I didn’t want to spend huge amounts of time on chassis work and appearance, so I purchased a “Mod Squad” passive on the Internet used for $350. The interior was well thought out with obviously a great deal of care used to run bare silver wire everywhere.  It didn’t sound all that great; somewhat better than a Conrad Johnson PV12, mainly in extension not so much in clarity.

I thought the Alps volume and balance pots were the most likely culprit and since I had decided long before to build my own switched attenuator I ordered the Vishay S102 resistors and a Shallco silver contact switch and mounted them into the same box (almost fit, I had to cut a clearance for the Shallco).

The sound was quite improved but still a long way from stellar. The next most likely problem I thought would be the silver wire or possibly the gold plated RCA jacks. So I bought Cardas 5 nines silver (continuous cast and annealed) and Cardas one step down from the top jacks. Now there was some additional improvement but still a hardness that was out of place. I removed the input selector and tape loop switches from the signal path – wow, that was it! The improvement was immediate and substantial.

Finally the expected results from a passive pre; very open, grainless sound with full frequency extension and great dynamics. Many people have said passives lack dynamics I am loath to understand how this is possible, mine certainly doesn’t suffer from this.

So my point is that even something as simple as a passive will only accomplish great results with great care and the choice of great components. (I think your example design with a 1 meg pot will suffer from cable capacitance and that the sound will change with volume setting, most preamps can easily drive far lower resistance why not default to a 100K or even a 10K pot?)