Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: Incendie on March 28, 2019, 04:24:51 PM
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I noticed that some of my connections were left unsoldered so I went back to solder them in, but afterwards I noticed a few peculiar things:
1. I re-did the voltage checks at the end of the manuals and pretty much every terminal is at double the voltage of the top range mentioned in the manual (the 0V is at 120V so maybe it wasn't double but +120V)
2. One or some of the capacitors still hold charge. I found this out the hard way when I tried to clamp a wire to its lead and it sparked. I measured the voltage of some capacitors after unplugging them for 24 hours and they still measured 1V across.
The result is I heard a constant buzzing and my right channel doesn't work.
I have no idea how to troubleshoot this. My initial guess was that there was some disconnect somewhere because the capacitors maybe didn't have a load across them to discharge, now my guess is there might be a short circuit somewhere.
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I would recommend posting photos of your build. It's almost certain that you have grounds that aren't well connected. These are the black wires that start at the RCA jacks and run up to the front of the amp, then to the headphone jack, then back up to the power supply. I would bet you have one loose black wire at the headphone jack.
Also, you have failed your voltage checks. Your amp doesn't work. Attempting to use an amp that you know isn't working is a very poor decision.
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I will go back and double check the grounds, but I'd appreciate if you don't just assume I'm some sort of idiot. Like I said, I WENT BACK to double check the connections, as in it was working ever since I finished it. This means that it obviously passed the voltage checks before I started using it and something I did when "fixing" it must have done or changed something. I came to this forum with a question because I needed help, not because I was looking to be put down.
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If you look back at your initial post you may find that it is not clear what state the amp was in when you found the problem. No one is even remotely assuming you're an idiot. PB was simply giving you the most logical approach to solving the problem. You have a loose ground somewhere. We always recommend not running the amp again until you have that connection resoldered because headphones could be damaged. It takes just a few minutes to go over every connection and reflow it to make sure every wire attached to a terminal is well covered with solder. That's one thing we always do when an amp comes into us for repair.
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as in it was working ever since I finished it. This means that it obviously passed the voltage checks before I started using it
This is new information, but it's still most likely a loose connection, but I would be looking a lot more closely at the black wires in the power supply (the section built on the power transformer), as well as the connections of the 270 ohm resistors. An amp that passes its voltage checks but is noisy will also tend to indicate that one of the 220uF caps isn't properly soldered.
My advise was intended to be more of a public service announcement. We have had more than one customer fail voltage checks then proceed to use their headphones anyway and toast the drivers. One gentleman in particular put a coupling cap in backwards, had 80V or so on one of the outputs, then proceeded to plug every pair of headphones he owned into the amp to try and listen to it. Ever since that even in particular, I try to remind folks that this can happen.
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I apologize for immediately being defensive, but when I saw "Also, you have failed your voltage checks. Your amp doesn't work. Attempting to use an amp that you know isn't working is a very poor decision." it sounded very condescending, but I do realize that I had not provided that this amp was working beforehand.
Pertaining to checking the connections, I found more loose wires and have soldered them to their sockets. The voltage check still fails the same way: most of the expected 0V terminals are at 120V, the 170V (T2, T4) expected are instead at 420V. I should also mention that I have the Speedball upgrade.
I also re-did the resistance check at the end of the Crack manual:
T1 - 194kΩ
T2 - Creeps up to 0.9MΩ and fluctuates
T3 - 0Ω
T4 - Creeps up to about 0.8MΩ and fluctuates
T5 -194kΩ
T6 - 2.45kΩ
T7 - Creeps up past 300kΩ
T8 - 0Ω
T9 - Creeps up past 1.5MΩ
T10 - 2.45kΩ
T13 - Creeps up past 100kΩ
T14 - 0Ω
T20 - 0Ω
T22 - 0Ω
B3 - Same as T7
B6 - Same as T9
OB - Creeps past 600kΩ
OA - Creeps past 1.2MΩ
Voltage Checks:
T1 - 150V
T2 - 420V
T3 - 0V
T4 - 420V
T5 - 167V
T6 - 0V
T7 - 254V
T8 - 0V
T9 - 240V
T10 - 0V
OA - 253V
OV - 240V
G - 0V
B+ - 420V
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T6 - 2.45kΩ
T7 - Creeps up past 300kΩ
T9 - Creeps up past 1.5MΩ
T10 - 0Ω
T10 is showing a proper connection and T6 is not. This suggests a grounding issue at the headphone jack.
Normally I would suggest pulling the Speedball and putting the loading resistors back in, but it's pretty clear that you have a black wire in your kit that is loose in its terminal or not well soldered, so you'll have to keep checking them over to fix that issue before proceeding. It is also worth asking what your AC line voltage is and what you wired the transformer for, though this is 99% not the problem in your amp.
There are about 8 solder joints where black wires go, just reheat them all.
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There are about 8 solder joints where black wires go, just reheat them all.
