Crack w/speedball sends a jolt when unplugging HD800 [resolved]

[vchan]

I am having an issue with unplugging the HD800 from the Bottlehead crack.  Every time I do it, and I am using one hand to hold onto the chassis so that I can pull out the headphone cable, I get a jolt/shock.  I have done a resistance measurement from ground of a power cord plugged in only to the amp's socket and the chassis, and it reads ~3 ohms.  I have also followed the sticky for the resistance checks on tracing the signal and power supply common/ground.

EDIT: T22 is reading 30-40 ohms.  This might be my issue.

EDIT #2: T11, T16, T17, and T22 seem to vary in resistance...

I have done this numerous times with the HD650 without the jolt/shock, and I am guessing that I am protected due to the non-conductive shielding on the headphone plug.

Any one else have this issue, and know if there is a solution for this?

 

[Paul Birkeland]

You have at least one flaky solder joint on your Crack.  Have you performed voltage checks? 

 

[vchan]

Yes, I have done voltage checks pre and post speedball installation.  The voltages seem to be within 20V, and to my understanding that is normal based on tube variances, right?

Following Grainger's grounding post, everything seems to be near 0 ohms except the 4 terminals that connect to the transformer screws.  They seem to jump all over the place randomly every time I measure them.  Since the ground post on the IEC power connector is soldered with bare wire to T16, it reads the same ohms as the other 4 terminals.

Any ideas on where to start reflowing solder?

EDIT: I tightened the screw nearest to the plug and it seems to have fixed my resistances. 
Is there perhaps a better way to test for jolts other than exposing oneself to it? 
Well, it seems I have fixed my grounding issue, but just tried plugging in the HD800 and unplugging it (while holding onto the chassis) and still got a shock.  I realize that this is only happening with the HD800 plug because the plug connector of the stock cable is made out of metal.  The HD650 has a non-conductive shielding around its plug, which is why I do not feel a jolt when I unplug it while holding onto the chassis.

Does anyone else have this issue, and/or a fix?  I guess I could always use some type of non conductive material to plug and unplug the HD800, but if there exists an issue with my circuit, I'd prefer to find it.

 

[Paul Birkeland]

If you're getting a shock at that terminal, then there is significant DC voltage at either terminal 6 or terminal 10, which would cause you to fail your voltage checks.

In the absence of this measured voltage, a loose ground connection could cause a similar problem.

The next step that you'll want to take is to measure the DC voltage at terminals 6 and 10, but have the black probe of your meter grounded at the #8 screw by the power entry module.

Also, use this voltage measurement to determine the operational condition of your amplifier, not your body.

-PB

 

[JamieMcC]

I have experienced this problem in the past and it turned out to be a ground wire I had forgotten to solder I think it was the one from terminal 3 to the volume pot. But it was a couple of years ago now so not 100% sure.

 

[vchan]

I have redone the voltage checks at T6 and T10 and they still read 0 volts even when I use the #8 screw as a ground.

I have also redone all of the voltage checks listed in the Speedball manual and the numbers are ok.  Resistances as T6 and T10 are 2.49k
I checked the ground tracing thread again and my resistance is less than 1 ohm everywhere that is supposed to be tied to ground.

Should I test voltage with headphones in the jack and RCA plugged in?

 

[vchan]

I believe I found my issue.  Seems to have been a flaky solder joint as PB mentioned in his post above.  The headphone jack ground pin that connects to T12 was the culprit.

I found this by flipping the unit so I could measure the headphone jack connections with a headphone plugged in.  I was using the HD650, as its connector has non-conductive shielding.  As I started to unplug the headphones, I noticed all of my LEDs turned off.  I measured from headphone plug (partially plugged in still) to chassis, and I was getting -240ish volts.  I then measured each of the 6 headphone jack connections using chassis as ground, and the connection to T12 was the only one that read -240V, while everything else read 0.

A touch up solder job, and a re-test later... now the LEDs don't shut off as I unplug the headphone cable!  Also, the voltage remains 0V regardless of how the headphone is plugged in.  Hopefully this is an indication that I will not get a small jolt the next time I decide to unplug my HD800 from the Crack  ;D