and R68 to 1K). I did wnders for the left channel, no more buzz. On the right channel, it did not eliminate the hiss/crackle but actually made it worse.
I also changed out R88 as the manual indicates.
The sound on the right sounds like a HIGH GAIN hiss. It also crackles and oscillates. I noticed last night, I left the amp on with no input and every one in a while it would burst like a static discharge (like a radio picking up a static frequency).
Yes, I have tried a variety of tubes, so its not tubes. If I remove the 12AU7, the noise does not change. If I remove the 12AX7 for that channel, it goes quiet (as it should)
I have checked all solder joints, checked all PCB paths (solder spot to solder spot) for continuity.
I am hoping you can help me narrow down where to look or what to change. Thank you in advance…
If the inputs are left open, it is normal that the units pics up every little thing that happens, such as switching of lights, equipment, fridges, etc…
We’re sorry, but solving this problem is impossible from a distance.
We need to be able to test the amp and perform measurements using test equipment.
We have two repair depts.
One in the US, for US customers. They can be reached at (817) 284 77 85
Our main service dept is located in Belgium
Velleman Projects Tech. Dept.
Legen Heirweg 33
If you decide to ship the amp, please note that in no way we can accept liability for damage during shipping. Make sure it is extremely well packed AND insured.
Make sure to include a detailed fault description.