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Old 4th May 2011, 06:41 PM   #1
ATAUDIO is offline ATAUDIO  Austria
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Default JAS - Just Another Sziklai

OK,
As I have said in some other thread, here is a DIY project that I am working on.
It does not want to be nothing very special, but just something that we can play with and hopefully sounds well!
It does not want to be a production item so it might be necessary to tweak it to reach maximun performances (i.e. THD) and stability, but that is the juce of this game, for me.
The schematic is pretty standard and resembles many around: OSs BX Mongrel, P3, Baby AKSA, etc.
The output is CFP (thanks, Mr Sziklai!) and can be arranged in two ways: a "pure" CFP with onlly one pair and a "modified" version suitable for two or more pairs. I see a lack of multiple pair CFPs around, so this is my proposal.
I have arranged a PCB that can support both the versions and lets space for some tweaking.
I am posting first the multiple pair version (-200) that is the more interesting, I believe.
The four output devices should be mounted on a separated Heat Sink, and their emitter resistor simply wired. (Nothing forbids you to make an add-on PCB)
Just think that ALL the four OP devices can be put directly on the SAME Heat sink WITHOUT insulators, provided that the heatsink itself is insulated from the chassis.

Driver devices AND VBE device MUST share another, small heat sink ( a small alluminium bar will suffice). Also the VAS needs a small heatsink, alone.
Hope that somebody is intersted. Comments, suggestions, questions are highly appreciated.
Attached Files
File Type: pdf JAS200_1b.pdf (22.8 KB, 564 views)
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Old 4th May 2011, 06:53 PM   #2
Mooly is offline Mooly  United Kingdom
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It looks fine... hard to comment without building and listening.

Only thing that comes to mind is R10 and R27. Is there enough current drive for the drivers and outputs ? CCS maybe.

The IN5400's used as clamps are only 50 volt devices ! They will see twice that under full drive. Use IN5404's or 5408's
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Old 4th May 2011, 07:18 PM   #3
ATAUDIO is offline ATAUDIO  Austria
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Originally Posted by Mooly View Post
It looks fine... hard to comment without building and listening.

Only thing that comes to mind is R10 and R27. Is there enough current drive for the drivers and outputs ? CCS maybe.

The IN5400's used as clamps are only 50 volt devices ! They will see twice that under full drive. Use IN5404's or 5408's
True, for the diodes, I just used the wrong generic symbol. I meant to use a 3A -600V Fast device.
R11 - R12 should allow about 400mA that should be enough for the bases, considering a total OP hfe of 30 at least.
Don't see the problem for R27.
Thanks a lot for the suggestions.
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Old 4th May 2011, 07:29 PM   #4
lineup is offline lineup  Sweden
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MJE15034/35 are good gain.
So, I think it will work with the bootstrap, 2k7 and 3k9

I should use a normal RED LED for CCS.
It will follow the transistor Q4 well at different temperatures.
There is a reason many designers use RED LED.
But this is a rare occation with BLUE
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Old 4th May 2011, 07:34 PM   #5
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It just looked a little on the low side for VAS current thats all... I know its bootstrapped... just thinking worst case, low impedance load, high output swing, high current at high frequency and so on. As I say it was just something that struck me.

See how it performs
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Old 4th May 2011, 09:04 PM   #6
ATAUDIO is offline ATAUDIO  Austria
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Quote:
Originally Posted by lineup View Post
MJE15034/35 are good gain.
So, I think it will work with the bootstrap, 2k7 and 3k9

I should use a normal RED LED for CCS.
It will follow the transistor Q4 well at different temperatures.
There is a reason many designers use RED LED.
But this is a rare occation with BLUE
In my opinion Blue LED has some advantage. I has a l bigger bias voltage that helps the transistors (in case you use not very high Vce models like BC546) and lets you use a bigger Re for the same current, that makes the CCS more stable. You could use a WHITE as well.(ab. 3.9 V). I believe the main reason that they are not so common is that they did NOT exist in the past. Blue and UV leds are GaN devices, a more recent technology than the GaAs used for Red , IR, Yellow and Green, thanks to the wonderful work of Mr Nakamura. Of course if you would have to use the same reference for the VAS CCS, the bias voltage might be too big, but it is not the case since we have a simple bootstrap here.
Thanks for the interesting comments.
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Old 4th May 2011, 10:23 PM   #7
ATAUDIO is offline ATAUDIO  Austria
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Default Single pair version

This is more standard - single pair CFP.
Note the different values of R13 R14.
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File Type: pdf JAS100_8b.pdf (21.9 KB, 223 views)
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Old 4th May 2011, 10:28 PM   #8
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I can't say as I see any emitter resistors on those OP's..?

Doug
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Old 5th May 2011, 06:28 AM   #9
ATAUDIO is offline ATAUDIO  Austria
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I can't say as I see any emitter resistors on those OP's..?

Doug
With a single pair you do not need emitter reistor on the OP, since there is no current sharig problem due, say, to hfe unbalance.
You can think at the CFP compund as a single device, which emitter resistor is the drivers' emitter resistor.
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Old 5th May 2011, 07:35 AM   #10
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Quote:
Originally Posted by ATAUDIO View Post
In my opinion Blue LED has some advantage. I has a l bigger bias voltage that helps the transistors (in case you use not very high Vce models like BC546) and lets you use a bigger Re for the same current, that makes the CCS more stable. You could use a WHITE as well.(ab. 3.9 V). I believe the main reason that they are not so common is that they did NOT exist in the past. Blue and UV leds are GaN devices, a more recent technology than the GaAs used for Red , IR, Yellow and Green, thanks to the wonderful work of Mr Nakamura. Of course if you would have to use the same reference for the VAS CCS, the bias voltage might be too big, but it is not the case since we have a simple bootstrap here.
Thanks for the interesting comments.
2/3 reds = blue w/ better delta (temperature) characteristics. In my next hawksford cascode I will use 3 reds per rail to set my base voltages. SUPERIOR. Best red led is GaAs/1.65-1.8Vf.
PS - on a LIN amp cascode , I got 10V by chaining 6 SMD LED's together. Final strip was 3 X10mm w/ leads (like a small transistor).
OS
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Last edited by ostripper; 5th May 2011 at 07:39 AM.
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