I swear baby, this has never happened before (please help me, Crack won't work)

[Todd R]

The Crack is my 7th  (or 8th if you count the Paramount as 2) Bottlehead kit.
Everyone of them has worked right out the gate except this one.

I hear music faintly in only the left channel if I turn it up all the way. Basically no sound.

I will list only the resistance & voltage checks that differ significantly from the manual.

Resistance, terminal with meter set to the 200K scale:
1 - 22.6
2 - .5
4 - .5
13 - .5 steady

Voltage. Little confused here because it says clip it to terminal 12, but then it says reconnect to ground buss. Which is it?
I used terminal 12 and got basically 0 volts everywhere except...
19- 76.9
21 - 206
A1 - nothing, no wire is connected there.

Will go back & try again using ground buss this time for voltage readings, but for now does anyone have a clue where to start looking?
TR

 

[Dr. Toobz]

The manual has 2 errors I can see: there is a wire that should go to A1 that is going to A2 in the instructions, and the resistor going from the output of the rectifier bridge should go to pin 21, not 22 as in the manual. I caught the A1 error, but not the power supply one, until I got no voltage and realized (when looking at the schematic) that the manual had the resistor going to 22, which is chassis ground.

Interestingly, the Crack is about the 7th BH thing I've built (if you include CCS boards, upgraded irons and 4 amps) and is the first time I've ever had something not fire up right away on the first try. I pride myself on meticulous build skills, so it's a real letdown when it happens! The first clue for me was that the cathode LED's weren't lit, even though the heaters were. Then, I got a nice spark from the first power supply cap, which then made me realize that it wasn't being bled and therefore, the problem was just after that. All resistances checked out normal, though, so you may have a slightly different issue. Make sure to check all of the usual suspects, such as component polarity, unsoldered joints, shorts, etc. It's easy, even for an old-timer, to overlook the obvious.

 

[Todd R]

Dr.
The wire going to A2 instead of A1 makes sense to me. As for the resistor that's going to 22 instead of 21, shouldn't the black wire from terminal 4 of the transformer move to 21 also?

 

[Doc B]

Guys, I will have to sort the typos in the manual when I get back in the office tomorrow. The photos are of a working prototype, so you can be confident that the way that it is wired in the photos will work.

 

[Grainger49]

  .  .  .  
The manual has 2 errors I can see: there is a wire that should go to A1 that is going to A2 in the instructions, and the resistor going from the output of the rectifier bridge should go to pin 21, not 22 as in the manual. I caught the A1 error, but not the power supply one, until I got no voltage and realized (when looking at the schematic) that the manual had the resistor going to 22, which is chassis ground.

My emphasis in the above quote.  Shorting the B+ to ground or common is a bad thing.  I suppose that this didn't blow the fuse.  But it will yield pretty high current.  

Do check the resistance of the power supply resistors while making the wiring change.

 

[Dr. Toobz]

Guys, I will have to sort the typos in the manual when I get back in the office tomorrow. The photos are of a working prototype, so you can be confident that the way that it is wired in the photos will work.

The photos are indeed correct - ideally, people should look at the manual, consult the photos, then look at schematic in case there are any questions. I couldn't see the photos all that well, as my contacts were out, but I had the text zoomed up (contacts make it harder to focus on something 4-5 inches away, but without them, I'm basically blind!).

 

[Dr. Toobz]

Here's some more specific info on errata: on page 23, it says "Cut a 12‖ (50mm) piece of red wire and strip both ends 1/4‖ (6mm). Attach and solder one end to A2. Attach the other end to terminal 5U." The arrow, however, clearly points to a red wire going to A1 (plate?), which is correct. IIRC, A2 is the grid, since the signal is being routed to it from the 100k ohm pot. Thus, the manual is wrong, but the photo is right (as Doc himself states above).

On page 28, it says "Attach one end of a second 270 ohm 5W resistor to terminal 22U. Attach the other end of the resistor to terminal 15U." This is also incorrect; the resistor should go to 21U. The arrow on the photo points to 21U, but due to the angle of the shot, one can see the number "22" very close by, written with a marker. 22U appears to be ground for the 6.3VAC winding of the power transformer! My fuse didn't last long after this mistake - it blew after fixing the amp, listening to it for the first time, turning it off, and then coming back to listen to it again. A new fuse fixed the problem, and all voltages/resistances/wiring are spot on.

2 errors is not bad for this sort of thing - everybody makes typos. Tracing the schematic on one's own usually fixes them, as in my case.

 

[Dr. Toobz]

shouldn't the black wire from terminal 4 of the transformer move to 21 also?

No!! The black wire from terminal 4 of the power tranny goes to ground. Note the "0V" on the label. It has and should have absolutely nothing to do with the resistor we've been discussing, which is hot, part of the separate HV circuit (i.e., B+), and helps form a filter network after the diode bridge.

 

[Todd R]

OK Running now!
Moved the red wire that goes to 5U to terminal A1 (which if I was thinking, should have realized it wasn't wired symmetrically since it's a dual triode)
And,
Moved the resistor from 22U to 21U.
Now to hook it up to the main system & do some listening tests. 

 

[Todd R]

shouldn't the black wire from terminal 4 of the transformer move to 21 also?

