L 300 Bi amp

[300_Summit]

Hello all, I have a question. I'm in the midst of ordering parts to build Giskard's "L-300/4333 Bi-amp circuit". Do I need to install a 20uF protection cap for the mid frequency driver (LE-85) or is this circuit fine as-is?..........Thanks, Lamont


http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=21664&stc=1&d=1167584814

[johnlcnm]

Yes I would install a protective capacitor in series with the mid driver. If your amp has a turn on thump or the output section shorts it could destroy the mid diaphragm. There is a JBL chart of recommended protection caps on this site. I am going out on a limb here, but you should measure your final response. My system response, (4333B), exhibited a hole around 6Kz. It does not appear that the mass dominant rolloff was compensated for with the crossovers used in the 70s. My compensated response:

[300_Summit]

Yes I would install a protective capacitor in series with the mid driver. If your amp has a turn on thump or the output section shorts it could destroy the mid diaphragm. There is a JBL chart of recommended protection caps on this site. I am going out on a limb here, but you should measure your final response. My system response, (4333B), exhibited a hole around 6Kz. It does not appear that the mass dominant rolloff was compensated for with the crossovers used in the 70s. My compensated response:

The series cap would go in front of the 0.3mh inductor or right before the speaker terminals??

[4313B]

Yeah... about that schematic... basically one would want to wire it just like the 3133A network in bi-amp mode... ;)

http://www.jblproservice.com/pdf/Network%20Schematics/3133A%20Network.pdf

As you can see, JBL left what looks like 33 uF of protection capacitance in line with the 1" compression driver during bi-amp operation. :D


The series cap would go in front of the 0.3mh inductorYes.

[300_Summit]

Yeah... about that schematic... basically one would want to wire it just like the 3133A network in bi-amp mode... ;)

http://www.jblproservice.com/pdf/Network%20Schematics/3133A%20Network.pdf

As you can see, JBL left what looks like 33 uF of protection capacitance in line with the 1" compression driver during bi-amp operation. :D

Yes.

Thanks a lot Giskard, I really appreciate it. One last thing, if I wanted to do a Nelson pass top section (mid and high frequency, leaving out the low section; it would be connected to an active crossover) could that be done as-is without any modification to the Nelson Pass circuit?

Lamont