First time solderer. Amazing experience

[haihaowu]

Never soldered a thing before in my life.  Followed the excellent manual almost religiously (e.g., putting one hand in pocket while testing voltage ).  Took me 6 hour straight to build the kit and another hour testing.  Miraculously everything tested out except finding one cold joint.  Plug the Sennheiser HD 650 and music heaven fell upon me.  Beautiful, beautiful, beautiful.  Not just one or two songs but all the genre I threw at the crack from Adele to Andrew Bocelli to Hefeitz to some Tibetan singer.  Simply amazing.  Compared to my old setup but with Aune T1 as the DAC/amp combo (now I am just using Aune T1 as the DAC), the crack opens up a brand new level.  Thank you Bottlehead for the amazing kit and the instruction!  Will try the speedball upgrade in a few weeks after thoroughly enjoying the current one.

One question: there's a deep hum on the right can.  Barely affect music quality when music is playing.  The hum is there whether there is source plugged in or not and doesn't change a bit when turning the volume knob.  I read the Kent Crack thread and seems that Bryan's hum noise is fixed by re-soldering the capacitors.  I indeed had difficulty solder the capacitors, so I will double check tomorrow.  Also noticed the manual says "Deep hum without any buzz ... Usually a touch up of the hum balance pot will eliminate it".  I have no idea what is the "hum balance pot".  Googled it quickly but didn't find relevant information.  Can someone kindly tell me what/where is the pot?  Also, any other suggestion to eliminate the hum sound?  Thanks in advance!

 

[Grainger49]

Crack has no hum balance pot.  Is there mention of the hum balance pot in the Crack manual?

 

[haihaowu]

Crack has no hum balance pot.  Is there mention of the hum balance pot in the Crack manual?

Thanks for replying.  Yes, in the troubleshooting section.  Top of P42.  Too bad.  Will see if warming up killed the hum overnight.  If not, will try to resolder the capacitors.

 

[Grainger49]

Ok, opening the manual I have...

Those are generic tips.  It says on DHT amps (Direct Heated Tube), Crack is indirectly heated.  That is confusing. 

Hum is often a ground or signal path problem.  I have posted the Crack Ground and signal common path in a couple of threads.  I should do a tracing of the audio path to go along with that.

Here is the ground path.  You want to touch up every connection.

The start of the grounding points is terminal 3.  Clip one lead of your meter to this terminal, better yet the chassis itself.

It jumps to the 2 left lugs of the volume pot, measure both lugs.  Then it jumps to the back to the RCA jacks.  Measure to the outer jacket of the RCA jacks.

From the top left lug of the volume pot there is a grounding jumper to the two bottom lugs of the headphone jack.  The jack in the picture may be different than what is being delivered today.  Measure to both headphone jack lugs.

The power supply ground comes from those bottom headphone jack terminals to terminal 12.  Measure to terminal 12.  From there it jumps to terminal 14 and ends at terminal 20.  Measure to both.

Also from terminal 3 you go to the center lug of the 9 pin tube socket.  This is the ground route for the LEDs in the cathode circuits.  Measure here.

The heater (AC) supply gets its ground from a wire from transformer terminal 4 to terminal 22.  Measure both.

Other points that should be a solid ground are pin 8 of the large tube, pin 4 and 5 of the small tube, T8, T11, T14, T16, T17, T20, T21 T22 and the ground post on the IEC power connector, the one with the bare wire to the chassis.

 

[haihaowu]

Great.  Will give this a try today and let you know how it turned out!

Saw the other post about the almost identical symptom.  May try swapping the tube too.

Ok, opening the manual I have...

Those are generic tips.  It says on DHT amps (Direct Heated Tube), Crack is indirectly heated.  That is confusing. 

Hum is often a ground or signal path problem.  I have posted the Crack Ground and signal common path in a couple of threads.  I should do a tracing of the audio path to go along with that.

Here is the ground path.  You want to touch up every connection.

The start of the grounding points is terminal 3.  Clip one lead of your meter to this terminal, better yet the chassis itself.

It jumps to the 2 left lugs of the volume pot, measure both lugs.  Then it jumps to the back to the RCA jacks.  Measure to the outer jacket of the RCA jacks.

From the top left lug of the volume pot there is a grounding jumper to the two bottom lugs of the headphone jack.  The jack in the picture may be different than what is being delivered today.  Measure to both headphone jack lugs.

The power supply ground comes from those bottom headphone jack terminals to terminal 12.  Measure to terminal 12.  From there it jumps to terminal 14 and ends at terminal 20.  Measure to both.

Also from terminal 3 you go to the center lug of the 9 pin tube socket.  This is the ground route for the LEDs in the cathode circuits.  Measure here.

The heater (AC) supply gets its ground from a wire from transformer terminal 4 to terminal 22.  Measure both.

Other points that should be a solid ground are pin 8 of the large tube, pin 4 and 5 of the small tube, T8, T11, T14, T16, T17, T20, T21 T22 and the ground post on the IEC power connector, the one with the bare wire to the chassis.

 

[haihaowu]

After a month of out of country travel, I finally sat down to fix the static humming thingy.  Hope others who run into a similar problem may benefit from my experience. 

I tried Grainger's suggestion of testing the ground path.  Everything tested out fine.  (except Granger mentioned T21 port in his post but that was most likely a typo, 'cus T21 shouldn't be ground).  I then followed the suggestion of another post in the forum by re-soldering the three big capacitors.  Somehow that miraculously fixed the humming thingy.    I should mention that I did have difficulty fitting and soldering the capacitors during the initial assmbly although the resistance and voltage tests all passed.

I am so happy that the Crack is finally producing perfect music!  Speedball next.

 

[Grainger49]

The ground path is now a sticky in the Crack folder.  T21 has been corrected.

The cap leads are difficult to fit into the terminal strips.  But, you only have to do it once, or twice.  They should never give a problem again.

Another recent poster was getting scratchy noise and it was his digital server being too close to the Crack.  Anything like that, digital servers, PCs or cell phones can inject noise into a tube.  Remember, when tubes were first made these things didn't exist.

 

[haihaowu]

Thanks a lot for your help!  Happy new year to you.

The ground path is now a sticky in the Crack folder.  T21 has been corrected.

The cap leads are difficult to fit into the terminal strips.  But, you only have to do it once, or twice.  They should never give a problem again.

Another recent poster was getting scratchy noise and it was his digital server being too close to the Crack.  Anything like that, digital servers, PCs or cell phones can inject noise into a tube.  Remember, when tubes were first made these things didn't exist.