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Crown XLI1500 a modern day staple?


jwc

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I pulled power for the board from the +/-50VDC lower rail leads that connect the power supply to the amplifier board.  The filter has Zener regulated supplies to provide the +/- 15V rails for the op-amp packages (AD713).  If there's one place where this amplifier can be improved is the power supply,

power_supply_taps.jpg

power_supply_taps_1.jpg

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I can't follow all your charts/graphs....but very interesting and I believe I understand your goal here.

 

I would  love to hear one of these.  

 

On 4/29/2017 at 9:22 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

 

Do you have a stock Khorn around to try this on.........with your ears...or something else that is a 3 way horn loaded speaker?

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1 minute ago, jwc said:

I can't follow all your charts/graphs....but very interesting and I believe I understand your goal here.

 

I would  love to hear one of these.  

 

 

Do you have a stock Khorn around to try this on.........with your ears...or something else that is a 3 way horn loaded speaker?

 

Been there, done that.  Works perfect.  It's a project I did some time back. 

 

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1 hour ago, jwc said:

I can't follow all your charts/graphs....but very interesting and I believe I understand your goal here.

 

The plot below is the small signal bandwidth of the XLi with the filter installed.  The low end responses shown are with different R/C combinations on one section of the filter.  The 6dB max assumes balanced inputs.   The response is the signal being sent to the error op-amp  (where output stage feedback is introduced).  The -3dB frequencies shown are 47, 36, 28 and 25Hz.   The top end -3dB is 460Hz.  The 4th order bandpass at 36Hz eliminates the low end stuff where the Klipschorn no longer behaves as a horn, it's filtered out.  Need a sub however to handle the low stuff. 

XLi1500_band_pass_HF_response.jpg

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Is that low end 

On 5/7/2017 at 11:56 AM, John Warren said:

The -3dB frequencies shown are 47, 36, 28 and 25Hz

Is that something adjustable for the end user....or fixed internally

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3 hours ago, jwc said:

Is that something adjustable for the end user....or fixed internally

 

The capacitors C1, C2, C3 and C4 determine the low end, -3dB frequency.  I designed the filter such that C1=C2=C3=C4 so changing the -3dB frequency means changing all caps from one value, say 1.0uF, to another, like 1.2uF.  There are two channels on the board, a total of 8 caps need to be swapped out so not "end user" friendly but hardly difficult for anyone that has basic solder/de-solder skills.  The caps in this configuration are polyester film at about $1 each.  I used Panasonic on the first builds and the results were excellent.

  

 

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  • 4 weeks later...

FINALLY some time to play with this little project!

 

Got the boards last week and popped the on-board supplies in for testing with the amp lower rails as inputs.  The on-board supplies provide the +/- rail voltages to the 8 op-amps on the board (MJE340/350 complimentary transistors are used here).  There's a photo of how the board gets installed in the amplifier.  The board is on the air-intake side of the heat sink and shouldn't have any effect on cooling of the output devices.  I also installed sockets so other op-amps can be tried.  For this build I'm using AD713s.

 

filter_board_5.jpg

filter_board_2.jpg

filter_board_4.jpg

filter_baord_6.jpg

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8 hours ago, jwc said:

I am assuming you have the board just "sitting" in there and that there is some soldering to do.

 

Yes, but not difficult to install.  The two leads from the lower PS rails are soldered to the +/-V solder pads on the board.  J1, J2, J3 and J4 will be used to connect the filter to the amplifier and front panel potentiometers.  Those connections will be made using the terminals show in the photo (the white part with pins will be soldered to the filter board at J1, J3, etc).  The "finesse" part is stripping the 26AWG wire leads that feed the potentiometer and then connecting the small signal cabling into that.  That's where the right wire stripping tool comes in.  A Stripmaster or other tool is a must.   The splice is then covered with adhesive shrink tubing and shrunk tight.  

 

So not too difficult if the tools and hardware are on hand.

 

terminal.jpg

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Here's what we're going after (in theory!).  For the Klipschorn will run something like the red response and for the Jubilee the blue.  I don't have a Jubilee here to measure however so will need some guidance from those that have them.  I could also look at what Delgado has posted for a design and use that to derive an upper corner frequency.   This is small signal simulation mind you, what's fed to the front panel gain potentiometer.  The low end corner is -3dB at 28Hz.  I have found that placing a low end filter on bass horns cleans them up a bit.

