Just built, very low volume, Headphones?

[Shappers]

Hello all,

Just finished building my Crack (it's only taken me 3 months)!

All resistance and voltage checks were just fine but I have very low sound coming out from the headphones with the volume pot fully up.

I tried 3 different input sources and settled on the Airport Express as that had the loudest sound. My best headphones are at work (HD650), so I am testing it with some old vintage headphones that I also own. They are Sansui SS-80s, the impedance is 200 ohms and the sensitivity is 108dB.

Could they cause the low volume? The sound I can hear is clean, no distortion, just quiet!

I will start to build the Speedball while I wait for some advice. 

Thanks in advance,

Steve

[adamct]

That definitely doesn't sound right...

[dwilli852]

Reheat all the connections at the tube sockets, RCA jacks and volume control pot.

Make sure the tube pins are clean.

Try different tubes if you have them.

I've had a similar problem that was a result of a bad connection at the 12AU7 socket. This was after several months of use. Too much tube rolling was my guess.

[Grainger49]

You should read this thread:

http://www.bottlehead.com/smf/index.php/topic,1667.0.html

It gives the way to start troubleshooting in a logical way.  Since all your voltages are right then we have to ask if the headphones are ok.  Dan posted that Crack is best with headphones above 120 ohms, 200 should be fine.

Hold off installing the Speedball till you have the volume problem sorted out.

David's advice above is exactly what I would give.  But you should read Dan's thread and inspect all connections first.

[Shappers]

Hello again,

Thanks for the replies and the links. I had already checked and re-checked all the connections before resorting to the board.

I got down to basics and started checking the circuit according to the schematic and made an interesting discovery. B3 and B6 which previously read 105v and 108v when carrying out the voltage checks, now read only 2.1v and 2.2v. These are the cathodes of the 6080, so I assume this is not a good thing and the cause of my problem 

It was a brand new tube that I fitted (Thomsom CSF), I'm unsure why it read okay initially then not. Does this sometimes happen with new tubes?

If this indicates a faulty tube then I will have to go into work tomorrow and get another one from my stash. I'm hoping it was only a bad tube 

Thanks for any advice,

Steve

[Paul Birkeland]

Nice job on the diagnosis!!!

Does the 6080 glow still?

How are the other octal socket voltages, are they still about right?  (You could also just measure terminals 1 and 5, those bias the 6080)

-PB

[Shappers]

Hi Paul,

The tube still glows (beautifully), and I have 81v and 87v on terminals 1 and 5 (and at the octal socket).

I thought these tubes were quite rugged but I'm not so sure now.

I will have to post up some pictures of it once it's working, I made it up in a custom chassis, it looks a bit different than regular Cracks.

[Paul Birkeland]

Cool, 81 and 87 V-DC are solid numbers.

[Shappers]

Success 

I must just be unlucky with tubes, the first didn't survive the shipping, the 2nd although brand new failed almost immediately, the third gave a big flash and a pop in my right ear, but after that started to play sweet music, and loud!

The amplifier sounds very fine even with my terrible sounding headphones. I'm really happy that it is only going to get better once I get it Speedballed and my decent phones and source hooked up to it.

I posted some pictures up in the gallery. Many thanks to all for the advice.

Steve.