New build for two hours then sounds like a distant concert hall [solved]

[phaselock]

Hi All,

After spending 14 hours of of painting the aluminum plate (a first), constructing the wooden base (a first for 15 years), and first time ever soldering I am proud to be hooked on the crack. Thanks Doc, one of the most rewarding projects in my entire life. Thank you.

But after listening for two hours after completing the build, specifically the next night I have turned it on and the musical liquid gold has disappeared replaced with massive recessed concert hall sound, with little to no bass, limited mids and some upper. Basically the mids from a drum, the snare drum and upper vocals.

Specifically for Moby's Extreme Ways -The overall sound stage is recessed, the upper drums and snare are present, the vocals are presented OK but more recessed than the drums, guitar is very distant - it's just all wrong.    ("Oh Baby, Oh Baby, then it fell apart") - I hope that explains it OK, I haven't master the audio lingo yet.

When I built the unit all voltage and resistance tests passed (I don't have a meter on me at this moment otherwise I would check).

I'm wondering what could I check and what could it be.

I have turned the power off, pulled the power cable and pulled the tubes out and reinstall them. That worked for about 2 minutes but has returned to the concert hall effect.

I have replaced the 12AU7 with another that I have had, but no change. I don't have a spare 6080 to try at the moment.

Thanks in advance

[Grainger49]

Since removing the tube and replacing it helped for a while it sounds like the tube pins or socket is in need of cleaning.  Remove and replace the tubes 10 times. 

If this doesn't fix it then it might be a solder job on one of the tube pins.  Retouch the solder on every tube pin.  Don't add a lot, just a touch and when you see the solder on the tube pin flow remove the iron.

Remove the tubes of course before soldering.

[John EH]

My wild guess would be to check the tube voltages.  You said it sounded good at start up.  Maybe pull your voltages at start up and then do them again after the sound gets worse.

If there is no difference in voltages and it sounds good and then doesn't after a few minutes I'd be thinking tube.

John

[phaselock]

Thanks Grainger and John,

The removal and replace worked for a few minutes, but not joy.

I think it is the 6080 or the solder on the 6080 tube pins - I replaced the tubes ten times in isolation and the Crack worked after working with the only the 6080, I will run through the entire resistance and voltage check, and solder if required. Hopefully it is just a dodgy solder and not the 6080.

The biggest problem is I will have to wait for the weekend to try or even longer if it is the tube. Oh well. I need to stain the wood anyway, now have the time to complete that task

Cheers

[John EH]

The good news is the 6080 is an inexpensive tube.  I ordered an RCA and 5 JAN Phillips tubes.

The bad news is even though I was prepared to do all this tube rolling the Sylvania tube that came with the Crack kit sounds far and above the best to my ears.

But it is always a good idea to buy a spare tube or two on ebay or somewhere when you order the Bottlehead kits.

John

[phaselock]

Yeah, I'm hoping that it is just the solder.

But it might be an excuse to fork out for a 5998

Jim

[Paul Birkeland]

Do check your voltages and let us know.

-PB

[STURMJ]

I recently had the same effect in my cigar box quickie. In that case it was one of the input wires shifting over and touching the other creating a short. So check at the pot to make sure bare wires have not come into contact with each other.

[Doc B.]

This kinda sounds like a polarity issue. Is one channel somehow out of polarity with the other and thus 180 degrees out of phase? I'm not picturing how that could happen intermittently with hard wiring and a headphone jack, but the sonic description fits.

[phaselock]

Solved. 

In the end it was a bad solder on the right channel 2.49 K resistor, the one connected to the headphone jack specifically the outboard sleeve terminal solder.

The damn thing was intermittent to the end. It gave false positives from the U6 cap solder, the L6 wire solder, and the inboard ring terminal solder. Made a mess to the neat original solder job too.  .

Well it looks like I don't have an excuse to purchase a 5998.

So far so good 30 minutes in. 

Thanks for the responses! Cheers.

[4krow]

 Sturmj,  I had a similar thing happen during a project. The strange part was that in my case, a bare wire was touching the body of a metal film resistor, causing that channel to sound louder. Still doesn't make sense to me, but when I lifted the wire away from the resistor, problem was solved, and still works fine to this day. Kits have a way of teaching like no other.