 

Note the response is +6dB in the passband because the model considers balanced inputs.  And yes, the output at that the Speakons is in-phase with the input!

 

filter_board_sim_1.jpg

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  • 3 weeks later...

Finished a couple of the filter boards.  When I was testing them I took a few pics.  The first set of tests are to drive the board off the lower rail taps and measure the heat dissipation in the power supply transistors.  I pulled the amplifier board out to avoid damaging it with an unexpected pop or blowout.  Good news was nothing happened.  The current regulating transistors on the board are MJE350/340.  No over temps, no oscillations.  The FFT plot shows the filter response of the two channels driven by the XLi power supply after about two hours of operation.  The small signals were applied directly to the input pins of the board.  This would be the response for a Klipschorn bass unit. The big caps on the board are Panasonic polyesters which is over-kill but easy enough to install.  

 

filter_board_8.jpg

filter_board_7.jpg

filter_2.jpg

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Placed the amplifier board back into the chassis and made the small signal connections to the filter.  For the Crown XLi, the connections are very simple and requires only one pair of wires to be connected to each channel of the board.  The black and white leads are the taps off the lower rail voltage that drive the op amp powers supplies on the filter board.  The entire board draws about 25mA of current which the SPICE model predicted exactly, btw.  

 

FWIW, I've treated this amp like a "rented mule".  I had a few screw-ups with it and had to repair it a couple of times.  While inside I changed things too but more for my own interests.

 

filter_board_9.jpg

filter_board_10.jpg

filter_board_12.jpg

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Some responses with the amplifier connected to a Klipschorn bass unit.   First plot is the horn measured with and without the filter operating.    Second plot shows the response with different front panel pot settings.  Nothing fancy with the measurements.  The mic is laying on the floor facing the front of the horn and located at the centerline.  Although simple it reproduces a similar response plot to the anechoic chamber response.

 

The filter is a bandpass and you can see there's a tad of attenuation at the low end.  That can be increased by lowering the cap values on the high pass section of the filter and would be the way to go about incorporating a sub-woofer into the system. 

 

It would take a wheel-barrow of parts to make this in a passive, no thank you.  

 

filter_5.jpg

filter_6.jpg

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After all this testing at full power, the unit has been on for about 3h.  Now's a good time to measure the power transistors on the board to determine if I screwed something up with the temperatures.  The max. junction temp for an MJE350 is 150C so we're looking good there and no need to add a sink.

 

filter_board_14.jpg

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The installed 14 pin DIP sockets allows for device rolling.

 

Analog Devices AD713 (red) and TI TLE2074 (green) packages compared.  FFT is measured across 8Ohm power resistor.  The low-pass section of a cascaded Sallen-Key band-pass filter is where different op-amps show measurable differences for a fixed circuit design as is shown in the plot below.   Truth is instability in the stop-band can't be simulated in any of the SPICE engines I've used so it has to be determined experimentally, hence the sockets 

 

The AD713 is a "smidge" better than the TI device but both would work fine.  The blue is the amplifier response with the filter defeated.

 

What's interesting in this plot is the amplifier will produce output well below 20Hz which, without the high pass filter section,  the K33E will respond to.  It's useless mechanical garbage that does nothing but modulate the cone and contribute to resonance.  So putting everything below 30Hz in the stop band it's goodness.    

filter_10.jpg

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Distortion measurements across the pass-band of the filter with both the AD713 top and TLE2074CN bottom.  Top curve in both plots is 400Hz then 300, 200, 100 and finally 50Hz.

 

The AD713 is 3X the cost of the Texas Instruments package but distortion is about the same.  Might have something to do with the fact that Analog Devices is headquartered in Norwood, Massachusetts and TI isn't! 

 

Distortion is very low up to about 300W(!).  That's what happens when you filter out all the HF content from the amplifier.

 

It's really shooting fish in a barrel.

 

filter_12_AD713.jpg

filter_12_TLE2074CN.jpg

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  • 1 month later...
On 4/29/2017 at 9:22 AM, John Warren said:

The horn loaded range is where it makes the best sound.  

I always thought the same thing about a LaScala with K-43's and a horn loaded subwoofer below 100, like Bill Fitzmaurice's Tuba HT. So I'm assuming this bandpass filter could be implemented for a LaScala as well as a Khorn?

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