Slight DC current at headphone jack

[Rory]

Hi All,

Just finished my Crackatwoa. Much easier than i anticipated. It's not even burned in and sounds great. Here's my question: I measured a very small DC voltage at the headphone output jack: 24mV and 33mV. All resistances and the other voltages were within tolerance (once I clipped a resistor tail that was grounding out the left channel regulator tube). DC current into headphones/speakers is undesirable to say the least - but is this voltage tolerable?

Thanks,
Rory

 

[Paul Birkeland]

0.024V and 0.033V is not particularly concerning, I'll often notice that these voltages on our cap coupled heapdhone amps will wander around a bit too. 

Even at 0.033V, that's about 15 micro amps of leakage current, which isn't anything to worry about IMO.

 

[Rory]

Thanks Paul. I will keep an eye on it - remeasure once I have some hours on the amp.

 

[Deke609]

I've read that film caps have much lower leakage current than electrolytics. A common mod to the Crack and C2A is to replace the electrolytic coupling cap with an equally rated film cap (e.g., a metallized polypropylene cap). So if you plan on doing this mod, the dc you are presently seeing on your outputs may disappear.

cheers, Derek

 

[Rory]

Thanks Derek. At some point I will make that mod. I made it to my Bottlehead Crack and was very pleased with the sound.

 

[Tom-s]

Do let us hear your opinion on your new C2A vs Crack

 

[Rory]

I gave my Crack to my son for Christmas and he's off to college so I have not been able to make a direct A/B comparison, but here are my thoughts on C vs C2A. I have about 40 hours of break in and 10 of listening on the C2A. I've rolled in a Winged C output tube and am playing with the stock driver vs. Northern Electric 12AU7, so the unit and tubes are not yet broken in. I have the stepped attenuator kit but have not yet added it. The Crack was fully burned in with Mundorf M-cap Evos and a ridiculous $250 Goldpoint 47 step attenuator, so the total cost was not too much lower than the C2A. The Crack sounds fantastic - very, very quiet and very clear, but lacking a little bass. That's where I find the C2A noticeably superior. It's better balanced than the Crack, but I find that takes away from the sharpness and clarity a bit. I think the stronger bass might contribute to that - but overall the sound is more natural. The difference in clarity is also likely due to break-in, lack of upgrades, etc. We will see!

EDIT: forgot to mention that I listen with HD600 headphones.