First Watt F1 Compatible with Passive Preamp (Miller Capacitance)?


2008-03-10 2:13 am
Greetings everyone. I own a First Watt F1 Amplifier (using the XLRs). I'm in abit of a sticky situation because I have two passive preamps that seem to sound great with my setup but technically shouldn't (according to a knowledegable friend of mine). I have a Slim Devices Transporter as my source from the XLRs (Specs: 3Vrms, Impedance: 100Ohms) and AKG K1000 earspeakers as my "speakers". According to my friend the F1 Amplifier has a high miller capacitance which makes it a not so great candidate for passive/resistor based preamps because it forms a low pass filter with the output impedance of the preamp which rolls off treble. He said that a transformer volume control could work much better or an active preamp with low output impedance. I am a bit lost because I don't hear a rolled off treble in my system, yet curious, because if a passive isn't the best solution my rig is capable of much more.

The passive preamp(s) I have are Scott Endlers BALANCED ShotGun Attenuators (4k resistors):
as well as a Luminous Audio Axiom Balanced Passive with 2.5K output:

I know this seems like alot to ask but I was just wondering if a passive can work with my First Watt F1 given my source specs or if the passives I have now are fine. I have little knowledge about this type of thing and I'm only really basing the above claim on what my friend said.

Regards and thanks for your time

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
It is correct that a higher source impedance will reduce the
bandwidth due to input capacitance. I would estimate the
rolloff with a resistive load slightly above 20 KHz, and if the
headphones have inductance, which I believe they do, then
you may get a little better.

If they sound good, then there you are. If you have the
opportunity to try them with a balanced active source, then
you might hear a difference.


2008-03-10 2:13 am
Thanks Nelson for your response. I don't mean to be a bother but I do have one more quick question about the F1 and it is in regards to input sensitivity. I've checked both the owners and service manual but haven't found any specs. Would you be able to tell me what the input sensitivity of the F1 is?

Best Regards,