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Old 20th October 2012, 12:17 PM   #3501
naf is offline naf  Indonesia
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To try it too on my experimental board is a nice little phrase that translates to "much rework".
too try your experimental board for me is look like building from the start sir .
i just want to try lowering bias VAS....currently i'm using 32vdc supply and my VAS current reach 22mA... all getting hot
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Old 20th October 2012, 12:38 PM   #3502
Salas is online now Salas  Greece
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For you is 5 mins. Me, I will have to convert a bunch of stuff to go same circuit first.
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Old 20th October 2012, 12:45 PM   #3503
shaan is offline shaan  India
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i just want to try lowering bias VAS....currently i'm using 32vdc supply and my VAS current reach 22mA... all getting hot
Increasing the current feed resistors in small steps is the trick, as I mentioned before.
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Old 20th October 2012, 12:51 PM   #3504
MiiB is offline MiiB  Denmark
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I have scaled the SSA to 60V. using higher voltage transistors...and heavier drivers..
I have made different versions .. as Nico stated the design is circular in a way that thermals in the input drives the current in the VAS/driver as well. Through house keeping with current sources, this issue has been greatly reduced.
I have made a version where i have taken the 12V cascodes away (using 80V transistors for the input) and made a current mirror into the VAS/driver. This keeps the thermal balance in the VAS very good as the current is set by CCS and mirror scale.

I have made some different outputs. from laterals to Bipolars and a combination of both.

Sound is very very good. I believe its the simplicity and short current feed-back path that plays a major role in this. Like less is a lot more. The SSA is for sure a strong concept. But it really does require some good housekeeping. This type of simple current feedback circuits benefits a lot from fixed working conditions. Simple voltage/resistor biasing is not good enough for current feedback, as the feedback currents will alter/modulate the working conditions . The current feed-back needs to be purely additive process, for this you need a good high impedance CCS driving the circuit.
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Old 20th October 2012, 03:03 PM   #3505
naf is offline naf  Indonesia
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dear Salas and Shaan,
channel 1 done, current feed change by paralelling 3k3 || 2k4.. Vas current down to 14.2mA
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Old 20th October 2012, 04:30 PM   #3506
shaan is offline shaan  India
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Congrats naf. How does it sound with higher PS voltage?
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Old 20th October 2012, 05:27 PM   #3507
sonnya is offline sonnya  Denmark
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Originally Posted by MiiB View Post
I have scaled the SSA to 60V. using higher voltage transistors...and heavier drivers..
I have made different versions .. as Nico stated the design is circular in a way that thermals in the input drives the current in the VAS/driver as well. Through house keeping with current sources, this issue has been greatly reduced.
I have made a version where i have taken the 12V cascodes away (using 80V transistors for the input) and made a current mirror into the VAS/driver. This keeps the thermal balance in the VAS very good as the current is set by CCS and mirror scale.

I have made some different outputs. from laterals to Bipolars and a combination of both.

Sound is very very good. I believe its the simplicity and short current feed-back path that plays a major role in this. Like less is a lot more. The SSA is for sure a strong concept. But it really does require some good housekeeping. This type of simple current feedback circuits benefits a lot from fixed working conditions. Simple voltage/resistor biasing is not good enough for current feedback, as the feedback currents will alter/modulate the working conditions . The current feed-back needs to be purely additive process, for this you need a good high impedance CCS driving the circuit.
So you are at around 160watt @ 8r?
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Old 20th October 2012, 05:33 PM   #3508
MiiB is offline MiiB  Denmark
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Last take is 196W in 8-ohms.. Its getting better too... no DC drift and more sparkle like in your TSSA...but huge power, like it's limitless (you know the difference).
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Old 20th October 2012, 06:01 PM   #3509
sonnya is offline sonnya  Denmark
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I guess you use seperate front end supply?

My calculation was with out.
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Old 20th October 2012, 06:03 PM   #3510
MiiB is offline MiiB  Denmark
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No I run it on slightly higher rails.. my output looses some voltage, so separate ralis is not needed...a diode and good caps makes it sag free...
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