Crack 1.1 with hum in right channel, goes away at full volume [resolved]

sinbonders · 361

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Offline sinbonders

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Hey, just completed my Bottlehead Crack!
I thought everything went great, all ohms and voltages seem right, but for some reason the right channel has a low hum that increases with volume, but at full volume it goes away.
Also, I notice that the rear LED gets brighter as the hum gets louder, but then also goes dark at full volume.
Additionally, the right channel is MUCH quieter than the left, really almost silent compared to the left.
Also, when adjusting volume, the right channel is very scratchy whereas the left is nice and smooth.

Switching inputs and RCA cables and things prove that it's not the source.

I've tried resoldering all over but nothing seems to fix it. It would help if anyone could point me to likely culprits.

Seems like maybe a grounding issue or something in the right channel but I can't seem to get it to go away.


Thanks!

Voltages:
1. 67.8
2. 176.5
3. 0
4. 176.7
5. 66.6

6. 0
7. 97
8. 0
9. 94.5
10. 0

11. 0
12. 0
13. 177.3
14. 0
15. 197.5
16. 0

17. 0
18. 93.1
19. 0
20. 218
21. 0
22. 0
« Last Edit: July 06, 2021, 08:22:46 AM by sinbonders »



Offline Paul Birkeland

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Do the voltages change as you move the volume pot?  Did you install the jumper between the upper and lower decks of the volume pot where the black wires mount?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline sinbonders

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Update:
Just realized that the voltage and ohms at Terminal 1 are very much dependent on the volume pot position.
Voltage is somewhere between 0 and 68V depending on where it's at. At full volume, it's at around .4V. As 0 volume it's basically 0.

The ohms are close to 0 at 0 volume and full volume, in the middle it floats in the 3K to 12K range as expected.

Edit: I swear I was writing this before I saw your reply!  :o
Yes, they do change!
I believe this is the jumper you're talking about...

i.imgur.com/RXDI5sv.jpg (can't post the full link)

It looked much better before I started randomly prodding with a soldering iron :(
« Last Edit: July 06, 2021, 07:14:18 AM by sinbonders »



Offline sinbonders

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Figured it out!

Somehow I had both terminal 1 and the volume pot connected to A6. Detached volume pot from A6 and reattached to A7 and we're good!

Hopefully I didn't screw up anything too bad in the process.
I did have to replace both LEDs because I burnt them out or something in the process. Took a couple from my speedball kit. Hopefully I can find more before it's time to do that...
« Last Edit: July 06, 2021, 08:25:08 AM by sinbonders »



Offline Paul Birkeland

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I'm glad you got it sorted.  We do sell replacement packs of LEDs.
https://bottlehead.com/product/hlmp-6000-leds-prod/

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline sinbonders

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Thanks for the link! I actually wanted to get badge too, but I might hold off because it's wanting to charge $8.50 for shipping  :o
I'd imagine both of those would fit in a normal envelope.