Crack as preamp for class D power amp

[vanishingstyleofmind]

Hi everyone,

I have a Crack headphone amp I put together in maybe 2016 or 17. Someone lost my Beyerdynamic headphones that I barely used anyway, so now I have an unused, but pretty box doing nothing.

I have a Cambridge Dacmagic with built in preamp running into a class D amp for my streaming needs, but the lack of analog inputs on the Dacmagic prohibits me from using my turntable. Other forums here and elsewhere say the Crack can function just fine as a line level preamp for a power amp. I got the correct 1/4 headphone adapters and tried it a few times. It sounds great until a few minutes go by and it starts to sound tinny and trebly and vocals are very faint.

Is it possible the much lower than intended impedance of the load damaged something in the Crack? I don't understand these things well and am confused. Are there other tubes that I could swap out that would work better?

Here is the link to the thread from 2012 where people discuss what I am trying to do working well:

https://forum.bottlehead.com/index.php?topic=2729.0

Thanks in advance.

 

[Paul Birkeland]

The input impedance of a class D amp is much, much higher than typical headphone impedances, so the Crack is running basically unloaded.  Which class D amp are you using?

 

[vanishingstyleofmind]

I see.

I am using a Snap / Episode EA-AMP-2D-150A.

I ended up finding a Schiit headphone amp locally that works pretty well.