Which subwoofers have at least a 20k input impedance as required for ARC preamp

Most or all of the JL Audio Gotham and Fathom series subs have unbalanced input impedances of 50K. (Their balanced input impedances are only 10K). Those numbers are indicated in their manuals, which are linked to under the "Support" tab that appears in the description of each sub at jlaudio.com.

However, schematics I’ve seen for several ARC preamps all show that their unbalanced outputs are provided with the same signal that is provided to one of the two signal pins on their balanced outputs. And furthermore, if they provide dual output connectors of each type, for each channel, the connectors are wired in parallel.

Therefore what should be at least 20K is the parallel combination of the sub’s input impedance and the input impedance of your power amp. That number would be the product (multiplication) of the two impedances divided by their sum.

It can be calculated from that relationship that if the sub has an input impedance of 50K the power amp would have to have an input impedance of at least 33K to result in the preamp seeing a load impedance of 20K or more. If the input impedance of the power amp is less than 33K, a sub having an input impedance that is higher than 50K would be necessary for the preamp to see a load impedance of 20K or more.

Good luck.  Regards,
-- Al

thanks al. very good info. i need to do some studying. have passed on arc preamps in the past bc of the dicey nature of the pre driving a main amp plus a subwoofer. 

the nitty gritty. i’m interested in a ref 6 to drive a 20k sub plus either an arc amp w a 300k ohm input impedance or a Dag amp with a 1M? input impedance. Would either work well? Also the 50k JL might work better? Just not proficient enough to decipher. I hope i got the specs correctly. what do you think al?