Crack V1.0 Failed resistance check

[Imperiumdx]

I've just finished building a Crack V1.0 240v
And I get a strange result on the resistance check

Terminal
1 *
2 *
3 0
4 *
5 *
6 2.45
7 2.92
8 0
9 3
10 2.45
12 0
13 262 (still climbing but VERY slow )
14 0
20 0
22 0

B3 2.93
B6 3

RCA
Ground Lug 0
Center pin L Starts at @ 30 and keeps climbing
Center pin R 92.5

 

[Paul Birkeland]

Did you have something plugged into the headphone jack when you took these readings? (Maybe a 1/4" to 1/8" adpater?)

The center pin L may indicate that you don't have the jumper installed between the ground lugs on the volume pot.

 

[Imperiumdx]

There is nothing in the TRS jack at the moment.
I built the Crack with an Alps pot using a PCB where all the ground lugs are connected.

 

[Paul Birkeland]

Can you show me the wiring at the headphone jack? Are all the black wires at the headphone jack captured by solder?

 

[Imperiumdx]

Here are some pics of the headphone jack

 

[Imperiumdx]

I will reflow the wires

 

[Paul Birkeland]

Ah, you have a 1.0, I didn't notice that in your original post!

No worries about 6 and 10 then, can we have a look at the volume pot wiring?

 

[Imperiumdx]

This is the volume pot:

 

[Paul Birkeland]

Can I get a link to where you got the PC board? It may need some grounds jumpered.

 

[Paul Birkeland]

I looked over the pictures you PM'd me and I found the Alps board you used. All the grounds are tied together on that board, so it's not a problem. I'd suggest reflowing the solder joint on the left jack ground lug, but also the joints of the white and black wires going into the volume pot from the RCA jacks.

 

[Imperiumdx]

I just reflowed the joints and the rca in to the pcb
It still reads the same left channel @30k ohms and climbing.

Do you have any other suggestions or what I can do?
Could the volume pot itself be faulty? or the assembly with pcb?

 

[Paul Birkeland]

I'd also reflow the joints on the pot itself.

You can measure the resistance between the outer solder lugs on each level of the pot to see if the correct ~100K appears there.

 

[Imperiumdx]

I removed the rca input wires in order to get to the solder lugs of the pot.
Reflowed them and got to 90k ohms on the upper row ( left channel)
Reconnected the wires now it measures 78-79 k ohms

The lower level measures consistently at 92.5k ohms

 

[Paul Birkeland]

That's close enough to keep going.

 

[Imperiumdx]

Is there going to be a mismatch in output if lets say there is a difference in resistance between channels?
Also is it safe to move to voltage check?

 

[Paul Birkeland]

You can move onto the voltage check.

A potentiometer is a variable voltage divider, so one track being a different impedance doesn't necessarily tell you much about channel balance.

 

[Imperiumdx]

Changed back to the original potentiometer.
Passed all resistance and voltage checks and voltage check on TRS.

Upon first startup with source and headphones connected, just when the tubes began to glow there was an immediate flash in the big tube
and a loud pop in the right channel of my headphones.
Turned it off immediately, started it up again with a set of cheaper headphones plugged in.
The amplifier plays normally no pops or anything strange whatsoever.
Switched back to the original headphones and it operates normal.

Is this something I need to investigate or is a one time pop on first startup under load something that can occur?
Subsequent startups were all normal.

Just checking before I move on to the Speedball upgrade.

 

[Paul Birkeland]

I'd just be extra sure your solder joints are nice and solid.