Crack Grounding, Tracing The Signal and Power Supply Common/Ground

[Grainger49]

There have been a number of builders who have had problems with the ground path in their Cracks. 

Here is a method to assure that all grounds are continuous and good.  First, put your meter on ohms, the lowest scale.  Touch the meter leads together.  You will read the resistance of the leads.  That is a good solid zero reading.  Anything near this reading means you have a good solid ground path.

Measure resistance through this grounding path:

The start of the grounding points is terminal 3.  Clip one lead of your meter to this terminal, better yet the chassis itself. 

It jumps to the 2 left lugs of the volume pot, measure both lugs.  Then it jumps to the back to the RCA jacks.  Measure to the outer jacket of the RCA jacks. 

From the top left lug of the volume pot there is a grounding jumper to the two bottom lugs of the headphone jack.  The jack in the picture may be different than what is being delivered today.  Measure to both headphone jack lugs.

The power supply ground comes from those bottom headphone jack terminals to terminal 12.  Measure to terminal 12.  From there it jumps to terminal 14 and ends at terminal 20.  Measure to both.

Also from terminal 3 you go to the center lug of the 9 pin tube socket.  This is the ground route for the LEDs in the cathode circuits.  Measure here.

The heater (AC) supply gets its ground from a wire from transformer terminal 4 to terminal 22.  Measure both.

Other points that should be a solid ground are pin 8 of the large tube, pin 4 and 5 of the small tube, T8, T11, T14, T16, T17, T20, T22 and the ground post on the IEC power connector, the one with the bare wire to the chassis.

If I have missed any ground points please PM me.

[adamct]

What an awesome reference to have available. Well done, Grainger!

[beegee]

I haven't built the Crack yet, but when is it necessary to test the ground path?  And what types of problems were people having?

[Mike B]

I deleted the top ground from the pot to the phone jack.  The top of the pot was allready connected to the bottom.

I used the bottom pot ground to the terminal lug and then went lug to phone jack.  The other way looked like a ground loop.

[Grainger49]

Beegee,

You might test the ground path before the voltage checks.  It is not called out in the manual.  But there have been guys who had missed soldering one or more of these connections.  It messes up the whole thing, sonically that is.

Mike,

I take it that your post is a suggestion rather than a correction, right?

[Mike B]

Not a suggestion or a correction, it's just what I did to the kit I built.

I will add that it does work.  My Crack sounds supurb and I tested it with no input cables, no input shorting plugs, and with the pot turned all the way up there was nothing coming out of the HD600's.  No hiss, no hum, just nothing -

[Paul Birkeland]

Try cranking the #8 screw down perhaps.

You may also be reading through the flux residue on the solder joint itself, so you might try measuring from the chassis plate to part of the ground lug on the IEC socket that isn't soldered.

[Doc B.]

Firstly I think it is confusing to post a troubleshooting request in a sticky, that is better done by starting a new thread about the issue. Secondly we need to know what headphones you are using to have an idea of what their sensitivity is and thus get a handle on the magnitude of the noise. Thirdly, thank you for mentioning the OCD. It can be difficult to get a reading on how loud a noise is by reading a post and if a builder has OCD it can help us to understand the issue and what might be most effective in remedying it.

The hiss could be one of two things - a noisy 12AU7 or a noisy semiconductor on one of the speedball boards. Noise is always there, it is always a matter of degree and not absolutes. If the headphones are very sensitive the amp may be functioning nominally, but if they are not it could be that a different tube or transistor or LED might make the amp more quiet. If voltages are in the proper range the easiest place to start might be the 12AU7.

[Lar]

 Thirdly, thank you for mentioning the OCD. It can be difficult to get a reading on how loud a noise is by reading a post and if a builder has OCD it can help us to understand the issue and what might be most effective in remedying it.

So does this mean your can prescribe meds Doc?   

[Doc B.]

Only for the amp.