volume pot gave me a scary shock!

dusk · 3371

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Offline dusk

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on: August 24, 2015, 02:28:25 PM
the volume pot on my crack is LIVE after installing the crack, and I don't notice any wires touching it.  all the readings are fine, and I listened to it and it sounds amazing.. but I'm worried about it and want to fix it before I continue use.

do you think I should strip it down and resolder it?  Is this a common problem?

I have a volume pot I got off ebay in the mail, and I might wait until i get that if I can't figure it out.

In other news, this was the first shock of my DIY life! I did not use two hands, and I was wearing big rubber soled boots while working.


Offline Paul Joppa

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Reply #1 on: August 24, 2015, 02:51:07 PM
If the kit was wired correctly, the chassis, volume pot shaft, and transformer - basically everythihg that can be touched from above - would be connected to safety ground, which in the US is the round third connector on the power cord. So the first thing to do is check whether your home power is correctly wired to safety ground. Inexpensive testers are available in hardware stores, etc. Don't plug it (or anything else) into that socket again until you have checked this important point!

If the power is OK, then we need to search for where the missed safety connection might be. But first, check the safety ground on the outlet!!!

Paul Joppa

Offline dusk

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Reply #2 on: August 24, 2015, 05:18:23 PM
oh, nothing on top is giving me a shock... just on the underneath


Offline Doc B.

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Reply #3 on: August 24, 2015, 05:40:26 PM
Strongly suggest you use a meter to measure voltage. Do not touch parts on the amp to see if you get a shock!

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline dusk

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Reply #4 on: August 24, 2015, 05:47:29 PM
Quote from: Doc B. on August 24, 2015, 05:40:26 PM
Strongly suggest you use a meter to measure voltage. Do not touch parts on the amp to see if you get a shock!

that's the weird thing, all the voltages are measuring fine.  I only shocked myself when I was flipping it over


Offline dusk

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Reply #5 on: August 24, 2015, 06:10:22 PM
ya, just checked everything again twice and all the reading were in the acceptable ranges

even performed the headphone TRS jack test which passed... looked around at every wire with a magnifying glass and didnt see any exposed metal touching anything it shouldn't.. and just tested the sound and it sounds amazing!

not sure what's going on...


Offline Strikkflypilot

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Reply #6 on: August 24, 2015, 06:22:22 PM
Did You test the power in Your home if the ground is actally connected? Even if You have a ground connector in the socket doesn't guarantee that it is connected.

Home system:
Sources: Ibasso DX90, Google Chromecast Audio optical out
DAC: Schiit Gumby
Amp: Bottlehead Mainline
http://bottlehead.com/smf/index.php?topic=7463.0
Phones: HD800S

Office:
Sources: Iphone/ Ipod
DAC: Dragonfly Red+Jtrbug
Amp: Crack/Speedball heavily modded
Phones: HD580,HD600 grilles

Offline JamieMcC

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Reply #7 on: August 24, 2015, 08:36:22 PM
Quote from: dusk on August 24, 2015, 05:47:29 PM
that's the weird thing, all the voltages are measuring fine.  I only shocked myself when I was flipping it over

Was your mains lead still plugged in when you turned it over as even with the Crack switched off if you touched the underside of the power input plug with fingers while flipping you can get a shock?

Shoot for the moon if you miss you will still be amongst the stars!

Offline Grainger49

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Reply #8 on: August 25, 2015, 01:02:18 AM
What Mark said above.  Never turn it over with it plugged in, much less turned on.  Turn it off, unplug it and wait a couple of minutes.  That gives the power supply capacitors time to drain down with the bleeder resistors.  All that is there for your safety.


Offline Natural Sound

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Reply #9 on: August 25, 2015, 05:05:28 AM
Invest in one of these. https://en.wikipedia.org/wiki/Receptacle_tester. They can be purchased at any home improvement center or hardware store and cost less than $10.


Offline dusk

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Reply #10 on: August 25, 2015, 05:35:26 AM
cool, thanks for all the tips guys, I'll put an order in for a receptacle tester


Offline Paul Birkeland

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Reply #11 on: August 25, 2015, 09:17:14 AM
Did you flip the amp over with the power cord plugged in?  You wouldn't be the first person to do so, and the sensation from accidentally touching the AC mains is like a very aggressive tingle that will leave you briefly numb. 

Touching the amps power supply will not really produce the numbing sensation, but will just hurt like hell and feel like more of a stiff snap.

As said before, if the amp is wired properly, you will not be in any such danger.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline dusk

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Reply #12 on: August 25, 2015, 06:37:36 PM
Quote from: Caucasian Blackplate on August 25, 2015, 09:17:14 AM
Did you flip the amp over with the power cord plugged in?  You wouldn't be the first person to do so, and the sensation from accidentally touching the AC mains is like a very aggressive tingle that will leave you briefly numb. 

Touching the amps power supply will not really produce the numbing sensation, but will just hurt like hell and feel like more of a stiff snap.

As said before, if the amp is wired properly, you will not be in any such danger.

no it was the volume pot, I think, it def felt weird and tingly and numbing, and left and odd feeling for a few days... I double checked for loose wires, and all voltage reads were within normal limits.

It was right after I installed the crack, and the device was turned on its side, and I got a shock from trying to stick a voltage read under the crack PCB board and accidentally brushed the volume pot... Im betting there might be a problem inside the pot that is causing the casing to be live?

I have a new pot coming soon, and will install that and hopefully everything will be fixed...

nothing on the top of the device is live, and it sounds amazing.. Ive been using it every night since I installed the crack :)

mega caps and choke next! :D


Offline JamieMcC

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Reply #13 on: August 25, 2015, 09:12:39 PM
Is your top plate still bare metal on the top or have you painted it? Just wondering if any applied finish might be insulating the top. A live top can be caused by a missing black ground lead that connects the volume pot to terminal 3L. The charged capacitors can still keep it live even after power is switched off . You might want to check you have all three black wires connected to the volume pot.

One from the rca input grounds
One from the headphone out socket
One to terminal 3L


Shoot for the moon if you miss you will still be amongst the stars!

Offline Grainger49

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Reply #14 on: August 25, 2015, 11:32:22 PM
The pot itself should have, at most, 2V AC on it from the source.  That is why PB is trying to determine if there is a grounding problem on the chassis.  The volumes have the input from the isolated RCA jacks, they have a ground which should be 0V potential and they have the feed to the grids.  Again the highest voltage there is 2V AC which is considered safe.

It sounds like there is either a grounding problem or a mis-wire somehow picking up a higher voltage.


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