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

[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.....

[Jim R.]

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

[Paul Joppa]

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?

[Grainger49]

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.

[Todd R]

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.

[Doc B.]

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.

[Grainger49]

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.

[Todd R]

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?

[Dr. Toobz]

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.

[Todd R]

weird....
But, just had a thought.
What size fuse should we be using? I've got a 500ma in there as per the manual.

[Doc B.]

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.