New Crack Build - First Power on issues [solved]

[pts211]

Hello everyone,

I'm new to this forum and am very excited that I just finished my initial Crack build! I stayed up way too late getting it put together and today I went through the resistance and voltage checks successfully. I was looking forward to having my first listen but haven't quite gotten there yet. When I initially plugged in my 650s I heard a disconcerting pop.

I went on just a little further and started playing some music while turning the pot up. The good news is I did hear music! Unfortunately, I also heard an interesting clicking/bubbling type of noise, or perhaps a clicking (like the noise that hot metal makes while it is heating up or cooling down sometimes.). At that point I unplugged my cans, turned the crack off for a moment and then turned it back on. This time, without headphones plugged in the 6080 tube was making audible noises that I can best describe as sizzling and some light clicking (like I heard in the headphones the first time).

Though I'm confident in my building ability and the tests passed something seems wrong here. I am new to tube amplifiers, do (new?) tubes tend to make noise when they are used the first couple of times? Or, is something else wrong?

Any help would be appreciated!

Thanks,
Paul

[Paul Birkeland]

Hello Paul,
I'd suggest double checking your voltages, just to be sure.

Otherwise, ad glass heats up, it can ping and pop a bit, this isn't abnormal.

A sizzle or sputtering would lead me to look over the solder joints carefully, then run the amp for a 10+ hour stretch cook the tubes in.

-PB

[pts211]

I double checked all of my voltages and they are all within or at the 15% tolerance of the manual. B1 and A6 are on the upper end of the tolerance at 15.2% off (78.1 V each), additionally A1 and B4 are both about 12.5% off (80.2 V each), all others are under 10%.

I've left it on for the last couple of hours and the noise did go down but every now and then I hear a sizzle. I pulled out a cheap pair of headphones to try and still have a pretty nasty sounding "pop" when I plug them in regardless of the current volume on the pot. The pop is loud enough that I'd be concerned plugging much into it.

I'll take a closer look at my solder joints but at first glance they seem alright to me.

[pts211]

I took a closer look at all of my joints and did find a bad one on the potentiometer. I fixed that as well as went over a bunch of my joints with my soldering iron to try and wipe out any other issues. Upon plugging it back in and giving it a shot the pop on insert and removal was gone!

The only other thing that I am noticing is that I am hearing a dim high pitched whine. It sounds like it is primarily in the left channel but it is sometimes coming through the right channel also. I can hear the same noise without the headphones on coming from the tube. It is definitely warmed up but I have yet to run it for an extended period, I'll wait and see if it goes away unless I hear that this is a sign of something.

It's not performing perfectly just yet, but I think I am already a Crack addict!

[Grainger49]

There is a 2.49k Ohm resistor on each channel to bleed DC off at startup.  There should be no lingering DC after 30s.  Verify that these two resistors are in the circuit properly measure resistance from the left channel and right channel hot leads to ground (the chassis).  You should read over 2,000 Ohms for each channel.

[pts211]

I verified the resistance on my output and everything checks out there. Thankfully I think I have the pop taken care of after going over some of my solder joints.

I took PB's advice and kept it running for an extended period to burn everything in. Today it seems that the tube noises have finally died down and it sounds fantastic! I can't wait to hear it once I add the speedball upgrade.

Thanks for the help - I'm sure I'll be lurking around the forums a little more now that I have my Crack.

Paul

[jboehle]

There is a 2.49k Ohm resistor on each channel to bleed DC off at startup.  There should be no lingering DC after 30s.

Is it safe to have headphones plugged in at amp power on?  How much DC is seen by the headphones at startup?

[Grainger49]

I think the manual says 20V DC or less.  I would never leave my headsets plugged in.  That is just me. 

The DC on the outputs disappears (if the resistors are in place) in a few seconds, say 10s.  It is the result of the power supply charging the output capacitor.  The resistors safely bleed that voltage to ground.

[jboehle]

Won't 20V DC fry just about any headphone out there?  Maybe it's 20mV?  I should check the manual I guess.

[Paul Joppa]

The "20v or less" is with no headphones. Because the headphone DC resistance (30 to 600 ohms) shunts the 2490-ohm output resistor, the actual voltage with headphones will be substantially smaller when discharged with phones.

Whether the thump is acceptable for the headphones is a judgement call with no solid information to base it on - unless the headphone manufacturer is willing to provide advice.

[Paul Birkeland]

I can speak to the DC thump at startup.  I believe with HD-800's, we measured something like 1.5V for a brief moment.  Having had my HD-800's since a month after they were released, and using them nearly exclusively on a myriad of Cracks over the years since I've bought them, and never having bothered to unplug them when turning my Crack on, I can say with some confidence that this hasn't presented itself as an issue.

Lower impedance headphones will be both more efficient at shunting the voltage and more sensitive to the spike itself, so YMMV. 

[Grainger49]

Paul and Paul have a thousand times more experience with Crack than I have. 

Hearing them say this I wouldn't worry about keeping my headsets plugged in (after checkout) all the time.