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Old 21st March 2012, 06:36 AM   #2151
sonnya is offline sonnya  Denmark
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Any measurement of thd and other figures?
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Old 21st March 2012, 08:32 AM   #2152
hahfran is offline hahfran  Germany
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This topology works fantastic in terms of thermal tracking no test of audio qualities yet.
In theory note that it employs current amplification throughout and the power stage is NOT EF .

D1 D2 are the on chip thermal trak diodes Q5 Q8 are thermal trak BJTs.
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Last edited by hahfran; 21st March 2012 at 08:34 AM.
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Old 21st March 2012, 08:47 AM   #2153
Salas is offline Salas  Greece
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What is the output impedance, roughly speaking? You tested a prototype and it tracks nice you meant?
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Old 21st March 2012, 09:42 AM   #2154
hahfran is offline hahfran  Germany
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No such I attempted a topology inclusive of SSA predriver and inclusive of bias control vs junction temp using thermal trak BJTs. The latter is excellent quiescent at 25 50 mA at 125 90 mA. And the second goal all current amplification - BJTs are perfect current amplifiers FETs are not - is achieved with this circuit.
So far just academic.
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Old 21st March 2012, 03:29 PM   #2155
vgeorge is online now vgeorge  Greece
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A pcb group buy would be most welcome!
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Old 21st March 2012, 09:55 PM   #2156
AKSA is offline AKSA  Australia
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Hahfran,

Could I ask how the bias current is set in the output stage? I see no bias generator on the output stage, though Q4 and Q12 do pass a consistent current at idle.

Hugh
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Old 21st March 2012, 10:12 PM   #2157
MiiB is offline MiiB  Denmark
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The diodes sets the constant current and also gives the thermal stabilization.. clever circuit...
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Old 21st March 2012, 10:30 PM   #2158
hahfran is offline hahfran  Germany
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Quote:
Originally Posted by AKSA View Post
Hahfran,

Could I ask how the bias current is set in the output stage? I see no bias generator on the output stage, though Q4 and Q12 do pass a consistent current at idle.

Hugh
No there isn't any bias generator. The bias is set with the current Q1Q2 Q9Q10
and the drop across R15 R16 and the temperature dependend drop D1 D2 the thermal track diodes. Thus the idle current Q4 Q12 is 1 mA. As said it is an current driven amp. The amplification factor is set to 12 or 21.6 dB.

I have very few reliable (!!) BJT models for LTSpice but so far there is considerable crossover distortion that cannot be blamed on the model.
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Old 21st March 2012, 10:42 PM   #2159
hahfran is offline hahfran  Germany
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Apparently some miscalculation because the switching already happens in the cascodes
Q1Q2 Q9Q10
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Old 22nd March 2012, 12:40 AM   #2160
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Quote:
Originally Posted by hahfran View Post
This topology.
Nice one, indeed.
About BJTs vs FETs, i prefer FETS for their bandwidth, larger flat slope area and roughness. With the complex charges loudspeakers are, we do not have to worry too much about "perfect current amplifier", omho ;-)
Well, i agree FETs or MOSs are not easy to drive, because their gate capacitances.
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