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Hi ,
im building a stereo 70 that will be used in a biamped system , its basicly going to be for 125 HZ up and a solid state amp will be 125HZ down for the subwoofer . Was planning on replacing C1 & C2 in both channels with .05 cap and adding a passive fiter to the input with a multiturn pot to ajdust the roloff between 100 and 150 Hz .
This is being built for a friend ,and want to know where natural roll of woud be changing C1 & C2 to .05UF .Math is one thing that never came back after the head enjury ( I know its 5 times the time costant ). Will fine tune it with a scope and signal generator after its built .

The amp will be driven by a modified PAS 3 with a cathode folower. There will be two RCA input jacks on it for each channel of the ST70 one with out the filter and the with the filter .Will use a FET folower after the preamp to buffer the filter for the subwoofer with the sub woofer filter built into the preamp .

Have you given any thought to making an electronic crossover @ 125hz 24db per octave?

Yeah, a few op-amps might be in order.... I have yet to see a subwoofer whose plate amp didn't have some tube-impossible low input impedance

Cheers!

The person its for doesn't want opamps , it will be a sony power amp for the subwoofer .

In that case, a plain passive 2nd order?

Have to get the loading impedance perfect, but you could use a cathode follower

Cheers!

Maybe using Duncan Amps Tone Stack Calculator software would be helpful.

EDITED ... (Are you talking about the .1 coupling caps?)

If you change those caps to match the 125hz bandspass they will still be active when you switch to the non bandpass inputs. It may not be worth the trouble to change those if the input is bandpassed. There won't be anything there for them to do under 125hz, anyway.

Have you thought of just running an equalizer in front of the '70 and just killing the 100hz with that? No input switching required...

Have you seen the Harrison Labs 150Hz. in-line RCA jack crossovers?

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=266-276

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