New left channel crackling on previously OK Crack [resolved]

[greb]

Hey,

Finished Crack about 1.5 years ago. Initially, worked great. More recently it developed a persistent L channel crackle that is present even when the volume is off - no change in intensity with increased volume. With the volume off the crackle demonstrates some variation in intensity, at times quiet to noiseless. Never very loud. No channel imbalance to music.

Voltages and resistances are normal. I've re-soldered all the connections - left channel connections twice, switched over LED's (no change), replaced LED's (no change), switched across the L and R 100µF capacitors (no change), switched red and white wires on headphone jack as a test (crackle went to right ear), found a 12AU7 tube, courtesy my father in law - crackle persisted. Poked connections with chopstick - no discernible differences.


Confused. What's up?

KG

[Doc B.]

Try changing the 6080.

[greb]

Just changed the 6080. No luck - crackle persists
Given that it is left channel crackling only, am I correct in assuming that the problem should reside with the L signal circuitry? Can a power circuit issue cause unilateral noise?
What should be my next step? Resolder again?

Thx

KG

[greb]

After new tube (guess I'm officially rolling now!) and more resoldering I switched around the 22.1K ohm resistors.  Crackle now in R ear after resistor switch.
I can only get 22K ohm 2% 1 Watt resistors locally. Will this be OK? Will this compromise sound quality? If OK, should I replace both resistors (for balance??)?
Also, for my own interest, as I asked a few days ago, does abnormal unilateral (single channel) noise exclude the power circuit as a source?

Thanks in advance

KG

[Paul Birkeland]

A 22K resistor will work fine.  Is that particular resistor damaged somehow?  I haven't run into a noisy resistor that was made in the last 40 years. 

[greb]

Wow, 40 years, that is rare! Lucky me...

Replaced both 22.1 KΩ 's with the 22 KΩ's that I bought. Works like new! Thanks for the guidance.

The faulty resistor appears fine - looks just like the other one. I can detect no mechanical instability between the wires and the body.

Time to play with tubes.

[anei]

I had the same issue (crackling on one channel after 2 years without any problem; after switching the resistors I had the crackling on the other channel)

Replacing both 22k/1W resistors with new ones solved the problem.

Thank you for the hint.

[Logan B.]

Just wanted to echo my experience concerning the solution to this thread.

My crack (w/o speedball) was working perfectly; however, one day i started to hear a random static in the left channel. It would occur even if the volume pot was off and there was no input source.

Re soldered questionable joints. No dice.

Replaced both tubes. No dice.

Replaced both 22.1 K resistors. Eureka, works like new.

So if anyone has this left channel static problem, go ahead and replace the resistors first to save time and money.

Thanks for the help everyone.

Cheers!

[Doc B.]

This problem can sometimes be caused by bending the leads sharply right where they enter the resistor body. The interface between the metal lead and the resistive element is a weak point and stress like that can compromise the joint. The issue was bad enough with the old carbon composition resistors we used to supply for grid stoppers that we now supply carbon film resistors instead. The Holco metal film resistors with the metal end caps were sometimes problematic too. But any leaded resistor can suffer from this.