[phaselock]

Bummer,

Same problem is back, let it cool down over night and decided to enjoy the music in the morning, no joy.

Such a pain.

Edit: Both resistance and voltage test passed, now I'm really confused. ( could the Crack pass the tests with the board upside down but fail when right side up? )

I didn't see any indication of a wire connected to the plate.  As a newbie could I have heat damaged a component?

I have try running with only one channel connected via RCA, same problem.

Is it worth swapping the 6080?

Sorry guys, as the tree said to the lumberjack... I'm stumped!

[phaselock]

Ok,

So a tried testing again whilst testing voltage, I discovered that terminal 15 is now 0V, and I accidentally bridged terminals 20 and 21 while testing so I'm assume 206v was bridged for a fraction of a second. Gez I jumped 6 feet when the sparks started to fly  , I'm glad that my friends multimeter was fused! I didn't try getting a reading from terminal 21 again and won't until I purchase some clip leads.

Could 0V at terminal 15 cause this problem? The voltage on the value slots have been consistently passing.

I have tested the diodes and resistors around the transformer for damage, but it appears the components are ok.

Thanks in advance,
Jim

[John EH]

Check the resistor from 15 to 21 and see if it's still good.  270 ohnm.  And you need that voltage check at 21.  You've got a straight shot at 21 from the side.  Put the red lead steady on 21 and then power the amp up or have somebody power it up for you.  Then touch the black lead to chassis somewhere.

Check and see if you have 100v coming off of terminal 9 on the transformer as well.

[phaselock]

Check the resistor from 15 to 21 and see if it's still good.  270 ohnm.  And you need that voltage check at 21.  You've got a straight shot at 21 from the side.  Put the red lead steady on 21 and then power the amp up or have somebody power it up for you.  Then touch the black lead to chassis somewhere.

Check and see if you have 100v coming off of terminal 9 on the transformer as well.

Thanks John,

I think you are right, after getting the confidence to try again I went through everything.... and I think I have shorted at least the Diode from T19 to T21, on top of the probability that I originally has a dodgy solder somewhere along the Transformer T9, T19, Diode, T21, 270 Ohm, T15 path.

I have the 240V version, Transformer 9 is delivering 78V, T19 gets 78, but nothing on the other side of the Diode.

Full Details are:

Resistance Test Results:

T01  *         T11  0      T21  No Reading
T02  *         T12  0      T22  No Reading
T03  0         T13  *     
T04  *         T14  0     
T05  *         T15  *     
T06  2.49k  T16  0
T07  2.94k  T17  0
T08  0         T18  No Reading
T09  2.94k  T19  No Reading
T10  2.49k  T20  0

A1 N/A      B1 N/A      RCA Ground   0
A2 N/A      B2 N/A      RCA Left    97k
A3 N/A      B3 2.93k   RCA Right  102k
A4 0          B4 N/A     
A5 0          B5 N/A     
A6 N/A      B6 2.93k   
A7 N/A      B7 N/A
A8 N/A      B8 N/A
A9

Voltage Test Results (after shorted T20 and 21)

T01  76.3    T11  0        T21  No Reading
T02  178.8  T12  0        T22  0
T03  0         T13  178.5     
T04  178.6  T14  0     
T05  76.6    T15  No Reading     
T06  0         T16  0
T07  104.6  T17  0
T08  0         T18  83.3
T09  104.3  T19  78
T10  0         T20  0

A1   75      B1   76
A2   0        B2   178.8
A3   1.5     B3   104.7
A4   0        B4   76.4
A5   0        B5   178.8     
A6   76      B6   104.5   
A7   0        B7   0
A8   1.5     B8   0
A9   0

I believe the current problem are shorted Diodes on T18, T19, T20 and T21 (or at least the T19 to T21)
and probably solder issue.

Specific voltage across T19, over the Diode, to T21:

T19 --(78V)--> ->|- (No Reading) --> T21

Umm, If think I need some spare parts... and now understand why Dan he is called the Doc 

I hope I haven't screwed anything else.

Thanks again John.