1st time DIYer - tales of my build - questions in 1st post

[grufti]

The quote below describes a fix that keeps the startup voltage down. You might as well do this while your soldering iron is still warm.

I guess I forgot the most important thing: congratulations on getting your first Bottlehead amp to glow!

I'm not sure how Doc and I missed this in the prototyping and manual writing process, but there's an easy modification for your Crack amp that will keep the startup voltage at the output down to 0v with no headphones plugged in.

Look at the 1/4" jack and find the two unused solder terminals.  Connect both of those to ground (the terminal row closest to the chassis plate).

The 1/4" jack supplied has a switching function built in, so when no headphones are plugged in, the output is shorted to ground, and thus the coupling caps at the output will charge without restriction.

When you plug your cans in, that connection is lifted and your music will flow through.

Our apologies for missing this!

-PB

[Grainger49]

Check out this tip from the Crack designer:

http://www.bottlehead.com/smf/index.php/topic,2946.0.html

This allows all the DC created when Crack turns on to go to ground immediately. 

[Laudanum]

Congrats and enjoy!

[SteveH]

Hey Dave - a big thumbs up to you!

So, how does it sound?

SteveH

[Jim R.]

Yeah,
ave -- how does it sound? :-)

Ok, maybe you can't pull yourself away from it... that can happen :-).

-- Jim

[wullymc]

Thanks very much guys!!!!

I am sooo looking forward to listening to it.

I am going to either tonight or tomorrow night do the update mod for the voltage for the headphone jack.  Probably tomorrow night I will have my first listen.

I am anxious.  Too bad I don't have more time.

Thanks again everyone.

Take care...Dave

[SteveH]

Well, I have to admire your patience!  I don't think I'd be able to wait that long...

SteveH

[wullymc]

Hey guys,

I did the headphone jack grounding.  Using one black wire I grounded the 2 vacant terminals to the chassis outboard terminal.  Everything measured okay for grounding.

Everything looks good, however, when I went through the resistance check fix I now get different values at Terminals 6 and 10. They now measure at 0 ohms.  They should measure 2.4k ohms each(according to the manual before the headphone jack grounding).  I know that this grounding has affected that.

Should I be concerned over the resistance check at these points or should I just go on and remeasure the voltage?

Thanks ...Dave

[wullymc]

Couldn't wait,

Rechecked the voltage.  Everything is good.

I check the voltage on headphone jack on start up and everything stays at 0 ohms.

Now for the listening......YAY!!!!

[wullymc]

Sounded good!!!!

Got a little bit of static at one point.

Looking forward to my tubes burning in....

...have to investigate

kind of disappointed.    

[wullymc]

 
I did the 0 voltage at headphone jacks on start-up mod.  Basically, I used 1 black wire and threaded it through the 2 vacant terminals(ring and tip) at the headphone jack and then to the outboard terminal closes to the top plate and soldered all 3 connections.
 
Tested Resistance - everything was okay, other than the 2 terminals #6 and #10 which in the manual should have tested 2.4k ohms but tested 0 ohms.  I believe this to be because of the new mod to ground the 2 vacant terminals on the headphone jack.
 
Tested Voltage - everything was okay (within 10-15% of voltages).  At the headphone jack neither the inboard tip or ring terminals indicated any voltage on start-up.
 
Turned off amp and connected my dac to the amp.
 
Started amp with volume at 0.
 
Connected my headphones after 30 seconds, still with volume at 0.
 
Started music.
 
Everything was okay and it started to sound good after a few minutes.
 
Then I heard a few cracks
 
There was never any smoke or burning smell.
 
I am going to test the resistance and voltage again and report back.
 
Does anyone have any ideas?
-Maybe the resistors at the headphone jack are toast?
When you pull out your headphones is the headphone tip hot?
 
Am I using the amp correctly regards to connecting and disconnecting headphones?
1.  Turn on amp with no headphones and volume at 0.
2.  Wait 30 seconds or more then connect headphones with volume at 0.
3.  When done listening to music turn volume to 0 and disconnect headphones
4.  Turn off amp.

Is it alright if I start the amp with my dac and after 30 seconds put in a cheap pair of headphones in and start playing some music while monitoring the voltage to the headphone jack.  Would this not be a good idea ...could I get hurt?

Thanks for your help.

[Doc B.]

Carefully go over all of your solder joints. It could be that one connection was attached but not soldered and it came loose as the amp warmed up.

[wullymc]

Thanks very much Doc.

I went through all the joints and can't find anything.

I just check the resistance and everything checks ok.

Would resoldering all the terminals be a good idea?

I know that during building I had problems with terminals:

14U
15U

In particular I am wondering about the 270 ohm resistor going from 15U to 21U.  In redoing 14U I soldered 15U with just the cap and forgot the 270 ohm resistor and had to attach and solder the resistor to it.  I am wondering if maybe that could be the problem.

I will try to figure out how to post some pictures in hopes to solve this problem.

Thanks!

[wullymc]

Okay,

After checking the voltage, resistance I started listening to it with cheap $1 16ohm earbuds.

I had the volume around 9 o'clock and listened for about 40 minutes with no signs of crackling.

Now with the 600ohm headphones I was more around 12 - 1 o'clock position.  I decided to go to that area of volume and bang crackling and popping started!!!

Now would you say to look at my connections to the volume control?  Would that be a good place to look?  Maybe resolder all connections there and make sure that there are no connections that after soldering might touch another terminal?

Thanks for the help...I feeel like I am almost there!

[Grainger49]

It sounds like the volume control itself.  Try this, use the 600 ohm headphones and crank it to the 12-1 position and then when crackling starts pull up and push down on the volume knob.  It may be that the wiper is intermittent in this area of the volume range.