[Crown XLI1500 a modern day staple?]

On 4/29/2017 at 4:22 PM, John Warren said:

 

The idea was to develop an active bandpass filter for any bass horn (say a Klipschorn) that's otherwise impractical to realize using passive components.  The XLi is low cost, has excellent %THD below 1kHz, is class AB and lends itself to the mod.   The actual filter is text book Sallen-Key, very easy to implement in the small signal section of the amplifier.  In the schematic, the filter is outlined in red.  I've placed it between the input op-amp (U2) and front panel pot comprised of R35, R44 (pot is at full CW).  The schematic shows just the small signal processing of the XLi.  U1 is the gain amp, U3 is the error amp. 

 

The response plots shown are small signal simulations that are possible using cascaded Sallen-Key filters.  The PC board for the filter is installed vertically sharing a couple of the mounting screws used to mount the amplifier board to the chassis.   By implementing a 4th order bandpass in the small signal domain the amp drives the Klipschorn to work within its horn loaded range.  The horn loaded range is where it makes the best sound.  

 

 

 

Good day John Warren. i have been following this thread over crown xli amplifiers. I have an xli 3500 i am working but am having challenges. Can you please share a full picture of the bottom image so i can do further troubleshooting.

 

thanks in advance