Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: meeklo062704 on September 13, 2013, 04:19:29 PM
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I just started getting a low hum from my crack, inordinately I'm not sure what range it's in. The hum goes away if I turn the power off then right back on. I didn't build it myself. I saw how long delivery was going to be, so impatience got the better of me and I bought one from head-fi. So I don't have a manual to troubleshoot either, soim turning to the forums for advice. There's no speedball in it yet. One time when I was turning it off I accidentally bumped the tube next to it, and got some crackle. I let it cool and reseated the tube, but it didn't fix the problem. Any advice?
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This is likely a loose cap in the power supply that needs to be resoldered in place.
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Is there a place to download the manual? Buying it assembled is biting me in the @$$ right now, because I don't know exactly what's what, or how to fix. I don't wanna guess and mess it up.
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I'm pretty sure there's a bad joint that's causing the hum. I noticed when I set a drink on the desk, and the hum kicked in right away. I tapped the top right next to the power tube with my finger, and the hum went away. Am I correct in assuming I have a weak joint somewhere? If so, any advice which ones to check?
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If so, any advice which ones to check?
If it came into our lab we would reflow every joint. If you want to take a more direct path, inspect every joint with a magnifier to see if there is one that has poor contact.
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If so, any advice which ones to check?
If it came into our lab we would reflow every joint. If you want to take a more direct path, inspect every joint with a magnifier to see if there is one that has poor contact.
Ok, thanks doc. Is that symptomatic of a particular area, or it could be any of them?
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. . . The hum goes away if I turn the power off then right back on. . . .
This points to the heaters. Or it did in the FP 2 and some other kits long, long ago when I was a newbie.
The Crack has AC heaters on both tubes. Check the routing, twists and solder joints on the transformer, big tube and small tube. Somewhere there might be a problem that is causing the hum.
If in doubt post pictures of the underside.
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It's symptomatic of a bad solder joint. Just reflow all of them. I can't be more specific without the amp in front of me. It could be a heater connection as Grainger suggests. It could also be a ground connection, tube socket connection, power supply connection, or something else. If you want to flip over the amp, turn it on and poke around at various connections while you listen you can probably find the offending one. But you can get a bit of a zap if you are not careful and if the bad connection is in a place that makes a lot of noise when you work it around you could damage headphones. So you would have to decide if you want to take the responsibility of testing that way - or just check everything you can with a magnifier and reflow the solder joints with the amp off and disconnected from power and headphones, then hook it back up and see if the probem is solved.
Another way to look at it is this - PB would redo every joint if it came in for repair, because it would cost me a lot less of his time to do that than having him fart around trying to figure out which individual joint to reflow. And if we sent it back with the offending joint fixed and then a different one went loose because, say, all of the solder joints were a little shaky due to builder inexperience, we would look like poltroons. So we just do them all in ten or 20 minutes, check it out, and send it home confident that all the solder joints are now solid.
So I still say do them all, and if the noise is still there we will move to plan B.
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Dan,
I have a pretty good vocabulary, although I don't use it that often. But... what is a poltroon?
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A poltroon is one whose cowardice is utter and complete.
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I grabbed a few pictures for a shot in the dark. Sorry it took so long, it was more difficult than I thought it would be to grab a few closeups.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi647.photobucket.com%2Falbums%2Fuu192%2Fmeeklo062704%2FIMAG0222.jpg&hash=c237408e32d3a674fcfbeddfba9585076ab7145c)(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi647.photobucket.com%2Falbums%2Fuu192%2Fmeeklo062704%2FIMAG0223.jpg&hash=a82204968184233b1ee62a0b163871a7b6cc744f)(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi647.photobucket.com%2Falbums%2Fuu192%2Fmeeklo062704%2FIMAG0224.jpg&hash=b59a4393e21488ac1e5fa54abc25462a65a4808f)(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi647.photobucket.com%2Falbums%2Fuu192%2Fmeeklo062704%2FIMAG0228.jpg&hash=ad0b54b8d45bbe2af6e56017819068d72e6d57f7)
I'm more than likely going to end up reflowing everything, I was just trying to hold off until I got my speedball. This is what I get for being impatient and buying one from head-fi instead of waiting for shipping to catch up. I did the best I could on the closeups Grainger49, sorry for the blur. I also included a shot of the whole setup, if anything looks iffy, let me know so I can redo it. Is there a place to download the manual since my Crack didn't come with one, or would I need to purchase it? It says a lot about a company when you can get the owner fielding questions. Awesome.
p.s. Any word on the Bottlehead DAC? I'm getting ready to pull the trigger on a Bifrost, but would love a matching dac for the Crack.
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How tight are the wires that go from RCA to volume pot?
I think having those wires as close to the transformer as you have it could introduce noise.
with unit on, safely, take a pencil and push the wires to the side to see if it helps.
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Ok, I am looking at and zooming in on the pictures.
There is no doubt that the LEDs on the 9 pin socket are oriented properly.
The heater wires on both sockets look good. The twists are regular and tight. Those wires shouldn't inject hum anywhere I see. (I didn't remember that Crack is delivered with stranded wire)
You might want to tin the wire on the octal socket that runs from pin 5 to pin 2. That means put your soldering iron in the middle, touch the solder to the wire and when it begins to flow onto the wire move the solder and iron from end to end.
I'm throwing in that the solder joints could be touched up. If you don't know, that means to heat the iron, touch a tiny bit of solder to the tip then apply it to the terminal or tube pin. A tiny bit more solder could be added to most of the terminations I see. You are not at all guilty of making solder balls.
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You are missing the 270K bleeder resistor in the power supply. This is incredibly important for safe operation.
It gets pretty tough when you wire a kit with stranded wire. There could be strands poking around here and there where they shouldn't be, and this very likely could be the cause of your hum.
It also looks like you painted the bottom of the chassis. Can you measure the resistance between the #8 screw at the back of the chassis and terminal 3? A poor connection to the chassis plate at either of these points will indeed make the amp hum.
-PB
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D'oh,
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg7%2FGrainger49%2FSmiles%2FSlapHead.gif&hash=e5c580c3cfdf525c26703ae0328aefb586b04de5)
I noticed that the underside of the top plate was painted on my first look and forgot to post it.
BTW, I read my wife the title of this thread and she just said, "BOYS!"
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.... I didn't remember that Crack is delivered with stranded wire ....
It isn't. No doubt just another unfortunate byproduct of the rampant cable upgrade shilling on head-fi.
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It isn't. No doubt just another unfortunate byproduct of the rampant cable upgrade shilling on head-fi.
Then I should comment:
Think about this guys, the same gauge of solid wire is smaller than the same gauge of stranded wire, there is space between the strands of the stranded.
Stranded wire doesn't "form" like solid wire does. Forming allows you to put the heater wires flat against the chassis plate, thus decreasing the chance of hum pickup. It also allows you to route the wires so signals cross DC and AC feeds at 90 degrees.
Increasing the gauge wire within any Bottlehead product makes no sense as increased gauge only improves current carrying ability. Trust me, us, Bottlehead doesn't undersize their wire. Larger wire, be it either larger gauge solid or same gauge stranded, is much harder to get through tube pins and terminals, as witnessed in the pictures on page one.
I'm not one that eschews stranded wire because of skin effects or any other pseudo science. It has its place. In power feeds, and most interconnects it is a must. Stranded is flexible, solid isn't.
Ok, end of sermon.