This. It takes less time and energy to reflow them all than it does to fiddle around trying to sort which one is bad and guessing wrong.
Speaking of using the least amount of energy to reach a solution, this reminds me of an interesting exchange with an ebay seller a couple days ago. The seller had posted a stock image of a used item he was selling, that was fairly expensive and listed as "no returns". I asked if he had a picture of the actual item he could send. He answered back a couple hours later that the item looked exactly like the stock photo except that it was sitting on a table with a FOR SALE sign, in front of his RV, next to the remote control, which looked just like the picture, and so on.
I thanked him for his taking the time to compose this lengthy reply with no picture and suggested it would have taken a lot less work to just send a picture. And then removed the auction from my watch list.
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T6 - 2.45kΩ
T7 - Creeps up past 300kΩ
T9 - Creeps up past 1.5MΩ
T10 - 0Ω
I apologize, that was a typo. T10 is also at 2.45kΩ. I will edit the post. Also, would it not make sense for these connections to have resistance since it is the resistance of the resistors at the headphone jack? I tried reflowing the ground (black) connections and they still read the same, at 2.45k.
Here are a few photos: https://photos.app.goo.gl/64gx1oGtw7YQuRvA8
Also, I have 120V coming out of the wall and was following those directions.
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How old is this kit? This would make sense if the kit is more than 3 years old, but not for the Crack 1.1.
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It's the 1.1 and only about a year old.
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I apologize, I didn't realize I had my headphone adapter plugged in. Took it out and the two terminals now read 0, but the voltages remain the same.
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Can you measure the DC voltage between terminal 3 and each of the terminals on the 6 lug strips that have a black wire on them?
-PB
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Apologies for the late reply, I had a tournament to play in this weekend.
Difference (DC, not AC) between T3 (middle of the 5-lug strib near the POT) to:
T11 - 0V
T12 - 0V*
T13 - 190V
T14 - 0V*
T15 - 202V
T16 - 0V
T17 - 0V
T18 - 73V*
T19 - 10V
T20 - 0V*
T21 - 215V
T22 - 0V
* = Lugs with black wires attached
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You have 190V at T13 and 420V at T2? (I'm betting you do not)
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You're right. I redid the voltage checks and realized that I must have been reading it as VAC instead of VDC because here are my results:
T1 - 71V
T2 - 192V
T3 - 0V
T4 - 192V
T5 - 77V
T6 - 0V
T7 - 117V
T8 - 0V
T9 - 111V
T10 - 0V
OA - 70V
OV - 77V
G - 0V
B+ - 192V
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That is a working set of voltages. Buzzing would usually be caused by a loose connection (some of them can be loose and not alter the DC voltages) in the amp. Sometimes loose hardware can also allow this to pop up.
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I just plugged it back in and my right side is still dead. Any ideas as to why?
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Actually, I noticed that if I slowly try to plug the jack in, it's perfect about 3/4 of the way down.
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Nevermind, it loses stereo audio and the left channel feeds to both that way.
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If your voltages now measure OK the next place to start looking is in the signal path. Check over the RCA jacks to be sure the right one hasn't had a wire break. This can happen sometimes when an interconnect cable is inserted or removed if the jack is a little on the loose side. If that is all OK move on to the volume pot and make sure there are no cold solder joints or shorted wires.
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https://photos.app.goo.gl/KD8iyWniNVbf2Hdt8
I checked and reflowed most of the red wire connections, but still nothing. Tried to take a few photos of the connections. I even checked that there's no resistance along the red wire coming from the right (red) input to the lug on the POT.
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The red wire going to the center pin of the RCA jack is not soldered. There is solder there, but it's not flowing around the wire. There could be enough flux in there that the wire is totally insulated.
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https://photos.app.goo.gl/DE6sCWSFJeLZC6UF8
Re-did it and still nothing in the right side
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I was looking over your photos and noticed that the 2.49K resistors on the headphone jack are a bit charred. Was there an issue with the initial build that caused this? If you plug in a 1/4" to 1/8" headphone adapter but no headphones, what DC resistance do you get from ground to 6 and ground to 10?
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I actually didn't notice that they were discoloured like that and I don't remember there being any issues that may have caused that. I'm away from it right now, but last I checked the resistance was 2.45k because that was what caused the original mixup in the resistance checks earlier in this thread.
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There's another set of tests we can do if your meter has a reasonable number of AC scales. Can you post the model of your meter?
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Mastertech MAS830
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Yeah, the 200V AC range won't resolve what needs to be measured. The $20 meter at Harbor Freight will do the job, or if you can borrow one with a 2V AC scale, we can send a tone into your amp and measure where it doesn't exit.
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It took me a while, but I finally got my hands on a new multimeter, the MTP 2322. Let me know if this would be suitable and what needs to be done next.
Thanks
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That meter will do the job. Set it to the 2V range on the AC section. Play a 60Hz tone with your phone into the input of the Crack, then measure the AC voltage between ground and the center pin of each RCA jack.
-PB