Looking to build a SE Class A amp...
either a MOSFET or NPN output..
what are adv vs disadv?
Can I use a choke to load either of these?
Thanks!
either a MOSFET or NPN output..
what are adv vs disadv?
Can I use a choke to load either of these?
Thanks!
AudioGeek said:
Go to the Pass Labs forum. You will be able to find everything you want and more. Also check out http://www.passdiy.com if you haven't already.
There are a lot of pro's and con's for each device. It's impossible to say which is better, because no device is ideal.
MOSFET advantages:
Very high input resistance
No second breakdown
MOSFET disadvantages:
low gm
high and nonlinear input capacitance (HEXFET & co)
sensitive to parasitic oscillations
BJT advantages:
high gm
BJT disadvantages:
low input impedance
second breakdown effects
base currents
MOSFET advantages:
Very high input resistance
No second breakdown
MOSFET disadvantages:
low gm
high and nonlinear input capacitance (HEXFET & co)
sensitive to parasitic oscillations
BJT advantages:
high gm
BJT disadvantages:
low input impedance
second breakdown effects
base currents
Not to mention that the Pd losses in a MOSFET output stage are considerably greater than a BJT stage - at least for emitter followers! Even greater waste of energy.
so for a BJT output stage...
Ok... well back to basics:
how do I design an emitter follower class A SE output stage with BJT using a choke as a load?
Ok... well back to basics:
how do I design an emitter follower class A SE output stage with BJT using a choke as a load?
amplifierguru said:
If the output swing is Rail to Rail and the output mosfets are only N-channel Vertical ones than NO BJT ON THIS PLANET DARES TO TOUCH THE EFFICIENCY CRITERIA OF N_CHANNEL VERTICAL MOSFETS...IN CLASS-AB AMPS
Greg,
I donot ..not at all agree with you......at this time.....
K a n w a r
Kanwar
Greg considered emitter (source) follower. Do you know any NCHMOS P-P amp with follower output (low open loop impedance)?
Greg considered emitter (source) follower. Do you know any NCHMOS P-P amp with follower output (low open loop impedance)?
darkfenriz said:
In N-Mos PP upper rail mos act as source follower amplifier and lower rail mos act as common source amplifier but it can be made to achieve Av=1 using "current gain cell" which qsc uses....
Hi Kanwar,
As Darkfenriz noted I was talking of EF output stage, so I agree with you that N channel with booitstrapped upper EF and CE lower half is R2R efficient. So is complementary CE output stage and with voltage gain in the output stage can have a higher slewing rate from same driver current as I = CdV/dt.
I have yet to see a simple N channel 'gain cell' that does not aspire to the dreaded cross conduction - especially those humongous monsters you use Kanwar!
Cheers,
Greg
As Darkfenriz noted I was talking of EF output stage, so I agree with you that N channel with booitstrapped upper EF and CE lower half is R2R efficient. So is complementary CE output stage and with voltage gain in the output stage can have a higher slewing rate from same driver current as I = CdV/dt.
I have yet to see a simple N channel 'gain cell' that does not aspire to the dreaded cross conduction - especially those humongous monsters you use Kanwar!
Cheers,
Greg
amplifierguru said:
I have never ever constructed the gain cell in reality..oh yes i have tried it on the simulators....
regarding monsters i use my own customed designed pp drivers with floating power supply of 15voltsdc regulated to quench the thrist of huge gate capacitances......
cheers to you too.....
K a n w a r
Such a gain cell has been build, did sound good, cross-conduction was only a problem at high freq square waves.... read all about it at diyaudio.com
tschrama said:
Thijs, can you give a hint to the thread it's at ?
I did a search but came up empty, even dug through your posts.
btw: are you still on a holiday, your profile says so?
LOL holiday.... my whole live is one big holiday .... thx..
brb with link.... it's in the JLH 10 watter thread..
😉
brb with link.... it's in the JLH 10 watter thread..
😉
Here is goes... a N-channel MOSFET gaincell in a working amp..I ahve posted a lot of comments about this about all around the thread... even did some THD measurements... also posted somewhere ...
http://www.diyaudio.com/forums/showthread.php?postid=287957#post287957
http://www.diyaudio.com/forums/showthread.php?postid=287957#post287957
Workhorse said:
hm.. a term 'follower' might be understood in a different way?
I thought upper NMOS works as current source because previous stage basically adjusts G-S voltage (same as lower) making the amp work like 'transconductance' one.
Follower in contrary is (for me) driving gate from fixed voltage (set to be adjusted comparing to ground, not output) and huge source local feedback.
Voltage source (follower) with current source (common source) in class (A)B simply doesn't make sense, what if I and V have phase difference of 40deg. ?
regards
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