Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: keithpgdrb on November 30, 2013, 10:43:29 AM
-
I picked up a used Crack amp. I am doing the manual corrections outlined in the threads here. Question about this one in particular.
"Page 19 - you could change 2" wire from power trans terminal 4 to 22L at the bottom of the page to 3" and connect it to terminal 14U rather than 22L. It will work either way, but this may give a slightly lower noise floor. (This is mostly correct after 4/26 but manuals labeled 4/26/10 say mistakenly 15U rather than 14U)"
As I did not assemble this crack originally, I do not have any extra hookup wire from the build, and the existing 2" wire is just a little too short to just make the run.
So.. I do have the thinner wire that came with the speedball upgrade. would that be ok to use?
OR
Option 1 - 12 wag stranded household wire, 600V nylon coated. There is also a bunch of information on the wire that I don't understand.
Option 2 - 14 awg solid core household wire, 600V gasoline and oil resistant coating. lol.. and again, a bunch of other information I don't understand.
option 3 is a roll of solid core hookup wire I got from radio shack. 22 awg, UL recognized, whatever that means, and no idea of voltage
Can I use any of this for this 3" connection? any help would be greatly appreciated.
-
Does the Crack work?
-
Yes, the crack works. But I would like to lower the noise floor, and there is a little bit of a hum in the right channel that I plan to deal with. Going to start by reflowing all the solder joints after I do the corrections.
also, need to get a new power tube. I have 3, and all of them make noise. driving me nuts.
-
I would go with the thinner wire that came with the Speedball upgrade. Bottlehead wouldn't send wire that wasn't up to the voltage and current requirements of the Crack.
BTW, stranded is a nightmare in a kit as the strands don't behave well.
I'll admit I am a little wary of using the thin wire that came with the speedball. maybe its thinner because it doesn't see the voltage the other one does. I just want to do what is best for the connection. I tried to write Doc about this, but I have no idea if my message went through, because I haven't gotten a response.
-
The thin wire is fine. There is no more than 200 milliamps (.2 amp) flowing anywhere in the Crack except the filaments.
Wire guage is not about voltage, it's about current. Insulation is about voltage.
Go ahead with that transformer wire swap, it might help. You can use that 22g radio shack wire, it will be fine.
-
I used the radio shack wire, don't really hear any change. it shouldn't make it worse right?
I am noticing the electrical noise is fairly prevalent. I really want the black background I hear about. going to have to do some reading on what to try next.
-
Post pics of the underside - there may be something obvious that needs to be moved around or adjusted.
-
Thank you..
will get that pic up tomorrow. Here's a separate question. I know I got a little over zealous when I was soldering up the speedball boards. I tend to use too much solder, and a little bit starts to ball up on the "wrong" side of the board. would this cause noise? or is just sloppy soldering? I planned on fixing in anyway.
-
That's probably not concerning. To get those out, I generally just reheat the joint and use gravity to let it run back through the hole.
-PB
-
That's probably not concerning. To get those out, I generally just reheat the joint and use gravity to let it run back through the hole.
-PB
thats what I was going to do as well. do you just want a overall pic of the whole underside, or a specific section? I just snapped one with my phone, and its hard to see anything I would think. I'll do it in the daylight tomorrow.
-
Here's a pic.
my symptoms right now are:
general slight hiss after about 8 seconds after turn on.
something that sounds like a ground buzz in the right channel that gets louder as the volume is turned up.
-
I'm not super excited about the twisted pair of wires leaving power transformer terminals 4/5 and going to B7/B8. In the manual, those run along the chassis plate, then pop up to pins B7/B8. In your photo, these wires float up and over the octal socket. You could pop the wire off B6 and likely smoosh them back into place.
There's something kinda funky on the back of terminal 5, though I can't tell what it is. It kind of looks like there's some stranded wire?
I'd slide the input wiring away from the power transformer. It may not make any difference, but it won't hurt anything.
I don't remember if it was your post that received the suggestion, or another user, but with 470K at the input, you are up high enough that noise becomes a bit of an issue. To circumvent this, the 470K value can be decreased if another pair of resistors is soldered from input to ground on the pot (the outer 2 lugs on each level). For the 470K/100K combo, you're padding about 16dB. If you solder a ~25K resistor across the input/ground on each level of the pot, then use a 100K resistor at the input, you'll have the same level of pad but with a whole heck of a lot less resistance.
As always, try each of these one at a time.
-PB
-
man, you've got quite an eye. I did indeed add the 470k resistors to get more turn on the volume knob. ( a lower value is in the pic) But when I did, the amount of noise remained about the same, I could just move the volume a bit more. I'd have no problem at this point either taking out the resistors or lowering their value. I'll start with the other suggestions tomorrow and take a look at what you were seeing at terminal 5.
-
Here's a closer view of terminal 5. Its not stranded. looks to be the same hookup wire as everything else.
I had to use some radio shack hookup wire to go from terminal 4 to 14u, as I was not the original builder.
I'm going to try to post a sound file link of what I hear as far as buzz.
-
I was eyeballing terminal 5 down by the 9 pin socket. (The terminal all the way over by the headphone jack)
-
here is my repair job. the original builder took some strange wire paths. but when I listened, it seems a that it might be hissing a bit less. interestingly, when I crank the volume, I now hear the ground type hum equally in both channels, but less of it.
I think i am going to start by yanking my resistors I was using to give me more volume control turn. I can always go back and put them in, but I'd like to get things out of the signal path. plus, I didn't really have the proper resistors anyway. and if they might add noise, I want them gone.
-
here?
-
Looks good from that shot.
-
removed the resistors. I do wish the volume had more turn, but since there is no imbalance, I won't worry about it.
The ground type hum is there, but at a high volume level that I would never use.
Still a slight hiss after about 8 seconds. would love to get rid of that, but not sure where to start on that. It doesn't seem to increase with the volume control.
probably time to take some measurements.?
-
The slight hiss is generally typical tube noise. There are certain specimens that will fare better than others. So removing the resistors ended up helping?
-
I think that it did. I had some unexpected improvements. after I shifted and desoldered/resoldered those wires, the ground noise moved from the right channel, to equally in both. But I thought that overall noise was less as well. I would not have thought just routing wires differently would do much. It may have been the resolder as well, but whatever. After I removed the resistors, the ground noise doesn't really become detectable until the volume is Really high. so I'm just left with the hiss right now. I would like to eliminate the ground type noise completely, but thats just my OCD. I know its there, even though it doesn't effect general listening.
The hiss I can deal with if thats just a tube thing. have to fine one though that doesn't sound like there is a fly trapped in the right ear cup, and sitting next to a guitar amp that is feeding back. lol.
Would it be better for me to use the speedball wire that I originally asked about in this thread? I can't imagine the radio shack wire being good, but maybe in doesn't matter in its placement. referring to the page 19 correction.
"Page 19 - you could change 2" wire from power trans terminal 4 to 22L at the bottom of the page to 3" and connect it to terminal 14U rather than 22L. It will work either way, but this may give a slightly lower noise floor. (This is mostly correct after 4/26 but manuals labeled 4/26/10 say mistakenly 15U rather than 14U)"
-
The Speedball wire is very expensive, high quality wire, so I would recommend using that.
Wiring layout is pretty critical.
-
ok, I'll use it. I was just worried about the difference in thickness. its an easy change out.
Thanks for all your help here. Looks like the tube rolling forum is my next stop I think.