Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: Nick Tam on August 17, 2012, 03:40:36 AM
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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.
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Forgive me I am a noob. I've swapped tubes but that did not help.
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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.
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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.
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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 :(
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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.
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According to the first post, he replaced the 12AU7.
"Update 3:
Replaced input tube. Same popping noise comes through"
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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...
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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.
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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.
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Do the Sennheiser headphones play louder than the other ones at the same volume setting? If so, you may be finding the noise floor.
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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.
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Have you reflowed every solder joint? That is the first thing we would do if you sent it to us to fix.
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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.
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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.
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There are a few questions outstanding. It will help others help you.
Have you swapped the 6080?
Did you try diddling the volume control, I was serious?
Did you check the input RCA jacks?
Is the noise still a static sound?
Dan suggests to reflow every solder joint, not just the signal path. Good advice!
BTW, the noise floor is regular, so you have something else causing the noise.
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Yeah, what Grainger said ... did you swap out the 6080?
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Yes, UPDATE 4: Rolled in Tung Sol 5998 which is the output tube. Problem persists.
RCA jacks are fine, I've resoldered them too. Didn't help either.
Volume pot seems fine, the noise is constant regardless of the pot. The noise is as loud as always even when turned all the way down...
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If the noise is constant volume the source is after the volume control.
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Basically everything else... oh my.
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At least you have started the process of elimination. You know it's after the volume control. You know it's only in one channel so it's not the power transformer. So there are at least 50% fewer places where the problem could be than when we started. You have already swapped both tubes and it doesn't seem to be related to them. So you are getting down to the stuff in the left channel of the amp itself, that might be a problem. My gut feeling is that it is either a bad joint or it might be a semiconductor in that channel. Did you build the circuit in its most basic form before adding the Speedball? Or did you build it with the Speedball incorporated? If it was running OK before the Speedball was installed then the problem is probably related to the installation of the Speedball components. If it all went together in the initial build it will be a little more challenging to isolate the problem.
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So i should try running it without the speedball again?
i built straight to the speedball and it was fine, then one or two LEDs died so i reverted to stock form during the initial build. that was long ago though, so i should try taking off the speedball and see how it goes? but could i be assured that if the noise is still there the speedball circuit is definitely not the problem?
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If you remove Speedball and revert back to stock form and the noise persists, it isnt speedball. If you pull speedball and the noise is gone, then it's on the speedball board or in the wiring to and/or from speedball. I would try the chopstick test first while listening with an inexpensive headset ... poke around with a non conductive probe touching solder joints, terminals, passive components, wires, etc. and listen for increase or decrease in the noise. A wooden chopstick is actually a good probe. Or, small dowel rod, etc. You get the idea. If that doesnt get you anywhere, pull speedball and see if that's it. I should mention that Im no expert like a lot of the gang here but the chopstick test is a common troubleshooting method when the noise source isnt easy the figure out.
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Update 6: Was nudging some of the speedball board wires and some broke off... resoldered those. Was going to resolder joints anyways so I decided to replace some parts as well... replaced 270kOhm Resistor with a Kiwame and stock Octal Ceramic Tube Socket with a teflon one and resoldered completely, looks like the pops are gone for now. Now just waiting for it to pop or not at all. So far so good. Say give it 24 hours more run time? If problem still persists, then I'm probably going to replace all the wires as well...
Next up:
Replace volume pot with a DACT step attenuator, probs?
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You werent specific where your wires broke, solder point or above but it's not uncommon for them to break where the insulation was stripped off. You have to be careful not to nick the wire and it's more difficult with that teflon insulated wire. Plus it's smaller gauge so easier to break if nicked. Lesson learned, right? If it stays silent, and I bet it will, I'd just leave it alone. If you suspect more wires are on the edge ... you can find weak wires that may have been nicked pretty easily. A little manipulation of the wire and if it's weak it will snap where it's been nicked.
As far as the DACT stepped atten., never used one. Personally, I havent had any interest in a stepped attenuator for Crack. Being a headphone amp, I want the finer control of the poteniometer. But many use a stepped atten. Consider whether you think you will miss the fine control if going to a stepped attenuator. If you think you want to go that route, plenty here with experience with all types of attenuators. Ask in a new thread here or in general forum. There are also some nice sounding pots that track very well if you want to retain the fine control. The PEC carbon is supposed to be very good sounding at about $35. The Alps Blue sounds good and tracks very well at about $15. Then there is the TKD for about 100 which is a conductive plastic like the ALPS but is supposed to be a sonic upgrade, very smooth and apparently tracks very well. Im happy enough with the Alps. Tracks well at low volume and is smooth and sounds good to me. I would like to try the PEC carbon though. Lots of stepped atten. options as well like DACT that you are thinking about. Goldpoints seem popular as well but the SMD resistor models dont seem very well received here (with FPIII atleast).
Glad to here it's working well now. Hope you have no more problems. I think you got it figured out.
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The wire that broke off specifically was a ground wire from 9L to the board and the red wire going to the I slot the PCB board of the problematic channel, seems like it fixed it. Although I'm pretty sure the resoldering did the job as well.
Probably thinking of replacing the wires with OCC or silver, although that would be left to another discussion forum.
Later and thanks guys!
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Yes, sounds like it was a wire nicked right at the insulation that gave from working around. We've had amps across the bench with that problem before. It would be worth taking a scrap piece of that wire, stripping the end and sliding the insulation back with different settings until you see a clean strip with no nicks, to make sure the problem doesn't continue to 'pop' up (sorry for the pun).
I'll put a post up in the tech tools section.