Channel imbalance after padding pot

[Jamus]

Today I worked on installing resistors as described in FAQ #3 to pad the volume on my Crack with Speedball. Now there is a massive channel imbalance. The right channel seems good but I can only hear music from the left channel when volume is at full. All resistances and voltages are in spec. I resoldered all joints on the volume pot and the problem persists.

One issue that occurred during the addition of the pad is I melted the white wire that runs from the center bottom pot terminal to A2 so I replaced it with some leftover black wire (same gauge). Is there any difference in the properties if the white and black wire?

I also had to cut/replace the black wire that runs from RCA ground tabs to inboard terminals on pot and then re-braid the red/white/black input wires. I wonder if the un-braiding/re-braiding caused a break in the white (left channel) wire. Is there a way to test that theory other than replacing wire at random?

Anything else I could be missing?

Thanks,
Jamus

 

[Jamus]

After reflowing a few terminals on the pot I now have a loud hum/buzz in the left channel which is present and unchanged at all volumes and without a source connected. :-\

Now with music playing, if I unplug left interconnect I get music through right channel as expected but I also get very quiet music through left channel (and buzz too), left side unchanged at all volume settings. Then, if I only use left interconnect I get full volume music (and buzz) through left channel, again volume does not change, both music and buzz are just as loud with volume set to zero.

 

[Jamus]

One last observation, I used a chopstick to try to track down the source of the buzz. The buzz would completely disappear when I pushed on either of the black wires that connect the inboard pot terminals (top to TRS, bottom to terminal 3L). Moving either wire 1mm would eliminate the buzz. However, the channel imbalance issue remains.

 

[Paul Birkeland]

There is a black wire connected to the center lug of the bottom level of the pot, which is inconsistent with how the stock circuit is wired.

A major channel imbalance from this mod would occur by not putting the correct resistor values in the correct places.

 

[Jamus]

There is a black wire connected to the center lug of the bottom level of the pot, which is inconsistent with how the stock circuit is wired.

That black wire is a direct replacement of the white wire that should be there (to A2) which I melted during the mod :-\ the black wire was the only spare I had laying around from that kit build. Seems to be same gauge as the white it replaced.

 

[Jamus]

A major channel imbalance from this mod would occur by not putting the correct resistor values in the correct places.

I'll triple check when I get home but I'm certain I had those right. Whatever sound I do get in the left seems to be bleeding over from the right side, is that possible?

 

[Paul Birkeland]

If you're getting channel bleed, then you have something connected incorrectly, or perhaps a grounding issue on the pot itself.

 

[Jamus]

Thanks PB. I confirmed the resistors are in the right locations, however I'm going to go back and dismantle all connections to the pot and start over. Is it possible there is damage to the internals of the pot from too much heat on any terminal?

 

[Jamus]

So I gave up on the mod and pulled out the extra resistors, put everything back to stock. But... All the issues remain, horrible buzz (both channels), massive channel imbalance, volume attenuator doesn't seem to change volume at all. I'm really stumped here. Any suggestions? Could the pot just be shot at this point?

 

[Doc B]

It is possible the pot was damaged during all of the rework. What you should do first is measure resistance from the center terminal to an end terminal, and then from the center terminal to the other end terminal. Do this on each deck of the pot. You should see resistance vary from roughly 0 ohms to roughly 90K-100K ohms as you turn the pot shaft from one extreme to the other.  If you see the meter go to infinity at some point you know the pot has an open, i.e., the wiper is lifting or there is damage to the carbon track or some connection inside the pot.

 

[Jamus]

Thanks Doc, I'll try this tonight.

 

[Jamus]

So I measured resistances as you said. The only instance that even gave a reading was across the left in- left out terminals. All others gave readings too high for my multimeter. Does this confirm the pot is done?

 

[Paul Birkeland]

What range are you using on your multimeter?

 

[Jamus]

200k ohm setting gave me the volume dependent range from 0-90k ohms across the left in/out terminals. All other terminal combinations gave the OL reading at all settings up to 2M ohms.

 

[Paul Birkeland]

It's probably time to replace the pot.

-PB

 

[Jamus]

Pot is cooked, huh? Sorry, couldn't resist. 

Would this be a worthwhile place to upgrade to something other than the stock part from BH?

 

[lth1]

Absolutely!!!!!!!!

 

[Jamus]

What would you recommend Lee?

 

[Paul Birkeland]

No, if you've cooked the stock volume pot, most of the more expensive potentiometers are considerably more fragile.

 

[Jamus]

The issue with this particular mod for me was that the bottom ground tab was difficult to reach for solder removal and without complete solder removal the terminal hole was a tight squeeze for the resistor.

I like to think I'd have more luck starting with a clean slate even if the pot is more delicate (says the guy who's already melted power switches on 2 builds)  :-[