Bottlehead Forum
Bottlehead Kits => BeePre => Topic started by: Alby0521 on February 04, 2021, 01:19:30 PM
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Hello
I finished to put together the Beepre 2.
It works and make music!
It’s connected to a Kaiju.
I get a hum (from 1/4 of the volume) that grows increasing the volume and it does not follow the channel balance on knob (even if o put the knob all on the left channel the hum is still there in the right channel at the same intensity. And viceversa if I balance all right channel I still get hum on the left).
I replaced all the the transformer washers with fresh ones and made sure there is ground continuity. (under and on top of the bell too).
The hum is still the same. I think it’s 60hz but not 100% positive.
I also re soldered several power supply points.
Any idea?
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I would replace the transformer insulators that we gave you if you used something else as replacements.
What is your incoming AC line voltage and which range did you use in the manual?
Can you post some build photos?
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Hi
I used the kit transformer insulators.
AC incoming is 121.3V. I used the connection greater than 115 and lower than 130.
Attached pictures.
Any idea?
Thank you.
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What DC voltage do you get between A1 and A4? (One probe on A1, the other probe on A4) How about B1 to B4?
With your source connected but not playing any music, is the hum present? There will be some noise on any open inputs with this design, that's not abnormal.
I would definitely listen to a 60Hz and 120Hz tone to see which you have.
Were all your voltage checks OK? How about the A2/B2 voltages?
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So with the tubes in i read:
Between A1 and A4: 4.87V DC
Between B1 and B4: 4.87V DC
The hum is there with a source connected or not. Also I shorted 2 RCA plugs and inserted them in one pair of input and the hum is still there.
All the voltages were good during the built.
Between A2 and B2: 0.7V DC.
I listened the hum tone again and i really think it's 60hz.
Thank you.
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What's the voltage between ground and A2? Ground and B2? You can use 14 as a ground.
Also the DC voltage between Reg+ and Reg- on each side of the filament supply board?
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Voltage between Ground and A2: 101.2V DC
Voltage between Ground and B2: 100.6
Left side Reg+ Reg-: 6.23V DC
Right side Red+ Reg-: 6.24V DC
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Well, you have a perfectly functional preamp there.
It would be good to have you listen to a test tone at 60Hz and one at 120Hz to verify that the noise you have is 60Hz.
It would also be helpful to know that you have continuity (set your meter to beep when you touch the leads together) between all the transformer screws. It's possible that this is just related to power transformer hardware.
It's also possible that there's some kind of cabling issue between the Kaiju and the BeePre. Having the volume down all the way on the BeePre also shorts the input to the Kaiju and would knock out hum pickup in a cable at the same time.
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Hi
I checked the continuity between the screws and they are all in continuity.
I changed 3 different cables between the beepre and the kaiju but the hum persist.
I listened again to the tone and I think it's 60hz. I recorded it and put it on youtube so you can take a look. Here the link: https://youtu.be/jsmkXBl-b0E
Let me know your view.
Thanks
AB
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What is the DC resistance between the chassis plate and terminal E on the IEC power entry module?
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Di I need to measure ohms or V?
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Ohms.
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It’s 0.2ohms. I took it in different spots from below the chassis and its always 0.2 ohms.
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this is a long shot but is there any other source of 60Hz hum in the room that it is picking up, such as fluorescent lights?
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No there is no 60hz source that I know of. Also I tried during the day with everything turned off in the house and just the Beepre and Kaiju on and the hum is still there.
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That is not smooth 60Hz hum from a transformers magnetic field. That is classic buzzy 120Hz hum from either a bad ground connection somewhere or a ground loop. Probably time to inspect ground connections and reflow some stuff.
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Hello.
I reflowed the 2 ground tabs (see pictures circled in red) and all the IEC connection. Is there anything I'm missing. What other solder point would be involved?
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Everywhere there's a black wire or the banded end of any capacitor other than the ones on the PC board.
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Ok I'll re solder all the points with those characteristics this afternoon and report back.
Thanks for the help so far.
Best
AB
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You probably want to check the connections around the little double diode, cap and resistor filter thingamajig between terminals 32 and 36.
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Hi
I solder again all the black wires, all the banded caps, removed the strip on 31 32 33 and re built that with new solder. Also I re solder all the 3 strips in that corner including 36, 35 and 34.
Nothing changed. Still the same hum.
Also I connected the beepre to another amp in another room. Still same hum.
I’m out of ideas.
Any ideas?
Thanks
AB
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Are the outlets in your house earthed?
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Yes l, I plug all the equipment into a power bank. And that it’s plugged into a earthed outlet.
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I would unplug (not just turn off) all the sources from AC and see if hum is still there. I once had an issue with hum and it turned out it was the cable box causing the ground loop. I ended up getting a power-strip with coax in and out and connected all the equipment to it, and this broke the ground loop
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Ok I unplugged everything but the Kaiju and beepre. Still hum. So I plugged the Kaiju alone in the power bank and run an extension cord to the garage to plug the beepre on another breaker. Still hum.
Any other idea?
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While it's on, if you touch to metal of the chassis plate, does that change the sound?
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This could also be something as simple as a loose filter capacitor that isn't sucking down the power supply noise like it should.
I had a SEX amp in for repair last year that made a similar noise to this. I went through and repaired a bunch of other operational issues with the amp and was ultimately left with an amp that functioned fine but had that kind of dirty 120Hz buzzy noise at the output. It took me forever to track down that what had happened was the builder put a lock washer from one of the binding posts on the ground screw between the chassis plate and the #8 ground lug. This is very unlikely to be what's going on with your BeePre, but it may help to illustrate the kinds of things that can cause that noise that you're having.
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Should I re solder the black banded caps on the board? I already re soldered all the 3 brown. Anything else to look at while I’m on the board?
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You could pop the screws off the board and show a photo of the bottom of it.
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While it's on, if you touch to metal of the chassis plate, does that change the sound?
No it doesn’t change. I also run a wire from the bell to the chassis and no change.
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You could pop the screws off the board and show a photo of the bottom of it.
Here it is
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And if you pop the volume pot out it says 10K on it? It occurs to me that swapping the pots on accident could cause problems.
If all else fails you can send this BeePre in for repair, but I would suggest grabbing a three light outlet tester to be sure this isn't something simple like a flaky earth connection. There's nothing worse than getting a repair that works perfectly fine.
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Hi Paul,
Just checked and Yes the volume pot is the 10K .
I'll get a 3 light tester and check the wall plug.
Thanks.
AB