[Crown XLI1500 a modern day staple?]

On 4/22/2017 at 8:52 AM, John Warren said:

 

Agreed.

The sinks are shrouded using a poly type of fiber reinforced "paper" which guides airflow across the fins.  A couple of fans draw the air across the fins.  The fans are quiet.

 

The down side of the assembly is that it's near impossible to get at the output devices.  At the factory, the output devices are attached to the heat sinks, the heat sinks then attached to the board (using machine screws that pass thru the bottom of the board into threaded holes in the sinks) and then the devices are soldered manually to the solder pads.  So it really wasn't designed to be repaired a the device level.  That said, the amplifier board is designed to be pulled and swapped for a new unit which is unfortunate because with a few design changes the devices could be relatively easy to replace individually.        

hello john I really liked your work with this amplifier I am a beginner in electronics you have the schematic of the crown xli 2500 I have this same amplifier and I would like to start this project thanks

[Crown XLI1500 a modern day staple?]

On 4/29/2017 at 6:22 AM, 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.