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Old 19th August 2011, 12:24 PM   #301
alex mm is online now alex mm  Romania
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Default PCB rev 1.2 for MiiB and not only ...

....... I have done requested , hope to not forget something Space between input transistors are for small heatsink ....
Alex.
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Old 19th August 2011, 12:34 PM   #302
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Exclamation SSA IGBT version

To put another version to DIY maybe sombody will find this IGBT as the most suitable for him, lets see.

Another comment to my yesterday test with real PWS is about PSRR. I am impressed how good the +/-15V DC rails are in real SSA amp. They completelly serve the purpose without any need to have regulated or other kind of +/-15V supply whatsoever.
The result is impressive, at the speaker's tweeter there is absolutely nothing, no sound, black silence. So we really need PCB LEDs to show power on operation.
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Old 19th August 2011, 01:27 PM   #303
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Default DC offset stability

On more good thing about the SSA in any version, is DC offset stability. Once it set to 0V at the ouput, it is stable within +/-10mV regardless to thermal conditions of the output's heatsink. The only condition is proper thermal connection between input pair BJT's, so no need for any kind of DC servo circuits whatsoever.
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Old 19th August 2011, 01:35 PM   #304
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ANy suggestion for other BJT's for seconf set of transistors? I have BC 550/560 and lateral ouput fets, but nothing for other bjt's.
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Old 19th August 2011, 01:51 PM   #305
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Hi buzzforb

It all depends to rail's voltage potential, if it is 35V like on this last sch, than you would have only 0,1W power on thermal dissipation + 0,07W max extra dissipation at full signal present. So for +/-35V BC550C/BC560C are OK.

For higher rail voltages and thus power dissipation you would need TO-126 case for cascodes BJT's, like BF471/BF472 etc.

The most important thing to maintain quality of this symmetrical SSA design is gain factor equality for all complementary semiconductors in the circuit. The input pair is the most critical and it is recomended to choose current gain more than 600 +/-0,5% tolerance between NPN/PNP device, and similar to the other semiconductors.

In simple designs like SSA is, it is allways very important to choose the best parts possible.
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Old 19th August 2011, 02:01 PM   #306
MiiB is offline MiiB  Denmark
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I do blive that all components matter in this Design...I look to use melf resistors, Panasonic FC capacitors. polystyrene/tin for the decoupling..SA970/SC2240 for the input/cascode. SA1381/SC3505 for the drivers and the EXICON lateral-fets for the output.
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Old 19th August 2011, 02:30 PM   #307
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the driver BJT's are what i am looking to source. i cannot get the ones in the schemtic over on this side of the atlantic.
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Old 19th August 2011, 02:39 PM   #308
MiiB is offline MiiB  Denmark
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the mje 350/340 could be an alternative...
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Old 19th August 2011, 03:01 PM   #309
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Hi all,
Thanks for the interesting work.
I have a set of the world's most demanding speakers (Apogee Sinctilla). Impedance drops to 0.4 ohms on the mid range ribbon.

Would it be possible to use this amp with several paralleled output devices to drive such a difficult speaker?

What about using ut to drive 50ohm headphones?
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Old 19th August 2011, 03:46 PM   #310
MiiB is offline MiiB  Denmark
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The lateral fets are quite easy to drive....so it should be possible to extend to 6 set of output devices...Its possible to adjust the drive current by increasing the resistors to maybe 150 ohms and at the same time decreasing the spreader...6 pairs should have app 30 mA give or take a little... and plenty of current capabilities. think a version like that with app 45 V rails will do the job..
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