Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: Labyrinth52 on January 08, 2020, 01:54:38 PM
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Hey folks!
First time Bottlehead user. I just finished assembling my Crack 1.1 W/ Speedball and have been really, really enjoying it. However I've ran into a minor issue. After full assembly was the first time I tested out the volume potentiometer. As the title would suggest, it's only changing the volume on the left channel. I've done a quick search and I couldn't find a post on here with a similar issue.
Isn't my first time doing a soldering project, or building an amplifier (O2 previously). Would anyone have any suggestions as to what might be going on or how to resolve this?
I can provide a list of voltages and resistances if need be, but when checking throughout the build they were all within range.
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This is probably best resolved by posting some build photos.
Back in the Crack 1.0 days, it was super common for people to forget the connection that goes between the pair of pot lugs where the black wires connect, is yours present?
Is the volume stuck all the way up or all the way down? If it is always all the way down, that could be too much solder on the center pin of the jack shorting it to the shell of the jack.
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Stuck all the way up, it almost seems to get a little louder as the other channel fades. But might be my imagination. I do have the bridge in place, and all of the connections seem rock solid.
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On the upper level of the pot, the middle lug should vary in impedance to ground as you rotate the control. What range do you see? (you can measure this with the amp off)
What range do you see from the middle lug to the outer lug?
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What range do you see from the middle lug to the outer lug?
Upper middle to upper right (ground) I get 1.8 ohms to 93.6k ohms.
Upper middle to upper left is the polar opposite.
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I would resolder all of the joints where black wires land. Those readings tell us that the pot is working just fine, so that leaves the most likely problem to be that the pot isn't well connected.
At the 1.8 ohm resistance reading from center lug to the ground lug, the output of the pot will be muted unless the ground lug on the pot isn't well connected.
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I'm confused. It looks the pot wiring changed in the current instructions (my 1.0 has the red wires on top furthest from chassis). Should the measurements have been from the lower lugs closest to the chassis where the red wires are attached?
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The left channel is the level of the pot with white wiring.
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Welp. I removed all excess solder, re-soldered all my grounds, and redid my red wire from pot to a7 as it was pretty mangled. Plugged it back in and I lost volume control on both channels. I decided to take a break and just listen to it for 15 minutes (probably a bad idea in hindsight), and part way through listening I lost left channel. Powering on the amp now, LED from center lug to A3 is blank and no longer shines.
Terminal - Resistance
1 - *
2 - *
3 - 0.3
4 - *
5 - *
6 - 0.3
7 - *
8 - 0
9 - *
10 - 0
12 - 0
13 - *
14 - 0
20 - 0
22 - 0
Wasn't able to get resistance on OA/OB
G - 2.3
Terminal - Volt
1 - 71.6
2 - 176.8
3 - 0
4 - 177.1
5 - 172 - Running high
6 - 0
7 - 100.4
8 - 0
9 - 170.9 - Running high
10 - 0
OA - 170.5
OB - 100.5
G - 0
B+ - 176.9
Hopefully these are enough to narrow down suspects to at least get the missing channel back.
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Do both halves of the 12AU7 glow?
Can you carefully measure the DC voltage on pins A3 and A8?
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Hey Paul, only the back half is glowing currently.
A3 - 0V
A8 - 1.6V
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The solder joint at A4/A5 is not sound. Reheat it/reflow it to restore glow to both sides of the tube, then that LED should come back on.
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Is there some type of reading I should potentially be getting off these pins?
Under the small board is currently (visually) a mess from me trying to sort this out. But all the connections look solid to my eye and terrible photo.
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I should add, I've lost the two B-side led's on the small board. I seem to be doing more harm than good at this point.
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If the tube doesn't glow on both sides (but does glow on one side), then the solder joint at A4/A5 needs attention. Unscrew the PC board, slip some of the bare wire through A5, then loop a little more through A4.
That is what you absolutely must focus on 100%. The LEDs will not light up unless that issue is resolved.
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Did as you said, stripped of solder, pushed through more, crimped the end on A4. Still got nothing lighting up. I'll try and fiddle with this connection more tomorrow.
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Also double check that one half of the 12AU7 isn't lighting still.
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I've continued messing with the connection today, even so far as removing the connection entirely and redoing it. Still missing those 3 LED's and only half the input tube.
I still find it very odd that the left channel dropped while I was listening to it.
I have a friend who has access to some diagnostic equipment who is going to help me troubleshoot on monday. But I don't think I could do any better on the connection than it is now. I've ordered some tubes to roll in as well. So I don't know where to proceed from here.
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You could try a different 12AU7 just to rule that out.
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I have had a channel dropout with a loud popping sound and it was due to the leds having a mechanical break from removing tubes and inserting new ones.
I replaced all of them and made sure they were strain relieved them so the wiggling that occurs when taking out tubes doesn't pull or move these leds leading to this issue.
Had this happen twice before I figured out my issue...been solid for several years...and being careful about removing tubes .
Alex
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So a quick update, it was the tube. Replaced it with a Tung-Sol 12AU7W and both sides sprung to light.
I had mentioned that I had a friend come over to help me diagnose. Turns out one of the LED's essentially wasn't allowing current through it (if I remember correctly), and I had messed up the volume potentiometer trying to wick off excess solder to redo the connections. So I have replaced the broken LED and have an Alps RK27 Velvet pot on the way to replace the one I butchered.
Essentially had three issues wrapped into one giant mess. But seems to be on the up and up.
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I'm glad you got it sorted!
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Great News!!
Another one of those LEDS! Be careful in the future if you start swapping out tubes..you could break another one if not strain reliefed etc..
Enjoy!
Alex