Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: alihill77 on May 01, 2019, 04:16:35 AM
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I built the amp with the speedball around a year ago. Recently I noticed that there was a faint humming and decided to reflow all of the solder joints. Since then there has been a loud humming coming from the amp. The humming/buzzing inceases the more the volume is turned up but is obviously noticeable at low volumes too.
Weirdly if I plug the RCA jacks directly into my computer there is no humming but if I plug the RCA jacks into nothing, a phone or my dac there is humming. I thought there might be a grounding issue but I checked every ground point they seem ok. My resistances and voltages seem fine too. My voltages are:
T1 - 74
T2 - 183
T3 - 0
T4 - 183
T5 - 72
T6 - 0
T7 - 107
T8 - 0
T9 - 110
T10 -0
T11 - 0
T12 - 0
T13 - 183
T14 - 0
T15 - 202
T16 - 0
T17 - 0
T18 - 91
T19 - 91
T20 - 0
T21 - 222
T22 - 0
A1 - 71
A2 -0
A3 - 1.5
A4 - 0.01
A5 - 0.01
A6 - 73
A7 - 0
A8 - 1.5
A9 - 0
B1 - 73
B2 - 182
B3 - 107
B4 - 72
B5 - 182
B6 - 110
B7 - 0
B8 - 0
SMALL CURCUIT
OA - 73
IA - 182
B-A/B - 0
IB - 182
OB - 72
BIG CIRCUIT
G - 0
OB - 107
B+ - 182
OA - 110
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Weirdly if I plug the RCA jacks directly into my computer there is no humming
This is likely to not be an issue. Is there any hum with the volume pot turned all the way down and nothing plugged in?
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With nothing plugged in I can only hear a buzzing when I turn the volume up a quarter of the way or more.
With the rca shorted I can start hearing the buzzing from turning the volume up an 8th of the way.
This is a problem because the buzzing is louder then the music when I plug the amp into my dac.
Also it sounds like a techno beat is coming from my computer when I plug it in now.
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Also if I touch the rca jack with my finger I can hear buzzing in the relevant ear.
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With nothing plugged in I can only hear a buzzing when I turn the volume up a quarter of the way or more.
That's very likely normal.
With the rca shorted I can start hearing the buzzing from turning the volume up an 8th of the way.
There shouldn't be any buzzing with the RCA jacks shorted. What are you using as the short?
This is a problem because the buzzing is louder then the music when I plug the amp into my dac.
What're you using for a DAC.
Also it sounds like a techno beat is coming from my computer when I plug it in now.
Can you try using just an 1/8" to RCA cable to connect the Crack to your phone. What issues (if any) are present under these conditions?
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My DAC is a modi 2 uber which is plugged in to the wall.
I get buzzing with heavy distortion on the music when plugged into my phone as well as my dac.
The buzzing is a lot quieter when shorted I just plug the + and - of an rca cable into the amp.
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OK, the distortion is definitely an issue.
Can you post some photos of your build? I'd be interested in seeing the power supply wiring, headphone jack wiring, and each socket.
-PB
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Here are some images I have just taken: https://drive.google.com/drive/folders/1NsMXJbQKXy6rDGqEzuT6w1vEd_q3OZTS?usp=sharing
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Was this issue present before you installed the Speedball?
You have many, many connections in that amp that are just the stripped wire passing through a terminal with a little solder on it. I would recommend going back and bending all those wires up against the terminals they are passing through (this is the "attach' part of the instructions), then reheat the solder joint and flow a little solder between each wire and terminal where the wire is resting against said terminal.
There are also some leads that aren't well trimmed that may cause some problems. Specifically the area around the 220uF cap by the UF4007 diodes is concerning. If you lay down two of the three power supply caps like we show in the manual and take new photos, I could see much more of the build under there.
I would suspect that the noise you are hearing is related to a power supply capacitor that isn't well connected/soldered. The distortion is most likely a poor solder joint making itself audible.
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No my speedball worked before with a light hum at low volumes that I could usually remove by hitting the amp with my hand. This louder hum and distortion that I am getting now has only happened since I tried to fix the light hum by reflowing solder joints.
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Did you want picture like this?
I added two more angles to the shared folder
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Yeah, you need to bend the leads up against the terminal strips and then reflow the solder joints. I've circled potential issues in that photo; I wouldn't ignore any of these.
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I did the "chhopstick test" and when I pushed the capicitors there was a crackle and pop when I touched any of the capitors.
I have reflowed all of the joints you have circled and now none of the capicitors crackle and pop but the buzzing is still there.
