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

 

[jrebman]

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.

 

[Laudanum]

Those Alpha pots are really inexpensive.  They often dont track well at low volume but they sound fine (to me tin ears).  Not many reports of bad ones here but it's not uncommon for them to be noisy just as you describe.  Ive used them in other projects before and have had a noisy one (crackling and static).  I probably have 1/2 dozen stashed away.  Follow Graingers advice on the pot.  Bottlehead will send you a replacement if needed. 
You could also consider something like the Alps "Blue Velvet" (conductive plastic type).  They track really well even at the bottom of the range and they sound fine and are quiet.  Good pot for the price but a little tricky to solder because of the pin terminals instead of lugs.  They are made for through-hole mounting.  Under $15 at Mouser.  $25 give or take at most audio parts sites.  Just something to consider of you want an inexpensive upgrade in the future.

Im curious as to your Beyers being ok?  I see you edited your post but I know you had posted that you plugged them into another amp and they didnt sound right and you were concerned they were damaged.  I assume they are ok.  Crackling and static from a noisy pot shouldnt hurt them in and of itself.  Of course, if the volume was up far enough I imagine it could.  But anyway, just wanted to check to see if they were ok.  I love my Beyers and they are great on Crack  ;D

 

[wullymc]

Thanks guys for your suggestions.

I think I will resolder the pot and see if it is okay.  When doing the listening test if it starts to crack and pop I will try the method of pushing down and pulling out.

Unfortunately, my headphones are not doing well.  When I was preparing the cmoy they said to use a cheap pair to test.  I should have used that strategy with the Crack.  I am going to keep going with the cheap pair and see where I go from there.

The Alps pot sounds interesting.  In looking around it seems like a lot of people have done that upgrade.  I am very novice and don't know what wires go where.  I do have a helping hand so I think I could solder it first and then attach it to the chassis later.....well another option.

Thanks again.  I truly appreciate the help.  I figure I am getting there.  I was getting excited but I have to think of this as the challenge.  I find for the most part the build wasn't that bad.  I had a few problems, but with going slow it is coming together.  I think the more difficult part has been the testing.

 

[Grainger49]

Check FAQ #6 for help on installing an Alps pot:

http://www.bottlehead.com/smf/index.php/topic,2408.0.html

 

[Laudanum]

Thanks guys for your suggestions.

I think I will resolder the pot and see if it is okay.  When doing the listening test if it starts to crack and pop I will try the method of pushing down and pulling out.

Unfortunately, my headphones are not doing well.  When I was preparing the cmoy they said to use a cheap pair to test.  I should have used that strategy with the Crack.  I am going to keep going with the cheap pair and see where I go from there.

The Alps pot sounds interesting.  In looking around it seems like a lot of people have done that upgrade.  I am very novice and don't know what wires go where.  I do have a helping hand so I think I could solder it first and then attach it to the chassis later.....well another option.

Thanks again.  I truly appreciate the help.  I figure I am getting there.  I was getting excited but I have to think of this as the challenge.  I find for the most part the build wasn't that bad.  I had a few problems, but with going slow it is coming together.  I think the more difficult part has been the testing.

Sorry about the phones.  If new, you may be able to exchange them defective.  Im not suggesting that you "lie" to the dealer.  Just that some have a no questions, unconditional return (Amazon comes to mind as an example)  so it would depend where you got them, and, of course, if they are indeed new and within the refund/exchange period.

The Alps pot is indeed easier to wire before installing.  The FAQ covers the wiring and I believe they just wire up exactly like the stock pot.  It's really not hard.  I just crimp the wire to the pin first so I have positive contact and then normal soldering.  I use a lighted magnifier as my eyes arent getting any younger but it really isnt difficult at all.  You're in Canada, right?  Parts Connexion has the Alps for $18.  Probably cheaper for you there over saving 4 or 5 dollars from Mouser in the States and paying the extra shipping. But first things first. Regarding the stock pot, I was suggesting that it is possibly just a bad/noisy pot.  Not sure resoldering will help but it's worth a shot.

 

[wullymc]

Thanks guys,

I will try the resolder today.  If that doesn't work I think I will buy a Alps pot.  Does it make a big difference?

Thanks for the partsconnecXion suggestion.  I am looking at the page.  I have a question though since there are about 8 of them.  I wouldn't buy the motorized or mono ones but what one would you suggest for the stereo ones?  They have 10k, 50k, 100k, and 250k.