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 .
Using a ST 70 biamped
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by burnedfingers » Thu Dec 01, 2011 6:17 am
Have you given any thought to making an electronic crossover @ 125hz 24db per octave?
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by Geek » Thu Dec 01, 2011 7:02 am
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!
Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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by Geek » Thu Dec 01, 2011 4:55 pm
In that case, a plain passive 2nd order?
Have to get the loading impedance perfect, but you could use a cathode follower
Cheers!
Have to get the loading impedance perfect, but you could use a cathode follower
Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Geek - KT88
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by mesherm » Fri Dec 02, 2011 6:10 pm
Maybe using Duncan Amps Tone Stack Calculator software would be helpful.
Mike's N-1 Rule: When looking for N number of components to finish a job, you have a 95% chance of only finding N-1 of them.
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by 20to20 » Fri Dec 02, 2011 8:53 pm
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
20
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
20
Headed for Tishomingo to sing in a can...
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