I used to think passive preamps were superior to active preamps given right the setup, but

I had a DAC with passive volume control, then a DAC with active volume control. The latter one sounded better.

Nowadays I don't care about the buzzwords the product is advertised with, I go for bang for the buck and my ears.

Myself being in audio gof over 40 years now have bought from the A groups 
In recommended componends and have had some great equipment
I have found having an active Linestage preamplifier dynamics and imaging 
Especially complex orchestra dound more real especially Vacuum tube.
Recently I did something totally different .since I have owned single ended amplifiers  and wanted to see what was all the fuss .I can say by keeping things 
Very simple in one gain stage the sonic purity is second to none.after yhst experience I had a very gifted Electronics designer build me a DHT preamplifier Single ended -Direct Heated Triode Preamplifier completely transformer based 
Including the Audio output section.the only capacitors are 2 Big poly oil caps and 
Copper bypass caps . Using 6 Lundahl  transformers and chokes.
Using the WE 274 rectifier tube, WE 101D aufio tube ,as well as a choice to use the 26 tube.these are far more linear then a 12ax7,or 6sn7 indirect heated tube.
These tubes run very cool and the magic is incredible . The transformers Make a huge step up in sonics accuracy and dynamics and Bass using a 300b
Or 2-3 does also work but it is a power tube first and a waste of heat to achieve the same goal. If this were commercials sold it would be at least  $1 3k
I have yet to find a another passive or active preamp that is built this well with all premium parts including all Neotech Single Crystal wire used throughout 
Including their best Silver Gold Alloy signal wire.  The famous Coincidence DHT 
101D preamplifier uses solid state rectification and capacitor coupled.
Which is very good but a solid step below rectifier, Transformer coupled unit.
Once you experience a top DHT model done correctly ,9 out of 10 would want one if they can justify the price.

Audioman58, would you care share who made your preamp? You can PM me if you like.

But if for example the source component has a coupling capacitor at its output, resulting in a substantial rise in output impedance at deep bass frequencies, or if the output impedance varies significantly in other parts of the spectrum for whatever reason, using that same passive preamp may result (depending on the specific numbers that are involved) in objectionable irregularities in frequency response and/or phase response.

This comment by Al gets to the issue that I often hear about- when a passive is used, bass impact suffers (I hear about this far more often than a high frequency rolloff, for which George supplied pretty good numbers earlier in this thread).

This is because many sources, analog and digital, use an output coupling capacitor. The series resistance added when a passive is inserted into the signal chain can exacerbate the increased output impedance at low frequencies caused by the coupling capacitor. This explains why the bass often has less impact at any setting below full volume.

This is not to say that this happens in all cases! But it happens often enough that the passive/active 'conversation' is not likely to go away anytime soon.