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1980 Cornwall Crossovers


Pstores

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7 minutes ago, captainbeefheart said:

I wonder if anyone has measured more distortion with these in the circuit. The non-linear load of the rectifier may introduce unwanted harmonics into the signal.

What about wiring in a filament type bulb.  Harder to get nowadays but what do you recommend?  Adds a little resistance I think. 

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52 minutes ago, tigerwoodKhorns said:

What about wiring in a filament type bulb.  Harder to get nowadays but what do you recommend?  Adds a little resistance I think. 

 

It will increase resistance with increased current.  A PTC Thermistor is much better, it will have a much sharper knee at a specific current you choose, at this current and where you pass the knee increases resistance very quickly to a very high level. The light bulb will have much more gradual transfer between current and resistance and not offer as good protection.

 

 

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4 hours ago, Pstores said:

is this a stock part in this crossover.

NO  for the klipsch crossover   , but YES , for the  EV STR and the K77 since  both components were Made by Electrovoice  to compliment each  other .

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15 hours ago, captainbeefheart said:

 

It will increase resistance with increased current.  A PTC Thermistor is much better, it will have a much sharper knee at a specific current you choose, at this current and where you pass the knee increases resistance very quickly to a very high level. The light bulb will have much more gradual transfer between current and resistance and not offer as good protection.

 

 

Do you put it in series with the tweeter in the negative line to the tweeter?

 

How do you size these? 

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19 minutes ago, tigerwoodKhorns said:

Do you put it in series with the tweeter in the negative line to the tweeter?

 

How do you size these? 

 

Yes they go in series with the tweeter, shouldn't matter + or - leg

 

As for size, If memory serves correctly I don't think the K77 want anything over 2-2.5 watts maximum power, we'll say at 6 ohms, that's 645mA for 2.5 watts.  So you look for a PTC that has a It (current trip) of 600mA. This littlefuse brand says Tt (trip time) of 2 seconds. So if current reaches 600mA or higher for longer than 2 seconds it will raise from a resistance of .8 ohms to 4 ohms, once current is reduced it will reset back to Rmin (resistance minimum) of .8 ohms. At $.82 they are cheap insurance for K77 protection.

 

https://www.digikey.com/en/products/detail/littelfuse-inc/TRF250-180-2/1114120

 

 

 

 

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