Do all tube preamps leak DC?

Thanks Erick, the Audible illusions L1 has four dip switches that can be turn off four caps on the output. Audible Illusions recommends for better sonics and after the preamp breaks in to keep them caps (dip swithes) in the off position. Would this further open the possibility for DC leakage?

Talk to them, I am not sure how their caps are arranged, and it's most likely that these caps are in addition to the main cap. There's no way I'm aware of to make a single-ended preamp without a blocking cap. :)

The voltages inside the pre are around 300V and would easily fry electronics expecting a maximum range of +- 2V.  This is part of what a DC blocking cap would prevent.

Like I said, if in doubt, measure and listen.

Best,

Erik

So I just found a picture of the guts. As expected, it has two very large caps and a relay at the output. :) I think you are all set, but caps do fail, film caps VERY VERY rarely, so by all means, spend $20 on a multimeter with 100mV resolution and you can see it yourself. :)

If you measure any DC offset at all (relative to connecting the meter’s pins together) then contact the amp maker and ask them if it’s within tolerance.  Remember to use a 30K to 100K resistor while measuring, as this will be more realistic than the voltage across an open circuit.

Best,

Erik

The AI preamp have a protection circuit that will not allow the unit to output if there is excessive DC at the output. I wouldn't worry about it. Just use the basic protocol. Amp on last, amp off first.

I have been running Audible Illusions preamps (Modulus3, Modulus3A, and Modulus3B) for years into 3 different power amps, 2 Classe' amps and an Odyssey and never ever had a problem.  My only gripe is the preamps have too much gain!!!