AMB Laboratories DIY Audio

[robparits]

In the CK2III headphone amplifier can i replace the DC servo circuit with input and output capacitors?
I have a fear of DC, because it was the cause of the destruction of a tweeter and an expensive MC cartridge too.
As always your comments are precious to me.

[DorkVader]

I think you probably can in theory, but I wouldn't recommend it.

The problem is that capacitors (apparantly) change the sound of the amplifier. The CKK-iii has been designed to avoid this. Also, the amp uses a DC servo opamp. I'm pretty sure this works by amplifying any tone below 2 HZ or so, and remove it from the signal. This very effectively prevents DC-offset and should keep your gear safe. Here is a quote from the "tech hilights section:

The servo was decoupled from the current mirror, and instead acts on the input stage without being directly in the signal path. It adjusts the constant voltage sources that bias the sources of the input JFETs in order to zero the offset. Under AC conditions, the bases of the constant voltage transistors are held at a constant DC voltage by the various capacitors to ground. Therefore the servo doesn't really impact the AC behavior of the amp but it still has plenty of gain to zero the output DC offset.

Also, if you're really worried about it, the epsilon12 exists to protect form DC offset (among other things). You may want to consider adding it.

[robparits]

Thanks for your answer DorkVader.What is the epsilon12?

[hagak]

Note the e12 is to protect from a catastrophic failure that would cause dc offset. Not to correct dc offset present in the amp like coupling caps or servo would do.

[amb]

You should never remove the DC servo from the CK²III. The amp has no global negative feedback and requires the presence of the DC servo to keep its output DC offset in check.

ε12: http://www.amb.org/audio/epsilon12/

[robparits]

I am grateful all to you for your replies. Ok, i am going to use the DC servo circuit.

[DorkVader]

You should never remove the DC servo from the CK²III. The amp has no global negative feedback and requires the presence of the DC servo to keep its output DC offset in check.

ε12: http://www.amb.org/audio/epsilon12/

Wow, that's good to know. I will have to start learning about things lie this in earnest.