Subtle Channel Imbalance, Is It My Tube?

[mtheshark90]

Have had my crack w/ speedball for 3 years now, has always worked fine. But over the past month or so I've began noticing a slight imbalance between the left and right channels, with the right being a bit louder and crisper.

Things I've tried so far:
-swapped to different headphones
-tested a different DAC
-reversed the headphones themselves on my head, the appropriate channel does still sound louder, hence not an ear problem
-cleaned the pins on both tubes to rule-out oxidation
-tested the potentiometer (blue alps) at all knob levels; channels do not even out or have larger discrepancy, just remains consistent

One thing I've noticed, however, is that when I first start up my amp, the right channel comes into effect significantly earlier than the left. I'll hear sound from the right channel, and after it warms up for about another 30 seconds, then I hear the left fully. Of course, even after a full warm-up, the right remains subtly louder.

So my question is:
Is this more classic of a tube issue, or do I have to now go re-solder every joint in the amp?

[Karl5150]

Both my SEX amps start with the right channel and the left comes on more slowly, drawing the image to the center. Can't say with the SMII, I always try and let it and the Eros warm-up a bit before spinning vinyl.
Karl

[Paul Birkeland]

I would resolder all of the joints in the amp and consider posting some build photos. How are the voltages?

It's not at all odd for the channels to come up at different times (about 5 seconds or so of difference), but that's a very large difference.

[mtheshark90]

Thanks for the response Paul. I was afraid it would come to that, but it's probably the best bet. Would you recommend starting with certain joints? Or literally a full redo, including the speedball?

I'll be able to check the voltages hopefully soon, currently don't have the equipment at my place. I know they were all good after the initial build, though. I'll post some build photos later today.

[Paul Birkeland]

Three years shouldn't be enough time to wear out a tube, but you could try a different 12AU7 and 6080 just to be certain.  Of course when you swap tubes, that can temporarily restore iffy solder joints. 

I can resolder all of the joints in a Crack in about 10-15 minutes, so there isn't a huge time concern here to just reflow all of the joints.

[mtheshark90]

Alright ordered a new 12AU7 and 6080, will try that first since I don't have a soldering iron at the moment. Will let everyone know if it solves the problem.

Of note, I forgot to mention earlier that over time I've had to change my knob position for optimal volume. Whereas it used to be perfect at about 11:00, now the 12:00 position has become optimal. Is it possible there are resistors going bad? My understanding is that resistors tend to have a short life.

[Paul Birkeland]

Is it possible there are resistors going bad? My understanding is that resistors tend to have a short life.

I suspect the resistors in the Crack will last 200-500 years.

[oguinn]

I better stock up, then.

[mtheshark90]

As promised here are some build photos. Let me know if any specific shots are needed.

[Paul Birkeland]

I see lots of wires that are run straight through the terminal strips, then soldered in place.

To get a good connection, these need to be bent up and crimped around the terminal strip.  For the lower terminals, you can just bend the end of the wire up so that there's more area for the solder to contact. There's a red paragraph on page 21 in the manual that discusses this in more detail.

[Deluk]

The red/black/white wires from RCA's to volume pot should be plaited together. This minimises noise pick up. Plaited not twisted. Details in the manual. Using the cutting lengths in the manual are a bit short if you do the plait tightly. I did and could have usefully have done with an extra inch on each.

[mtheshark90]

Good call, Paul. My new tubes are on the way so if those don't fix it, my next step is to reflow everything, and during the process I'll get some better connections in those regions.

At this point in time, the issue has actually become worse and the sound is now about 50% reduced through the left channel, whereas before it was about only 20% reduced.

And it occurs to me that I forgot to mention -- prior to this issue, every now and again I'd experience complete sound loss in the left side, but it would fully return if I twisted the headphone jack in place. It never occurred to me that these were related, but now I'm thinking perhaps there's poor contact or a malfunction with the headphone socket itself. I've tried cleaning with an air can, but no luck. Perhaps it's worth picking up an entirely new socket?

[Paul Birkeland]

That kind of symptom would be more indicative of a solder joint issue on the headphone jack or one of the wires connected to the headphone jack.  Unless you have really badly melted the headphone jack, the jack is working just fine. 

[mtheshark90]

Alright so for the sake of any future individuals having similar problems, I'm going to keep posting my results in this thread.

My new 6080 arrived, a Thomson (previously was RCA). At first test, I was convinced the issue was fully resolved. I could not tell a difference between the left and right channels anymore, thus assumed the prior 6080 was bad. However, after listening to multiple songs, testing different sounds, and playing different games on my PC, I can say there IS in fact a discrepancy between the L and R channels, but only for certain sound wavelengths. The RCA, which was far more bass heavy, definitely made it obvious that the L channel had a problem. However, the Thomson, which is far more mid and treble heavy, mostly masks this issue. But after some time and careful listening, I can say there is STILL an issue with just the lower wavelengths in the left channel. Not only that, but it's become apparent to me that bassy sounds actually produce an almost crackly-hiss, whereas in the right channel they are very clean. So at this point I'm convinced the issue is with the 12AU7, and not a solder joint. I cannot possibly fathom that a faulty solder joint would only affect the bass-end spectrum of the left channel.

My new 12AU7 is still on the way, so when that arrives I'll be able to test my hypothesis, and I'm extremely curious at this point to see if I'm correct. I'll keep everyone posted.

[Paul Birkeland]

I cannot possibly fathom that a faulty solder joint would only affect the bass-end spectrum of the left channel.

When I listen to a Crack and I hear horribly weak bass on one or both channels, that's one indication for me that there's a solder joint issue.