B1 Korg loud continuous beep...

Need help here... the unit is producing a loud continuous sharp beeb over the playing music which is independent of the volume setting, both channels. I lowered the t7 and t8 to 11v from 12v. This happens so far after some time of playing music.

Now those voltages were set it to 10v. The voltages at t5 and 6 are 0.65


Unit is sounding ok and balanced in both channels otherwise and no other strange noises. Was the t7/8 voltage too high? If not, what could be causing this? Thanks.
 
Need help here... the unit is producing a loud continuous sharp beeb over the playing music which is independent of the volume setting, both channels. I lowered the t7 and t8 to 11v from 12v. This happens so far after some time of playing music.

Now those voltages were set it to 10v. The voltages at t5 and 6 are 0.65


Unit is sounding ok and balanced in both channels otherwise and no other strange noises. Was the t7/8 voltage too high? If not, what could be causing this? Thanks.
 

JSA1971

Member
Paid Member
2016-01-10 12:38 am
North Toronto
Need help here... the unit is producing a loud continuous sharp beeb over the playing music which is independent of the volume setting, both channels. I lowered the t7 and t8 to 11v from 12v. This happens so far after some time of playing music.

Now those voltages were set it to 10v. The voltages at t5 and 6 are 0.65


Unit is sounding ok and balanced in both channels otherwise and no other strange noises. Was the t7/8 voltage too high? If not, what could be causing this? Thanks.

Hi Manolo, is the board in a case or “out in the open”? Does the “beep” or ringing stop when the music isn’t playing? If so, with music not playing does the sound come back if you tap on the case or around the preamp? You may be experiencing microphonic noise from the NuTube and will need to investigate some dampening methods of various types, which luckily are available throughout the build thread.
 
Last edited:
the ringing stops when there is no music. the board is inside the case all wired up, no top plate yet, though. It comes and go...yesterday it was going on and i touched the volume control and it stopped. couldn’t this be some kind of rfi noise or interferance also? The Korg tube was mounted on a thick double side tape and then soldered. Thanks
 
confirmed just now, after 2 hours of playing the beep started. And even without music playing... My interconnects are not shielded, would that be a cause? I made a shield on top of the Korg using a piece of the cardboard box that it came in, though it says it’s antistatic...also had dampened it on top with a foam dot. BTW when the beep comes, pressing on the Korg top does not do anythyng.
 
Using shielded interconnects solves the issue, so far. And changed B1 location and rerouted unshielded interconnects and it looks like the issue is also solved. The original input interconnect route goes very near an AC outlet and a bunch of ac cables.... So it looks like it is an interconnect issue, which leaves me worried because it means this nu tube is rather sensitive a picky... Could this be also solved by using shielded cabling in the input of the
B1?
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
I think it is oscillation, and since you can hear it I conclude that the output of the
preamp is bleeding back to the input at audio frequencies.

I would start with wiring layout, proximity of input to output cables, and shielding.

Does the noise go away when you turn the volume control down or switch inputs?
 
.......it means this nu tube is rather sensitive a picky... .....

proper procedure must be maintained , regarding all signal routing and supply lines ........ do not forget that picky one is working with uA range of currents ..... if you still have FM tuner , most likely its input 2-gate mosfet critter is working with higher currents

so ...... that's more realm of fine instrumentation equipment than usual no brainer 6DJ8 flopitalltogetherandpoweron line stage....
 
Photo here

I rewired the ground cabling and changed inputs. Input selector is the switch provided in the kit. Board vr1. It is still beeping. but it goes in and out on its own now and more ethereal.
All the music is there as it should be. Including a photo, maybe something is obviously wrong.
 

Attachments

  • image.jpg
    image.jpg
    555.6 KB · Views: 207
If you have a scope, this might reveal something useful. My NuTube rings a bit at 5300Hz when I change the stepped attenuator. It dies down within a few seconds and adding some damping materials helped reduce it to the point where it is no longer a problem. You might be having a similar issue - what is the proximity of the NuTube to your speakers? Some time ago, someone reported some interference issues with a fluorescent light bulb.