Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: 3ph00n on August 28, 2018, 12:50:38 AM
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Hi everyone,
I built the standard crack a few days ago. The process was pretty straightforward.
However after some time I discovered 2 issues:
1. some cracking in the left channel when the tubes warmed up (no problem so far as it stopped after 1 minute, the cracking was also audible with no headphones on just by listening to the tube) but after some listening time and a few days later the cracking doesnt stop when the tubes are warm (cracking not audible outside the headphones).
I can create some strange cracking sound in the left channel by tapping the chassis next to the 6080 tube or the base of the 6080 tube itself but the cracking won't stop after tapping.
From time to time the left channel also hums slightly (not the typical 50 Hz buzz, it's slightly higher)
I already tried reflowing the solder on the 8 pin socket and the terminals near it... No effect (I don't think i got a cold spot, I had soldering experience before however you can never be sure)
2. the right channel is louder than the left one
I already tried padding the pot (which looks a bit funky because i only got smd chip resistors around) but the imbalance is still there
The left channel puts out .125 V while the right channel puts out .155 V with the pot turned halfway up
Can you help me with this?
Kind regards,
David Bacher
[Edit] My setup looks like this: PC -> Schiit Modi 2 -> Crack -> Sennheiser HD 6xx I tried different sources and different headphones but the problems were still there
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How are your voltages?
If you tap on the chassis and get pops and crackles, there is a solder joint that isn't doing its job. (I would look beyond the octal socket)
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thats the strange thing... it's not really a popping sound but more like some kind of metallic sound as if the filament inside the tube is expanding and scratching somewhere (I know that because of the heat this is the case but you shouldnt hear it... Right?)
I turned the chassis around and resoldered some spots but the problem still persists.
After visual inspection of the solder spots I tapped every single spot but couldn't recreate the noise... however i could do so by tapping on the 8pin socket and the tube directly.
I rechecked the resistances and everything is correct, my voltages are as follows:
1 74.7 V
2 183.2 V
3 0
4 183.2 V
5 80.1 V
6 0
7 106 V
8 0
9 113.8 V
10 0
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You can also try removing and inserting the 6080 a few times, in case the tube pins are a little oxidized and not making good contact.
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I tried that (even cleaned all the pins + socket with isopropyl alcohol) and it had little to no effect.
The crackling seems to fade away after some time leaving the crack on (maybe due to burn in of the tubes, a few days ago this didn't happen even after listening for a few hours).
The channel imbalance however is still there (I fed the crack a 50 Hz sine signal and measured the output voltage with an AC voltmeter)
Thanks for your help anyway! Is there anything else I could try to do?
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What voltages did you get at the output with your 50Hz tone?
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I measured the following (after padding the pot):
Pot Left Right
1/4 .08 V .10 V
1/2 .23 V .28 V
3/4 1.11 V 1.25 V
1 1.83 V 2.01 V
1/4 of the pot means I turned it to nine o clock, 1/2 is 12 o'clock etc.
1 is as far as it goes
I don't know the exact input voltages as I used my smartphone with volume turned to maximum and a signal generator app to feed the crack.
At first (right after assembly) I thought the issue is the pot so I padded it...
Resistance before padding:
Left: 98 kOhm
Right: 88 kOhm
After padding:
Both: around 98 kOhm
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It is odd that everything is about 1dB off, especially if the pot is turned all the way up. I would repeat this test but measure the AC voltages available at the RCA jacks themselves.
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The Input voltage is 0.98 V (Left) and 0.99 V (Right).
I just realised that I made a slight mistake at measuring the output voltages the first time... I measured them without load (I just plugged an adapter in so the plug isn't shorted and then measured the voltage directly on the pins of the plug body).
After this I re-measured the voltages and they are slightly lower (about 10 percent) but still not in balance.
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When the pot is all the way up, the input and output are shorted.
I would redo the measurements with the pot all the way up, as the outputs of the pots should be as balanced as what comes into the RCA jacks.
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Input Voltages: 0.98/0.99 V
Output Voltages: 1.35/1.53 V
Measured with load (headphones plugged in) and volume pot at max.
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The output of the pot is the middle lug on each level of the pot, you'll want to check there to measure channel balance of the pot itself. You do not need headphones connected for this.
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Oh sorry I misread that, I thought you meant the output of the amp.
The voltage at the output of the pot is 0.233 V (Left) and 0.236 V (Right) with the input voltages I mentioned above...
(The pot is padded so I think these measurements are reasonable?)
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OK, turn the pot down half way and repeat the measurements, then down 1/4 of the way and repeat.
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Pot Left Right
1/4 0.01 V 0.011 V
1/2 0.03 V 0.032 V
3/4 0.144 V 0.146 V
Please notice that the voltmeter I use isn't very reliable with voltage differences as low as a thousandth of a Volt. Sometimes I got measurement errors as big as 0.025 V (guessed average) in between measurements.
