Redesign Crown K2/1 BCA amplifier (with schematic) pls help with the feedback - diyAudio
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Old 15th January 2007, 09:36 AM   #1
mrx23 is offline mrx23  Hungary
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Default Redesign Crown K2/1 BCA amplifier (with schematic) pls help with the feedback

Here is the schematic of the K1/2 amp.
You can downloaded it, but you MUST delete it after downloading I take no responsibility for it.
The scematics are only for 1 channel!

http://onlany23.atw.hu/Crown Input Board.pdf
http://onlany23.atw.hu/Crown Main Board.pdf
http://onlany23.atw.hu/Crown Output Module.PDF
http://onlany23.atw.hu/Crown K serie...ice Manual.pdf

So we can start rebuild it!!!!
Its way better than ClassD, the FETs have got
separate Drivers with NO deadtime.
The high side fets have got +Vcc+12V driving source from the PSU. There is no need of Bootstrap! And half bridge drivers have dead time, so the are completely wrong for BCA!
Thanks to NO dead time the THD will be very low!!!

The whole amplifier's heart is 2 LM361 precision comparator! (you can replace with other comparator (T<=20nS differential output), and the differential output is not needed, for shutdown use SHDN pin!

I want to rebuild it (in a 100W version first with only using few parts:
4Mhz clock (divided to 250Khz), integrator, 2 precision comps, fet drive+fet,filter,overcurrent protection,temperature protection,and an input buffer,
----------
Please explain me how does these feedbacks work in the amp!

So there is an I monitor at the output the signals from it gos to an error amplifier (that varies the sound input), and goes to the triangle generator.

The second feedback is the "FO" and its goes to the
triangle generator and the DC servo (the dc remover).

But the feedbacks are after the coils so the signals from them are phase shifted?

What does happening when the I monitor recognises
normal currents? How its modifing the sound signal, and the triangle?

The T100 is not sensing the Over current!
It just a feedback. The over current is sensed by
a windows comparator that mesures the current flow in the mosfet line.

There are a lots of R-s and C-s on the feedback line what do they do? Do they correct the shifted phase?

The white paper of BCA is not complete, the BCA isn't
using only 2 inductors! It has 3 LC lowpass filters at the output (two 250Khz and one 500Khz, the 500Khz is for bridging), so there is 5 aircore 30A inductors!
But we cant remove any of them because its affect
phase shifting so the feedback will not work.

If DC servo circuit sees DC on the output what does it do?

What doese the response EQ circuit do?

The I monitors output is 1V/5A, so the maximum is about 2,5V.

What kind of diode do you recommend?
The service manual says only : 4x300V ultrafast TO-220
(current rating?)
I read the service manual many times but there are some things that not mentioned.

So please help me to understand these feedbacks,
I only need that to redesign the amp (ofcourse just for education purpose!).

This thread is not about:
-triangle generation
-MOSFET driving!
-the type of the MOSFETs
-PIC controlling
-SMPS
-Bridging
-Stereo BCA
-soft start

There are some unneeded circuits like:
-Thermal LED
-Clip
-IOC
-Output signal LED
So please forget these.

And please dont try to reinvent BCA, you CANT do better BCA amp then the professional K2/K1 series
Please concertrate on the feedback.

And before you post read carefuly the service manual!

Download the PDFs soon as possible (and delete after it), I cant hold on the server for a long time, because its not really legal! And please dont reupload, so this thread could work for a long time.
And dont forget the Crown workers could read this thread to
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Old 15th January 2007, 09:59 AM   #2
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Quote:
There are a lots of R-s and C-s on the feedback line what do they do? Do they correct the shifted phase?
Yes, they do !

Regards

Charles
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Old 15th January 2007, 11:31 AM   #3
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What is 7th order Gaussian?
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Old 15th January 2007, 11:38 AM   #4
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Quote:
What is 7th order Gaussian?
The same as seven first order filters of the same f3.

Regards

Charles
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Old 15th January 2007, 11:58 AM   #5
Vek
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Gaussian filters:

Quote:
From http://www.filter-solutions.com/gaussian.html
The Gaussian Filter is the filter type that results in the most gradual pass band roll-off and the lowest group delay. The step response of the Gaussian filter NEVER overshoots the steady state value. As the name states, the Gaussian Filter is derived from the same basic equations used to derive the Gaussian Distribution. The significant characteristic of the Gaussian Filter is that the step response contains no overshoot at all.
Cheers
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Old 15th January 2007, 01:21 PM   #6
fredos is offline fredos  Canada
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Cant help you more, server unavaible!

Fredos
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Old 15th January 2007, 01:23 PM   #7
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Is this "7th order Gaussian LPF" at input has relation with the output filter being so complicated, or these 2 are independent with each other?
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Old 15th January 2007, 01:45 PM   #8
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The real K1 schematic is too complicated for DIY project. Crown can fit all these into standard rack because they use SMD components.

Would be interesting if the essence of this BCA principle is implemented by PassLabs team
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Old 15th January 2007, 02:32 PM   #9
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Quote:
Is this "7th order Gaussian LPF" at input has relation with the output filter being so complicated, or these 2 are independent with each other?
NO

A filter of that high an order is IMO not necessary at the input of a switching amp.

Regards

Charles
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Old 15th January 2007, 03:08 PM   #10
mrx23 is offline mrx23  Hungary
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Its really not that complicated!

If we want to build a mono amp!
We dont need these:
-Common mode input (XLR) /U100,U101
-Compressor /U1B, U102B
-Thermal limit control /U4B,U4C,U3A,U3B
-sense of the output power (LED) /U2A,U2B
-clip detector /U1A
-distrorsion LED /U102C,U102A,U102D
-we dont need spleep circuit /U201C,U5C,U5D
-bridige /U101C
-stby /U5B
Mainb:
-crowbar /U2D, U7D,U7C
- and >10 OPamps


What we need:
3 OPamps for triangle generating (from 4Mhz precision)
1 OPamp input buffer
1 OP DC servo
4 OP (or less) for low pass filter <25Khz input
4 OPamp for error calibration
2 high speed comparator (MAX963) in 1 SO!, 4.5nS!, feeded with 0-5V signals, it also has SHDN pin which is simple to use.
fet drive: MAX5054 4-15V 4A! 20nS
Max ICs are for free samples

4 Opamps are in one packet so 4 SO/DIP can be used(4x4=16>15).
You can put very big current rated MOSFETs in the output stage! So you can achive 4 KW++ power, with ~90% effeince Maybe this inspires someone

We have to just work out the feedback to get a rock stable amp

Here is the stable working triangle generator without feedback, open with Multisim 9.
Attached Files
File Type: zip triangle gen!.zip (80.2 KB, 537 views)
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