Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: Todd R on April 25, 2010, 12:45:58 PM
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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
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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.
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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?
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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.
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. . .
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.
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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!).
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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.
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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.
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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.
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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.
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Ok! Now we're talking. So, what do you think of the amp?
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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.
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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.
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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?
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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.
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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.
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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.
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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.)
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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/ (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.
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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/ (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.....
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Dr. Tubes,
The Cambridge is indeed a very harsh sounding dac. I had one on loan here for a bit and couldn't stand to listen to it.
Check out the HRT MusicStreamer II and II+ dacs for $150 and $350 respectively. I have the original MusicStreamer+ that I paid $200 for, and it's incredibly good for the money.
The II version has some upgraded parts, an improved design, async usb connectivity, and handles up to 24/96 sample rates.
If your budget allows, and like me, you prefer the sound of a NOS dac, the db Audio Labs Tranquility dac at $1500 is the best 16/44.1 khz dac I've ever heard, including a lot in the $10k price range. It is a superb dac that sounds so close to vinyl it's scary, but also with the best that digital has to offer.
Of course we're all waiting for the BH dac, but until then...
HTH,
Jim
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Some folks are sensitive to inverted absolute polarity and some are not. Second verse, some albums preserve absolute polarity and some do not. ...
Third verse, some albums preserve phase on some songs, invert it on other songs.
Fourth verse, some albums preserve phase on some instruments (i.e. some recording tracks) and invert it on others. You want that trumpet in phase, or the guitar?
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Yup, those are albums that drive me crazy. And maybe that's why I'm so crazy. I hear it and want music to be "right."
I have found that Rounder is good at recording and mastering a believable soundstage and preserving the absolute phase together. Sometimes positive, sometimes negative, but the whole album and all the instruments preserved the same.
So I have a lot of Alison Krasuss, Jerry Douglas, Etc.
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Well darn it, the Crack is not working again!
I stained the base, brought it back into the house and hooked it up, but the fuse blew. Thought maybe I accidentally had the switch on when I plugged it in, so I tried another fuse & it blew too.
The AC socket did feel a little funny and made a clicking sound if I rocked the cable, but other than that I can't see anything wrong anywhere.
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Plugging the power cord with the power switch on probably won't hurt the fuse. I would look first for some errant, untrimmed lead that might have been moved to where it is touching something it shouldn't, and also check to see if maybe something metal in either the IEC socket socket or power switch got loose from the plastic deforming a bit under soldering.
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Since it worked you can be certain that it was wired correctly. Because it stopped working you should look through the power supply. Blowing the fuse really indicates some kind of short. If it were on the IEC socket it would trip your breaker on the circuit feeding it. But the clicking sound in the IEC socket is odd.
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Guys,
I just don't know.
I've been looking at it under the magnifying glass, blowing it all out with compressed air, tapping & shaking to see if any loose bits fall out.
Nothing....
Is it possible that a bad tube could cause this? Maybe shorted heaters?
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FWIW, I also blew a fuse shortly after getting things up and running. I had also made the manual's mistake of wiring the first resistor off terminal 22U (ground) instead of after the first capacitor in the filter network for the B+ (21U). The amp played fine for an hour; then, I turned it off. When I turned it on again, nothing happened. The fuse had blown. After checking everything and not finding any shorts or errors, I put in a new fuse and have used the amp for at least 10 hours now without a single problem.
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weird....
But, just had a thought.
What size fuse should we be using? I've got a 500ma in there as per the manual.
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You guys might want to measure the resistance value of that first 270 ohm resistor to make sure it didn't drift when it was connected wrong. I would think it would hold up OK, but it's easy to check. The two different fuse problems could be from different causes, e.g, the fuse blowing when the amp isn't even turned on indicates a problem in the IEC socket or power switch wiring, while a fuse that blows after an hour usually indicates that it was previously stressed and just finally let go.
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You guys might want to measure the resistance value of that first 270 ohm resistor to make sure it didn't drift when it was connected wrong. I would think it would hold up OK, but it's easy to check. The two different fuse problems could be from different causes, e.g, the fuse blowing when the amp isn't even turned on indicates a problem in the IEC socket or power switch wiring, while a fuse that blows after an hour usually indicates that it was previously stressed and just finally let go.
FYI, I checked and it did not blow when plugged in but amp left off, so it's not an IEC problem.
Resistor checks fine at 270 ohms.
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It's possible that the 1/2A Slo Blo fuse could be marginal. If all the resistance checks are still good you could maybe try a 1A. I've seen the situation happen in the past where we spec the smallest fuse that holds OK on the prototypes, and then end up going up one size because we see the occasional failure in the field during the startup current surge. It could be that there are variations in how much and how fast various tube heaters pull current when they start up.
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You guys might want to measure the resistance value of that first 270 ohm resistor to make sure it didn't drift when it was connected wrong. I would think it would hold up OK, but it's easy to check. The two different fuse problems could be from different causes, e.g, the fuse blowing when the amp isn't even turned on indicates a problem in the IEC socket or power switch wiring, while a fuse that blows after an hour usually indicates that it was previously stressed and just finally let go.
Doc,
I get a reading of ~320 ohms on that resistor as opposed to 270. My meter is really old and cheap, so it's possible that could be part of it, but usually, the resistances are within 5%. That would be 18.5% off. Are these 20% tolerance or something?
I visually checked my new 500mA fuse, and it looks like new. So I think that the last one indeed became stressed and just "let go." The local Rat Shack has a bag of .5A ceramic fuses for something like $1.99, so this was easily fixed.
EDIT: Just to clarify, I cannibalized the .5A glass fuse that came with my Seduction for the Crack, and replaced that with a ceramic fuse in the Seduction. Can't really "visually inspect" a ceramic fuse..... :-)
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It's possible that the 1/2A Slo Blo fuse could be marginal. If all the resistance checks are still good you could maybe try a 1A. I've seen the situation happen in the past where we spec the smallest fuse that holds OK on the prototypes, and then end up going up one size because we see the occasional failure in the field during the startup current surge. It could be that there are variations in how much and how fast various tube heaters pull current when they start up.
Slo Blo? The one it came with & the ones I've been blowing are fast blow. Ok, will go up to 1A if I can't find 1/2 amp slo and let you know here in a couple min.
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Alright, found a 1.6A fuse in my arsenal and gave it a try.
The amp is on now. I'm going to leave it running with an iPod on repeat while I work on my kitchen floor project and check it periodically.
What would be the maximum fuse size that would be safe to put in this amp?
Thanks,
TR
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I would first try a 1/2 A slo blo (I thought that was what we had in stock here) and if that doesn't hold try a 1A slo blo. We can mail some to you if you like.
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I would first try a 1/2 A slo blo (I thought that was what we had in stock here) and if that doesn't hold try a 1A slo blo. We can mail some to you if you like.
That would be cool if you could since I've already made 2 trips to the "shack" today.
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Got the fuses, thanks.
TR