But once I connected all the leads the measured voltage was stable at the values you can see above.
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I will try to follow the signal path from input to output and try to get some measurements using the 50 Hz tone. Maybe this could help?
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Now you can repeat this test with the amp running and no headphones connected. See if your meter can read AC volts between ground and terminal 1, as well as ground and terminal 2.
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Both readings are around .007 V
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Yeah, some meters won't measure AC in the presence of DC.
If the pot isn't the balance issue, then it could either be a flaky solder joint or a tube that isn't well balanced. Often times a tube that has a channel imbalance will remedy itself if you leave it running for a few days.
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Is it possible to check if the problem is the tube beside using it and waiting for the problem to fade away?
If it's the tube, does the warranty cover a replacement of the tubes?
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Is it possible to check if the problem is the tube beside using it and waiting for the problem to fade away?
This becomes a little difficult, as almost all of the tubes that we have had returned to us over the years quiet down after a day or two of use.
If it's the tube, does the warranty cover a replacement of the tubes?
The warranty covers replacement of tubes that don't work properly.
Depending on where you live, you may be able to borrow a 12AU7 or 6080 from a local tube seller (they are out there) to see if one or the other is causing your issue.
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Sadly there are only onlineshops in my area... But a music store I know has a tube checker.
I will try checking the tubes there...
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After some listening time the noise and channel imbalance is still there.
It wasn't 100+ hours of burn in time, maybe 30 to 40 but I didn't discover any changes.
The music store doesn't doesn't sell any 6080 or eguivalent tubes and therefore can't check them.
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I got no other idea than changing the tube.
Is it possible to get a refund for the tube?
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We can exchange the tube, but do be aware that most of the "bad" tubes sent back work perfectly fine. (We also test our tubes prior to shipping)
What part of the world do you live in? Perhaps there's a fellow kit builder close by who can lend a hand.
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Actually we only get a few tubes back. But PB is right, when they do come back they are most often just fine. If you want to send it back we can send a replacement.
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I am from Germany so the shipping will probably cost more than buying a replacement tube here.
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Where in Germany? I'm in Belgium/The Netherlands.
PM me for replacement tubes, try that first. If needed/possible i'm also willing to take a look at your Crack.
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I would also add that if you get a replacement tube and the problem appears to resolve itself, do go back and try the other tube again.
There have been a few times where the act of replacing a tube will jostle a strange joint or a broken wire enough to get things working, which convinces the builder that there is just a tube problem, only to have the issue return in a few days.
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I am from saxony which is quite far away from belgium...
Thanks for your help anyway!
I will see if I can get a replacement tube somewhere else.
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You can find good 6AS7G/6N13S svetlana and 5963NOS or 5814A to get your Crack "new" tubes @ https://www.btb-elektronik.de/home
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Hi everyone,
It has been a long time since I last posted here but for anyone interested and people with a similar problem:
Changing both tubes fixed all the problems I had.
First I exchanged the 6080 for a 6as7g Svetlana and all the problems in the left channel disappeared.
Directly after that a much quieter noise in the right channel appeared (I think it was always there, I just couldn't tell before)
This new noise could be fixed by tapping the input tube.
This was also fixed by changing the tube and finally I got the sound I was looking for!
Thanks alot for all of your help and support and the amp that now works really well!
(Btw: is it possible to file a warranty claim for my issues as the tubes set me back another 40€?)
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I'm very happy it all worked out for you and Crack is working as it should. It is a great amp indeed! One of the best price/performance ratio's available. And for what it can teach you in the journey of building it and all that comes after, one of the best amps you will ever buy.
Personally, i think buying NOS or old tubes comes with a calculated risk for the buyer. Although most are generally reliable products they have had a long shelf time before you get them. And the noise issues with these old things can't always be checked for. And they can appear after some use without any symptoms prior to that point.
Second. I think a company can't be held responsible for the price you paid for a spare set of tubes. As you can buy tubes for a few cents a piece when you are lucky (or free even), or pay hundreds of euros for a single tube.
I know i'm not making any friends with you right now. This is a personal opinion. This is not at all the Bottlehead company opinion/policy. In general i think the support received from Bottlehead is among the best you can get. They stand behind their products and are always willing to help out a Bottlehead user in need.
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(Btw: is it possible to file a warranty claim for my issues as the tubes set me back another 40€?)
The challenge that we have is that there are a pretty good number of builders who run into problems and blame the tubes. Even when a different set of tubes appears to solve the problem, often it comes back at a later time (whatever solder joint isn't properly soldered gets disturbed enough when swapping tubes, then goes out again a few months later). What we most often found when receiving tube sets back is that they tested perfectly and sounded great. Occasionally we would need to let a particular tube run in for a day or two to get it quiet.
If we offered to reimburse builders for new tube sets, everybody would buy one!