[Groch]

I have a somewhat generic hook-up question, but my past experience with Mike and ACI makes me think this may be the right place to get the best answer.

ACI used to offer phono plugged cables for use connecting an amps speaker outputs to ACI subs with no speaker level inputs.   I got a set (don't remember whether they were free or quite cheap) and they worked fine with my Infinity CSW-10 sub.  If I remember right they were hooked up in parallel with the main speakers.

The cables did not appear to have any special circuitry to them...that is, they visually looked like speaker cables with phono plugs attached to one end.

I just got a Bada DC-222 hybrid amp (tube pre-amp/solid state power amp) with no preamp/sub outputs to drive my Infinity Sub and ACI Sapphire XLs. 

Can I assume that this kind of parallel hook-up should work on most amps and subs.  That is, should the high internal resistance of a sub's line level inputs generally allow for parallel speaker level hookups without effecting overall resistance?   Can one generally assume that no "Pad" is needed to get the subs volume adjusted correctly?

I know they used to make high to low level adapters for auto-sound...but never have seen one for home audiophile applications.   Any knowledgeable input on this would be appreciated

[genjamon]

I have some cables like this that I use as well.  Ed Schilling of Hornshoppe makes them for use with his subwoofer "The Cube" - he claims all line level connections will sacrifice sound quality, so this kind of high level connection is best.

However, I believe he has a resistor in line to drop the signal down to a level that the line level can accept.  Not sure exactly what the calculations are, but I don't think you can just connect cables to phono plug and be done with it.  Might fry your subwoofer amp that way.

[krikor]

I've got a couple of the ACI connectors at home. If you want, I can hook them up to my meter when I get home tonight and check the resistance.

They are not straightwire pass through... I remember testing this before and getting no continuity. So there is some resistance built in.

[Groch]

krikor, that would be great,  then I could make up a set of what Hornshoppe calls "Magic Cables".

I wonder if the optimum resistance would be pretty much the same across subwoofer brands.  Ed Schilling mentions that his version works with amps like the tripaths that lack a common ground.

[richidoo]

The input buffer circuit of your subs probably can't handle the 30-40V that the amp puts out, and if it could then the sub's volume control would be way too sensitive. So you need an L pad to attenuate the speaker level signal from the amp by about -26dB (reduce 40V to 2V) without changing the input impedance. The Infinity sub owner's manual will not download, so I can't check the input impedance. You'll need to know that to use the calculator.

http://www.muzique.com/schem/gain.htm

http://www.troester.org/ls/lpad.html

I think 1/4W resistors will work, but I'm not sure with the high voltage and unknown impedance.

Or just get this: http://www.crutchfield.com/p_142LOC80/Scosche-LOC80.html?tp=2001 

[krikor]

krikor, that would be great,  then I could make up a set of what Hornshoppe calls "Magic Cables".

I wonder if the optimum resistance would be pretty much the same across subwoofer brands.  Ed Schilling mentions that his version works with amps like the tripaths that lack a common ground.

Sorry it took so long... Completely forgot to do this.  Measurements as follows, but may be more confusing.

Red lead to center pin of RCA is 22k ohm (I assume this to be the resistance added inline with signal)

Red lead to outer shell of RCA is 25k ohm (not sure this means anything)

Black lead to outer shell is 104 ohm (assume this ground)

Black lead to pin is 3.4k ohm (again, not sure it means anything)


Hope this helps.