Left channel popping and noise/hiss [SOLVED]

[Nick Tam]

I've had my crack built well over 2 weeks now good and running, and i fired it up this morning and well, a loud pop on the left channel ensued. I didn't dare run music through to check because the pot was all the way down and the noise coming from the left side of my senns was definitely loud. there was white noise coming through the left channel with the pot on zero and it pops when i switch the crack off. redid the voltage test with no problems. all LEDs on the speedball and the tubes were well lit. I couldn't possibly have a cold joint because i reflowed it twice during the initial build after running into problems. my senns play fine with another DAC/Amp so i have no idea what had gone wrong. my guess is a bad tube but im not sure. All the tubes glow and i haven't done anything to my crack in particular over the last two weeks

Stock tubes:
GE 6080
(Probably) RCA 12AU7A Cleartop

Others:
Kit caps were 100V nichicons
Startup voltage mod with the phono jack grounded
isolated the ac power to the crack only, no dice.

Update 1:
Checked joints again. No dice.

Update 2:
Reflowed joints
Swapped different pair of cans. No difference

Update 3:
Replaced input tube (12AU7). Tried two different RCA 12BH7A tubes. Same popping noise comes through

Update 4:
Rolled in a Tung Sol 5998. No difference

Update 5:
Noise is definitely the noise floor. However, the noise comes randomly which is indicated by a loud static pop in the left or right channel.

[Nick Tam]

Forgive me I am a noob. I've swapped tubes but that did not help.

[Grainger49]

I removed my first post.  It was wrong and I don't like bad information staying out there.

Did you swap both tubes.  Do you have a spare 6080?  The OP says you swapped the input tube (12AU7) with no change.  If you have swapped the 6080 as well I'm running out of suggestions.  Pops are most often tubes.

The only suggestion I have left is to try moving the volume pot, pull and push on the knob to see if it is losing contact.  Unfortunately, you have to listen while doing this.

[Laudanum]

I could give my long version of why you should always have a couple spare tubes but I'll keep it brief.   Get yourself a spare or two of each tube type, even if they are cheapies, just in case you have a tube go south or need to troubleshoot and rule out tubes.   So, do as Graingers suggests and try a different 6080 (or 6AS7).   If you have a Guitar Center or similiar nearby, they may have new production Sovtek 6AS7's available.  They arent very expensive.

[Nick Tam]

Going out to fetch a NOS RCA 6AS7G to see if it rectifies the problem, though I'm not totally sure. The stock tube that came with my kit was very NOS, literally.

Reflowed all the joints where the L channel passes through. No luck... Reflowed joints on speedball PCBs as well


The pops seems to come and go, but I'm scared I might pop my cans ever so suddenly

[Doc B.]

Could be either tube, not just the 6080, so try replacing both of them. If the LEDs are all lit it's not likely to be a problem with the Speedball. Have you redone the voltage checks? Not too likely but there is a small possibility that you can catch what is going on with the voltage on the tubes when the pop occurs.

[Laudanum]

According to the first post, he replaced the 12AU7.

"Update 3:
Replaced input tube. Same popping noise comes through"
 

[jrihs]

I had some real bad pops and more a while back. After some gyrations with the tubes I finally figured out that my RCA plugs had become loose. So I tightened them up and all's quiet again!! Give the left one a check, just to make sure...

[Nick Tam]

So I plugged in my 300Ohm Senns and there's noise coming through the left channel. Tried plugging in a different pair of cans and the noise is going through the right. I tried to find out if my Senns are blown but it turns out that it isn't the case, my Senns work perfectly fine with a different amp without the left channel noise. I have no idea what is wrong.

[Doc B.]

Presumably the noise is still a static sound. Could be a component in that channel is noisy. Maybe the LED. It's pretty hard to offer anything more concrete without having the amp in front of me to test.

[Grainger49]

Do the Sennheiser headphones play louder than the other ones at the same volume setting?  If so, you may be finding the noise floor. 

[Nick Tam]

UPDATE: It's not the Senns. The pop and static is completely random now. Goes on and off on whatever cans I'm using halfway through the music.

Voltage checks are all fine, I've got some 10 spare LEDs but I really can't be arsed to replace them one by one to rectify the problem... all the LEDs are glowing brightly so I doubt it is the source of the noise.

And no, the sound is balanced.

[Doc B.]

Have you reflowed every solder joint? That is the first thing we would do if you sent it to us to fix.

[Nick Tam]

I've reflowed most of the joints but that didn't work, I'm going to reflow all the joints to see if it fixes the problem, and yes the noise appears to be the noise floor actually. What I don't understand is that the noise isn't regular in the sense that it occurs randomly for periods of time and disappears for awhile, then the noise returns.

[Doc B.]

I have seen cases where the semiconductors (transistors or LEDs) can develop that kind of behavior. The random nature is probably related in part to some kind of thermal expansion or drift as the amp warms up. Unfortunately it's a tough thing to verify by any other method but replacing them.