Hi !
I just designed a new ClassAB-Amp, but maybe it's a little
strange...
What do you think, should i give this a try ?
The THD in PSpice says 0.0005% @ 2.8v 4ohm 1khz
Its specially the inputcircuit that i haven't seen yet,
maybe i violate some semiconductor-rules ?
cu,
Michael
I just designed a new ClassAB-Amp, but maybe it's a little
strange...
What do you think, should i give this a try ?
The THD in PSpice says 0.0005% @ 2.8v 4ohm 1khz
Its specially the inputcircuit that i haven't seen yet,
maybe i violate some semiconductor-rules ?
cu,
Michael
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Hi,
there is nothing strange in Your amplifier. There are some unusual solution, such as Q29, and the 666ohms in the VAS stage.
But I think it will work, If You put together.
sajti
there is nothing strange in Your amplifier. There are some unusual solution, such as Q29, and the 666ohms in the VAS stage.
But I think it will work, If You put together.
sajti
Looks good, but why did you use current source against Q29?
You should use emmiter follower with Q30(as Q29) and place temperature compensation and bias circuit between colectors of Q31 and Q32. I think that it can be much better.
You should use emmiter follower with Q30(as Q29) and place temperature compensation and bias circuit between colectors of Q31 and Q32. I think that it can be much better.
DarkOne said:
I thought, do it a different way... ;-)
In fact, the construction with the current source against Q29
showed up much better results. Q29/Q30 form a simple current
gain. Because of the constant current through the emitter of Q29
this transistor has much better linearity and has nearly a constant
current at its base, which reduces distortions in the VAS.
Especially the high harmonics above K3 seem to be eliminated.
The strange part in this circuit (i thought) is the inputmodel, using
complementary jfets.
Mike
joan2 said:
Yes, i wanted to avoid a tripledarlington, and this kind of buffer
seems to be very friendly to the VAS.
The 2nd advantage is, that it doesnt use complementary BJTs...
So no matching of devices here 🙂
Mike
traderbam said:
It's not easy to match transistors in PSpice, so i compensated
with these differences. In real world, this would be a poti for
adjusting DC-Offset. With perfectly matched pairs, these two
would be identical.
I will try to match these in PSpice, this should greatly reduce K2,
i hope...
Good way to adjust dc offset. However, a side-effect is to change the feedback factor between the two halves, which may or may not be what you want.
No, i don't really want that, i think that this difference creates
many K2's, that's why the transistors should be matched.
But a minimal difference shouldn't do any harm.
I just ordered the jfet's (spuro.de), i will try this amp the next
days...
many K2's, that's why the transistors should be matched.
But a minimal difference shouldn't do any harm.
I just ordered the jfet's (spuro.de), i will try this amp the next
days...
Hi mike,
look at: http://perso.planetis.com/pcharlet/plan.html
called mosquito , if i remember right.
alf
look at: http://perso.planetis.com/pcharlet/plan.html
called mosquito , if i remember right.
alf
Okay, like always, you think you have a new idea, but most
new ideas are "old"... hmmpf
But this means, my construction is not weird or strange.
But connecting Mosfets directly to the VAS ? Poor high freqs !
I did this once, and had audible distortions with some selected
tones, mainly strings and other complex sounds...
Mike
new ideas are "old"... hmmpf
But this means, my construction is not weird or strange.
But connecting Mosfets directly to the VAS ? Poor high freqs !
I did this once, and had audible distortions with some selected
tones, mainly strings and other complex sounds...
Mike
Sinve you evaluated the projected THD with Pspice, can you run an AC analysis to take a look at at gain vs. phase? Just to be sure that the gain rolls off to zero before the phase lag reaches 180 deg. More than once using spice, I thought I had a brilliant new amp with increadible THD only to find that if I has actually built it it chances are it would have turned so slag in the first few seconds.
Hmm, now i'm a little messed...
I'm not a pro in using spice, so i am not sure if i understood you
correctly. I checked the circuit at 20khz with full power, and had
no decrease in gain. With 200khz it shows a slight loss in gain,
and how bad the model for the mjl3281 is. (downloaded at onsemi)
A storage time > 0.5us ? the mjl1302 performs fine and does not show
these symtoms. I have the same problem if i test the device alone.
What was the problem with your built amp ? Did it oscillate and
selfdestroy, or just bad bandwidth ?
Mike
I'm not a pro in using spice, so i am not sure if i understood you
correctly. I checked the circuit at 20khz with full power, and had
no decrease in gain. With 200khz it shows a slight loss in gain,
and how bad the model for the mjl3281 is. (downloaded at onsemi)
A storage time > 0.5us ? the mjl1302 performs fine and does not show
these symtoms. I have the same problem if i test the device alone.
What was the problem with your built amp ? Did it oscillate and
selfdestroy, or just bad bandwidth ?
Mike
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