Passive Pre Amps


Bronze Member
Username: Jim1961

Dublin, Texas USA

Post Number: 13
Registered: Aug-07
Ive owned a Adcom SLC 505 and a Reference Line Preeminence One previously. While I enjoyed the super transparency of these units, I also experienced a rolloff at the lowend. Using both warble tone generators and measuring output voltage, and using spl meters, I was able to confirm what my ears told me. The reference line unit was a bit less prone to this than the adcom, but still displayed the basic tendency. My question is: Is this the experience all users have with these units or was it just my set up? I was using a CAL Aria CD player, KCAG 1/2 meter interconnect, and a Krell KSA-200 power amp. Could it have been the Aria output stage didnt like seeing a variable resister? Will my Rega Apollo act differently? I did discover that when I put a active unit like a EQ after the Aria, but before the passive unit, the problem was minmized considerably, which supports my theory that maybe this was just a effect caused by the Aria output stage. Anyway, if you have thoughts on this or recommend any particular passive device, please share it. My system is completely a line stage system, so no accommodations are needed for a turntable.

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 11145
Registered: May-04

More than likely a low frequency roll off was caused by impedance mismatches between the player and the passive pre amp. Using a low impedance pot will cause problems in most cases. If the problem was variable with the position of the pot, then you have your answer. Switching to a higher impedance pot is typically the correct approach. Then you only have to worry about the pot driving your power amplifier. The alternative is to use an autoformer/transformer based passive unit.

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