[JamieMcC]

  Anyone have issues with the RCA 6AS7G background noise? Mine sounds like a quiet power line. Does it go away with burn in usually? Not a big issue but it is noticeable when I first put the headphone on.

 
Your Crack should be totally silent having had several issues with noise in the past they have all been due to outside influences and it took several weeks to dial them all out . The most frustrating was during the winter I and had a electric oil filled radiator in another room, in the evenings as the thermostat tripped it on it caused interference while heating up then 15-20mins later would trip off and all would be fine it drove me nuts till I figured it out. 
 
I do have a couple of tubes that have a slight noise that can only be heard in the quiet gaps between songs and sometimes that is down to the pairing of the 12au7 not the driver tube. The Speedball upgrade I thought made a noticeable difference to perceived 12au7 noise. Tubes that I had run without it that where very quiet all of a sudden had noticeable noise. So it takes a little fine tuning if you hunt about there are a some posts on this on the bhf

 

[cmander10]

Had the electric noise from the RCA 6AS7G with both an RCA cleartop and Amperex Bugle Boy 12AU7s. The Bugle Boy has a buzz in the right ear so I'm returning it. It seems that the JAN version has less issues with microphonics. Don't know if vacuumtubes.net has any Chantham 6AS7Gs either.
 
And my Crack is completely silent with the stock Raytheon 6080WA, so it must be the RCA 6AS7G.

 

[liamstrain]

I had some background hum/noise with my RCA 6AS7G - it cleared up after a dozen or so hours.

 

[cmander10]

  I had some background hum/noise with my RCA 6AS7G - it cleared up after a dozen or so hours.

I think the noise is purely microphonic noises picked up from the transistor since I can hear a faint electric flow in that area. Unless the microphonics decreases then it will probably stay. 
 
Did you have the standard RCA 6AS7G or the JAN version?

 

[liamstrain]

I have the JAN version.

 

[Barry S]

  @Barry S: That is a very clean build. I like the way you cleaned up around the nine-pin for the Speedball install. After seeing your build, I am seriously considering buying another Crack just so that I can get the wiring that clean. Currently I will really struggle to install the Speedball in my Crack.

Thanks. I assembled the Speedball and read through the installation instructions before I started working on the Crack. Maybe you can redo some of your wiring to help with the Speedball install. I can't imagine you'd have to do that much to make it go in smoothly.

 

[skeptic]

Buzz can sometimes be cured by sanding or deoxidizing the pins. Doc shared this wisdom with me a couple of years back and saved me from binning a nice 1950s rca 12BH7.

 

[grausch]

 
Thanks. I assembled the Speedball and read through the installation instructions before I started working on the Crack. Maybe you can redo some of your wiring to help with the Speedball install. I can't imagine you'd have to do that much to make it go in smoothly.

Yes, I like the planning that you put into this. I built mine exactly as per the manual, and if there is one weak spot in the manual I would say that the routing of cables and the two caps on the terminal, could have been done differently to make upgrading to Speedball easier.
 
Since it was my first build, I managed to nick some cables and capacitors with the soldering iron and being the perfectionist that I am, it bugs me. Would be nice to have a fresh attempt at another one and get everything really perfect. However, I can just replace the offending wires, and I am planning on upgrading some caps as well, so I might just go that route. Only problem I foresee is that I made sure I had excellent mechanical connections before soldering, and desoldering and removing those can get tricky.
 
Shouldn't complain though, the Crack sounds excellent, I have no hum, no noise and no channel imbalance. I really struggle to see how the Speedball upgrade can make this amp sound better. I have not heard a lot of headphone amps, but to me it is the best I heard by far.

 

[listen4joy]

i am in the middle of bulding a crack and i have 2 questions.
 
in the crack guide page 19

what should i do the the revision or what in above? its written that revision will give me more quiet opreation is it true?
 
 
the second thing that my little tube (12au7) is look like she is burned. on side has nothing and other side have blck grey thing with leak down that look like its burned
 
pics
 
1

 
2

 
3

 
 
vids
 
http://tinypic.com/r/ddl5xf/8
 
 
http://tinypic.com/r/312ehau/8
 
thnx for help!

 

[grausch]

I wired mine to 14U as the revision stated quieter operation. I did not want to desolder and I know that 14U can get crowded. Depending on how you decide to do this, you might need to use 14U from the beginning as desoldering there can be a pain.
 
W.r.t. the 12AU7, mine also looks a little burned on top. I have no issues with the tube.

 

[Doc B.]

Moving the wire is simply an option. It really makes no difference, it just makes the grounding for that point follow our grounding phlosophy a little more closely. It is theoretically better but I doubt you could measure or hear a difference.
 
The silver flashing you see in the top of the tube is the getter. It is supposed to be there.
 
Don't worry, be happy.

 

[mithrandir38]

i am in the middle of bulding a crack and i have 2 questions.

in the crack guide page 19


what should i do the the revision or what in above? its written that revision will give me more quiet opreation is it true?


the second thing that my little tube (12au7) is look like she is burned. on side has nothing and other side have blck grey thing with leak down that look like its burned

pics

1



2



3




vids

http://tinypic.com/r/ddl5xf/8


http://tinypic.com/r/312ehau/8

thnx for help!

I would say don't do the revision. That post gets really crowded with that extra wire in there.

 

[Utopia]

Has anyone here tried to use the Crack as a preamp? I know the possibility has been mentioned here, as well as over at Bottlehead. Perhaps it'd be great with low impedance headphones, like Hifimans, with a small power amp in between?

 

[liamstrain]

I don't think it would work very well, with the output impedence as high as it is. Better off getting the BeePre or similar, if that's what you need. 

 

[Doc B.]

  I don't think it would work very well, with the output impedence as high as it is. Better off getting the BeePre or similar, if that's what you need. 

???? The output impedance of Crack is exceptionally low for a tube output line level device. In fact it is lower than any of our purpose made preamps. The circuit works fine as a preamp except for the lack of selectable inputs and the fact that it has an RCA jack at the output. In fact the topology is somewhat similar to our old Foreplay preamp. I do think the Smash works better as a preamp for the same kind of money. And of course there is also the possibility of using the S.E.X. amp for both low and high impedance headphones.