No!! The black wire from terminal 4 of the power tranny goes to ground. Note the "0V" on the label. It has and should have absolutely nothing to do with the resistor we've been discussing, which is hot, part of the separate HV circuit (i.e., B+), and helps form a filter network after the diode bridge.

DOH!
Thanks, been a long day. 

 

[Dr. Toobz]

Ok! Now we're talking. So, what do you think of the amp?

 

[Todd R]

I like it.
It can definitely run with the big dogs. Incredible, especially when it only costs $199!
I kind of expected a similar sound to the Wheatfield HA-2 that I just sold since it uses the same 6080 tube, but it's cleaner & more detailed.

I'm going to guess that this amp inverts polarity? Just based on listening while flipping the phase switch on my DAC.

 

[Paul Birkeland]

Yes, the Crack is an inverting circuit.  Oddly enough, I have been screwing around with this type of circuit for several years, but it wasn't until going completely solid state in the power supply that the circuit snapped into focus. 

 

[Dr. Toobz]

Yes, the Crack is an inverting circuit.  Oddly enough, I have been screwing around with this type of circuit for several years, but it wasn't until going completely solid state in the power supply that the circuit snapped into focus.  

So, does this mean that one would benefit from switching polarity on DAC's that allow it? What would be the sonic difference between observing polarity vs. reversing it?

 

[Grainger49]

Some folks are sensitive to inverted absolute polarity and some are not.  Second verse, some albums preserve absolute polarity and some do not.  

I hear it best in the "tick" of a drum stick on a cymbal.  You can hear it in the pluck or pick of an instrument's string.  A number of folks hear it in voices.  If you don't hear it and don't want another neurosis, relax.  Sadly I hear it and have more than my share of quirks already.

Edit:  One more thing, absolute polarity is a problem with all sources so I have found it best to just swap both speaker leads.  That is why I use dual banana plugs at the amp.

 

[Paul Birkeland]

So, does this mean that one would benefit from switching polarity on DAC's that allow it? What would be the sonic difference between observing polarity vs. reversing it?

You could try it, this is very subtle and IMO way, way less obvious on headphones than loudspeakers. 

 

[Todd R]

Yes, the Crack is an inverting circuit.  Oddly enough, I have been screwing around with this type of circuit for several years, but it wasn't until going completely solid state in the power supply that the circuit snapped into focus.  

So, does this mean that one would benefit from switching polarity on DAC's that allow it? What would be the sonic difference between observing polarity vs. reversing it?

What I hear is slightly better transients/dynamics but the easiest place for me to hear it is on a cymbal decay. When it's wrong, the decay cuts off early, when it's right, it lasts longer. It's pretty subtle most of the time.

 

[Dr. Toobz]

I've played around with the switch before on my DacMagic, and could discern a difference, but never could tell what that difference was and could not reproduce it between recordings. This was on my S.E.X. amp with the same headphones (Beyers). I'll try playing around with the DAC when I go home to see if it makes any difference through the Crack. (On a related note, I had planned on selling the thing and just taking the output from my iMac's headphone socket, but the iMac headphone output has all sorts of high-pitched, squeaky "computer noises," and hiss is evident at high volumes. It's too bad that it will take holding on to a $400 DAC (whose sound I've never been all that thrilled by - it sounds a lot like any other digital source I've used, not better) to get a clean signal from the computer.)

 

[Todd R]

I've played around with the switch before on my DacMagic, and could discern a difference, but never could tell what that difference was and could not reproduce it between recordings. This was on my S.E.X. amp with the same headphones (Beyers). I'll try playing around with the DAC when I go home to see if it makes any difference through the Crack. (On a related note, I had planned on selling the thing and just taking the output from my iMac's headphone socket, but the iMac headphone output has all sorts of high-pitched, squeaky "computer noises," and hiss is evident at high volumes. It's too bad that it will take holding on to a $400 DAC (whose sound I've never been all that thrilled by - it sounds a lot like any other digital source I've used, not better) to get a clean signal from the computer.)

Dr.
I have a Channel Islands Audio http://www.ciaudio.com/ VDA 2 DAC with the VAC 1 power supply and it does a great job for me. You should be able to find a used one at a good price.
I think your iMac has an digital optical output, right? I wouldn't suggest using the headphone out from the iMac. 

 

[Dr. Toobz]

I've played around with the switch before on my DacMagic, and could discern a difference, but never could tell what that difference was and could not reproduce it between recordings. This was on my S.E.X. amp with the same headphones (Beyers). I'll try playing around with the DAC when I go home to see if it makes any difference through the Crack. (On a related note, I had planned on selling the thing and just taking the output from my iMac's headphone socket, but the iMac headphone output has all sorts of high-pitched, squeaky "computer noises," and hiss is evident at high volumes. It's too bad that it will take holding on to a $400 DAC (whose sound I've never been all that thrilled by - it sounds a lot like any other digital source I've used, not better) to get a clean signal from the computer.)

Dr.
I have a Channel Islands Audio http://www.ciaudio.com/ VDA 2 DAC with the VAC 1 power supply and it does a great job for me. You should be able to find a used one at a good price.
I think your iMac has an digital optical output, right? I wouldn't suggest using the headphone out from the iMac. 

The iMac indeed has an optical output; that's been what I've used through the Cambridge Audio DAC. The DAC sounds a bit harsh to me, though, so I've always intended to get rid of it. I'll have a look at the site you link to.....