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Just reflow every joint. That is the first thing we would do if you sent it to us for repair.
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I tried reflowing all the joints and the buzzing still persists. 'll get my friend to look at it and see if he can see any bad solder joints.
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Can you post updated photos of your amp?
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Here is a folder with some updated pictures: https://drive.google.com/drive/folders/1WvB65H1B09iLaMLstBxhV_yOqtW_AzUq?usp=sharing
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There are still many, many leads that need to be trimmed and resoldered.
A hum that is resolved by hitting the amp with your hand is a loose connection.
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The circles in green are connections that could make for noise issues. Those in red are more of a safety concern.
The circle around the headphone jack is the red wire not looking lit it was wrapped/soldered in another photo.
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Thanks for all your help. It is 10pm for me so I'll give this another go tomorrow and get back to you with the results.
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Based on your pics, it looks like the washers on the input jacks are in the wrong order. The washer with the metal ground tab should be sandwiched between the plastic washer and the nut. It looks like you have this reversed, with the ground tab washer sandwiched between the chassis and the plastic washer. If so, the ground tabs on both Red and Black inputs may be isolated from the shell of the input jacks or only making intermittent contact.
cheers,
Derek
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It is 2AM and I thought I would check the forum to see if anyone had posted any other ideas and when I saw your washer comment I could not go to sleep without seeing if this was the problem. It was 100% the problem and I don't even have buzzing at max volume now! I can't believe I made such a stupid mistake.
The real question now is why my amp worked for a year without having this buzzing issue.
I have tidied up my cabling anyway as suggested.
Thanks for your help
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Good stuff!
The amp could sound fine even with the washers reversed if the inside edge of solder washer was pulled up against the outside edge input jack shell - but then sound lousy if moved just a fraction of a millimeter. Simply removing or inserting RCA interconnects might break the contact.
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I wrote this post because I managed to make my amp worse when trying to fix another problem though.
This problem is that there is a low but noticeable when there is silence in movies etc hum in the left channel only.
This does not change in intensity when changing volume and is present with the volume is set to 0. This is the hum I can make go away sometimes if I hit the top of the large tube amp.
Should I still try and touch up the areas circled to try and fix this? Should I create a new thread or is this one fine?
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I would definitely do as PB suggested and try to get those leads crimped to (or at least bent tightly around) the terminals/lugs and resolder them.
A hum that goes away for a while when you bang the amp may be a less than perfect ground connection. I would take a screwdriver and wrench or pliers and go around and tighten all the nuts/bolts that are used as ground connections -- i.e., any spot that connects a wire to the chassis. I solved a hum problem that way in my Crack.
If crimping/resoldering and tightening ground connections doesn't solve the problem, I would look at whether it is a problem with the left interconnect (try switching left and right interconnects) or maybe a function of the amp or even just the left interconnect being too close to the tv or some other source of interference.
But that's all I can think of -- I'm just a novice audio DIYer. PB is the expert on these things. He will have more ideas.
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Another idea: if you're whacking the large tube and that makes the hum go away, the tube socket may have a flaky connection with one of the tube pins. Doc B. has posted numerous times about the potential benefits of cleaning and polishing the tube pins. But even repeatedly removing and inserting the tube could do the trick - essentially you;d be scraping some of the tarnish off the points of contact to expose clean metal.
If it's a loose tube pin socket, you can tighten the sockets (after powering down and waiting a bit) -- I can;t remember the structure of the Crack tube sockets. Depending on structure, you'll either have to GENTLY pry a contact plate towards the center of the pin hole or GENTLY crimp the metal socket to make a more snug fit for the pin. Either way, the goal is to make the socket grab the pin a bit more tightly.
Good luck!
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This is the hum I can make go away sometimes if I hit the top of the large tube amp.
This is still a loose connection.
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I ordered a Tung Sol 7236 tube because I was pretty sure the tube was causing the humming. As it turns out the humming has gone with the new tube and I have not heard any background noise in the hours that I have listened today.
One weird thing I noticed was that this tube seems to pick up interference from my mobile phone from further away than the old tube. Is this normal? Before I would not have any noise when my phone was also on my desk but now it needs to be around a metre away or I occasionally get bleeps.
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I rolled in a 6AS7G today and picked up interference from a cell phone I hadn't before so I don't think that's too strange.
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Yes that is normal. Cell phones radiate pretty strong signals and it is best to keep them some distance from tube electronics. The 7236 has somewhat less negative gain in a cathode follower (higher mu) than a 6080 and thus the output level will be somewhat higher for any signal, noise or music.
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Thanks for the help. I've set this thread to resolved now.